HEY GRUMPYVETTE?
I'm building a mild performance, 9:1 static CR, 350 for my 55 and looking into camshaft choices...I understand the intake closing point (degrees) will affect the dynamic compression ratio (DCR)....My question is what DCR should I be shooting for? and what rear gear and stall speed should I get?
heat, torque levels and shock loads are what kills transmissions
be wary of places that advertise transmission strength based on HORSEPOWER and not TORQUE CAPACITY
while a 2.87:1-3.08:1 rear gear if far from ideal for a performance application,and yes displacement does mater,as does the transmission gearing and/or converter stall speed, a great deal of the throttle response and the effect your carbs flow rate has on the torque curve,will be related too the cam timing, the engines
If your running an automatic transmission and torque converter, that torque converter does not know if you have it installed behind a mild 307 SBC or a performance 502 BBC, the effective stall will depend a great deal on the available torque the engine produces, and yes the mild 307 SBC will stall out at a lower rpm than a performance 502 BBC,with the same torque converter.
one very good reason to talk with the torque converter manufacturers tech dept before selecting a converter and NOT just looking at the rated stall speeds listed in a catalog.
compression ratio, the intake manifold design, and how your throttle is employed (IE an experienced driver can do a great deal to influence the way the car responds, an experienced driver that knows his cars characteristics can do a good deal to maximize acceleration.)
yes you can improve acceleration with a higher numerically rear differential ratio like a 3.73:1-4.11:1 gear especially with an over drive transmission, and a 2600 rpm-3200 rpm stall converter,
yes I have to admit that when I personally swapped from a stock stall speed converter
,in my 383 sbc corvette and a 3200 rpm stall speed converter the difference in performance was amazingly better.
swap too a 3.73:1 rear gear and you've noticeably further enhanced that seat of the pants and slam in the back acceleration.
people tend to not fully appreciate the fact that the performance cars drive train gearing, power to weight ratio and the converter stall
(in the case of automatic transmission) must match the engine torque curve if the car is to perform to anything close to its best potential.
while a manual transmission like a muncie has traditionally been used in performance muscle cars , the current technology with a higher than stock stall speed converter and a decently strong auto transmission like a properly built TH400 or $l80E makes the rather common 450-500 hp 383 small block a much more reasonable combo, with decent durability.
Ive built dozens of 383-406 SBC engines and properly configured and assembled 383-406 SBC engines are fully able to shred a stock 700r4/700r style auto transmission, over time as both transmissions were designed to operate with engines providing no more than 400 ft lbs of torque.
reading links and sub links will help
(and yes its likely to take a day or two to do so!)
generally youll want the transmission first gear ratio multiplied times the rear gear ratio to fall in the 10:1-10.75:1 range
as a general guide its usually suggested that for street performance use, the transmission first gear ratio times the rear gear ratio falls in the 10:1-10.75:1 range
most current auto transmissions have one or even two, over drive gear ratios, thus a rear gear ratio that would severely limit top speeds with a 1 to 1 top gear are no longer as big an issue
and ideally the 70 mph cruise rpm to fall at the lower end of the most effective torque curve, and yes this usually requires an over drive top gear ratio.
but its the driver who controls a good deal of the cars ability to put power effectively to the pavement. and the ability to match the cam timing, intake design and properly tune the combo you have is critical.
READ THE LINKS AND USE THE CALCULATORS PROVIDED
http://vexer.com/automotive-tools/1-4-mile-ET-HP-MPH-calculator
http://www.wallaceracing.com/et-hp-mph.php
http://garage.grumpysperformance.co...late-gear-ratios-and-when-to-shift-calcs.555/
http://garage.grumpysperformance.co...-info-worth-reading-through.11528/#post-53210
https://robrobinette.com/et.htm
http://hotrodworks.net/hotrodmath/quarter.html
http://www.ajdesigner.com/fl_horsepower_elapsed_time/horsepower_elapsed_time.php
http://www.tuneruniversity.com/blog/2012/03/power-to-weight-ratio/
https://www.ringpinion.com/calculators/Calc_RPM.aspx
the formula for HORSEPOWER is
torque/times/ rpm divided by 5252=hp
think about that a second
350 ft lbs at 6500 rpm= 433 hp
500 ft lbs at 4500 rpm=428 hp
the stock 700r4 trans is rated at 350 ft lbs
http://www.5speedtransmissions.com/calculators.html
Gear comparisons for 700R4 vs. other GM Transmissions:
.............................1st.......2nd....3rd....4th
Power Glide..............1.76......1.0
TH350 .....................2.52.....1.52....1.0
TH400......................2.48.....1.48....1.0
700-R4/4L60..............3.06.....1.63....1.0.....70
200-R4.....................2.74.....1.57....1.0.....67
4L80E......................2.48.....1.48....1.0.....75
http://www.magneticlynx.com/carfor/transc.htm
THESE CALCULATORS COME CLOSE, and may be very useful, that question, of Which gears to go with comes up frequently.
(youll generally want to select a rear gear ratio that multiplied times your transmission first gear ratio falls in the 10:1-10.5:1 range, for performance cars used on the street, with tires in the 24"-28" tall range)reading thru this thread and sub linked info should help, and yes, knowing your engines power curve and tire size and transmission gearing can help a great deal in selecting the correct rear gear ratio, and the use of over drive ratios adds to the flexibility of the choices.
your obviously going to need to consider tire diameter, rear gear ratio and transmission gearing, generally your want the first gear in the transmission multiplied times the rear differential gear ratio to fall in the 10:1-10.5:1 range and cruise at a bit higher rpm that the torque converter stall speed in 1:1 gearing, if you have a over drive gear having a lock-up converter sure helps and a trans fluid cooler is almost mandatory if you have a high stall speed torque converter.
EXAMPLE
if your transmission has a 3.00 low first gear you would take the average of 10.25 and divide by 3 and find a 3.4 gear is close to ideal,
do the same calc with a 2.48:1 first gear and you get a 4.11 rear gear., you can easily calculate rpms at 70mph and top speed in over drive gear if you know the transmission, rear gear and tire diameter. from info in the links below
USE THE LINKED CALCULATORS
http://www.wallaceracing.com/gear-speed.php
http://www.race-cars.net/calculators/et_calculator.html
http://www.wallaceracing.com/calc-rgr.php
http://www.datsuns.com/Tech/whentoshift.htm
http://www.frontrange4x4.com/forums/sho ... nformation
http://www.carcraft.com/techarticles/cc ... to_01.html
http://purplesagetradingpost.com/sumner ... index.html
http://www.tciauto.com/tc/gear-ratios
http://www.5speeds.com/ratios.html
if its a street driven muscle car, youll generally want to select a rear gear ratio that lets the car go thru the lights at the end of the 1/4 mile without having reached the extreme upper rpm range, of your engines power band in top gear, yet allow you to be taking full advantage of the power curve available, yet still maintain a semi reasonable 70mph cruise rpm level,
as an example
lets assume your car has 27" tall tires and a 4l80e transmission, and your engines max efficient rpm is 6200rpm
now if you have a 4L80E auto transmission , it has Gear ratios:
1 2 3 4 R
2.48 1.48 1.00 0.75 2.07
you generally want a 10:1-10.5:1 first transmission gear to rear gear ratio, so if we divide 10.25 by 2.48 we get 4.13:1
if we look at 70 mph with a 0.75 cruise we get a couple calculators to work with,the choice you make here is rather dependent on the intended power band and possibly the converter stall speed
http://www.wallaceracing.com/calc-rgr.php
http://www.wallaceracing.com/gear-speed.php
lets say we look at that 4.13:1 ratio, a 4.30 and a 3.73:1,
HERES A VERY COMMON RESPONSE I SEE POSTED ABOUT A REAR GEAR SWAP RESULT,S ESPECIALLY WHEN USING AN OVER DRIVE TOP GEAR TRANSMISSION
" GRUMPY, I Installed the Richmond 3:54 gears for my Dana 36 from Summit Racing. The part number was RMG-4901431.
Good choice, the vette woke up and runs like a bat out of hell."
http://www.wallaceracing.com/gearcalc.php
http://www.wallaceracing.com/gear-speed.php
http://www.summitracing.com/parts/rmg-4901431
keep in mind the rear gear ratio you select depends on BOTH the tire diameter and type of transmission you run, over drive ratios tend to help.Also depends on what size rear tires you plan to use.
here just for grins is what DD2000 makes its wild guess at my current corvettes combo, RUNNING WITHOUT THE NITROUS,notice torque peaks before the hp peak, and I must shift at 6300rpm because its starting to drop off by that point in the power curve (AS I DESIGNED IT TOO)as the engine combos designed to run nitrous from 3500rpm-6000rpm, if required but thats rarely been necessary for brisk performance on the street
you should ideally select a cam , tire diam. converter stall speed and differential gearing that put the engine rpm range in your power curve about 90% of the time
heres the resulting power band, of my corvettes 383 with an extensively ported custom stealthram intake and other mods like ported trickflow twisted wedge heads, erson roller rockers and a crane 119661 roller cam, with a 3200 stall converter stall and shifting at about 6350rpm N/A
notice changing the stall speed and shift points , by about 1000rpm, on both ends of the power band on the identical engine , being used on the transmission allows you to access a great deal more power from the engine far faster , the drive train change can easily result in 30% plus more power reaching the rear wheels, but it also allows you to select a longer duration cam, and is usually further enhanced with a matching change in rear gear ratio, from lets say a stock 2.87:1-3.08:1 to a more power transfer friendly 3.54:1-4.11:1 rear gear.
If you look at the graph the first stock converter power ranges from about a low of near 175 hp to near 500 hp, average near 338hp
If you look at the graph the second aftermarket,higher stall converter power ranges from about a low of near 300 hp to near 475 hp, average near 388hp, close to 80% more initial and easily 50 more average HP, yes that a bit mis-leading because in reality you can,t use the more effective cam with the lower stall speed converter so in reality the difference is FAR GREATER once the matched components are used, as the power curve on the stock engine would much lower
Example:lets say you run a muncie 4 speed manual transmission, M20 (1:1 4th gear), 27" diameter tires, 4.11 rear gear, and 60 MPH means the engine is running at 3090 PRM. If the tires are 26" then it's at 3200 RPM. 25" goes to 3300. If you want to actually keep up with traffic at 70 MPH then the numbers are 3600, 3700, and 3870, respectively.
http://users.erols.com/srweiss/calcrpm.htm
viewtopic.php?f=71&t=4696&p=12731#p12731
http://garage.grumpysperformance.co...electing-a-torque-converter-stall-speed.1715/
in a drive train set up for max efficiency the converter stall speed , and rear gear ratio will match the engines power curve and will be set up to have the trans let the converter spin up and grab at the lower end of the power band, and too shift to match the upper end to the most effective part of the torque curves upper end (a )and the transmission shift point will be set up near the upper end of the torque curve but past the peak power (b) set up that way, the engine can transfer power during the vast majority of its operation at near peak torque levels, looking at this engines power curve charted above that would be about a 3200rpm stall speed and about a 6400 rpm shift rpm point
Another example: M20, 27" diameter tires, 3.31 rear gears, and 60 MPH has the engine spinning at near 2400 RPM's, at 70 MPH it's at 2890.
now if you have a 4L80E auto transmission , it has Gear ratios:
1 2 3 4 R
2.48 1.48 1.00 0.75 2.07
as a general rule youll want about a 10:1-10.5:1 ratio with the transmission rear gear multiplied so 10/2.48=4.03:1 rear gear ratio, but the over drive ratio drops the effective cruise rpm to .75, so what would be near 3900rpm with the 4 speed manual trans above drops to 2925rpm
two engines producing the same HP at different RPMs will, given appropriate matching gearing, produce EXACTLY the same torque and EXACTLY the same HP at the wheels - provided, of course, equal amounts are lost within the drive train.
and thats true, but in most cases, cars are geared to maximize mileage to some extent the big block tends to have a broader torque curve that comes in at lower rpm making the gearing far more effective, its not PEAK power that counts its AVERAGE POWER. in the useable RPM BAND.
I constantly see guys who want to build a small block that will make 500hp at 7500rpm, then gear the car so the engine spends 90% of its time in the 1500-5500 power band, then they as why the cars a dog.
keep in mind , that if you select the cars rear gear and transmission gearing , correctly that your engines power band should be easily accessed by the cars gearing and allow the car to operate most of the time in or near its peak torque curve.
If you have an automatic transmission your converter stall speed should allow near instant access to the lower rpm end of your most efficient torque band , and the car should shift gears allowing the rpms to drop back near the peak torque level for max acceleration, if you engine can potentially make power from lets say 3200rpm to lets say 6700rpm but your transmission shifts at 5600rpm , and your converter stall speed limits you to 2500rpm, your not going to benefit from that combos efficient use of the power your engine can potentially produce., match that same engine to a 3300rpm stall converter and a trans programed to shift at 6800rpm, and you'll see a noticeable improvement in efficient use of your power band
READ THRU THIS RELATED THREAD
viewtopic.php?f=71&t=1715
http://www.grimmjeeper.com/gears.html
Realistically youll want to think thru the entire combo of engine and transmission, gear ratios, tires sizes etc.
and keep in mind , that if the engine in front of the transmission and its rear gear ratio makes decent power , the ratio of gearing the car has will be of less concern, to your cars acceleration, potential.
yes you should ideally get as close to 10:1 with the first gear ratio x final differential ratio,as you can to maximize the potential ,but if you have built a well matched combo with decent compression (usually near 10:1 if your going to use pump octane gas)and as much displacement as you can easily afford (383-406 in most small blocks and 454-496 on most big blocks when your trying to keep costs down) youll have little trouble spinning the tires with minimal effort even with less than ideal gearing , many guys fail to match the cars gearing to the engines power band, but just as many fail to build a well thought thru combo with matched components.
RELATED THREADS
viewtopic.php?f=69&t=7722&p=26767&hilit=logical+plan#p26767
viewtopic.php?f=50&t=428
http://garage.grumpysperformance.co...hysics-of-racing-info-lots-of-good-stuff.373/
viewtopic.php?f=50&t=1249
viewtopic.php?f=69&t=519
viewtopic.php?f=69&t=9930
viewtopic.php?f=71&t=10690&p=46305#p46305
viewtopic.php?f=69&t=5123
http://www.offroaders.com/info/tech-cor ... ph-rpm.htm
http://garage.grumpysperformance.com/index.php?threads/matching-the-combo.11020/#post-48707
http://www.jekylhyderacing.com/HeightofTires.htm
http://vexer.com/automotive-tools/speed-rpm-calculator
http://www.angelfire.com/fl/procrastination/rear.html
http://www.frontrange4x4.com/forums/sho ... nformation
http://www.carcraft.com/techarticles/cc ... index.html
the main idea of matching the drive train gear ratios is to keep the engine in its intended power band during the vast majority of its operation.
if youve got a 2.87:1 rear gear you'll spend a great deal more time in the 1500rpm-4500rpm band than if you have a 3.73:1 rear gear ratio simply because the engine can accelerate faster thru its power curve with the 3.73:1 rear gears.
It should be obvious that knowing the engines effective torque curve will be critical, and keep in mind that horsepower (THE ABILITY OF THE ENGINE TO DO WORK) goes up as the AVERAGE rpm band goes up if the torque remains constant or even similar.
you would ideally like the transmissions first gear ratio multiplied by your cars rear gear ratio to fall in the 10:1-10.5:1 ratio, and have a tire diameter that allows the car to cruise in the range between your engines stall and peak torque but much closer to stall speed.On most street performance cars the stall speed falls in the 2600rpm-3200rpm range and ideally the cruise speed at about 70 mph should fall a couple hundred rpm higher that the cars stall speed.there's several calculator links posted lower in the thread, to help you to figure it out
OBVIOUSLY theres a huge range of potential SBC builds possible and you'll want to select one that best fits your goals, If your intent on building a race 383-406 on a semi limited budget, for a light car Id at least look at these parts, installed on about a 10.5:1 compression short block, with a manual transmission and a 3.73:1-3.90:1 rear gear and 26'-28" slicks, some full length 1 3/4" headers and 1.6:1 ratio roller rockers,and a good 850 cfm holley carb, while that would not be my choice for a car designed for street use where you need some low and mid range, it would certainly produce good peak power
OBVIOUSLY KNOWING YOUR TIRE HEIGHT HELPS IN CALCULATIONS
http://www.brodix.com/heads/ik210dyno.php
http://www.summitracing.com/expertadvic ... calculator
http://forum.grumpysperformance.com/viewtopic.php?f=52&t=5078
http://forum.grumpysperformance.com/viewtopic.php?f=69&t=3814
http://forum.grumpysperformance.com/viewtopic.php?f=52&t=181
http://www.quickperformance.com/Suspens ... ep_44.html
you will find these threads useful if you read thru and look thru sub links most people don,t take the time to research and plan their engine builds to match the application, and as a result they tend to think they all want 500-600 plus hp from reading the magazine articles , but the truth is that a responsive engine with massive torque in the useable rpm range make for a far better choice if the cars street driven, now thats not saying you can,t have both impressive horsepower and a great torque curve but just keep in mind every choice is a compromise and if you concentrate on building an engine that works in the rpm band you actually use rather than getting mesmerized by peak hp numbers alone youll have better results youll also need to keep in mind it does no good to build a killer engine that produces 500-700 plus hp at 6700rpm and match it to a rear gear ratio and transmission gearing, and shift points or converter stall speed, that keeps the engine in the 1600rpm-6000rpm power range 90% of the time, if your smart your not competing for peak hp bragging rights your trying to build , impressive and instantly responsive torque in the useable rpm band, you also want to remember DURABILITY trumps PEAK POWER, you can,t win in the long term if the cars constantly needing repair and replacement of parts
AS A GENERAL RULE, a good compromise on a street strip cars gearing, will be found if youll match the transmission first gear multiplied by the rear gear ratio, to fall in the 10:1-10.8:1 range
as a rough guide
if the tire height is under about 28"
rear gear ratio x first gear ratio should be close to 10:1
if the tire height is over about 28"
rear gear ratio x first gear ratio should be close to 11:1 and match the tire size/diam. on the car, and rear gear ratio in top gear or OVER DRIVE to allow the car to cruise in the 2300rpm-2800rpm at 70 mph range...find the best compromise that gets as close to both as you can
read this
viewtopic.php?f=44&t=1010&p=1829&hilit=+horsepower#p1829
http://www.datsuns.com/Tech/torquehp.htm
http://www.coastdriveline.com/htmlfolde ... ator2.html
viewtopic.php?f=44&t=1010&p=1829#p1829
viewtopic.php?f=71&t=741
http://www.prosystemsracing.com/calculate.html
That answer depends on the fuel octane, cylinder head temp. and several other variables but generally 8.0-8.5:1 dynamic works out well if your going to run mid grade pump gas
READ THIS THREAD!
http://www.chevytalk.org/fusionbb/showt ... tid/92966/
http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html
HERES OTHER INFO LINKS
http://www.wallaceracing.com/reargear.htm
http://users.erols.com/srweiss/calcmph.htm
http://users.erols.com/srweiss/calcrpm.htm
http://users.erols.com/srweiss/calcrgr.htm
http://users.erols.com/srweiss/transc.htm#tabtop
http://users.erols.com/srweiss/transc.htm#Auto
heres some different calculators
http://www.kb-silvolite.com/calc.php?action=comp2
http://www.wallaceracing.com/dynamic-cr.php
http://www.smokemup.com/auto_math/compression_ratio.php
http://drag-zone.com/calculators.html#6
viewtopic.php?f=55&t=6546&p=20829#p20829
http://not2fast.wryday.com/turbo/compre ... sure.shtml
average the results
http://www.geocities.com/z_design_studi ... zx_tt.html
gear spread sheet that comes in handy THANKS TO 1FATGMC
http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html
HERES OTHER INFO LINKS
http://www.datsuns.com/Tech/whentoshift.htm
http://www.wallaceracing.com/reargear.htm
http://www.converter.com/vigilante.htm
http://transmissioncenter.net/4L80E.htm ... 7AodDjIACQ
http://users.erols.com/srweiss/calcmph.htm
http://users.erols.com/srweiss/calcrpm.htm
http://users.erols.com/srweiss/calcrgr.htm
http://www.gearvendors.com/hrgmratios.html
http://www.hotrod.com/how-to/transmissi ... axle-swap/
http://users.erols.com/srweiss/transc.htm#tabtop
http://users.erols.com/srweiss/transc.htm#Auto
http://www.thirdgen.org/calculations
http://www.corvetteactioncenter.com/tec ... scalc.html
viewtopic.php?f=32&t=430
IDEALLY you would sellect the horsepower goal, and the displacement,youll work with too reach that goal. then the cylinder heads, intake and exhaust are sellected that supply the necessary flow rates,in that rpm band, you pick the cam too match the intended rpm band,and flow rates and power range for the application, you then match the compression ratio, to the cam timing too maintain the correct dynamic compression ratio, and you sellect the matching drive train and gearing to keep the engine IN the matched rpm band the vast majority of the time.
naturally if your limited to a set displacement or compression ratio the other factors must be sellected with those limits in mind
IM reasonably sure this charts based on a 350-383 chevy or similar size engine, but its a good rought guide on most engines under 400cid displacement on matching the duration to the intended operational rpm band
In most cases the upper rpm band limit is either limited by valve float with the more common hydraulic lifters, or the auto transmissions shift rpm point,(yes there adjustable in some cases but rarely shift higher than 5500rpm-6000rpm even with a shift kit installed) theres not much point in designing a combo that runs into potentially higher rpms if you'll seldom reach, or can,t reach them., the lower rpm limits set by the necessary minimum lower rpm band the cam and compression ratio , and engine displacement will allow the engine to smoothly produce power from.
most performance cams list a MINIMUM converter rpm or cruise rpm
" GRUMPY?? I plan on adding a mild cam into the mix on my TPI corvette?.
whats the ideal power range in the TPI? "
a 2800rpm-3000rpm stall converter and ideally a 3.54:1-3.73:1 rear gear really wake up even a stock tpi corvette engine, but become almost mandatory when you upgrade the cam.
the stock TPI starts to get restrictive at about 4500rpm with the stock cam, by about 5500rpm its pretty much a lost cause UNLESS you do a bit of porting, add a better cam and ideally better cylinder heads, theres a nearly endless list of improvements that can be made, but to get the power efficiently to the pavement it helps top have the engine spend most of its time in the 3500rpm-5000rpm power band, thats what the higher stall converter, and rear gearing do.
trust me ask around to those guys who have done it, adding a 2800rpm-3000rpm stall converter and ideally a 3.54:1-3.73:1 rear gear really make the car come alive!
yes it helps even more if you install a better set of heads a better intake etc, but its the gears and converter allow you to stay in the engines sweet part of the power band
if you look around youll find guys that forgot that, fact, and concentrated totally on engine upgrades, they eventually find that the car just never responds correctly or they eventually learn and get the drive train matching the engines power curve.
heres your trans gears
2.74 1.57 1.00 0.67
rear gear 3.55:1
tires 27" tall
all the info you need to calculate gear ratios, speeds and engine rpms is here, or in the sub linked info
http://www.geocities.com/z_design_studi ... zx_tt.html
viewtopic.php?f=71&t=555
lets look at your particular
plug in your specs to the calculator and links, and look nup your cam specs for the suggested cruise or operational rpm band
heres free cam selection software
http://www.compcams.com/Camquest/default.asp
btw once you use it to find that approximate lift ,duration and lca, you can buy any companies cams with similar specs.
BTW HINT, with that rear gear and compression ratio , ID STRONGLY SUGGEST YOU stay UNDER 218-220 duration at .050 lift and with a 108-112 LCA
Most auto transmissions are either adjustable,OR PROGRAMMABLE in some cases, or there are aftermarket shift kits available too alter the shift points or convert to manual operation, but in most cases you'll still find 5500rpm-6000rpm about the max possible shift point, and frequently you can,t get quite that high with the less expensive kits.
for a street car the shift points are lower so the cam selected should be milder to match the realistic rpm band that's actually in use!
http://store.summitracing.com/egnsearch ... &y=13&x=26
http://www.jegs.com/webapp/wcs/stores/s ... 9_-1_10529
I'm building a mild performance, 9:1 static CR, 350 for my 55 and looking into camshaft choices...I understand the intake closing point (degrees) will affect the dynamic compression ratio (DCR)....My question is what DCR should I be shooting for? and what rear gear and stall speed should I get?
heat, torque levels and shock loads are what kills transmissions
be wary of places that advertise transmission strength based on HORSEPOWER and not TORQUE CAPACITY
while a 2.87:1-3.08:1 rear gear if far from ideal for a performance application,and yes displacement does mater,as does the transmission gearing and/or converter stall speed, a great deal of the throttle response and the effect your carbs flow rate has on the torque curve,will be related too the cam timing, the engines
If your running an automatic transmission and torque converter, that torque converter does not know if you have it installed behind a mild 307 SBC or a performance 502 BBC, the effective stall will depend a great deal on the available torque the engine produces, and yes the mild 307 SBC will stall out at a lower rpm than a performance 502 BBC,with the same torque converter.
one very good reason to talk with the torque converter manufacturers tech dept before selecting a converter and NOT just looking at the rated stall speeds listed in a catalog.
compression ratio, the intake manifold design, and how your throttle is employed (IE an experienced driver can do a great deal to influence the way the car responds, an experienced driver that knows his cars characteristics can do a good deal to maximize acceleration.)
yes you can improve acceleration with a higher numerically rear differential ratio like a 3.73:1-4.11:1 gear especially with an over drive transmission, and a 2600 rpm-3200 rpm stall converter,
yes I have to admit that when I personally swapped from a stock stall speed converter
,in my 383 sbc corvette and a 3200 rpm stall speed converter the difference in performance was amazingly better.
swap too a 3.73:1 rear gear and you've noticeably further enhanced that seat of the pants and slam in the back acceleration.
people tend to not fully appreciate the fact that the performance cars drive train gearing, power to weight ratio and the converter stall
(in the case of automatic transmission) must match the engine torque curve if the car is to perform to anything close to its best potential.
while a manual transmission like a muncie has traditionally been used in performance muscle cars , the current technology with a higher than stock stall speed converter and a decently strong auto transmission like a properly built TH400 or $l80E makes the rather common 450-500 hp 383 small block a much more reasonable combo, with decent durability.
Ive built dozens of 383-406 SBC engines and properly configured and assembled 383-406 SBC engines are fully able to shred a stock 700r4/700r style auto transmission, over time as both transmissions were designed to operate with engines providing no more than 400 ft lbs of torque.
reading links and sub links will help
(and yes its likely to take a day or two to do so!)
generally youll want the transmission first gear ratio multiplied times the rear gear ratio to fall in the 10:1-10.75:1 range
as a general guide its usually suggested that for street performance use, the transmission first gear ratio times the rear gear ratio falls in the 10:1-10.75:1 range
most current auto transmissions have one or even two, over drive gear ratios, thus a rear gear ratio that would severely limit top speeds with a 1 to 1 top gear are no longer as big an issue
and ideally the 70 mph cruise rpm to fall at the lower end of the most effective torque curve, and yes this usually requires an over drive top gear ratio.
but its the driver who controls a good deal of the cars ability to put power effectively to the pavement. and the ability to match the cam timing, intake design and properly tune the combo you have is critical.
READ THE LINKS AND USE THE CALCULATORS PROVIDED
http://vexer.com/automotive-tools/1-4-mile-ET-HP-MPH-calculator
http://www.wallaceracing.com/et-hp-mph.php
http://garage.grumpysperformance.co...late-gear-ratios-and-when-to-shift-calcs.555/
http://garage.grumpysperformance.co...-info-worth-reading-through.11528/#post-53210
https://robrobinette.com/et.htm
http://hotrodworks.net/hotrodmath/quarter.html
http://www.ajdesigner.com/fl_horsepower_elapsed_time/horsepower_elapsed_time.php
http://www.tuneruniversity.com/blog/2012/03/power-to-weight-ratio/
https://www.ringpinion.com/calculators/Calc_RPM.aspx
the formula for HORSEPOWER is
torque/times/ rpm divided by 5252=hp
think about that a second
350 ft lbs at 6500 rpm= 433 hp
500 ft lbs at 4500 rpm=428 hp
the stock 700r4 trans is rated at 350 ft lbs
http://www.5speedtransmissions.com/calculators.html
Gear comparisons for 700R4 vs. other GM Transmissions:
.............................1st.......2nd....3rd....4th
Power Glide..............1.76......1.0
TH350 .....................2.52.....1.52....1.0
TH400......................2.48.....1.48....1.0
700-R4/4L60..............3.06.....1.63....1.0.....70
200-R4.....................2.74.....1.57....1.0.....67
4L80E......................2.48.....1.48....1.0.....75
http://www.magneticlynx.com/carfor/transc.htm
THESE CALCULATORS COME CLOSE, and may be very useful, that question, of Which gears to go with comes up frequently.
(youll generally want to select a rear gear ratio that multiplied times your transmission first gear ratio falls in the 10:1-10.5:1 range, for performance cars used on the street, with tires in the 24"-28" tall range)reading thru this thread and sub linked info should help, and yes, knowing your engines power curve and tire size and transmission gearing can help a great deal in selecting the correct rear gear ratio, and the use of over drive ratios adds to the flexibility of the choices.
your obviously going to need to consider tire diameter, rear gear ratio and transmission gearing, generally your want the first gear in the transmission multiplied times the rear differential gear ratio to fall in the 10:1-10.5:1 range and cruise at a bit higher rpm that the torque converter stall speed in 1:1 gearing, if you have a over drive gear having a lock-up converter sure helps and a trans fluid cooler is almost mandatory if you have a high stall speed torque converter.
EXAMPLE
if your transmission has a 3.00 low first gear you would take the average of 10.25 and divide by 3 and find a 3.4 gear is close to ideal,
do the same calc with a 2.48:1 first gear and you get a 4.11 rear gear., you can easily calculate rpms at 70mph and top speed in over drive gear if you know the transmission, rear gear and tire diameter. from info in the links below
USE THE LINKED CALCULATORS
http://www.wallaceracing.com/gear-speed.php
http://www.race-cars.net/calculators/et_calculator.html
http://www.wallaceracing.com/calc-rgr.php
http://www.datsuns.com/Tech/whentoshift.htm
http://www.frontrange4x4.com/forums/sho ... nformation
http://www.carcraft.com/techarticles/cc ... to_01.html
http://purplesagetradingpost.com/sumner ... index.html
http://www.tciauto.com/tc/gear-ratios
http://www.5speeds.com/ratios.html
if its a street driven muscle car, youll generally want to select a rear gear ratio that lets the car go thru the lights at the end of the 1/4 mile without having reached the extreme upper rpm range, of your engines power band in top gear, yet allow you to be taking full advantage of the power curve available, yet still maintain a semi reasonable 70mph cruise rpm level,
as an example
lets assume your car has 27" tall tires and a 4l80e transmission, and your engines max efficient rpm is 6200rpm
now if you have a 4L80E auto transmission , it has Gear ratios:
1 2 3 4 R
2.48 1.48 1.00 0.75 2.07
you generally want a 10:1-10.5:1 first transmission gear to rear gear ratio, so if we divide 10.25 by 2.48 we get 4.13:1
if we look at 70 mph with a 0.75 cruise we get a couple calculators to work with,the choice you make here is rather dependent on the intended power band and possibly the converter stall speed
http://www.wallaceracing.com/calc-rgr.php
http://www.wallaceracing.com/gear-speed.php
lets say we look at that 4.13:1 ratio, a 4.30 and a 3.73:1,
HERES A VERY COMMON RESPONSE I SEE POSTED ABOUT A REAR GEAR SWAP RESULT,S ESPECIALLY WHEN USING AN OVER DRIVE TOP GEAR TRANSMISSION
" GRUMPY, I Installed the Richmond 3:54 gears for my Dana 36 from Summit Racing. The part number was RMG-4901431.
Good choice, the vette woke up and runs like a bat out of hell."
http://www.wallaceracing.com/gearcalc.php
http://www.wallaceracing.com/gear-speed.php
http://www.summitracing.com/parts/rmg-4901431
keep in mind the rear gear ratio you select depends on BOTH the tire diameter and type of transmission you run, over drive ratios tend to help.Also depends on what size rear tires you plan to use.
here just for grins is what DD2000 makes its wild guess at my current corvettes combo, RUNNING WITHOUT THE NITROUS,notice torque peaks before the hp peak, and I must shift at 6300rpm because its starting to drop off by that point in the power curve (AS I DESIGNED IT TOO)as the engine combos designed to run nitrous from 3500rpm-6000rpm, if required but thats rarely been necessary for brisk performance on the street
you should ideally select a cam , tire diam. converter stall speed and differential gearing that put the engine rpm range in your power curve about 90% of the time
heres the resulting power band, of my corvettes 383 with an extensively ported custom stealthram intake and other mods like ported trickflow twisted wedge heads, erson roller rockers and a crane 119661 roller cam, with a 3200 stall converter stall and shifting at about 6350rpm N/A
notice changing the stall speed and shift points , by about 1000rpm, on both ends of the power band on the identical engine , being used on the transmission allows you to access a great deal more power from the engine far faster , the drive train change can easily result in 30% plus more power reaching the rear wheels, but it also allows you to select a longer duration cam, and is usually further enhanced with a matching change in rear gear ratio, from lets say a stock 2.87:1-3.08:1 to a more power transfer friendly 3.54:1-4.11:1 rear gear.
If you look at the graph the first stock converter power ranges from about a low of near 175 hp to near 500 hp, average near 338hp
If you look at the graph the second aftermarket,higher stall converter power ranges from about a low of near 300 hp to near 475 hp, average near 388hp, close to 80% more initial and easily 50 more average HP, yes that a bit mis-leading because in reality you can,t use the more effective cam with the lower stall speed converter so in reality the difference is FAR GREATER once the matched components are used, as the power curve on the stock engine would much lower
Example:lets say you run a muncie 4 speed manual transmission, M20 (1:1 4th gear), 27" diameter tires, 4.11 rear gear, and 60 MPH means the engine is running at 3090 PRM. If the tires are 26" then it's at 3200 RPM. 25" goes to 3300. If you want to actually keep up with traffic at 70 MPH then the numbers are 3600, 3700, and 3870, respectively.
http://users.erols.com/srweiss/calcrpm.htm
viewtopic.php?f=71&t=4696&p=12731#p12731
http://garage.grumpysperformance.co...electing-a-torque-converter-stall-speed.1715/
in a drive train set up for max efficiency the converter stall speed , and rear gear ratio will match the engines power curve and will be set up to have the trans let the converter spin up and grab at the lower end of the power band, and too shift to match the upper end to the most effective part of the torque curves upper end (a )and the transmission shift point will be set up near the upper end of the torque curve but past the peak power (b) set up that way, the engine can transfer power during the vast majority of its operation at near peak torque levels, looking at this engines power curve charted above that would be about a 3200rpm stall speed and about a 6400 rpm shift rpm point
Another example: M20, 27" diameter tires, 3.31 rear gears, and 60 MPH has the engine spinning at near 2400 RPM's, at 70 MPH it's at 2890.
now if you have a 4L80E auto transmission , it has Gear ratios:
1 2 3 4 R
2.48 1.48 1.00 0.75 2.07
as a general rule youll want about a 10:1-10.5:1 ratio with the transmission rear gear multiplied so 10/2.48=4.03:1 rear gear ratio, but the over drive ratio drops the effective cruise rpm to .75, so what would be near 3900rpm with the 4 speed manual trans above drops to 2925rpm
two engines producing the same HP at different RPMs will, given appropriate matching gearing, produce EXACTLY the same torque and EXACTLY the same HP at the wheels - provided, of course, equal amounts are lost within the drive train.
and thats true, but in most cases, cars are geared to maximize mileage to some extent the big block tends to have a broader torque curve that comes in at lower rpm making the gearing far more effective, its not PEAK power that counts its AVERAGE POWER. in the useable RPM BAND.
I constantly see guys who want to build a small block that will make 500hp at 7500rpm, then gear the car so the engine spends 90% of its time in the 1500-5500 power band, then they as why the cars a dog.
keep in mind , that if you select the cars rear gear and transmission gearing , correctly that your engines power band should be easily accessed by the cars gearing and allow the car to operate most of the time in or near its peak torque curve.
If you have an automatic transmission your converter stall speed should allow near instant access to the lower rpm end of your most efficient torque band , and the car should shift gears allowing the rpms to drop back near the peak torque level for max acceleration, if you engine can potentially make power from lets say 3200rpm to lets say 6700rpm but your transmission shifts at 5600rpm , and your converter stall speed limits you to 2500rpm, your not going to benefit from that combos efficient use of the power your engine can potentially produce., match that same engine to a 3300rpm stall converter and a trans programed to shift at 6800rpm, and you'll see a noticeable improvement in efficient use of your power band
READ THRU THIS RELATED THREAD
viewtopic.php?f=71&t=1715
http://www.grimmjeeper.com/gears.html
Realistically youll want to think thru the entire combo of engine and transmission, gear ratios, tires sizes etc.
and keep in mind , that if the engine in front of the transmission and its rear gear ratio makes decent power , the ratio of gearing the car has will be of less concern, to your cars acceleration, potential.
yes you should ideally get as close to 10:1 with the first gear ratio x final differential ratio,as you can to maximize the potential ,but if you have built a well matched combo with decent compression (usually near 10:1 if your going to use pump octane gas)and as much displacement as you can easily afford (383-406 in most small blocks and 454-496 on most big blocks when your trying to keep costs down) youll have little trouble spinning the tires with minimal effort even with less than ideal gearing , many guys fail to match the cars gearing to the engines power band, but just as many fail to build a well thought thru combo with matched components.
RELATED THREADS
viewtopic.php?f=69&t=7722&p=26767&hilit=logical+plan#p26767
viewtopic.php?f=50&t=428
http://garage.grumpysperformance.co...hysics-of-racing-info-lots-of-good-stuff.373/
viewtopic.php?f=50&t=1249
viewtopic.php?f=69&t=519
viewtopic.php?f=69&t=9930
viewtopic.php?f=71&t=10690&p=46305#p46305
viewtopic.php?f=69&t=5123
http://www.offroaders.com/info/tech-cor ... ph-rpm.htm
http://garage.grumpysperformance.com/index.php?threads/matching-the-combo.11020/#post-48707
http://www.jekylhyderacing.com/HeightofTires.htm
http://vexer.com/automotive-tools/speed-rpm-calculator
http://www.angelfire.com/fl/procrastination/rear.html
http://www.frontrange4x4.com/forums/sho ... nformation
http://www.carcraft.com/techarticles/cc ... index.html
the main idea of matching the drive train gear ratios is to keep the engine in its intended power band during the vast majority of its operation.
if youve got a 2.87:1 rear gear you'll spend a great deal more time in the 1500rpm-4500rpm band than if you have a 3.73:1 rear gear ratio simply because the engine can accelerate faster thru its power curve with the 3.73:1 rear gears.
It should be obvious that knowing the engines effective torque curve will be critical, and keep in mind that horsepower (THE ABILITY OF THE ENGINE TO DO WORK) goes up as the AVERAGE rpm band goes up if the torque remains constant or even similar.
you would ideally like the transmissions first gear ratio multiplied by your cars rear gear ratio to fall in the 10:1-10.5:1 ratio, and have a tire diameter that allows the car to cruise in the range between your engines stall and peak torque but much closer to stall speed.On most street performance cars the stall speed falls in the 2600rpm-3200rpm range and ideally the cruise speed at about 70 mph should fall a couple hundred rpm higher that the cars stall speed.there's several calculator links posted lower in the thread, to help you to figure it out
OBVIOUSLY theres a huge range of potential SBC builds possible and you'll want to select one that best fits your goals, If your intent on building a race 383-406 on a semi limited budget, for a light car Id at least look at these parts, installed on about a 10.5:1 compression short block, with a manual transmission and a 3.73:1-3.90:1 rear gear and 26'-28" slicks, some full length 1 3/4" headers and 1.6:1 ratio roller rockers,and a good 850 cfm holley carb, while that would not be my choice for a car designed for street use where you need some low and mid range, it would certainly produce good peak power
OBVIOUSLY KNOWING YOUR TIRE HEIGHT HELPS IN CALCULATIONS
http://www.brodix.com/heads/ik210dyno.php
http://www.summitracing.com/expertadvic ... calculator
http://forum.grumpysperformance.com/viewtopic.php?f=52&t=5078
http://forum.grumpysperformance.com/viewtopic.php?f=69&t=3814
http://forum.grumpysperformance.com/viewtopic.php?f=52&t=181
http://www.quickperformance.com/Suspens ... ep_44.html
you will find these threads useful if you read thru and look thru sub links most people don,t take the time to research and plan their engine builds to match the application, and as a result they tend to think they all want 500-600 plus hp from reading the magazine articles , but the truth is that a responsive engine with massive torque in the useable rpm range make for a far better choice if the cars street driven, now thats not saying you can,t have both impressive horsepower and a great torque curve but just keep in mind every choice is a compromise and if you concentrate on building an engine that works in the rpm band you actually use rather than getting mesmerized by peak hp numbers alone youll have better results youll also need to keep in mind it does no good to build a killer engine that produces 500-700 plus hp at 6700rpm and match it to a rear gear ratio and transmission gearing, and shift points or converter stall speed, that keeps the engine in the 1600rpm-6000rpm power range 90% of the time, if your smart your not competing for peak hp bragging rights your trying to build , impressive and instantly responsive torque in the useable rpm band, you also want to remember DURABILITY trumps PEAK POWER, you can,t win in the long term if the cars constantly needing repair and replacement of parts
AS A GENERAL RULE, a good compromise on a street strip cars gearing, will be found if youll match the transmission first gear multiplied by the rear gear ratio, to fall in the 10:1-10.8:1 range
as a rough guide
if the tire height is under about 28"
rear gear ratio x first gear ratio should be close to 10:1
if the tire height is over about 28"
rear gear ratio x first gear ratio should be close to 11:1 and match the tire size/diam. on the car, and rear gear ratio in top gear or OVER DRIVE to allow the car to cruise in the 2300rpm-2800rpm at 70 mph range...find the best compromise that gets as close to both as you can
read this
viewtopic.php?f=44&t=1010&p=1829&hilit=+horsepower#p1829
http://www.datsuns.com/Tech/torquehp.htm
http://www.coastdriveline.com/htmlfolde ... ator2.html
viewtopic.php?f=44&t=1010&p=1829#p1829
viewtopic.php?f=71&t=741
http://www.prosystemsracing.com/calculate.html
That answer depends on the fuel octane, cylinder head temp. and several other variables but generally 8.0-8.5:1 dynamic works out well if your going to run mid grade pump gas
READ THIS THREAD!
http://www.chevytalk.org/fusionbb/showt ... tid/92966/
http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html
HERES OTHER INFO LINKS
http://www.wallaceracing.com/reargear.htm
http://users.erols.com/srweiss/calcmph.htm
http://users.erols.com/srweiss/calcrpm.htm
http://users.erols.com/srweiss/calcrgr.htm
http://users.erols.com/srweiss/transc.htm#tabtop
http://users.erols.com/srweiss/transc.htm#Auto
heres some different calculators
http://www.kb-silvolite.com/calc.php?action=comp2
http://www.wallaceracing.com/dynamic-cr.php
http://www.smokemup.com/auto_math/compression_ratio.php
http://drag-zone.com/calculators.html#6
viewtopic.php?f=55&t=6546&p=20829#p20829
http://not2fast.wryday.com/turbo/compre ... sure.shtml
average the results
http://www.geocities.com/z_design_studi ... zx_tt.html
gear spread sheet that comes in handy THANKS TO 1FATGMC
http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html
HERES OTHER INFO LINKS
http://www.datsuns.com/Tech/whentoshift.htm
http://www.wallaceracing.com/reargear.htm
http://www.converter.com/vigilante.htm
http://transmissioncenter.net/4L80E.htm ... 7AodDjIACQ
http://users.erols.com/srweiss/calcmph.htm
http://users.erols.com/srweiss/calcrpm.htm
http://users.erols.com/srweiss/calcrgr.htm
http://www.gearvendors.com/hrgmratios.html
http://www.hotrod.com/how-to/transmissi ... axle-swap/
http://users.erols.com/srweiss/transc.htm#tabtop
http://users.erols.com/srweiss/transc.htm#Auto
http://www.thirdgen.org/calculations
http://www.corvetteactioncenter.com/tec ... scalc.html
viewtopic.php?f=32&t=430
IDEALLY you would sellect the horsepower goal, and the displacement,youll work with too reach that goal. then the cylinder heads, intake and exhaust are sellected that supply the necessary flow rates,in that rpm band, you pick the cam too match the intended rpm band,and flow rates and power range for the application, you then match the compression ratio, to the cam timing too maintain the correct dynamic compression ratio, and you sellect the matching drive train and gearing to keep the engine IN the matched rpm band the vast majority of the time.
naturally if your limited to a set displacement or compression ratio the other factors must be sellected with those limits in mind
IM reasonably sure this charts based on a 350-383 chevy or similar size engine, but its a good rought guide on most engines under 400cid displacement on matching the duration to the intended operational rpm band
In most cases the upper rpm band limit is either limited by valve float with the more common hydraulic lifters, or the auto transmissions shift rpm point,(yes there adjustable in some cases but rarely shift higher than 5500rpm-6000rpm even with a shift kit installed) theres not much point in designing a combo that runs into potentially higher rpms if you'll seldom reach, or can,t reach them., the lower rpm limits set by the necessary minimum lower rpm band the cam and compression ratio , and engine displacement will allow the engine to smoothly produce power from.
most performance cams list a MINIMUM converter rpm or cruise rpm
" GRUMPY?? I plan on adding a mild cam into the mix on my TPI corvette?.
whats the ideal power range in the TPI? "
a 2800rpm-3000rpm stall converter and ideally a 3.54:1-3.73:1 rear gear really wake up even a stock tpi corvette engine, but become almost mandatory when you upgrade the cam.
the stock TPI starts to get restrictive at about 4500rpm with the stock cam, by about 5500rpm its pretty much a lost cause UNLESS you do a bit of porting, add a better cam and ideally better cylinder heads, theres a nearly endless list of improvements that can be made, but to get the power efficiently to the pavement it helps top have the engine spend most of its time in the 3500rpm-5000rpm power band, thats what the higher stall converter, and rear gearing do.
trust me ask around to those guys who have done it, adding a 2800rpm-3000rpm stall converter and ideally a 3.54:1-3.73:1 rear gear really make the car come alive!
yes it helps even more if you install a better set of heads a better intake etc, but its the gears and converter allow you to stay in the engines sweet part of the power band
if you look around youll find guys that forgot that, fact, and concentrated totally on engine upgrades, they eventually find that the car just never responds correctly or they eventually learn and get the drive train matching the engines power curve.
heres your trans gears
2.74 1.57 1.00 0.67
rear gear 3.55:1
tires 27" tall
all the info you need to calculate gear ratios, speeds and engine rpms is here, or in the sub linked info
http://www.geocities.com/z_design_studi ... zx_tt.html
viewtopic.php?f=71&t=555
lets look at your particular
plug in your specs to the calculator and links, and look nup your cam specs for the suggested cruise or operational rpm band
heres free cam selection software
http://www.compcams.com/Camquest/default.asp
btw once you use it to find that approximate lift ,duration and lca, you can buy any companies cams with similar specs.
BTW HINT, with that rear gear and compression ratio , ID STRONGLY SUGGEST YOU stay UNDER 218-220 duration at .050 lift and with a 108-112 LCA
Most auto transmissions are either adjustable,OR PROGRAMMABLE in some cases, or there are aftermarket shift kits available too alter the shift points or convert to manual operation, but in most cases you'll still find 5500rpm-6000rpm about the max possible shift point, and frequently you can,t get quite that high with the less expensive kits.
for a street car the shift points are lower so the cam selected should be milder to match the realistic rpm band that's actually in use!
http://store.summitracing.com/egnsearch ... &y=13&x=26
http://www.jegs.com/webapp/wcs/stores/s ... 9_-1_10529
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