calculate gear ratios, and when to shift calcs


Staff member
you really should read all the links and sub-links below to maximize your understanding of the concepts, in the thread


do a few calculations, think about the rpm band
YOUR engine makes its best power in,
and YOUR tire diameter
and YOUR cars weight
and YOUR rear gearing,
and YOUR trans GEARING
as a general rule if your looking for brisk street performance,
(especially with an over drive transmission)
youll want the transmission first gear . multiplied times the rear gear ratio to fall in the 10:1-10.6:1 range
and youll want the engine to cruse at 70 mph in the lower end of the engines effective torque curve

if we assume your looking at maximizing a performance cars acceleration while maintaining a reasonable cruise rpm for mileage, and you have a tire diam range of between 26-29" tall as, most muscle cars have, you can just find the ratio that multiplied times your transmissions first gear ratio falls in the 10:1-10.6:1 range and you'll find it works out rather well, especially with the OVER DRIVE TOP GEAR TRANSMISSIONS
if you don,t have an over drive transmission most guys just select the gear ratio that when matched to their tire diam. that will have the engine rpm range fall in the 2400rpm-2600rpm, or the lower edge of the engine torque curve, range at 70mph
Gear comparisons for 700R4 vs. other GM Transmissions:
Power Glide..............1.76......1.0
TH350 .....................2.52.....1.52....1.0

I know some people would rather gargle flaming broken glass than use info in links and sub-links but theres a great deal of useful info you can use
CALCULATORS CAN BE USEFUL ... index.html ... 3/10002/-1 ... calculator ... ph-rpm.htm ... ulator.php


you should ideally select a cam , tire diam. converter stall speed and differential gearing, THE CARS WEIGHT AND,AT WHAT RPM THE TRANSMISSION WILL SHIFT TO THE NEXT GEAR UNDER WOT RACING CONDITIONS, that put the engine rpm MOST EFFECTIVELY MATCHED TOO<or in your engines most effective power range, so your maximizing the torque in your power curve about 90% of the time
if your first gear ratio in your 4l80e transmission were to be a 2.48:1 you divide 10.25/2.48 and you find the closest ratio is a 4.11:1, if your more concerned with mileage than brute acceleration ,you should drop back to a 3.73:1 or a compromise 3.90:1 ratio
you get the advantage of reasonably low gears and highway drive ability if you install the correct over drive transmission, and reasonably low rear gearing, everything's a compromise but its easily possible to get a decent combo, lets say you want want to cruise at 2500-2800rpm and a top speed in excess of 120mph at a reasonable 6000rpm and a good launch with torque, and you multiplication that low gears provide, your running lets assume a 24"-26" tire

you want the first gear ratio times the rear gear ratio to fall in the 10:1-11:1 range



lets assume your dealing with a th400 and 2.73 rear gears you fall into the 2.48/2.73=6.77:1 range killing fast acceleration
swap to a 5.13 rear gear with that 2.48 th400 trans gear and you fall in the 12.73 range killing cruising speed, as well as top speed, which would be around 80mph in top gear.

but lets swap that 5.13 rear gear into a car with a 4l80e TRANSMISSION with its overdrive gearing, its 0.75 brings you a top speed of near 117mph , and a launch ratio of 12.7:1, not bad with big sticky slicks on a light weight car, but not ideal on the street

now lets try to get both a great top speed and a great launch plus a decent cruise rpm,
with a 26" tire

(obviously youll need to measure and calculate your particular needs)

we start with the 4l80e trans first gear divided into 10:1-11:1 and find a 4.11:1-4.33:1 ratio is a great choice, a 4.11:1-4.33:1 ratio gives you a 140mph-150mph theoretical top speed, and a cruise speed near 65mph, a 3.73-3.90:1 rear gear would probably be better on a car used mostly for cruising as it will drop the cruise rpm several hundred rpm



trans gearing ... earing.htm ... index.html ... index.html ... index.html

impalla65ss posted this link below

This is pretty extensive. Everyone will learn a lot from it.
get this excel-file downloaded and play with it <<<<<CLICK ON LINK

youll find what you want here ... ar%2Bratio ... zx_tt.html


HERES OTHER INFO LINKS ... zx_tt.html ... scalc.html ... tors.asp#8

heres some calculators to play with

if your looking for a 3.73-4.11 rear gear for your corvette,and can,t find a 4.11 gear,the reason is that the highest COMMON gear ratio is 3.73:1 in that differential for that C4 corvette, but heres a link, btw you do realize that 4.09, 4.10, 4.11:1 rear gears are all the same exact SAME ratio and the difference is in how they were calculated



btw, for anyone reading thru this thread,
if you've got a transmission without an over drive top gear ratio like a th400, th350, etc I would consider ,STRONGLY CONSIDER something in the 3.07-3.31 rear gear ratio range, if you have an over drive top gear, like a 700r4, 4l80e, 200r4 the same criteria apply but youll find , a 3.54.-3.90:1 rear gear as a good choice
remember this is for effectively gearing a mixed performance/transportation street/strip car, combo and
Id suggest gearing the car so your drive train gearing falls in a range where the transmissions FIRST GEAR x REAR GEAR ratio fall close to being in the 10:1-to-11:1 range and if your engines spinning at 6000rpm in top o.d. gear places the car speed no higher than 135 mph, the closer you can get the gearing to fall in that gearing range the more responsive most cars will be,get the rear gear ratio low enough that the rear gear ratio times first gear is over 11:1 and your first two gears become far less useful without major suspension mods and SLICKS, and truthfully, how many times do you need to exceed 135mph? ... ticle.html

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Re: calculate gear ratios
yeah, 10 bolt rear differentials and 700r4 transmissions don,t live a long happy life
if you get decent traction tires,
behind and serious BBC engine, especially if you drive it like you just stole it,
or want to smoke the tires every chance you get to impress your buddys

I've rarely seen any 700r4 last more than a year at most behind several of the BBC 454-468,489,496 engines I've built or helped build.
a well built th400 or 4l80e , especially if it has a large fan equipped aux fluid cooler ,has a much better chance of surviving. Calculator.htm

calculators like those linked above assume you have close to ideal,
(suspension, tires, weight transfer)
and gearing

( transmission gearing, stall speed and shift between gears effectively in the ideal power band)
to maximize the cars acceleration potential



keep in mind when I post info and links, in any thread,
it may be related to, but not specifically meant for your build or project,, I simply try to
post info that someone reading this thread months or years later might use.

Id suggest you look over all the kits and parts lists, watch the videos and purchase a few rebuild manuals,
and perhaps visit a few local transmission rebuild shops and ask what kits they suggest
tell them you want to learn how to rebuild a 700r4 and would like some info, tips and suggestions on how to do it and where you can learn to do so,
there may even be classes someplace that you can register for, if you look at this as a skill you need rather than an expensive P.I.T.A,
that needs to be dealt with it may prove very helpful in the long term

BLACKWIDOW POSTED THIS INFO, and hes made a few good points
First off there are two things you need to find the optimal shift point.

1. a dyno plot of the torque curve your engine puts out
2. all the gear ratios you will be shifting through
3.(optional) is the differential gear, the reason this is optional is that the gear never changes which makes it a constant that does not effect where you need to shift. But i will show you why it is fun to have.:twisted:

Runout - runout should be less than 0,25 mm (0,010 inch).

Balance - should be checked with the turbine in at least three positions. This insures that the converter will
not be internally out of balance. Overall balance should be held within 10 grams.

Internal Dimensional Standards:

Fit of pilot bushing
- 0,10 mm-0,20 mm (0,004 inch - 0,008 inch) typical.


All the math I give you is pretty simple. It is just that the process is lengthy.

Finding true torque.
The equation for this is
Flywheel torque x gear ratio you are in.
for example if you are making 150 lbs of torque at the flywheel and have a first gear of 3.549, and second gear of 2.197.

150 x 3.549=532.35 You are making 532.35 lbs in first.
150 x 2.197=329.55 You are making 329.55 lbs in second.

As you see here as your gear ratio drops you don't make as much torque. Which is why your car doesn't pull as hard in 2nd as it does in 1st, and so on all the way through the gear box.
Now for some real fun. These numbers are to our theoretical drive shaft. Now lets take into account the optional differential gear. And put in 20% drivetrain losses. For ease i'll use the numbers from above with a diff. gear of 3.9:1.

(flywheel torque)x(gear ratio you are in)x(final drive ratio)x(.80)
150 x 3.549 x 3.90 x .80= 1660.93 lbs at the wheels :shock:

Now if you didn't know before this is what you are really seeing at the rear wheels. Now the next time your friends ask what your making at the rear wheels, tell them the real number.

For reference your dyno plot to the wheels already has the drive train loss in so use the same equation but without the drive train loss on the end.

Finding RPM drop when shifting
The equation for finding RPM drop is

gear your shifting into
---------------------- x RPM before shift = RPM after shift
gear your shifting from

If your shifting from 1st(3.54) to second(2.197) at 7000 rpm it would be

------- x 7000= 4333.33 rpm

So you would be at 4333.33 RPM after the shift. Pretty easy stuff.

Making the graph and finding the best shift
Now lets take our math we have learned so far and put it to use. Take the formulas i have given you and make a chart so that you can see shifting points and
torque numbers for the corresponding shift(ie. first to second). now i am going to use MONZTER's dyno plot from the N/A engine setups with dynos and the gear
ratio's from a factory 240z 4 speed as my examples. You can find the dyno plot here in this post , and the gear ratios here


Start at your red line and go down 1200 rpm in 200 rpm intervals, charting your rpm start and drop, and your torque start and drop side by side. Along with the drop in torque from the shift.

First column is 1st gear rpm
Second column is 1st gear torque at rpm
Third column is torque diffrence before the shift
Fourth column is 2nd gear torque at rpm
Fifth column is 2nd gear rpm after the shift
Sixth column is torque loss after the shift
Seventh column is torque diffrence after the shift

7200..... 514.61..... -107... 369.10..... 4456 ....-145.51 .....+157
7000..... 550.10..... -71..... 336.14..... 4333 ....-213.96 .....+89
6800..... 578.49..... -43 .....329.55..... 4209 ....-248.94 .....+54
6600..... 596.23..... -25 .....318.57..... 4085 ....-277.43 .....+25
6400..... 603.33..... -18 .....318.57..... 3962 ....-284.76 .....+18
6200..... 610.43..... -11 .....307.58..... 3838 ....-302.85 .......0
6000..... 621.08........ 0 .....318.57..... 3714 ....-302.43 .......0

So now that we have our first to second shift chart lets find that perfect shift point. The key to finding the best place to shift is to find the point at
which you lose the least amount of torque during the shift without losing to much forward momentum before the shift. I do this by comparing the torque diffrence before the shift( Which goes with your forward momentum) and the torque diffrence after the shift.On this particular setup I think he should shift right around 7000-7100 RPM, if he had the gearing I used here. While there are less torque losses after the shift above this rpm, you have to much torque drop off before the shift, which causes a loss of the forward momentum you were building. Once you find what you think is the optimal shift point vary it up and down about 400 RPM to find what suits you best. Oddly enough most drag racers have a rule of thumb that the best shift point is 10% beyond peak horsepower. Which if you look at his graph is is right around 7100 RPM. But you should take this as a coincidence and do the math yourself.On his setup he said his redline is 8000 RPM but he needs to shift well before that. What this shows is just because you can rev to 8000 doesn't mean you should shift there.

Now take this info and do every gear shift in your setup. Plus don't forget that since the ratios change from gear to gear the best place to shift in one gear might be different than where to shift in the next. But it should be pretty close.

After I did this I found this was went over on someons page but I don't think it elaborated as much, but just for more reading you can find it here . I hope it helps some people out.
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Re: calculate gear ratios

btw I got asked
"how do you figure out the gear ratio of a ring and pinion set if its not stamped with the ratio"

if youve never dissembled a rear differential,
you find the ratio,by counting the pinion and ring gear teeth and divide the pinion count into the ring gear count?


If the ring gear has 37 teeth and the pinion has 9 thats a 4.11 set...
OR If the ring gear has 41 teeth and the pinion has 11 thats a 3.73 set

beats guess work


SOME GUYS STAY WITH THE STOCK 3.07-2.57 REAR GEARS to minimize the tire spin, and at lower power levels that works to prevent the tire spin that a 3.73-4.11:1 rear gear ratio would produce due to the extra torque multiplication,but its not that effective once youve got the necessary power to blow the traction at will,

the PROBLEM with that approach is NOT the traction, or lack of it in most cases,but the fact that your engine spends very little time in the engines most effective section of the torque curve , theres not much sense in building a killer combo with a cam and heads that flow impressive numbers and allow impressive hp in the 5000rpm-6500-7000rpm if your spending 70% of your time below 5500rpm and the transmission shifts at 5500rpm, due to the rear gearing and transmission shift point.
Its rather pointless to have a great deal more hp than you can effectively transfer to the pavement, but gearing the car so you can,t get into the most effective part of the power curve much of the time is hardly the best option.

play with the info in the links posted above and youll soon see the distance traveled and mph prevent a car with a 2.57 rear gear from spending the majority of its time in the efficient part of the tq curve.
yes your likely to need slicks and suspension mods but the car will be far more effective if your using the full potential of the power curve.
yes your going to need slicks and suspension mods to get the necessary traction.

quick posi check =put the car up on jack stands then, turn one axle and watch the other axle. If they both spin the same direction, its a posi. if the other axle spins the opposite direction its an open diff.

it may help if you think of it this way
if your engine puts out 400ft lbs of torque
a 2.57:1 rear gear ratio puts about 1000 ft lbs of twisting power to the axles
a 4.11 rear gear ratio puts about 1600 ft lbs of twisting power to the axles

if your car weights 3500lbs
youve got 29 percent of the cars weight applied in rotational force with the 2.57 ratio
youve got 46 percent of the cars weight applied in rotational force with the 4.11 ratio

its about mechanical leverage, or efficiency
assuming a 26" tire height and zero mechanical losses, the tires need to turn about 200 revolutions to cross a 1/4 mile
a 2.57 rear gear lets the engine spin thru about 2060 power strokes
a 4.11 rear gear lets the engine spin thru about 3290 power strokes
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these links may help, you find tire diameters, rear gear ratios stall speed etc.
the required stall has little to do with the type of lifter your using, its need, to be used, or changed is determined by the rpm range of the cam you select and your car weight,the cars automatic transmission first gear ratio, tire diameter and rear gear ratio.
a mild roller cam would work with a stock stall converter just as a mild flat tappet lifter cam will.
the whole idea of swapping to a higher stall speed torque converter is to allow the engine UNDER LOAD to jump in rpm up into the engines most efficient power range or the most effective part of the torque curve.


when most people look at a dyno sheet like this (posted below ) they may get the totally erroneous idea from the graph,
that they will lose a significant amount of lower rpm torque as the dyno graph tends to show,
but thats a fallacy, you don,t drive a car looking at the tachometer in low rpm driving you simply depress the throttle when you want to accelerate,
think about how you actually drive.... you give the car a bit of throttle and you move the car,
it takes about 30-35 hp to keep a car traveling at a steady 60 mph,
if you want to accelerate you depress the throttle and the car response is increased speed,
with most drivers, if you place a horizontal line between the two torque curves ,on the graph,
you'll notice about a 150 rpm difference in any torque value,
youll never notice that while driving.
if the cars drive train gearing matches the engines power band, you cruise around at about 1400-1800 rpm,
you quickly learn that its effortless to spin the rear tires on dry pavement,
and you learn from experience and engine sound to manually shift to the next gear at about 2500rpm-3500 rpm,
or the auto transmission will do it for you under part-throttle acceleration,
in normal driving,
if you had a chance to drive the car with either engine you would subconsciously,
adapt your driving style to match the car characteristics and,
I doubt seriously that you would notice any difference under a daily commute,
but you would darn sure notice if you were trying to race or max out the cars performance.
where that huge gain in peak power generated on sim 5 would be obvious,
but in daily low speed driving its just not obvious.
I drove a 496 BBC corvette for a few years that made almost 700 hp at peak rpms,
under most driving conditions on the street I doubt I exceed 3500 rpm.

these links may help, you find rpm and gear ratios
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Crusty66 said:
I’m looking for a stall speed recommendation for my ’66 Caprice.

Here are the specs
496ci – 454 with 4.25 stroker
9.5:1 compression
Oval port Edelbrock E-Street

Comp 276HR hydraulic roller;
Int 224, Ex 230 @ .050”
Lobe separation 110, centreline 106
Lift .510”

Edelbrock Performer intake with Quadrajet 800cfm
2” full length headers
Rear end ratio is 2.73 with 26” tall tires.

Maximum speed limit is 60mph in my country, trans guy supplied me with a 2,200 rpm stall speed converter which I think is too high & probably unnecessary with the torque this 496 should have.

I think you have the wrong Idea about how a 2200 rpm stall speed converter WORKS, that 2200 rpm stall speed seems about ideal to me,for the combo you list in the car you list above, and Ive built dozens of similar 454-496 engines.
many guys who have never had a different aftermarket stall speed converter are under the mistaken idea that the car won,t move until the engine rpms reach , the rated stall speed such as the 2200rpm,you mentioned, that ideas incorrect!
the car will drive and move at well under the rated stall speed, the stall speed just indicates what rpm the engine will jump too under wide open throttle if you stand on BOTH the brake and throttle petals so both are fully down under your foot towards the firewall floor, the FUNCTIONAL POWER RANGE of a higher stall speed allows you to jump into your more effective power band under high load and wide open throttle conditions but something like a 2200rpm stall converter on a 496 BBC will have little too no negative effect on daily driving, at part throttle



Crusty66 said:
Hi Grumpy,

I do understand torque converter operation, my only concern was that the stall speed was very close to cruising rpm where the usual cruising speed is 55-60 mph with the very tall 2.73 ratio.

I know I might be better off with moving to a 3.08, but I'm running short on funds right now.

but I also know most pick & Pull salvage yards frequently sell complete differentials for full size older cars for $50-$150 for older chevys, so I'd at least look into the possibility of finding a similar car in a salvage yard with a different different ratio gears and swapping differentials, ideally youll find a 3.54:1 or 3.54:1 rear gear differential

If you had more funds Id suggest upgrading the differential to a FORD 9", (ideally with disc brakes) from a later full size ford or pick up truck


viewtopic.php?f=39&t=7&p=10#p10 ... price.html ... asurements
Yes its worthwhile reviewing again Grumpy.
Check it out.
Takes a Tall rear tire to utilize the Brute Torque of a 455 Grumpy.
Have Mickey Thompson Drag Radials. 275/60 R15. Grow to 29-30-31 inches tall. Rub witness marks Verify on whee wells. Kissing light above 160.
HP Good also of course.

I will try the spreedsheets Tommarow.
Bump to the Top Grumpy.

Been Researching How Gasser Guys geared and why back in the day.
Well exceeded 10.0:1 overall ratio.

Pontiacs like to Pull a gear too.
I ran a 3.08 gearset with a 2.20 :1 Close Ratio muncie for a while.
Pulled effortless and Full Race cammed too.
Left a Twin strip burnout 1-2 2-3- 3-4 for 3 blocks in front of my old house past the Chevy Drag Racers in the TA.
They could not match with thier 9-second Nitrous drag cars.
long black tire marks on the pavement might look impressive,
but its usually a good indication that the traction provided by the combination of tire choice and suspension set up,
is far from ideal in maximizing the transfer of the torque the engine provides,
from the drive train gearing ,and weight transfer to the tire surface too the pavement
maximizing weight transfer in a race car suspension
I've always been a bit amused at the fact that so few guys think things through carefully, before something breaks, and they are forced to look into why some part failed or why the car ran into some track barrier!
most newer guys are far more concerned with adding engine power, and tend to ignore the drive train strength, suspension control and braking capacity and endurance and durability.
Well that is of course, untill they are forced into looking at those factors by a combo of parts failures and having a car fail to go where the driver wants it to or slow down rapidly and consistently enough to prevent body work costs from getting out of hand when the car hits things it should have been able to avoid in the hands of a skilled driver.

If you want to buy and install larger than original wheels and tires on your car, you need the accurate measurements, so you won,t waste a great deal of time and cash,
Id also call tire rack, discount tire, etc. and other major on-line tire/wheel set vendors and ask questions (link below) they sell hundreds of corvette tires a month and would know by now what fits and what causes problems
it also helps if you accurately measure your current car wheel well , tites and wheel, and off set clearances internally in the cars wheel well, so youll know what your dealing with!3756!3!254641198245!e!!g!!tires online&ef_id=WwSgkQAAAIJ8kji0:20180704125836:s Tires Will Fit My Car


grumpy, I,ve noticed that a great many of the links you post,
are too off site calculators, or charts based on calculators
do you really think those calculators are accurate?

If you break down that question your basically asking if
yes if you use valid info in those calculations, and use data thats valid for the application,
you can reasonably expect valid answers
well the basic rule applies,

of course having reference books helps define the questions,
and understanding what info valid
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That was 1994 Grumpy.
I have upgraded Tires and added Comp Engineering Slide A Links long Since.
Also I beat those 9-second Chevies Street Racing with the T/A.
All BS Ended with Hellcats.
Stay at home.
I am goingback to the Dragstrips.
Street Race again too.
a car may be impressively fast and leave long black pavement marks but it will generally be even faster once tires,suspension & traction's improved,

my old 1968 corvette with a 13.7:1 injected bbc would effortlessly smoke the tires when the throttle was opened with street tires at any speed below about 60-65 mph
once slicks were used that loss of traction was less pronounced and the car was noticeably faster, at the local track by at least .8 seconds and the tire tracks were significantly shorter in length

17" & 18" rim size slicks are available
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a car may be impressively fast and leave long black pavement marks but it will generally be even faster once tires,suspension & traction's improved,
my old 1968 corvette with a 13.7:1 injected bbc would effortlessly smoke the tires when the throttle was opened with street tires at any speed below about 60-65 mph
once slicks were used that loss of traction was less pronounced and the car was noticeably faster, at the local track by at least .8 seconds and the tire tracks were significantly shorter in length
My T/A Has done the same Grumpy.
Just no one wants to believe it because its not A Corvette with a BBC.

You should build it again.
Lets Go Street Racing Forum to Forum.
All BS has ended.
Time to Race.
I was recently over at a friends garage , he lives on a rather rural strait paved road on the perimeter of and behind a large farm,
out where traffic is not very frequent, where he had a friend he was helping tune his car, who was complaining ,
that his 1969 camaro with a 4 speed transmission, and a 3.73:1 rear gears,
, was just not as fast as he thought it should be.
I asked him to take me for a short ride and launch the car and go as fast as he could up through the gear shifts.
his problem seemed rather obvious to me, he only shifted to the next gear as the engine was obviously well passed
,the rpms where his engine made max power.
I suggested he shift at about 6300 rpm vs about 6900 rpm, with his solid roller equipped 427 BBC , and he complained,
that was ridiculous as the engine easily goes 7000 rpm.
so I suggested he race a buddies camaro that had a 383 with a tunnel ram, and he should do so shifting just like usual ,
at about the 1000 ft point he was only just starting to pull ahead of the small block car.
I then asked both cars to duplicate the test race, but he was to shift at 6300 rpm reguardless of what he thought he should do..
by the 1000 ft point he was easily three full car lengths ahead and obviously pulling ahead far faster than previously.
he said he would have to try that technique seriously, once the local track re-opens.
honestly, you want to shift so the rpms fall back near the engines torque peak, the object is not to run up into the rpm range,
where the engines no longer making peak power before you shift to the next gear.
"he said he would have to try that technique seriously, once the local track re-opens.
honestly, you want to shift so the rpms fall back near the engines torque peak, the object is not to run up into the rpm range,
where the engines no longer making peak power before you shift to the next gear."

This last sentence is how the best bracket racers found out how to win. No truer words until you get into 1000s of horsepower.
hey GRUMPY??

Hi guys

I am a total amateur with little wrenching experience.

Trying to put together a 50/50 street/strip car.

Small block engine 650hp at crank, 3100 lb with driver, 28" tall tires, manual transmission, N/A

1/8 mile only. I don't care about gas mileage or turning 3000rpm on the highway

What rear end ratio should i go??

370, 410, 456, or more??


obviously we would like to know the average trap speeds your seeing now ,
what rpm range do you generally launch at?

also if you have a dyno print out of your engines power curve?
and what manual transmission your using and what trans gear ratio, does your car now have

and what ate your peak engine rpms, what mph ,
are you seeing as you go through the lights in now,
to get some idea as to your current combos potential.

with that info you can get a good calculated ideal rear gear ratio.
guessing with near zero facts is going to result in less than ideal results unless you get very lucky:facepalm:
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keep in mind tire diameter and width changes affect handling, braking and cornering
and frequently cause wheel fender clearance, issues or handling issues,
your rarely going to benefit from tire size changes if you need very much of a drive train gear ratio change,
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I helped guys repair and replace many 10 and 12 bolt differentials over the decades,
those common G.M. differentials just could not in my opinion hold up to the power of a serious BBC engine,the torque loads and shock loads those engines can produce over a long term, especially if slicks and hard launches are common, both the differentials and transmissions take serious abuse if raced,
but I never had issues with a properly set up dana 60
I had a 1970 cuda dana 60 in my 1969 camaro, with a serious 13.7:1 compression injected, 496 BBC, and I never had issues
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