planing your engine combo

grumpyvette

Administrator
Staff member
NOW I can give you some factors to think thru here but about 90% of the guys reading thru this will , be starting thier engine component selection process with some mismatched components that they will insist on using to keep the costs lower, so my main point will be to show you what your looking for when selecting parts to maximize the combo potential and hints on starting to look at each component as a part of one smoothly working system.

step one

set aside a monthly budget and do the necessary research before you buy a single additional part.
building an engine is mostly, correctly sellecting components designed to work at a certain rpm, compression ratio and air flow rate, and insuring those components will remain correctly lubricated and cooled and under stresssed during thier intended opperational range.
MAKE A LIST of components and DON,T buy parts that are NOT on that list reguardless of the deals you may be offered


step two
decide on a REALISTIC goal for YOUR application, if its a street car DURRABILITY and reasonable DRIVEABILITY trumps peak horsepower concerns, building a car with 900hp-1000hp sounds great but if its always apart for repairs it gets old real fast and its not fun.
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its senceless to spend twice or three times as much on any component as you could on a cheaper component that easily matches your needs and goals, but its really stupid to try to get some part you currently own or can get cheaply, inclueded in your parts list if its going to be a restriction to reaching your horsepower or durability goals., call and discuss your choices with each manufacturer, if the cam you select is designed for 1500rpm-5500rpm the intake and heads should match that intended rpm band and the port size should reflect the displacement and intended pm bans as well.
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step three

performance is mostly the result of the ratio of horsepower too weight and the selection of components that will provide the accelleration,braking and handling you require, lighter weight, larger brakes, bigger tires and a large displacement help reach your power and performance goals, its far easier to have a 500 cubic inch engine in a 2600lb car with huge brakes and tires give neck snapping performance than trying to strain the limits on a 350 cubic inch displacement engine in a 4300 lb car, so before you just dive into modifying your current daily driver you might want to SERIOUSLY THINK ABOUT building a weekend TOY built from the ground up to be a TOY vs trying to convert a street car that weights a great deal more than it could if it was built as a semi-race car vs a converted street car.and that also has the benefit of your retaining daily transportation during its construction or repair down time. you can add hp or reduce weight to increase accelleration or increase the brakes effectiveness

step four
you must decide on an engine transmission and suspension package that can reasistically work well together, if the transmission or rear differential can,t be expected to stand up under the torque/horsepower levels than before you go dumping thou$ands$ of dollars into upgraded parts you might want to step back and think thru your options
example if your camaro has a 10 bolt rear diff, and a radiator that came with the current 6 cylinder engine and you want to install a 600hp big block chevy in the car you can pretty much figure those components are history

displacement
youll be limited to between about 1hp-and about 1.3 horsepower per cubic inch of displacement if you don,t want to start buying rather expensive parts

head flow rates

theres a rought guide of formula for gaugeing expected hp results from cylinder or head port flow rates, you take this formula .257 x #cylinders x flow rate= potential hp

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http://www.n2performance.com/archives.shtml

example
if your current heads flow 210cfm meassured at the peak valve lift your cam supplies with the intake runners and exhaust scavaging taken into account that 210cfm x 8 x .257=431 hp
your unlikely to exceed that hp level much with those heads
swap to heads that flow 260cfm, you get 260 x 8 x .257=534 hp
a noticable increase IN POTENTIAL, that does not mean youll reach that level, only that the cylinder heads are unlikely to be a major restriction to reaching that power level t that flow rate, naturally factors like displacement cam timing, compression levels etc will effect your results.

COMPRESSION

your engine only sees DYNAMIC compression, nothing gets compressed untill both valves are CLOSED, octane levels and heat levels along with a few things like quench, fuel/air ratios and spark curve on the ignition will effect your max effective compression levels but generally the higher the compression the more torque your engine can produce, but getting into detonation will quickly destrowy an engine so its usually best to try for about 8:1 dynamic compression with current pump high test gas.

EXHAUST SCAVAGING

generally the lower the restriction to exhaust flow exiting the header collectors the easier it will be to make decent hp, keep in mind as the rpms build so does the exhaust volume!
 
theres always those guys that say they want to build a 302-327, or 350 sbc combo, and spin it to 7000-8000rpm rather than a 383, and slap vortec heads on it so as to save the cost of better heads, then expect to spin the combo to 7000-8000rpm plus, on a stock 350,because it will rev higher, the problem is valve control and short block durability, every experianced engine builder will tell you that controlling the valve train becomes far more difficult as the rpms increase above about 6000rpm than below 6000rpm when stock or nearly stock valve trains are used, IE, just because you added roller rockers its not a cure for valve control issues, and that port size, and flow rates and cam profiles that work well at peak power production,above 6000rpm tend to work less than ideally in the 1500rpm- 4500rpm band where most cars spend most of thier time.
now IM not about to say you can,t build a killer 302--350 with vortec heads, but expecting to use those heads at 7K-8K plus is a joke!

I think your missing the point, if you think a 350 will be a better choice than a 383, that will cost a very similar amount if your starting from zip!,the object is to produce POWER from the engine over its ENTIRE rpm band NOT simply to get the engine to rpm well past the point where the cylinders fill effectively, if the engine is not in its effective power production rpm band theres no point in spinning it higher YOU SHIFT GEARS to drop it back into that power curve, the reason we don,t still see most guys build 301 chevys any longer, but we do see 383 sbc engines built frequently, is that a 383 when properly built will eat a 301-327-350 in the same car for lunch, a 383 will be limited to about 6500rpm in most cases but its the effective power transfered to the pavement NOT the rpms the engines spins that counts

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ok lets for the sake of discussion say both engines make exactly the same torque per cubic inch of displacement, and can produce that torque over the same percentage, and section of the power curve of each of thier rpm bands, the differance is that the power occures at exactly the same piston speeds and port flow rates for each

IE the 350 makes 350 ft lbs
and the 383 makes 383 ft lbs
the 350 can run up to 7000rpm
the 383 can run up to 6500rpm
this obviously seems to give the 350 a slight advantage but lets do it your way

350 ft lbs x 7000rpm/5252=466hp
383ft lbs x 6500rpm/5252=474hp
the truth is that both engines can be built to produce about the same power per cubic inch of displacement, weither its 1hp & ft lb or 1.5 hp & ft lb per cubic inch, and that the 383 will produce more low and mid rpm torque and similar peak hp, IE the car will be slightly faster with the larger displacement if geared correctly in identical cars

read thru the links provided above

vortec heads
vortec......................1.66sq inch.............170cc port

http://www.rbracing-rsr.com/runnertorquecalc.html
 
ok lets go thru this again, to get 425 rear wheel hp you need about 520 flywheel hp
you can,t just slap a few parts on the stock shortblock and expect to get to that power level, and most guys forget the drive train rear gearing,and trans stall,speed, cooling, a low restriction exhaust etc.
it takes (X) amount of fuel/air mix burnt per second to produce (Y) amount of horsepower,you can reach the goal by packing extra fuel/air mix into the cylinders with a supercharger, you can burm MORE fuel per stroke with the extra oxygen in nitrous, you can use a larger displacement engine, you can spin a smaller engine faster or you can make the current engine more efficient with a larger duration cam, more efficient high flow ports and a low restriction exhaust, but the results will be closely linked to the amount of fuel air mix that went thru the engine per second.

youll need decent cylinder heads that flow about 250cfm minimum at .500 lift, ID suggest the air flowresearch 195cc or the brodix 200cc IK as a decent option, trickflow and several other suppliers like dart could also supply a good cylinder head, youll need a cam that opens the valves far enought to get full use of the port flow rate potential and with durration matching the displacement and compression ratio, that will generally be a 383-396-401 stroker combo if you want to use the existing block, the stock TPI intake , CAM,and heads if used together,EVEN PORTED EXTENSIVELY won,t get close to flowing what you need.
your choice in component selection will limit the engines rpm and flow rates, the compression and cam timing will limit the torque curve.

heres some reading homework

http://forum.grumpysperformance.com/viewtopic.php?f=69&t=263

playing with dyno software can be informative

viewtopic.php?f=7&t=784&p=3796#p3796

your basic 383 short block can be built on a tight budget, but read thru these links,and sub links for info and tips


http://www.superchevy.com/technical/eng ... index.html

http://speedomotive.com/ps-523-85-383ci ... t-kit.aspx

http://www.popularhotrodding.com/tech/0 ... index.html

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