ok i just ordered my 383 kit from enginekits.com. im gonna order afr 195 eliminator heads on moday. also gonna order the edelbrock performer air gap manifold. dont know if im gonna go with the performer rpm air gap taking opinions on that. im going carb. so im thinking a 750dp mechanical secondaries. the cam im still thinking about, not quite sure yet. i keep on thinking about the comp cams xr270hr cam. the car is gonna be street driven. and might see the track a couple of times. it is not my daily driver. just my fun car for the weekends when i decide to bring it out. im also gonna run a t-56, with 3.73 gears in the rear. im thinking this might be a great combo and kick some stang A$$. all opinions and suggestions are welcome. on comp cams camquest6 simulation it said this combo is good for roughly 477.5 hp @ 6000 and 500.6 ft-lb @ 4000. is this true?

 

Probably not (quite)...

I assume you put in some numbers that generated an estimated compression ratio.What number did you put in for deck clearance? Do you know the actual "compression height" spec, which leads to deck clearance, for the particular pistons in the kit? (not just the "nominal" height for a 3.75" stroke piston, but rather, the way the piston is actually made)

Your combo is good as far as that goes, except the cam is quite a bit on the mild side (not necessarily bad, just an observation); but not putting the REAL numbers into engine simulators accurately leads to HUGE inflated output calculations, that may bear little resemblance to what you ACTUALLY get.

Also, see AFR's web site for their actual as-built results, and be aware that they probably didn't make the deck clcearance mistake: i.e. the motor they dyno'ed is probably as carefully tweeked out as they could get it, which means you probably wonn't be able to quite attain that either, but you can check and see if their dyno #s agree substantially with Comp's simulator.

 

as far as compression ratio, the pistons that are coming with the kit say 10.7:1 with 64cc heads. when i had the block at the machine shop i had them check to see if it needed to be decked. and they said it didnt. so i didnt get it get decked. yeah im gonna try to mimmick the afr engine on there website. i like the numbers and how the graph looks. i know i prolly wont get exactly what they get, but hopefully ill get close to them.

 

Right; that's what they ALL say.

If you take typical rebuilder pistons, which would include virtually ALL cast pistons, MOST hypereutectics, and MOST non-racing forged ones including TRW/SpeedPro, and actually LOOK AT the piston itself AND NOT what "they say", you will find that they are an extra .020" farther "down in the hole" at TDC than stock; which is already about .025" or so.

To give you some idea as to how much difference it makes, assume a 383 with flat-top pistons; 64cc heads; .039" head gaskets (1004 for example); and 6cc valve reliefs and chamfer around the piston edge.

With ZERO deck clearance: 11:1
With nominal STOCK (.025") deck clearance: 10.4:1
With REBUILDER (.045") deck clearance: 9.9:1

A bit of difference, eh??

Which one have you REALLY got? Since the shop didn't deck your block, it'll be, AT BEST, the middle one; but more likely, since most of those "kits" come with TRW/SpeedPro or hyper pistons except for the higher-$$$ ones like the Eagle all-forged ones that come with SRPs, it'll be closer to the LAST one, and NOT the FIRST one, which is what the catalog bases what "they say" on.

If you don't know, then your ACTUAL CR could be ANYWHERE around in there, and worst of all, since the factory's production tolerances are so poor, it can very QUITE A BIT from one cyl to another. Pretty hard to tune a motor when the compression is all over the map in different cyls. Pretty hard for simulation software to make an accurate, reliable, believable prediction, when CRITICAL pieces of info like that are left out.

This is just one of DOZENS of things that create what you always hear about, "so-and-so runs 12.8, and I put together the same parts and my car is the same, but I only run 13.4". Yeah, the PARTS LIST might be the same; but there are SO MANY details like this that can be different, that unless you really take good care of them all and pay close attention to everything, you have no way to know what you're going to get. About all you can be sure of, is that it won't be as good as the "ideal" or "theoretical" like all the sims assume.

Still, it should be a good combo; just don't be too surprised if it puts out NOWHERE CLOSE TO either the sim output or AFR's dyno sheets.

 

Sofa's right. This is the process called "blueprinting". Measure, measure, measure.
A lot of people say they do but actually don't.
The heads are "supposed to be" 64cc. But what do they actually measure?
I've cc'd "64cc heads" and some were 62cc (milled) all the way up to 69cc (valve regrind).
Needless to say, the heads that actually measured 69cc would make a whopping difference (add this to the piston-to-deck variable Sofa mentioned) in what the actual C/R of the engine would be when it is assembled.
You can put the parts together or you can "build an engine".

 

cam is wayyy mild but with good compression and those heads, it will make power, just dont think it will be much over 400hp on motor.

stepup a few sizes... atleast run the xr276hr, 224/230 with 1.6 rockers to bring lift up. for a weekend fun car, i'd run the xr282hr, 230/236 duration. that will bring your power up over 450hp on motor

definately get a 750 double pumper carb and performer RPM manifold. that thing needs some air, so feed it with the rpm manifold.

 

sofakingdom, wow that alot of info thanks a bunch. i think ill let the machine shop deal with all those issues. and your right i dont know what my actual compression will be. im hoping for something around 10:1. something higher than stock. as long as it will still run on pump gas (93 octane)

orr89rocz thanks for the cam suggestions ill look into those. i am gonna run the rpm manifold, and the 750 dp.

thanks for the suggestions people. and more is always welcomed. ill be getting the lower end in the mail here soon. so hopefully ill be able to give ya guys an idea what the compression ration will be after i have the shop assemble it.