Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - SBC build. compression, quinch and cam opinions wanted.
View Single Post
  #6 (permalink)  
Old 04-24-2009, 10:35 AM
oldbogie oldbogie is offline
Registered User
 
Last photo:
Join Date: Apr 2007
Location: Seattle, Wa
Posts: 6,827
Wiki Edits: 0

Thanks: 4
Thanked 451 Times in 386 Posts
Quote:
Originally Posted by techron
hi guys, i,m assembling my SBC 383 stroker build and would like some of you engine guys opinions.
some specs:
forged flat top pistons.
aluminum heads, 190 CC intake ports, 64 CC chambers (now at 67 CC after smoothing and a mild polish.
cam yet to be selected.
1 7/8" long tube headers (yeah, i know, too big but the car is an early corvette and has the hooker chrome headers and sidepipes. they only come in one dia. and i'm not willing to change them.
single 4 BBL cross ram intake with either a 650 or 750 holley DP (i have both)
car will weigh between 2800 and 3000# when finished.
driveline is a 4.11 rear and a muncie 4 speed.

the car is going to be a fun street car and i'm not looking for max. horsepower. real world i'm looking for good performance between 2500-3000 to 5000-6000 (probably very seldome see 6000 on the street and never above).
i know the intake and exhaust are a compromise but that is what i'm running due to their looks and uniqueness.

here's what i would like your thoughts on:
i was going to run composition gaskets .039 compressed, but after assembling the short block i measured the pistons at TDC and they are down .024 in the hole. this would give me a compression of 10.24 and a quinch of.063 (which i don't like).
i can go with an .020 gasket which will give me a compression of 10.6 (a little high but remember aluminum heads) and a quinch of .044, i like this better, your thoughts???

with aluminum heads, 10.6 compression and .044 quinch i'm now looking at cams. it's going to be a flat tappet hydraulic. i'm looking a these 4:
234-234 duration, .488/.488 lift 114 LSA
234-244 duration, .488/.510 lift 114 LSA
230-230 duration, .480/.480 lift 110 LSA
244-244 duration, .501/.501 lift 110 LSA
all durations are at .050 lift.
which cam would you choose and why? if you want to recommend another cam feel free to and tell me why.

thanks guys i feel the more opinions the better.

i know there are some mismatched parts but i'm a retired corvette mechanic and know how to dial in/tune hi perf engines so please bear that in mind.
Good combo everywhere I look, I wouldn't be concerned with the header tube size, big tubes really enhance the top end and surprisingly have a very minor impact to bottom end torque. Besides, with 4.11 gears and a 4 speed Muncie you have the control to easily manage where the engine is in its RPM band versus the load it's carrying.

I think the cam comes down to how much "hair of the dog" you want. Any cam's effects tend to appear milder as displacement goes up. As the LSA gets tighter, the rastier the idle becomes.

I don't think you've got a big concern with squish/quench distance as the cam overlap will spill a lot of exhaust into the mix at lower revs which calms the burn. The 4.11s give the engine a large amount leverage which reduces the tendency for detonation in the mid and upper ranges. So these characteristics will allow an optimum advance rate and amount even though the squish/quench is getting toward the high side of optimum. The other thing not discussed with squish/quench goes beyond the closeness of closure which is the area of the decks. Flat top pistons present a much larger surface than is present with circular dish designs and the heads you're using also feature a large surface, so one needs to consider that large surfaces will enhance the desired effects (especially that of quench) while allowing for a more piston to deck clearance. The larger clearance will surrender some squish, but given the ports are 190 ccs, this means mixture velocity for a 383 will be pretty high and that will enhance chamber turbulance covering much, if not all, the needed squish function.

Bogie
Reply With Quote