HI guys ,New to this site.Hope to gather alot of info.And share some as well.

But for now I do have a concern with this 383 I'm doing.The question is :
with a deck hight of 9.008
My pistons ar SRP that yeild 11.1 at 0 deck
I have AFR 195 heads @64cc.(milled from 74)
If I use a .051 gasket,this will bring my c/r to 10.5 and a quench of .057 from what I'm told.The cam is a XE274 The question is will the compression and quench be ok to run on 93-94 octain?Sory for the long post.

Thanx in advance Steve

Please do a search for Pat Kelly and his Dynamic Compression Ratio Calculator, either here or over at the sister site, Team Chevelle. There is a wealth of info on this if you want to do some reading!! And I mean a lot!!!

I love ta jump in when a real good long thread gets started b/c everybody comes out and offers so much great info!!!pdq67

.057" quench is borderline on being a very bad thing.

Keith Black has published some very good information on the subject. He explains that deck height in the .060 - .120" range causes abnormal combustion in the quench area because it starts to act like its own separate combustion chamber. Detonation occurs very easily within that .060 - .120" range. Above .120" there is no more quench area at all and combustion can occur normally across the entire cylinder.

The tighter the quench area below .060" you get the more pronounced the quench effect becomes and the more detonation resistance the cylinder becomes. Of course the limiting factor on the tight side is a physical collision between a piston and the bottom of the head, but generally speaking the tighter the better - most builders will agree that somewhere around .035" is a pretty safe minimum in most steel rod forged piston engines.

I'd use a thinner head gasket and shoot for a quench height of .035 - .045". The engine will be much less prone to detonation even though compression will be higher.

I am also running the SRP flat top pistons .009 in the hole with a Victor Reinz Nitroseal headgasket. The headgasket has a compressed thickness of .029 putting my quench height at .037". I am also running a 383 with 11.3:1 compression, 5.7" steel rods, and Trick Flow 64cc heads.

In my opinion (and I used Pat Kelleys calculator extensively) you need a cam with advertised duration of 288*-290* on the intake side in order to run on pump gas. I'm running a Comp Cams 294S and so far the engine does not detonate on pump premium gas and maintains good TQ at 2500 RPM on up (I run a 3000 converter and 3.55 gears)

I think that the XE274 will be way too small if you want to run pump premium pump gas.

Very good question! Sorry for the very lonmg reply.

[This message has been edited by Eric68 (edited 10-03-2002).]

ditto Eric68. In your case, I believe that running a tighter quench will reduce your propensity for detonation more than the resultant gain in compression due to the thinner head gasket will increase it. However, that cam is a little short for pushing around 11:1 compression.

Another aspect to consider is that this is a 383 you are talking about. Because of the longer stroke and the shorter rod/stroke ratio that this causes, the instantaneous piston accelleration is increased, causing less piston dwell at TDC and reduces the quench effect slightly. If you had a very long rod/stroke ratio, then the engine would tolerate more compression.

In your case, I don't think that you will be able to run pump premium with that cam and that compression.

We only have 91 Octane premium here in NM and my combo is very similar to Eric's, I know I will have to mix.
383
Edelbrock RPM 64 cc heads
JE 11.3:1 forged flattop slugs
CC294S
Weiand Xcelerator single plane
CC Pro Magnum 1.6 roller rockers
Demon 750DP
1.75" Hooker Super Comp headers

Thank you for the quick replies guys.I think I will get that bigger cam,and drop the gasket down to a .041 which will bring the quecnh to .049.Alittle better I guess.I realty don't want to run upwards to 11.1.
hanks again.........

You will definately need more cam. Whatever you decide to use, you will need to pay very close attention to the valvetrain geometry. Cutting 10cc from a set of heads is a pretty serious hack job. Also, pay close attention to piston to valve clearance...the valves are sitting that much closer to the pistons now. Oh, and with those heads, you don't need a dual pattern cam...thos eheads have an excellent exhaust port and it could actually cost you some midrange torque going with a dual pattern grind.

I know you don't want to run over 11.0:1 BUT in my opinion your engine will be LESS prone to detonation with 11.25:1 compression and a tight .035" - .045" quench then it will with 11.0:1 and a looser .050" (which is not really that bad).

Good luck.

ps. 67RS/SS350 how is your combo running? Had it to the track yet? I'm just now to the point where I can start getting on it and tuning for the track. Mine feels really strong so far.

Eric, I am still a couple three weeks away from putting it in, still waiting on parts, so keep me posted on what is happening with yours. By the way its about three decades since I last ran a quarter. I have been driving performance cars forever but I am sure there is gonna be a squadron of butterflies when I stage this thing the first time. I hope I don't blow up a Ujoint or something when I dump the clutch on this new beast for the first time. I think I will probably go conservative on the first run and leave at about 3000 RPMs and work up to it. Just hope I don't embarass myself. LOL