Need some help from the motor experts. I managed to get my compression a little too high when doing a rebuild and am trying to make changes to keep SCR down. This is a 383 with CI heads and if I got the figures right, I will have the following:

Dynamic Comp: 8.232

Static Comp. 10.07

Quench: .066

Cam advance 0

Will I have any problems with the cam advance being at 0, and the quench being .066?

Thanks in advance:

 

According to Smokey Yunick, your quench is already on the loose side, and at a point where excessive amounts of intake charge may remain in the quench area as the piston reaches TDC, especially if your domes obstruct the spread of the flame front.

Just what are your cam specs? Sounds like you may simply have too little cam, as 10:1 CR isn't outrageous, by any means.

 

Cam specs are:

Advertised Duration Int. 270 Ex. 270
Gross Valve Lift Int. 470 Ex 470
Valve Timing@.050 Int. 6 Btdc 38 Abdc
Ex. 38 Bbdc 6Atdc

Specs for cam installed @106.0 Intake Center Line

Duration @ .050 Int 224 Ex 224
Lobe Lift .3130 .3130
Lobe seperatioin 106.0

Hope this helps.

 

What are your other specs (e.g., head gasket thickness, deck clearance, etc.)?

Do you have all of the parts purchased already?

 

The specs are:

383
5.7 rods
-5cc flat top pistons
.025 deck height
Gasket bore 4.166
Gasket thickness .041
67cc cast iron heads

Hope this helps. If this does not work, I may go to a comp 280H. Your opinions would certainly be appreciated.

 

First, if it's not all a done deal yet, your piston deck shouldn't be more than 0.005" in the hole for good quench with that 0.041" gasket, but at least there's no dome blocking gasses.

You appear to be describing a CompCams 270H Magnum hydraulic cam, which has an LSA of 110* and with the intake LCA at 106*, which would be 4 degrees advanced (as ground by Comp). You'll need premium gas and a good tuning setup, but you might be OK with this cam and 10:1.

There are guys with significantly higher SCR's and DCR's on here claiming to have no detonation problems , but how many of them have iron heads I don't know.

Do you have a stick or automatic? With the auto, Comp suggest the 270H is the biggest Magnum you should use with the stock converter, but if you have a stick, you could consider the 280H without that worry.

With the 280H, you'd probably see about a 5HP peak increase while lowering your DCR a measurable amount. You'd also loose a little more torque below 3500 than you'd gain above 4000. Cranking compression could also drop as much as 10psi...

If it weren't for the iron heads, I'd be comfortable telling you to keep the 270H, possibly with an installed LCA of 107-108*, but a better small block guy than myself will have to help you with that call.

Hope the info helps, anyway.

 

I'm not a fan of KB pistons ... but they have a -18cc dish hyper KB135 with 1.433" CD ... those & a 0.020" Mr.G shim gasket will yield close to 9.44:1 scr & great 0.037" quench.