compression ratio

[David Redszus]

How much ignition timing? These heads are "fast burn" and do not need or want as much advance as is commonly used with other Chevy heads.

How fast is a "fast burn"? What exactly does that mean?
Do we have laminar or turbulent flame speed data?
What effect does squish velocity have on flame speed?
How about flame temperature? Mixture?

Other than empirically observed performance, how is ignition timing advance determined or predicted?

[cjperformance]

How much of an increase of torque/hp by changing ratio from 9.4:1 to 9.9:1?
93 octane gas
355 cid

9.4 to 9.9 isn't huge but lets say right now it has quench clearance in the .060" to .080" area, the comp boost as well as being able to reduce quench height still wont work a miracle but will be an improvement on the CR boost alone. Do you know what quench height/clearance you have now?

[88bluestar]

65cc chamber 4.030 over, 3.480 stroke, -5.5 flat top piston.
.0015 deck
.0061 head gasket
76

I was going to go to a .0039 Fel Pro Gasket,
Bore (in): 4.125 in.
Bore (mm): 104.775mm
Gasket Material: PermaTorque
Compressed Thickness (in): 0.039 + .015=.054
Compressed Volume (cc): 8.541cc

Also looked at the gm steel shim .028 but has a 4.000 bore, .028 +.015=.043 which would give it a nice squeeze. Steel (honda small journal) Eagle 6.125 rod

[DrillDawg]

65cc chamber 4.030 over, 3.480 stroke, -5.5 flat top piston.
.0015 deck
.0061 head gasket
76

I was going to go to a .0039 Fel Pro Gasket,
Bore (in): 4.125 in.
Bore (mm): 104.775mm
Gasket Material: PermaTorque
Compressed Thickness (in): 0.039 + .015=.054
Compressed Volume (cc): 8.541cc

Also looked at the gm steel shim .028 but has a 4.000 bore, .028 +.015=.043 which would give it a nice squeeze. Steel (honda small journal) Eagle 6.125 rod

Now you are on the right tract, coat the gaskets with some high metallic silver paint, one light coat, one med coat.

[groberts101]

Cometic makes MLS gaskets for your app down around .027". Pricy but well worth it and reusable too.

[steve cowan]

I used MLS 0.027" head gasket on my 383 sbc, my pistons are 13 down the hole.
They are an excellent gasket and fit nice and to suit a 4.030"bore not a 4.125" bore like some head gasket but I believe the bore gasket size in comparison is very little in compression ratio variation, so no big deal in a street application.

[cjperformance]

65cc chamber 4.030 over, 3.480 stroke, -5.5 flat top piston.
.0015 deck
.0061 head gasket
76

I was going to go to a .0039 Fel Pro Gasket,
Bore (in): 4.125 in.
Bore (mm): 104.775mm
Gasket Material: PermaTorque
Compressed Thickness (in): 0.039 + .015=.054
Compressed Volume (cc): 8.541cc

Also looked at the gm steel shim .028 but has a 4.000 bore, .028 +.015=.043 which would give it a nice squeeze. Steel (honda small journal) Eagle 6.125 rod

Ok with a .076" piston/head now it is well worth the effort of swapping head gaskets to get down to .040"ish. That small comp change plus the tighter quench and appropriate retune will make a small but noticeable difference in response and crispness.

[88bluestar]

I was incorrect about the intake I had. It is not the victor jr, it's a chevy bowtie 10051103 raised runner intake.

[88bluestar]

Anyone know wheres the cheapest spot for the air gap intake?

[DrillDawg]

Call edelbrock to see if they even make one or what they offer for those heads, you may be limited to two or three intakes.

[F-BIRD'88]

Professional Products makes a "Crosswind" dual plane hi rise air gap intake for vortec heads.
( I have this on my 406 vortec headed motor.)
Their Hurricane (vortec) single plane is good too.
check summit racing .

[Tuner]

The manifold on the engine I described earlier in this thread is a GM marine crate engine take-off from a local marina that replaced some engines in EFI applications. It isn't an air gap but the engine runs OK anyway. It is a dual pattern, square and spread bore carb mounting.