What is the stock head gasket thickness for a stock 305 TPI? I'm looking at several different heights from Felpro.
Im guessing the most common is 1003 which has a .041 thickness and a comp. vol. of 9.1cc
There also is .039 and .051 and .015.
If I went with the .015 head gasket which has a comp vol of 3.2cc,wouldn't that bring me closer to zero deck? This would increase my C.R. and give more power?
If the stock C.R. is 9.5:1 on my motor with
58cc heads,what would my C.R. be with a
.015 head gasket?
Am I barking up the wrong tree looking for free HP?
Thanks,
Don

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1990 Trans Am WS6
305TPI 700R4

ENGINE:
150hp NOS kit
March underdrive pulleys
Edelbrock headers(JetHot)
Mac off-road pipe
Flowmaster exaust
Jacobs ultra coil
K&N filter
Fulley ported base,
runners,& plenum
Crane AFPR
Hypertech airfoil
Crane 1.6 rockers
210/220 .533/.544 Cam
W/P Torquer heads
Edelbrock TPI Base
Edelbrock TI Runners
Edelbrock 52mm T.B.
TRANSMISSION:
Richmond 3.73's
Auburn posi
B&M Mega shifter
TCI shift kit
Vette servo
B&M 3-4 upshift kit
TCI Trans Rebuild
2800 stall 9.5" TC
Nitto Drag radials
FUTURE MODS:

BEST RUN:
12.48 @ 109.23 MPH
(with stock heads,cam,intake,and crappy Pep Boy's tires)

if your comp ratio is 9.5 now with a .041 think gasket using a .015 gsket will rais it to 10:1

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when the green flag drops the bull$hit stops

Curent: 350,performer RPM intake ,650dp, 700r4, headers, 3inch exhast
Spring 01: 406, Comp 282 solid cam, 2400 stall converter, every thing else the same.

R.I.P #3

The factory uses a thin gasket as it is, I cant remember the exact number, but its around .020-.025. This is of course assuming you havent changed it yet.

i wouldn't use a steel shim gasket. good chance you'll have leaks and that you'll have to retorque and the gain you see most likely won't be much. i'd use the thinnest coated perma torque type gasket.

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ICON Motorsports

1st & 3rd

Felpro has a .041 and a .039 head gasket.
Does any company make a thinner coated perma torque style head gasket?
The .015 head gasket is a embossed shim with precision rubber coating.I might just go with it anyway.
Im using a .041 Felpro now.
Don


[This message has been edited by Nitro Don (edited March 18, 2001).]

jegs has a coated shim .015, made by fel pro for 18 dollars. i don't know if that's a perma torque or not. give them a call and ask 1-800-345-4545

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ICON Motorsports

1st & 3rd

[This message has been edited by ede (edited March 18, 2001).]

I am running a .029 head gasket that I got from TPIS, they say its smaller than the stock gasket and will increase my compression by about 1/2 a point. I have been very happy with it, I only use 93 octane fuel though.

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1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission
Borg Warner 7.75" 9 Bolt Rear End

Current Mods: LT4 HOT Cam, Comp Cams 1.52:1 Roller Rocker Arms, Edelbrock TES 1 5/8" Headers, Hooker 3" Aerochamber Cat-Back System, Performance Resource Chip, Accel Ignition Coil, Cap, Rotor, 8.8mm Wires, K&N Filters, JET TPI Air Foil, All Free Mods, Falken ZIEX Z-Rated Tires.

Best ET (w/o LT4 cam): 14.32 @ 97.7mph
(corrected for elevation)

Soon to Come: 7.625" 10 Bolt with 3.42s and Accel TPI Intake Base

The only meaningful ways to get closer to Zero deck is to (1) change pistons or (2) have the block decked or (3) change the length of the rod or (4) change the stroke or turn down the mains of the crankshaft.

Zero deck is the relationship of the deck of the piston (the flat area) with the deck of the block (part the head sits on) at TDC.

So changing to a thinner head gasket doesn't change that relationship.

It does, however, tighten the quench, which is good as long as you don't go too far resulting in the piston kissing the head.

A thinner head gasket also increases the compression ratio and reduces valve to piston clearance (which can be bad if you go too far.)

A thinner head gasket can also require a shorter pushrod, but not usually, unless your pushrods are already a tad too long.

As a rule of thumb, each 9 ccs (gave or take)is 1 point in compression.

Jake

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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9

Dan,

I hate to be the bearer of bad news, but TPIS is wrong. According to the MVMA (Motor Vehicle Manufacturer's Association) Specifications Form for Passenger Cars (1987), the 5.7 Liter V8 (Tuned Port Fuel Injection) RPO L98 uses a compressed head gasket thickness of 0.021 inches.

The difference in volume between an 0.021 and 0.029 (your new gasket) would be
pi * (radius**2) * 0.008 = 0.101 cubic inches = 1.647 cc

Based on formulas used to calculate compression ratio but without going into the gory details, it's about 0.1 point increase in CR per 1 cc decreased. So in your case Dan, your CR is down ~0.2 from the stock 9.3 to 1 -- ~9.14 to 1.

Using the above formula, you can calculate compression ratios for any compressed thicknesses.

------------------
Willie

Supercharged 1987 305 IROC-Z, Daily-Driver, Emissions-Legal.
Paxton (6-psig): 12.57 @ 111 mph.
Paxton (6-psig) & 50-hp nitrous: 12.04 @ 114 mph.
ATI D1SC (10-psig): ?

http://willie.camaro-firebird.org/

1987 "20th Anniversary Commemorative Edition" Z28 Convertible -- Super Chevy Show Class Winner, 1998.

[This message has been edited by Willie (edited March 18, 2001).]

It's the same as the 350 TPI, 0.021 inches thick (compressed).

For a 305, the two-dimensional surface area is:
pi * (r**2) = 10.986 square inches

The difference in gasket thicknesses from stock to:

0.015 = -0.006 inches
0.039 = +0.018 inches
0.051 = +0.030 inches

The difference in volume from stock is:

10.986 * (-0.006) = -0.066 cubic inches = -1.08 cc
10.986 * 0.018 = +0.198 cubic inches = +3.24 cc
10.986 * 0.030 = +0.330 cubic inches = +5.40 cc

Based on the general rule of thumb that for each cc decrease, there is a 0.1 increase in CR and given:

0.015 gasket: -1.08 cc difference in volume
0.039 gasket: +3.24 cc difference in volume
0.051 gasket: +5.40 cc difference in volume

Based on a stock 9.5 to 1 CR with 0.021 compressed head gasket thickness, the resulting CR's are:

0.015 gasket = 9.6 to 1
0.039 gasket = 9.175 to 1
0.051 gasket = 8.96 to 1

Hey Willie,
Thanks a million.You had the answers I was looking for.If I dont go with the .015 gasket,I will go with the .021 gasket.
Thanks,
Don