I just recently put 081 TPI heads on my TBI 305 with a ZZ4 cam. I have to pull the heads again because I didn't get screw-ins and its pulling the studs. So, the heads had been cleaned rebuilt and resurfaced. Nothing was done to the block though.

I'm wondering, can I go with a thinner gasket to up compression a little, maybe squeeze out a little more from this motor. Or should I not use anything thinner than stock without knowing for sure the block is FLAT. Block has about 75k miles on it. It's in very good shape, but I'm not sure which gaskets I'm safe to go with. Any advice is appreciated, thanks.

 

it's not a bad idea to check for flatness every time you have a head off. as for the gasket you ought to be able to use a thinner one.

 

What's the recommended method for checking the block?

 

Lay a machined straight edge bar across a CLEAN block deck surface (top, middle, bottom and corner-to-corner in both directions) and try to shove a .004" feeler gague under it at various points along it's length. If it slides under at any point the block is beyond GM spec for flatness. For a performance application or for thin steel shim type head gaskets it's best if it's less than .002"

 

Thanks, I'll do that when I pull them and clean it up. Any specific gaskets recommended. Last I went with just standard replacement Fel Pro ones. Not sure on the compressed thickness, but I was shooting for something thinner this time if I could get away with it.

 

Fel-Pro 1003

 

FP-1003 has a high volume 9.158. A better boost in compression could be had from using the FPP-1094 it's volume is 3.245 compressed. On my engine that would equate to a change from 9.33:1 to 9.94:1

Here are some more:
Part# - Bore - Comp Thickness - Volume

FPP-1003 / 4.166 / 0.041 / 9.158
FPP-1010 /4.166 / 0.039 /8.711
FPP-1014 / 4.200 /0.039 /8.854
FPP-1004 /4.190 /0.041 /9.264
FPP-1034 / 4.200 / 0.041 / 9.308
FEL-7733PT2 /4.125 /0.039 /8.541
FPP-1094 /4.100 / 0.015 /3.245
MRG-5800 /4.130 /0.038 / 8.342
FPP-1044 /4.200 / 0.051 /11.578
MRG-3130G /4.060 / 0.040 /8.486
MRG-1130 /4.100 /0.018 /3.894
MRG-1134 /4.130 /0.028 / 6.147
FPP-1043 /4.080 /0.039 /8.355
FPP-1045 /4.180 /0.039 /8.770
FPP-1036 /4.250 /0.051 /11.856
MRG-3138G /4.165 /0.040 /8.930
EDL-7310 /4.190 / 0.038 /8.586
MRG-3132 /4.165 /0.040 /8.930
FPP-1142 /4.100 /0.040 /8.654
MRG-3131 /4.125 /0.040 /8.760
FEL-7733SH1 /4.100 /0.016 /3.462

 

I too recommend the FP1094 gasket. It is thin and coated, along with having a smaller bore then many others. This is important on a 305, and more so as the gasket thickness increases. Can produce a large dead-zone.

Handy chart Zed'er.

RBob.

 

Alright, thanks a lot guys, I'll probably check the block and go with the 1094 then if it's straight.

I'm figuring that it's impossible to get optimal quench on a motor that has not been zero decked and is still stock. Correct? Isn't optimum around .041.

 

Thanks. I just copied and pasted from an excel spread sheet I made for calculating engine compression ratios. I keep a database of gaskets, pistons, heads, blah, blah, to keep me from having to search all the time...

 

Are the 1094's good for alumnium heads?