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Old 07-19-2005, 04:17 AM   #1
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Location: Elgin, IL
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Car: 1997 Corvette
Engine: LS1
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Head gasket recommendations for high compression 355

355, 4.030" bore. TRW L2256F forged aluminum flat-top pistons with 4 valve-reliefs (anyone know the dish CC of these pistons due to the reliefs? Is it 5cc?), and I'm running aluminum 52cc heads.

First, what bore size head gasket should I look into? 4.060? 4.155? Second, what's the thickest gasket I could get away with? I want to keep compression at 11:1 or lower I think. Need to be able to run on 93 pump gas.

I had been considering buying a pair of those .020" copper shims at autozone and then buying some standard fel-pro gaskets there as well, but the more I'm looking into things, I might be better off going with a copper head gasket set, and they can be had for $60-90 on Summit. Just need to get an idea of what bore size I should go with or what thickness. I don't know if there is a downside to going with a bit larger bore gasket. I know it will help lower compression, but I don't know if it hurts quench or anything (I don't know what quench is exactly), etc.

If the pistons 4 valve reliefs is equivelent to a 5cc dish, then this question is fairly pointless as my CR should easily be at 11 or less. Otherwise, would it be okay to use a .072" gasket with a 4.060" bore? Summit carries a copper gasket set for $110 in that size.
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Old 07-19-2005, 01:14 PM   #2
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Okay, so I've discovered that the pistons have a 6.1cc dish, which is a bit better than I was hoping for. Means even with a .040" gasket, I'll still be at just 11.1:1. With a .060" head gasket, I'd be at 10.6:1.
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Old 08-24-2005, 10:30 PM   #3
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hey just out of curiosity, what cam specs are you running? your combo is very similar to mine, except i am planning on dish pistons to keep around 10.5:1. just wondering if i could get the flats and run higher cr.
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Old 08-25-2005, 12:08 AM   #4
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What is your deck height? I doubt it to be zero. I bet it is closer to 0.010 which would mean that you can add another 0.010 to your gasket for calculation purposes.

I would not go to a thick gasket as you would increase your squish area and reduce turbulance.

This may make the engine more prone to pre ignition and detonation than the higher compression.
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Old 08-25-2005, 12:47 AM   #5
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I ended up running some Felpro 7733PT-2 gaskets, which are .039" thick. I also used the .020" copper spacer shim designed for use with those gaskets. Compression is at exactly 10.50:1 with the pistons between .023-.025" in the hole when I measured.

Runs great without problems. No audible knock at all. I realize my quench could be LOTS better, but it runs well.

I ended up going with the XE268-14 cam which is a 224*/230* cam with .479"/.480" lift on a 114* LSA. Idles well (and will be even better with a tuned PROM) and pulls well to 5500RPM or so. I think my stock fuel pump is holding me back at this point. I have a Walbro 255lph, just need to install it.
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Old 08-25-2005, 12:47 AM
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