Compression ratio with 64cc heads
Thread Starter
Pro
Joined: Dec 2002
Posts: 522
Likes: 3
From: Rolling Meadows IL
Compression ratio with 64cc heads
I have a 85 with the one big valve relief on the piston. I am installing
64cc heads and I want to calculate the new compression ratio.
Does anyone know how many cc the valve relief is. One thought was
to use play dough and fill the relief then measure the volume of play
dough.
64cc heads and I want to calculate the new compression ratio.
Does anyone know how many cc the valve relief is. One thought was
to use play dough and fill the relief then measure the volume of play
dough.
Burning Brakes
Joined: Feb 2003
Posts: 1,246
Likes: 1
From: SouthBend IN
Re: Compression ratio with 64cc heads (dave_85)
Stock the 85 is supposed to be 9.75 with a 76CC head, the 64 will put you at 10.25 if i remember correctly. You can look at any SBC piston in summit and see what the comp ratio's are with the 76CC and 64CC heads.
You can switch to a 64 CC head IF IT'S ALUM. If your staying with cast iron you'll probably want to stay with the 76CC head
You can switch to a 64 CC head IF IT'S ALUM. If your staying with cast iron you'll probably want to stay with the 76CC head
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Re: Compression ratio with 64cc heads (mike 1985)
mike 1985,
Where are you getting your info? My Corvette parts book shows the 1984 and the 1985, as having the same forged pistons and 76 cc iron heads. Therefore, if he has the factory pistons, he should have the stock 9.0:1 compression ratio. Again, if the pistons are stock, one doesn't need to know the cc's of the valve reliefs. It's just math re figuring with the 64 cc heads. This is IF you trust the factory 9.0:1 rating.
RACE ON!!!
Where are you getting your info? My Corvette parts book shows the 1984 and the 1985, as having the same forged pistons and 76 cc iron heads. Therefore, if he has the factory pistons, he should have the stock 9.0:1 compression ratio. Again, if the pistons are stock, one doesn't need to know the cc's of the valve reliefs. It's just math re figuring with the 64 cc heads. This is IF you trust the factory 9.0:1 rating.
RACE ON!!!
Thread Starter
Pro
Joined: Dec 2002
Posts: 522
Likes: 3
From: Rolling Meadows IL
Re: Compression ratio with 64cc heads (mike 1985)
I think I can answer my own question. I found a web site that said the 85 was 9.0:1 with a .021 head gasket. I used the Dyno2000 compression ratio calculator. Choose a flat top piston and play with the Piston Down Bore number to get 9.0:1 with a 76cc head and .021 gasket. Then change the head to 64cc and the gasket to .039 and you get 9.79:1.
Burning Brakes
Joined: Oct 1999
Posts: 1,236
Likes: 91
From: Pittsburgh,PA
Re: Compression ratio with 64cc heads (dave_85)
dave_85, I know you can run 64 cc heads on the 85 with out any problem.
I've been running vortec heads on my 85 for a year now with no problems. I dont hear so well so I would not know if I had knock I just ran high test and had freinds tell me if I had knock.It works great.
I'm in the middle of building a 388 and I'll be running vortec heads on it as well
Dave
:flag
I've been running vortec heads on my 85 for a year now with no problems. I dont hear so well so I would not know if I had knock I just ran high test and had freinds tell me if I had knock.It works great.
I'm in the middle of building a 388 and I'll be running vortec heads on it as well
Dave
:flag
Team Owner
Joined: Sep 2001
Posts: 62,119
Likes: 1,725
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Re: Compression ratio with 64cc heads (CFI-EFI)
My Corvette parts book shows the 1984 and the 1985, as having the same forged pistons and 76 cc iron heads. Therefore, if he has the factory pistons, he should have the stock 9.0:1 compression ratio.
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