Compression ratio for L-98.
Thread Starter
Racer
Joined: May 1999
Posts: 290
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From: Nashville TN
Compression ratio for L-98.
The 1985 Vettes had a 9.5:1 CR. The iron heads I believe were 76cc. What was done to get the CR up to 9.5? Next question, how will 86+ Aluminum 58cc heads work on my 85? TIA... :cheers:
Team Owner
Joined: Sep 2001
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From: Athens AL
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Re: Compression ratio for L-98. (85z51vette)
i thought they had 9.0:1 compression, and 86+ will work but you might as well go for fast burns or AFR 190s.
Thread Starter
Racer
Joined: May 1999
Posts: 290
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From: Nashville TN
Re: Compression ratio for L-98. (vader86)
I'm trying to keep this cheap. I'm just trying to get my car back on the road and get rid of the '85 cast iron heads. Stock L-98s I believe are my best choice. Also, will my stock exhaust manifolds/headers be correct for the exhaust port on this head?
Thread Starter
Racer
Joined: May 1999
Posts: 290
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From: Nashville TN
Re: Compression ratio for L-98. (85z51vette)
I guess I should give you guys the complete story so I can get an accurate answer. My engine is dead. Has been for about a year (I know, I know). My dad has a good friend with a 4 bolt main 350, .60 over, X rods, and on a very recent rebuild (~1000 miles). He wants $500 for the long block. The heads, however, are 882 castings with 76cc chambers. I asked, but he won't sell it to me as a shortblock. The only other heads I have right now are my stock '85 iron heads which I believe MUST be damaged as my car got really hot toward its end. I haven't had them checked though. He said the pistons are flat tops with 2 valve reliefs and says the CR is probably 8.5:1. This is the motor the aluminum heads would be going on. Hope this helps. Thanks again.
Pro
Joined: Dec 2000
Posts: 700
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From: Derby Kansas
Re: Compression ratio for L-98. (85z51vette)
I believe the block is different between aluminum and iron head L98's due to the roller rockers on the aluminum. I MAY be wrong though, but I don't think it would be a "simple" swap.
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Thread Starter
Racer
Joined: May 1999
Posts: 290
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From: Nashville TN
Re: Compression ratio for L-98. (Ron78Z&85Vette)
The blocks are identical (I'm 99% certain). I don't believe aluminum head L98s came with roller rockers either, just plain stamped steel. Help us out here guys.
Pro
Joined: Dec 2000
Posts: 700
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From: Derby Kansas
Re: Compression ratio for L-98. (85z51vette)
Not positive about the late 86 motors, but according to the "specifications" section of netvettes.com , 87 and up Corvette L98's had roller rockers. If you haven't checked it out take a look, there's some interesting stuff there.
:cheers:
:cheers:
Thread Starter
Racer
Joined: May 1999
Posts: 290
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From: Nashville TN
Re: Compression ratio for L-98. (Ron78Z&85Vette)
I looked at that page, sure enough it says they came equipped with roller rockers...this is certainly news to me. I don't see how that would change the block though. Heads should bolt up and work fine.
Drifting
Joined: Jul 2001
Posts: 1,511
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From: Winter Park Fl
Re: Compression ratio for L-98. (85z51vette)
I guess I got cheeted when I bought my car! My '91 L98 had stamped steel rockers before I changed them to Comp Cams 1.6:1. Now I will say I got hydrolic roller lifterrs when I bought the car new.
Thread Starter
Racer
Joined: May 1999
Posts: 290
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From: Nashville TN
Re: Compression ratio for L-98. (C44ever)
I guess I got cheeted when I bought my car! My '91 L98 had stamped steel rockers before I changed them to Comp Cams 1.6:1. Now I will say I got hydrolic roller lifterrs when I bought the car new.
[Modified by 85z51vette, 3:23 PM 1/21/2002]
Safety Car
Joined: Dec 1999
Posts: 4,691
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From: Framingham MA
Re: Compression ratio for L-98.
The first corvette to have roller rockers from the factory was the Lt4.
The 87 up blocks are different as machined for roller lifters and one piece rear main seal. The 86 Blocks have a one piece rear main seal but don't have roller lifters (ie the block need to be machine or you neeed retrofit roller lifters)
The 87 up blocks are different as machined for roller lifters and one piece rear main seal. The 86 Blocks have a one piece rear main seal but don't have roller lifters (ie the block need to be machine or you neeed retrofit roller lifters)
Pro
Joined: Mar 1999
Posts: 678
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From: Oslo, Norway
Re: Compression ratio for L-98. (85z51vette)
Hi The blocks on 85 and 86 and up are different. On the 85 you have a large diameter bearing at the flywheel and two piece zimmer ring or gasket to avoid oil leakages. For the 86 and up there is a one pice Zimmer ring and a small diameter bearing
