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Old 11-16-2001, 12:11 PM   #1
Scooby Specialist
Member#: 2697
Join Date: Oct 2000
Location: Olney, MD. Work in McLean, VA
2000 Celica GT-S
Spectra Blue

Default Pat Olsen - head gasket question once again.

Hey Pat,

After driving with bad headgaskets for 20,000 miles I finally managed to blow them out completely. Oil was pouring out of the engine from the driver's side gasket at a rate almost as fast as if I pulled the drain plug. I've never seen that before.

Anyway. I'm going to get a new engine. Found a 99 with 49,000 miles on it for $1800. I plan on having my mechanic change out to the SOHC headgaskets (11044aa521) you described in your headgasket post. You noted that those gaskets are thinner than the DOHC "crap" gaskets. Couple questions, though:

How will this change the compression ratio on the car? (I'm assuming it'll bump up the CR since the gaskets are thinner. Also, will this new CR pose any problems while running the 97 ecu?


(Hoping to FINALLY settle the headgasket "weakest link" syndrome)
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Old 11-16-2001, 01:32 PM   #2
Patrick Olsen
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Member#: 120
Join Date: Jul 1999
Chapter/Region: AKIC
Location: Where the Navy sends me...
1997 Legacy 2.5GT
1996 Impreza coupe


It will marginally increase compression ratio, but I don't really know how much. If the techs at the dealer are willing to work with you, you could probably figure out what the change would be - their tech manuals probably have all the data you would need. You would need to know the cylinder head combustion chamber volume, the compressed thickness of each gasket, the bore and stroke of the cylinder, the distance below the top of the deck when the piston is at TDC, and (depending on what the piston looks like - I've never seen one) the volume of the dish or peaks or valve reliefs in the top of the piston. I think that's everything, but that's just off the top of my head - go here http://www.google.com/search?q=compr...tio+calculator and I'm sure one of the links there would tell you exactly what you needed to know.

I'll pass the buck and say "call Trey Cobb" since he was the one that suggested this to me. He also told me the SOHC gaskets are stack-able, so you could put two of them together and that would equal the thickness of the original DOHC gasket. Personally, I wouldn't want to go that route as it just gives one more potential gap to possibly develop a leak.

Anyway, my guess is that the change in compression ratio would not be large enough to cause any problems, but running 89 octane instead of 87 would probably be wise just to give a slightly larger margin to detonation.

Pat Olsen
'97 Legacy 2.5GT sedan
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