My friend just got a 1985 car (non-3rd gen...) with the L98 in it, stock. He was wondering (as am I) what the differences were with the 1985 TPI motor. I know there were some... and people shy away from this motor... but what was the reason again?

At first I thought it was the fact that it wasn't a roller motor, and had the 2 piece rear main... but if that was the case, wouldn't the 1986 be the same?

 

there were no L98 cars built in 85... also an 85 IS a third gen car...

 

He said the car wasn't a thirdgen. And yes, L98s were available in 1985 in the C4 Vette. My guess is he's talking about a vette or another vehicle with the vette motor in it.

 

Correct, but I didn't want to use the term "vette"... as it might get the thread locked!

So... assume someone took a 1985 vette L98 and put it in a 3rd gen. Now what are the differences with the 85 TPI in comparison to all the other years... and why do people shun them?

 

The 85 had a unique ECM used for that year only. The 85 got a unique MAF with an external "burnoff module" that's insanely expensive to replace if you can't find one used or in a bone-yard. This burnoff module piggy-backed the ECM.

The wiring harness was different due to the different ECM.

A long time ago when I was first starting to mod my car, I was told by a GM engineer that I was emailing back and forth that the 85 Corvette used a 35lb fuel pressure instead of the 43.5 that they went to in 86. The LB9s in the f-body used the 43.5lb pressure in 85. I haven't really seen this 35lb pressure mentioned by anybody else over the years, so I'm a bit skeptical about that claim. I'm not aware of the FPR having a different part number for the 85 Corvettes, but I never really bothered to investigate.

The 85 Corvette had the Iron heads and perimeter-bolt valve covers, but so did most of the 86s. Late in the 86 production run they converted to the aluminum centerbolt heads.

The Corvette L98s differed from the f-body versions in that they also had an oil pressure sensor that was tied into the ECM. I don't know if this went all the way back to 85, but if somebody else doesn't chime in, you'll want to find out.

If you can put up with the attitudes and the "my mechanic said..." type of replies, try 2005 www.corvetteforum.com. Mixed in with all the crap is usually some helpful tech information.

 

OK, thanks for the info. Also, is the intake manifold base different? For some reason I remember hearing it was.

 

*foot in mouth* I stand corrected... DOH!!

 

Only the angle of the bolt holes. There's 87-up, and pre-87. 85 shouldnt have the 'Corvette' EGR plumbing as the heads that year had an exhaust crossover. Fuel rails are different.

 

Didn't the Corvette heads/manifolds retain the old bolt angle?

 

Good point, that would be the same on a Corvette.