No, my LC2 and the GN LC2 compression is identical. That was the reason for the piston change. If you put my heads on a GN, it'll bump the compression almost a full point.

So the manual is right about the 8:1 and wrong about the 8.5:1. But it says both in the same book. And the TTA manual is only about the 89 TTA. Nothing else in that book is for any other car. It is a supplemental to the 89 Firebird book as it is only specific to the changes for the car. Basically engine, trans, electronics, and emissions. Everything else is covered in the regular book.

And it wasn't to clear the strut towers as most of the magazines said back then. I could put GN heads on and it'll fit with no problems on the strut towers. It was to keep the V8 GTA air conditioning. If I were to put GN heads on, I'd loose my A/C because of fit.

As for the LT1, true it only got 30HP. But it was also more of an economy move as mpg is quite a bit more. Same with the LS1. Performance is just a by-product. MPG is more important than performance in the corporate scheme of things.

 

GM makes mistakes all the time in their literature. I recall many years ago when I bought my 1987 Buick GN. I've got an original Buick Regal 1987 brochure lying around here somewhere about the car when it was new. I recall one part reading - "new for 1987, hydraulic-roller lifter followers for reduced friction and more power" or words to that effect. The LC2 never came with roller lifters in 1987, even in the later 1989 TTA. Yet there it was, plain as day in the 1987 brochure.

I have always read in road test magazines and various spec charts, the CR for the L98 was 9.3:1. The posts in this thread mentioning the CR was rated higher than that is the first I have ever read or heard of this, anywhere.

If you take a look at the 3 previous links posted about TPI info, you'll see all 3 jibe pretty much with each other on specs for all years of L98 and the 305.

 

Here's and iea...... throw that 350 out oput a nice carbed 406 in it and be done with .....

oh yea get the third gen 4 core radiator.........

L-98/LT-1 Yucky:

I've had exsperince with both there not as much fun as a solid 400chevy........Now 400 Poncho will Roast a 400chevy but in a thirdgen the 400 chevy is ideal but i am sure sombody somwhere made a 400poncho fit in a third gen.......
.................................................. ........................

But what do I know about Engine I only Put a TBI injected 390Amc in the 9.60's................... ....................................

 

I did a search over on thirdgen.org where I thought I found the compression ratios, and I couldnt find it again. I know it was Glenn91GTA who said it, and a few other trustworthy people. The Tech Data mentions the 350's getting a "lighter piston" in 1990, which accounts for the 5 horsepower upgrade, but I figure it was also the change to speed density and the higher compression as well. The speed density engines have a smaller cam than the 88-89 TPI cars, but are still rated at 5 horsepower more.

There are lots of mistakes on those articles mentioned, so as was said it all comes down to who and what you believe.

 

From what I understand, the 5HP gain was due to the loss of the MAF as a restriction in the inlet tract. I can see the engine getting a lighter piston for '90, but that in itself will not give any HP gain.

 

Alright, I spent a couple of hours measuring my disassembled L98, here's the results...Kevin you're right it is 9.81 even on my '90 model, my bad...
Well, since everyone can look up formulas I won't list them, just my calculations.
716.7cc (converted measurement of swept volume for a 350)
64cc (chamber volume)
9.1cc (gasket volume on a .041" gasket, ithought was thinner...)
2.05cc (deck height at .010"roughly)
6cc (piston volume = reliefs + ring crevice)

716.7cc + 64cc + 9.1cc + 2.05cc + 6cc = 797.85
Divide by
64cc + 9.1cc + 2.05cc + 6cc = 81.15

= 9.83179!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!
read it and weep boys....sorry


(Maybe I was wrong about the TTa, my bad, you know your own car better, and should...As I know my car better.. )

 

Also, I found some interesting tid-bits in my archives:
A DIRECT quote from CHP;
"In many quarters conventional wisdom has it that the only way to squeeze impressive times out of a TPI Camaro is to yank the TPI. **As is often the case, conventional wisdom is foolishly out of touch with reality.".......
On their first pass with a built "TPI" Camaro, they netted a 12.651 @ 108.55, and after bumping the fuel up 2psi and adding a couple degrees on pinion angle they netted, 12.384@111.06...
And go on to say, "not all Tuned port Camaro's are easy pickings."

L98 Aluminum Vette heads
TPIS ZZ9 cam
BigMouth Base/largeTR/ported plenum
52mm T/B
24#'ers/Prom
12"convertor/3.42's
Pretty mild if you ask me...

 

deck height at .010"roughly

I have yet to see any stock 350 with such good deck height. Usually the piston sits down in the hole at .025", not .010". My 400 for example was .026".

Good discussion BTW, but let's stick to facts and not 'guesses'.

 

I measured it as close as I could, rounding the ten-thousandths for clarity sake, NO GUESSING IN THERE!......

 

Previously, you posted:

2.05cc (deck height at .010"roughly)

Big diff between .025" and .010" in deck height when calculating compression.

 

What's your point? I measured, I told you my measurements...
Yep you're right, there would be a big difference between .010 and .025...glad I don't have .025"...
Yeah that would drop it down to 9.583233 or 9.6:1, still a far cry from 9.3...

 

Third gen Claim's all TPI's are 9.3:1....LOL

my 89 RS had 9.75:1in it's LO-3,But i bumped it up so 10.25:1,then threw it nabck together droped somes 3.73's in it and got in to run 14.80's.
Just like my 350TBI was running with 190,000miles on it.

so worn 350 Built fresh 305 run about the same time's witch was cool.

350 pull 14.80's at 95.78mph as where the 305 ran 14.80's at 93.76mph.

350TBI 91 GTA 14.86-14.84.94-96mph. 190K miles bad comp.

305TBI. 89 RS 14.89-14.87. 92-94mph.6K miles good comp.

ya your right compression don't mean Crap.......

 

Here's a tip. Many Thirds are already and have been appreciating. I know because I'm always in the market and have been watching for 4 years. TPI cars especially. L98 G92s, LB9 G92 5-Speeds, and IROCs especially. If you've got a mint one or low-moderate mile nicely taken care of stock car, maybe you should find a high mile car to mod because they are gonna be worth more than you think in years to come. It always happens. It seems that these cars are getting up there faster than later 2nd Gens, which is wierd because they're newer. Maybe because of their popularity, who knows, all I know is that they are going up. Sometimes people like a little modding though when buying cars like these.

 

You mean a third gen might be worth more then $750????

Soon awsome,Good to hear man I was about ready to mod Out and Blow my L-98 all over 3 lanes of east wash.......

But maybe I'll have to rethink that thought...........

I still Like the Idea of Having a TBI406 and TPI406 powered F-Body's...............

But For some $$$$$$ I might keep the 87 GTA together even tho it's only a 16 second car......

 

91 GTA Ramair2, what's wrong with your '87, I don't see many l98/350 TPI cars running that slow?
What mods have you done?