wannafbody

iTrader: (1)

I blew my tpi and found a rebuilt 350 tbi motor.
I was wondering what is differnt on the tbi short block from the tpi?

Thanks

Atilla the Fun

the TBI engines didn't get roller lifters, but you can swap all that stuff over. Otherwise, they're functionally identical. Have at it.

wannafbody

iTrader: (1)

what about the pistons? Are the l98 ones better? compression the same?

built91Z28

Are you 100% on that? Not doubting you, just making sure. My GF's 91 RS has a roller short block. We always assumed it was the stock 305 motor, but now I may need to go check what it really is.

Atilla the Fun

All the '87-up passenger car 305s were roller. All the '88-'95 truck TBI V8s were non-roller. All the '88-up 4.3s were roller. All '87-up blocks will accept stock rollers.

Atilla the Fun

If it's been rebuilt, then it got new pistons anyway, it's luck-of-the-draw. But to start with, both came with dished pistons. Only 'vettes had flat-tops, and I'm not sure when those stopped.

wannafbody

iTrader: (1)

So would it have the same compression as my l98 if I use my l98 heads?
I just dont wanna lose power at all

Atilla the Fun

I just answered that in post #6

thomas1976

You need to find out, cylinder bore, piston to deck, compressed head gasket and piston dish mesures to calculate the compression. The 083 heads should be around 64cc chambers.

http://www.kb-silvolite.com/calc.php?action=comp

91-92 firebird service manual says 9.75:1 CR for the L98.

TGO tech shows 9.3:1 CR for the 88 L98 https://www.thirdgen.org/1988-pontiac-firebird

Atilla the Fun

9.75:1 was a typo.
And if the TBI short block you're looking at does have dished pistons, then you don't HAVE to do all what Thomas typed, it'll be close enough to safely use on pump premium. When winter arrives, then you can safely experiment with lower octane.

thomas1976

What would the correct CR be for a 91-92 L98 with flat top pistons, for comparison?

Atilla the Fun

that's the thing, NO '91-'92 V8 F-cars actually came with flat-tops. 9.25:1 is close enough to precise, a quarter ratio either way has no real impact on choosing a cam for one of these engines. You're still looking at pump premium for over 90% of the possible situations.