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I have searched and searched but can’t find a clear answer to my question. Will LT1 manifolds bolt to the y-pipe on an L98 car without modifications. If not, what needs to be changed to switch them over. Before we get started down a rabbit hole, I am not interested in doing headers. My car is a 1991 convertible. TIA
Thanks Vader, I have spent a lot of time combing through old threads. I appreciate the contributions you’ve made to this forum over the years, they’ve been very helpful.
I want to build this car to be just a little more stout than factory without going overboard, 300 crank hp is kind of what I’m shooting for. Aftermarket support for this platform is not what it was 15 years ago and parts seem to be more limited making these decisions more difficult (especially considering current supply issues). It’s looking like headers may be the only option here for what I’m wanting to achieve.
Thanks Vader, I have spent a lot of time combing through old threads. I appreciate the contributions you’ve made to this forum over the years, they’ve been very helpful.
I want to build this car to be just a little more stout than factory without going overboard, 300 crank hp is kind of what I’m shooting for. Aftermarket support for this platform is not what it was 15 years ago and parts seem to be more limited making these decisions more difficult (especially considering current supply issues). It’s looking like headers may be the only option here for what I’m wanting to achieve.
Should be able to get there with just exhaust, intake, cam. The stock heads should breathe enough for 300 crank with those changes.
Might even be able to skip the cam, people who know more about these engines than me can chime in.
That’s the way I think I’m going to have to go. I might just have to bite the bullet and order some TPIS headers but my god the wait on those is crazy right now.
As vader said they bolt to the heads fine. The holes on the Y pipe that slide over the studs need to be elongated because the LT1 studs are slightly further apart. A die grinder and a few minutes will take care of it.
As vader said they bolt to the heads fine. The holes on the Y pipe that slide over the studs need to be elongated because the LT1 studs are slightly further apart. A die grinder and a few minutes will take care of it.
That’s great to know, ideally I’d like to run the LT1 manifolds with a true dual/h-pipe. I appreciate the input 👍🏻
You do know that there are still four items to modify the LT1 manifold to work on the L98 heads right? Two center bolts, distributor, crossover water-pipe, and rad hose.
What after market fuel system you expect to use? I have thought about your exact dilemma for upgrading L98 for a couple years.
You do know that there is still four items to modify the LT1 manifold to work on the L98 heads right? Two center bolts, distributor, crossover water-pipe, and rad hose.
I’m referring to exhaust manifolds. I would never attempt to try and put an LT1 intake manifold on an L98.
If you can find a complete LT1 exhaust system that would make life easy and work well for you. I picked up one locally for $150 without the exhaust manifolds but with the cats. Sold the cats to a club member and now this will go behind the long tube headers keeping my original parts intact.
I did the LT1 swap on an '89 truck block with #113 L98 aluminum heads....and kept the HEI in back where it belonged....by cutting an aluminum carb manifold and cutting the EGR? pollution crap that was in the way of the dizzy...a pro welder buddy welded it all up...he is GOOD, I seen him weld aluminum to concrete and make it stick GOOD!!!
;-) I machined the intake so to take a 3/4 inch copper pipe elbow on each side, and 3/8 nipples in the back dizzy region....so it's plumbed to a remote stat housing hung up top/behind the radiator.....
all this on my '72 vette.....also, it's a roller engine...1.5 rockers.....
I want to build this car to be just a little more stout than factory without going overboard, 300 crank hp is kind of what I’m shooting for.
A well tuned stock TPI engine will make 300 crank HP with factory exhaust manifolds. You'll need cat delete, x pipe, glass packs and a good tune. And then you should be at 300 CHP.
My 90 TPI is setup that way and here's a 1/4 mile time slip. That's 300 CHP in a 3400 pound car.
And here's what John Lingenfelter had to say about the stock L98 exhaust manifolds in his "Modifying Small Block Chevy Engines" book.
Last edited by C4industries; Jul 30, 2025 at 12:55 PM.
LT1 Manifolds on L98
