Well, the 350 tpi in my 88 GTA has been making smoke and smells that are anything but encouraging. It's leaking oil something terrible, and I feel like some internal work is gonna be inevitable. Of course, if I'm going to all that work, why not do some mods? She's not stock to begin with, the po swapped in a crate tpi with 10.5 compression and a hot cam etc. But last night I remembered my old 350 project engine that I put on the back burner in my parents garage (read: I ran outta money) turned to have already been stroked to 383. The block was iffy, the pistons and rods were cast and rough looking, but the crank seems solid. And it's just gathering dust. While my GTA engine is probably 10-12 years newer, the crank should fit right in correct? My real question is regarding the rods: if I want to keep the forged pistons already in the bird and maintain the 10.5 compression, what length rods will I need? Or will I have to actually pull a piston from the TPI to measure the wrist pin location etc.? Because I have few actual details about what specific brands and components went into the crate engine, it was purchased in the early 90s.

 

Quick answer, no. Your old 400 crank turned for 350 main journals is a 2 pc rear main seal and will not fit your newer 1 pc rear main seal block. To keep the forged pistons from the 350, you would have to use shorter 400 rods. The 350 piston and stock 400 piston have the same compression height so shorter rods were used to achieve the correct rod/piston length in the 400. For any type performance build, the shorter rods are junk. Most 383 builds are using 6 inch rods which require special compression height pistons.


P.S. If you were to use your forged 10.5:1 pistons and short rods, your compression ratio would be a lot higher due to the longer stroke. Just another reason this combo will not work.

 

They sell an adapter for installing two piece rear main seal cranks into one piece blocks

 

playing mix n match with engine internals CAN be done . BUT it takes quite a lot of measuring , and a fair amount of skill to not create a grenade. it can be done but know what youre doing first

 

Yeah... Think I'm going to save that for a later project. For the goals I'm looking at, I think a cast Eagle crank should be more than sufficient, without any seal adapting. I'll aim my budget at forged 6 in rods, and the inevitable battle with the computer.