ok after blowing up my standard chevy 305 engine am going new and improved but before i do need a little help, ppl say 350 model is better, why is this and also while ive been looking for 1 i have a choice either:

350 2pce seal- approx up to 1985 250bhp
or
350 1pce seal- approx 1986 on 250bhp

with mine being a 1983 Trans Am i would go for the first, but what is this 2pce seal?? i hear its part of the crank and flywheel connection, i got my THM 700R4 overdrive Tranny rebuilt and ready will this be a simple matter of, attaching a flywheel to the new engine then the torque coverter and finally the rebuilt tranny??? i live over the pond so excuse my stupidity

 

The block is different at the back to accomodate the later style, 1 piece rear main crankshaft oil seal. There is no real difference in performance between the two as a start for a place to build. Typically, the one piece rear main seal engines have the lifter valley and the timing face of the block machined to accept a roller cam. They also use a different balance on the flywheel and require a different crank/flywheel combo compared to what you have now.

The easiest direct swap that you have is the older 350 block because you can re-use your old flywheel on the back and you can re-use your pushrods with a flat tappet cam. If you go with the newer short block, you will need the pushrods and flywheel to go with that engine since they are different.

Regardless, you can keep your 305 heads as they are good stock pieces. Make sure you have 1.94" or 2.02" valves for the intake and 1.60" for the exhaust. Then do a little port work. You'll be happy.

In your profile it says 82 T/A, 305 TBI engine. What year is your engine now? If you have the original cross fire injection 305 with the two separate throttle bodies, then you have good heads. If you have an 87 or newer TBI 305, then get new heads with your new 350.

Good luck!

 

There are two reasons you want want to consider getting a 1 piece main seal block.

1 they are almost all setup for if not equipped with hydraulic roller lifters, little bit of a power gain, especially if you are looking at about the same price for either.

2. if you decide to go to a manual setup, and want to run a T56, having a 1 piece seal keeps you from having to buy an expensive aftermarket flywheel, for the $30 or so for a 1 piece flexplate to go with your auto right now, and the money it saves if you are considering going manual, it'd be well worth it.

 

While there is certainly nothing wrong with one-piece rear main seal, I disagree with your reasoning. Less than half of the one-piece rear main seal blocks are set up for hydraulic roller lifters. Many more came in trucks than in passenger cars, and the trucks didn't get roller lifters (a very few were machined for them). Crate engines typically are set up for, if not equiped with, roller lifters (the 330 HO engine is machined for them, but comes with flat tappet lifters, for instance).