okay im thinking about pulling the stock 305 in my 88 Trans Am, I want to go with either a 350 or a 400 small block. which would be easier? I like the sound of having a 400 under the hood but i dont want to have to go too much trouble on putting it in.

 

Since you have a late model block, you probably have a one piece rear main seal. This requires a flywheel/flexplate that is specific to that application.You also have a passenger side dipstick and earlier blocks had the dipstick on the opposite side. this is important if you plan on using stock manifolds because interference.
A late 350 is a direct swap. It also has roller lifters.As far as I know
no one builds a 400 with a one piece rear main seal.You might be able to find one from a custom engine builder.
Try a search in this boards archives. There is a wealth of information there. I use it often.

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Nor Cal Mike
Red 84 Z28, stock L82 350, L69 carb, intake, and air cleaner
5 Spd, 3:73 Posi, 1 5/8" SLP headers, 3"cat connected to
stock L69 exhaust, KYB's
Some are faster but mine's fast enough.

 

Both the 350 and 400 are small blocks, with all the same bolt patterns on the block as your 305. Neither would be easier or harder than the other.

In either case, watch the accessory bolt holes in the head. You may get one that doesn't have all that you need.

I assume you have TPI or TBI that you'll use on the new engine. '87-later factory engines have the center two intake bolts on each side at a different angle that the others, and different than '86-earlier heads. One way to solve that is to get a 350 or 400 short block and buy new aftermarket heads that have the later intake bolt arrangement, and proper accessory holes as well. Or, your intake bolt holes can be modified to work on the older style heads.

You'll also need a different flex plate/flywheel if you get an engine with a two-piece rear main seal. I don't believe any 400's came with one-piece like your '88, but 350's came in both styles.

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82 Berlinetta, orig V-6 car. Rescued w/86 LG4/TH700R with all harnesses, sensors, ECM, etc. 3.08 open, cat-back from '90 305HO, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress.
57 Bel Air, my 1st car. Currently 396 .030 over, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.