Just curious as to what performance upgrades would still be usable on various engine swaps.

K&N, Spark plugs & wires
Rodney dickmans free flow cat
Ocelot Performance exhaust
Ported exaust manifold
Ported throttle body

what of the above be reusable first on a 3.1 swap, then a 3.4 swap and finally a 3800 swap?

Also how is the 4:10 tranny in these swaps? Would it be a good idea to use a different tranny?

All of those can be used on a 3.1 and 3.4 engine.
The 3800 is a totally different engine.
As for trans, The 4:10 will be great for acceleration and getting low 0-60 times but for regular highway driving, your economy will be low. So it depends on how you want to drive the car. For economy at highway speeds, many prefer one of the 5-spd transmissions.

Orief is exactly right.......as usual!

The 3800 will bolt right up to the tranny too and the items you mention are minor in any engine swap. The 3800 Gen II has 205 HP stock! Lots of torque and HP. Check out this site. This guy goes into great detail and has pics of every step of swapping in a 3800. http://www.ipass.net/~fieroman/terranexus/fieroman/index.html

Phil

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GTDude
25 years GM experience