how much hp/tq gain would i see if i got a lt4 intake manifold?
-mike

mods-93 z 28 M6
SLP CAI, Trick Flow Elbow, 160* stat, Hypertech, Pacesetter Long Tubes, 3" ORY no cats, SLP Loudmouth, AIR!, EGR!, Strange 4.10's

 

A grand total of zero.

 

Without the LT4 heads it won't fit without a bunch of work.

 

Hell probably lose power.
Do a search you are not the first one to mistakenly think the LT4 intake an upgrade.
Basically there are no reasonably priced effective intake upgades for the LT1 because while not perfect the LT1 intake does a damn good job as is for a suprizing range of applications too.
There are "upgrades" just not hugely effective on anything resembling stock and nowhere near cost effective at your modest mod level.

 

The LT4 intake ports are exactly like the LT1 intake ports... only the LT4's are relocated about .010" skyward to match the LT4 heads.

 

They are identical to the LT1's. They just have more meat at the top of the runner so they can be opened up to match the 0.100" taller ports on the LT4 heads. But from the factory, they appear to be identical, at least putting my LT4 side-by-side with my stock LT1 intake. And the taller casting on each LT4 runner interferes with the valve cover rail on LT1 heads, so either the heads or the intake need to be machined to bolt them together.

 

A $4 can of red spray paint will achieve the same results as the $250 LT4 intake with your LT1 heads. Put the money towards a cam or having your stock heads professionally ported.