350 tbi to lt1

[gaboi68]

I have a 91 9ci with a 350. Anyone know which parts will interchange between the 350 tbi and the lt1(exhaust, engine parts, ect.)?

[silicon212]

Mostly nothing will interchange. If you're thinking about swapping an LT1 into it in place of the current engine (L03 or L05), you will need to take a number of steps, including upgrading the fuel system (LT1 requires 50-60 PSI vs. TBI which requires 9-13 PSI), completely replacing the ECM with the LT1 PCM, and of course the engine/transmission combo (L03/L05 + 4L60 to LT1 + 4L60E), and all associated wiring harnesses. Of course, the LT1 exhaust will then bolt right up.

As far as the LT1 exhaust is concerned, it's a true-dual system which basically on the right-side, cat-back is the same design as what you have but 2.25" vs. 2.5". The left is of course, all new. You can of course get the cats to fit older cars but the biggest problem is the turndowns from the exhaust manifolds to the cats. These are LT1 specific, or LT1-exhaust-manifold specific, and the LT1 exhaust manifolds will not properly fit Gen 1 small-blocks. You might have to do some fabricating here, but the exhaust will be federally legal due to its being factory on a newer car than you have.

[kdrolt]

The full N10 dual exhaust from an LT1 will fit a TBI Bcar v8, but several mods are needed to make it work.

The LT1 exh manifolds each need one extra hole drill in the flange to bolt onto the TBI heads, and then you use the LT1 downpipe/cat. The EGR and AIR hole(s) in the LT1 exh manifolds need to be plugged, and you'll need to either use the 94-96 Bcar trans crossmember + 94-96 trans tailshaft housing to allow room for duals, OR you have to modify your existing crossmember. The TBI cars had body provisions for duals on the left side that were engineered into the car but never used. IIRC my neighbor used a hybrid of 91-93 upper hangers and 94-96 lower hangers (to mate perfectly with the 94-96 factory dual exh).

The bottom line is that the N10 duals from a 94-96 LT1 Bcar have been used by at least 3 people (all in New England) on TBI 305 and 350 engines.

Other than the exhaust, and the body/suspension parts, there's veryy little of the 94-96 engine that can be easily used on a TBI car.

[1968 Pontiac]

What about changing the diff? I was thinking about putting a 96 disc brake diff I have into my 91.

[kdrolt]

It's been done. Look for Kevin Moore's posts here:

http://impalassforum.com/cgi-bin/ult...;f=23;t=001757

http://impalassforum.com/cgi-bin/ult...;f=23;t=002034