I work in a salvage yard(makes it easy to get all the little parts to finish the swap), and today I noticed a 89 Caddy 4.5 with tubular manifolds instead of the cast ones on my 92 4.9. I did not think to check the interchange, but I wonder how they would work.
Will they fit from a TBI engine to a PFI engine?
I am not sure about the flow rate compared to the cast ones, but they should save a least several pounds each.

Gene

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IS it from an Allante?

If so, GRAB IT FAST!

They flow insanely better than the plain intake.

Rumor has it 40hp from the manifold alone... Not sure about exact numbers, though.

If it is an Allante grab the intake as well!

I should clarify they are the exhaust manifolds. It is not an Allante. I put a search up on our system for an Allante intake, and found several but even between yards they want big money. Best I found was 225.00 for the upper and lower.

Gene

Your regular intake can be modded to flow much better than the Allante manifold and this is one of the mod we use on 4.5& 4.9 we tune and it has made a huge difference.

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Tuners of the Quickest 4.9
12.51@118 mph