Weber Manifolds

DavidPorter · 05-07-2002, 02:16 PM

Did the manifolds for the Weber 40 IDA carbs come in two sizes to match the 32mm or 36mm intake port sizes on the 2.4 engines? That would make sense, but I haven't been able to find out.

I have a 1973.5 T engine with 32mm ports and a set of Webers I want to use, but the manifolds I have are 36mm diameter.

Thanks.

jluetjen · jluetjen's Garage

I don't think that there were ever factory weber manifolds for 2.4 engines since they all came with injection of some sort or another.

I believe that there were two flavors of manifolds pre-69; as you described the large bore model for S's and the smaller bore model for the other models. I believe that PMO also makes manifolds in both flavors. It sounds like you have an S manifold which is a cool thing to have since it doesn't need porting to match the 36 mm ports of S's and other modified engines. It saves the trouble of having to port out the 32 mm T manifolds. That being said, I believe that the time and effort of porting them is the only change. So they most likely aren't worth any more then a standard T manifold + the porting cost.

BTW - I wouldn't use them in your engine unless the heads have been ported out to 36 mm's to match. Having the step down in size on the intake would be an evil thing.

T Bird · 05-08-2002, 05:09 AM

As a point of correction, not all 2.4s were injected. ROW 2.4s had Zenith carbs. I would call the guru of Weber carbs, Richard Parr at PMO, and ask him if you can get away with using 36 mm manifolds for your setup. If I were to hazard an uneducated guess, I don't think that it would matter. If Richard says no, he can sell you the correct manifolds, insulator blocks, and gaskets.

Good luck.

gregk1 · 05-08-2002, 06:03 AM

Hmmm I have a set of 32mm and need 36mm want to Trade????

jluetjen · jluetjen's Garage

T-Bird, the engine might run, but I doubt that it would run well. The issue would be where the 36mm manifold faces up against the 32mm intake port. There would be a 2mm step around the circumfrence of the port with the face of the step facing back up to the carb. The result would be an accoustic "echo" back up the intake manifold which would be bound to mess up the carb. It would basically be a "worst case" porting scenario. I could only imagine that this set-up would have an awful reversion problem.

BTW - having this set-up on the exhaust ports on the other hand can often be a good thing. In this case the step from the larger diameter exhaust pipe to the smaller diameter exhaust port can often help when cams have a lot of overlap. The step reduces the tendency of the cylinder sucking the exhaust back during the period of valve overlap.

T Bird · 05-09-2002, 05:55 AM

John
From a theoretical perspective, I don't argue with you. The better the match between the port and the manifold, the better the situation. However, having seen how poorly most factory manifolds (exhaust and intake) match up to ports, 2mm doesn't appear to be much to be concerned with. As I said, that's an uneducated guess. Personally, I would rely on Richard Parr for a definitive answer, since he wrote the book on Weber carb applications for the 911 engine.