I'm working on a 12a bridgy for my RX3. I have twin webber 45's and a RB header to bold on. I noticed that there is a poor match between the block and the manifolds.

The manifold for the webbers have smaller passages than the 12a block and the RB headers are conciderably larger than the exhaust passages. I would think the variation would cause increased flow resistance.

I think I can figure how to machine the intake manifold to match the 12a block, but the RB header pipes are huge compaired to the block.

what have you all done???

 

did you get the correct RB header? I know there is a differnce in the 13b headers cause some 13b's are 6 port and the early 13b's were 4 port. did you buy the header new?

 

Not new. I have 3 sets. One set I stripped off a wrecked RX7 15 years ago. Its got a lot of miles on it and been work around so much I'll use them for an engine testing stand I'm building.

The other 2 sets came with the 12a bridgy I bought. All 3 have the same tube size and port openings!

I've only ever run a stock engine so I don't think I've been pushing the need to look at such details.

I'm trying to make this next rebirth of my RX3 a more detailed engineered project.

Sounds like port matching the intake manifold will be my primary target. I think I'll spend more time on the whole exhaust system than the exhaust port matching.

With the bridgy, I want as free flowing a system as I can.

 

NO, do not port-match the manifold. The small step is there to fight reversion. Do a search on "port matching intake".

The header primaries are the size that was determined by Racing Beat after years of dyno testing to be the correct one for rotaries. Specifically, they say a 1.7" to 1.8" ID is correct for a bridge-port with a Weber. The RB header primaries are 1.75" ID.