13bbuggy

I just bought this motor yesterday and was looking it over today and noticed that the exhaust openings are larger than the last 2 motors I had (an 86 and 90 NA). The outside hole on those engines measured 2 inches across and these ones are 2 1/2 inches across and the diffusers have been removed and the holes enlarged but i can't tell if it was just the outside or if the port itself has been altered from stock. I am attaching a few pictures in hopes of someone being able to tell me if the ports look stock or have been ported (maybe I lucked out and the motor has had some porting done):-).

mazdaspeed7

The port looks stock, but the exhaust sleeves are missing

13bbuggy

Do I need to put some in there or is it ok without them?

mazdaspeed7

It will run better with them. The tricky part is they come pinned into the rotor housings through the side, that is inaccessible unless the motor is apart. But you could probably just stick some in there and be fine. Just make sure they dont move around too much.

13bbuggy

Since I'm running this in a sandrail and sound isn't an issue and I already have 2 1/2 inch exhaust from the flange back, could I just open up the RB flange hole to match the size and run it like that? I know it will hurt my low end power a bit, but I mostly run towards the top end of the power band and almost never see below 3500 RPM, unless I'm stopping or just getting going.

mazdaspeed7

The sleeves smooth the flow coming out of the ports. That area becomes a large expansion chamber without the sleeves in place, which can make the exhaust tuning less effective, as well as decrease overall flow. The sleeve also helps to keep some of the exhaust heat from heating the housing, and thus the coolant.

You dont have to run the factory sleeves, you could also weld some fabricated sleeves onto the engine side of the header flange. They dont need to be tight to the housing, 1/8" gap is fine(probably preferred due to thermal expansion).

13bbuggy

Thanks a lot for the information, I'll take my exhaust down to get some sleeves welded on and try that.