What restriction from 2.5" bore at flanges on 3" exhaust?
Discussion
I'm fitting a 400 bhp+ turbo rotary engine into a Mazda RX8 where, even with the additional 10%-15% exhaust flow of a rotary for a given power level, a 3" exhaust should be fine. The 3" bore Racing Beat RX8 decat and catback I've got are reduced to 2.5" at their flanges to match the standard RX8 bore.
I'm planning on removing the restrictions by getting 3" bore flanges and tubing welded on in place of the 2.5" sections, a shame given the quality of the original work but needs must. However, I'm curious to see how much difference the reduced bores would make - does anyone have any information?
I'm planning on removing the restrictions by getting 3" bore flanges and tubing welded on in place of the 2.5" sections, a shame given the quality of the original work but needs must. However, I'm curious to see how much difference the reduced bores would make - does anyone have any information?
Pumaracing, thanks for the sizing info.
Your table shows 3" to be on the small side for me, 3.5" probably being better. If I were starting from scratch then I would indeed look first at 3.5" as it should allow earlier spool and more power at the top end. I'm considering going to 3.5" but am held back because of the potential extra cost, noise issues and available space for the downpipe; here:
@ For cost, I already have the [used] decat and catback. Selling them and getting a bespoke system may be expensive (perhaps I should find out, but I'm strapped for time) and I'm concerned about my costs running out of control.
@ I'm concerned about noise for track days, where I have a good idea of the effectiveness of the current decat and catback and a bespoke 3.5" system may be too noisy.
@ A 3.5" downpipe may cause me packaging issues as the downpipe is very close to the inlet manifold and I'm concerned over heat insulation. If I have a 3"downpipe then I fear the extra breathing of a 3.5" system might be limited by the comparative restriction of the downpipe.
Ah well, more things to think over . . . . . .
Your table shows 3" to be on the small side for me, 3.5" probably being better. If I were starting from scratch then I would indeed look first at 3.5" as it should allow earlier spool and more power at the top end. I'm considering going to 3.5" but am held back because of the potential extra cost, noise issues and available space for the downpipe; here:
@ For cost, I already have the [used] decat and catback. Selling them and getting a bespoke system may be expensive (perhaps I should find out, but I'm strapped for time) and I'm concerned about my costs running out of control.
@ I'm concerned about noise for track days, where I have a good idea of the effectiveness of the current decat and catback and a bespoke 3.5" system may be too noisy.
@ A 3.5" downpipe may cause me packaging issues as the downpipe is very close to the inlet manifold and I'm concerned over heat insulation. If I have a 3"downpipe then I fear the extra breathing of a 3.5" system might be limited by the comparative restriction of the downpipe.
Ah well, more things to think over . . . . . .
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