RB25DET Intake Plenum change

[Guest MFX_R33]

I have heard of a few cars doing this and when tuned they ran fine. I don't think it would be the most even flowing option, but if you aren't talking rediculous power levels I don't think it would matter a great deal.

Jeff.

[JimX]

Hills Motorsports have a custom front-facing plenum which flows evenly for all cylinders. I imagine most expensive ones would be similar. At the other end of the spectrum there's the cheapass type which I have, and I do think it starves the front cylinders of a little air than the rear.

But that only means these cylinder runs richer than normal, evidenced by a little more popping/backfiring than usual. The engine is still running rich enough overall that the rear cylinders aren't leaning out. I still get more overall power out of the engine and much better throttle response so while not perfect, I still think it was more than worthwhile despite the uneven airflow.

[Steve]

JimX, if it runs rich on front cylinders, good chance it is lean on rear cylinders, as dynos measure the average AFR, not individual cylinders.

[JimX]

Steve I know, but the plug colours all seem to be fine. My S-AFC wasn't tuned to the leanest possible mixture either, was was done to around 11:1 at the higher RPM's (up from high 9's:1) so I'm pretty sure I'm safe. Will get everything re-done to around the same ratio when I put the new fuel pump in which should help even more with preventing leaning out.