NoPistons -Mazda Rx7 & Rx8 Rotary Forum - Half Bridge Exhaust Port Timing

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- Rotary Engine Building, Porting & Swaps (https://www.nopistons.com/rotary-engine-building-porting-swaps-55/)

- - Half Bridge Exhaust Port Timing (https://www.nopistons.com/rotary-engine-building-porting-swaps-55/half-bridge-exhaust-port-timing-34357/)

Quote:

Originally Posted by Travis R' date='Feb 25 2004, 02:32 PM

Thanks for the link.

That's why I thought an aux. bridge would work well. Good low/mid range with the ports closed then a pretty good top-end with the ports open... the problem is I can't make it work with the stock manifold.

So the basic dillema becomes: Is the weight penalty worth the trade off of driveability. It's very close in my mind, but I honestly don't know what kind of midrange power I'm looking at. I've only drive rotaries a couple times.

Heres my recommendation. Run a SP 6 port engine, S5 internals, but concentrate on the exhaust port, and the exhaust system to tune your powerband to where you want it. I would go with a wider exhaust port for the necessary flow, but keep the duration somewhat short so it doesnt shift your powerband too high. Also, I wouldnt port up at all. I wouldnt do anything more than clean up the top edge of the exhaust port, and do most of the porting on the sides and bottom of the port. If doen right, the exhaust port should have a more consistent cross section from the port to the end of the runner. This will increase velocity and decrease turbulence in the exhaust port. It will also make the runner angled up more, and that will offer a more natural flow path for the exhaust gas.

That and a header tuned on the dyno should give you a very strong midrange with a very broad torque curve. You will want gears, because the power below 3k will be down some, but you should have a huge, mostly flat torque curve that covers most of the powerband. And it will have enough top end that you wont find yourself running out of rpm's.

The intake porting wont need much work. The 6 port housings have a lot of port area/timing. The center housing has a lot of potential, but not much needs to be done to the end housings.

Keeping the overlap to a minimum will make the engine have a strong midrange.

Thanks for the input.

Do you think that setup will make the kind of power I need?

u can do about 180 at the wheels if you get a good exahsut, and an aftermarket intake manifold with idividual throtltle bodies with stock ports.

i dont think that an fc can ever be a competitive auto crosser.

So you've never heard of Steve O'Blenes then?... BP National Champ? https://www.nopistons.com/forums/pub...IR#>/smile.png

Woo Hoo! My life just got a lot easier (potentially). SCCA is talking about phasing out the weight penalties for fuel injection. Hopefully they won't change the min. weight very much, if at all.

Aux. BP with custom manifold here I come! https://www.nopistons.com/forums/pub...IR#>/smile.png

Ive seen NA fc's dyno at 174rwhp with bolt ons and a street port. a bridge is only worth 6 hp?? stock FC's with all the bolt ons do 160+ rwhp..

where did u see a bridge with 174whp?

Quote:

Originally Posted by kahren' date='Feb 27 2004, 12:45 AM

where did u see a bridge with 174whp?

Quote:

Originally Posted by Drago86

Ive seen NA fc's dyno at 174rwhp with bolt ons and a street port. a bridge is only worth 6 hp?? stock FC's with all the bolt ons do 160+ rwhp..