heretic

The RX-8 makes way more power than previous PRODUCTION n/a engines.



The side exhaust is 100% for emissions. Because emissions are better, they can run what would otherwise be radically large ports, and they can be tuned for more power versus keeping the converters happy. Also, the engines seem to be quieter than the old ones, so they can run a less restrictive exhaust system



The engines, however, are no match for a decently ported traditional engine.



I was reading an interesting article about finding more power in the new LS2 engine from Chevy. I haven't been keeping up on my competition surveillance, but apparently the LS engines, including the Z06, run with a rather large lobe separation angle. Minimal overlap so it will idle nice at 500rpm and make the EPA happy. Downside is that it hurts midrange torque. Swapping in a camshaft with the same lift/duration but a tighter LSA, basically moving the lobes closer together, increases midrange power and brings the RPM that peak power occurs down. The intakes are open for the same length of time, but the tighter LSA closes them earlier so the engine works better at lower RPM. So you get a fatter midrange, and you waste less time revving the engine out into the wrong end of the rotational inertia spectrum. And the LSA's are still fairly wide even on these cams (112 versus 116?) compared to what we see in our engine shop, but they are trying to make engines that will still idle nice enough to keep the computer from setting misfire codes.



The Renesis has goodly amounts of timing, only because there is no overlap, the intake port has to close much later.



I will let you know when my Anti-Renesis engine gets dynoed. I am hoping for Turbo II like power numbers (around 180-200 at the crank, down low in the curve) from a naturally aspirated engine. Should be entertaining, and no turbo lag.

Jeff20B

Is anything D-shaped that we should know about?

rx7tt95

According to Speed Source, the stock ports are maxed out as is from the factory. They found no hp gains from porting the renesis motor. That was at the beginning of last season. Maybe they've found something since then, dunno. I have someone in the know and I'll ask on Saturday when I see him.

guitarjunkie28

we gained 16 whp with very conservative porting the first time.



i think a major problem with these is you can't just port and be done with it. the first time, afr's dropped from ~12.2-4 down to ~11.8-12



with just a little bit larger port (but still conservative), afr's were in the 10's a lot of the time!!



i don't think the maf sensor is happy with the porting, so if you do it, make sure you tune it!!! easy 35-45 more hp!

heretic

So the RX-8 uses a MAF sensor. Does it also use a MAP sensor, the way the FC double-teamed an flapper door AFM and a MAP?



If it only has the MAF, then this makes sense. If you think about it, if there is no MAP sensor, the only way the computer can determine engine load is comparing the airflow against RPM. Similar to how a MAP sensor measures load and calculates airflow, but in reverse. The computer reads how much airflow, then it compares that airflow to an internal map to see what air/fuel ratio and ignition timing to run. If you move enough more airflow, the computer goes deep into the map and pulls out a super rich mixture and knocks back the timing. Assuming that it doesn't go off-scale and barf up a code and go into limp-in mode.



One reason why the FC setup is so nice. You don't have to worry about the computer reading things funny.

guitarjunkie28

actually, the mass air metered system is the most accurate production-type system on the market. i just don't think the sensor is calibrated for the increased airflow.



remember how mazda got all the wires for the fc harnesses at a big flea market? maybe they did the same b-rated shopping with the maf sensors for the rx8?



maybe ito can chime in and tell us what happened to his after the porting.

C. Ludwig

Am I reading this correctly? You guys made 176 wheel HP with a ported RX-8? Stock was 150?

heretic

If the computer doesn't use a MAP sensor to measure engine load, then it has to go off of an internal airflow versus RPM map or algorithm to determine engine load, and thus run the correct fuel ratio and ignition timing. This is standard procedure.



It is also common for these systems to do strange things when airflow increases beyond factory-expected norms. This is why even MAF cars can and do require chip tuning once the engine has been modified.



The best way, from a performance modifications standpoint, is to have a separate MAP sensor to determine engine load, and strictly use the MAF for measuring airflow. This requires extra sensors and complexity, which costs money and potential reliability, so the OEM's just diddle with code in the computer to make up for the "missing" sensors.

guitarjunkie28

176whp

-16hp gain



160 whp stock.

mazdaspeed7

Most stock RX8's are still putting out more power than your ported one... Ito did 197 rwhp completely stock.