OK got it straight now. I had it backwards. A good piston engine will make about 10 hp per lb of air whereas a rotary will make about 8 hp per lb of air. This means it takes more air on the rotary to make the same power which is why the comparison to a Miata engine is absurd.

An Eaton that is maxed out to the point of absurdity and unreliability that can make 360 hp on a piston engine can only make about 288 hp on a rotary. If that is an M62, it is spinning really fast, making tons of heat that need "all the tricks in the book" to control it, and it is probably making an awful lot of boost. That proves an M62 would be way too small. If the average power of an M62 is 170-250 hp on a piston engine, then it would only make it about 136-200hp on a rotary at 6-8 psi. The rotary can hit the upper end of this range with no boost. Too small. An M90 is nearly 50% larger but it isn't going to give a 50% increase in power over the M62. To many other variables and losses with spinning a heavier blower among other things.

I stick to my story that to make large horsepower over 300 on a rotary isn't going to happen with an M90 for the above air usage differences with the rotary. If you do, you're using "all the tricks in the book" and it would just be easier to size a different blower. It'll take at least an M112 to have that potential but then again other issues arise with larger units. You can't go larger forever.

 

Yes that is about it. We need to be carefull here because we assume a perfect engine build. But a rule of thumb for the well built piston engne is 10hp for 1lbs of air per min.

We use min because that is what the HP is using. Remember it has a time factor in the equation. RPM being time. Work done in time. If you want to just know how strong it is you use torque.

If you want to use CFM it is a little tricky because you must factor in the barometric pressure, humidity and temp.
I use .072 but it can be as low as .069 (or less at true sea level)
one lbs/min over .069 is aprox 14.5CFM
Edit) .069 is for 85 degrees f at 28.4hg.
The constant will go down if the temp goes down or the press goes up.
It is my experience that ten hp from that much air is a good engine at 6000 or maybe less. As you go up the rpm range you lose to friction so the numbers must be adjusted.
Example might be an engine tuned for low RPM might get 10hp for 10cfm at 3000.

 

Yep - 10 hp per lb of air per minute.

I reckon 8 is about right for the Renesis, in stock form. MAF readings I've taken are about 220 g/s at max power. I've publised that graph elsewhere in this place. That works out to 29.1 lbs/min. Therefore, 29.1 lbs/min @ 8 HP per lb/min is about 233HP. The Renesis is rated at 238, so for a sanity check it is pretty close. Flywheel figures we are talking about.

The problem is that it is not widely known what they actually make on an engine dyno. I have the means to do that, if enough folk are interested. It all depends on if you all want to help fund it It would be interesting to see how close we get to the "claimed" figures, especialy in light of the HP debacle in the early days.

Of course, there are others who have claim they make lower that that. If anyone published the figures, please point me to them.

Cheers,
Hymee.

 

^^ under the new SAE ratings isn't the RX-8 being rated as 232hp now?

... yep... just checked MNAO's website...

And it looks like the new 6-speed AT still has the 4 port motor...

Anyway... by your figures Hymee, the RX-8 is making the power that mazda claims (now).

 

Well, there you go!

 

Interesting, shows how much (read: little :D) I know about the Wankel; I was unware that they're incapable of converting the same amount of air into power as a piston engine. Yes, the Eaton used on the Miata kits is the MP62, which is the 4th or 5th generation of the M62. And yes, if you're using all the tricks in the book with a particular compressor to utilize all the CFM of air it can provide and turn it into usable power, then that's probably a pretty good sign you need to move up to the next size compressor I was merely using these as examples of what the Miata world sees from a positive-displacement "Heaton" supercharger (and twin-screw)

BTW, what do RX-8's typically dyno at the wheels? I seem to recall some rumors of seriously low numbers that were possibly caused by engine management/traction control systems being thrown into limp mode due to the front wheels not turning on the dyno? Aside from that, I would guess somewhere in the 185-195rwhp range?

 

185 whp seems to be typical for the RX-8.

 

Red Devil,
As usual, you are on the money. That's about the average.
Paul.

 

I can validate that one. I recorded in third gear the following:
RPM 8425
Advance 30
Throttle WOT
Lambda .8898985
Airflow in g/s 218.02
MPH 88.2388

I think if I was at .91 lambda, I would have made more power, but 200 to the wheels feels pretty good.

 

Our horses must be bigger over here. We only get about 170-ish at the wheels.

Cheers,
Hymee.

 

thats about where nemisis started i think. 175ish - 180

 

Hmm, interesting. Wonder where they dug up 15hp then? Could be a typo I guess, but I hope not. More than 15 with the switch to SAE.

 

^^ Either that or a higher redline afforded by the new tranny combined with the SAE rating gave the engine a boost. Not really sure though. I'd like to know what the REAL story is...

 

Isn't this the axial flow thread?

 

Hmm I though it was just me.. I did not see when lanes was changed.. ha ha

 

So, lets get it back on track then

If RAP makes a S/C that makes 80 lb/min of air, and takes 100HP to drive the thing, he should end up with 8 x 80 = 640HP, less 100 HP to drive the blower = 540 HP.

Cool

Note well: Numbers made up!!!!

Cheers,
Hymee.

 

Speaking of axial flow... How many more years until it's ready?

 

Its the 6port used with the 6AT. thats the truth.

 

^with the lower 4 port redline.

 

It'll be ready when I say it'll be ready. Right now I'm pouring all my efforts into rebuilding my house. When I get five minutes I'll give Richard a bell, we'll nut through any niggles the project has outstanding.....and release it to market.

PM me if you want pictures of the ongoing construction at Château Gomez. You'll get some kind of idea how long it'll be before Richard and I can get together.

Cheers,

Gomez.

 

With "4-port" in it's name/description ! ? ! ?

Cheers,
Hymee.

 

Website typo?

 

'spose so. Just blindly accepting what Japan 8 posted.

Cheers,
Hymee.

 

^^ could be a website typo, but companies this size supposedly heavily check the copy and the UAT pages before uploading the to the Production server. This doesn't mean no,... just that it seems odd...

 

I guess they supposedly check the power figures before they publish them as well

Cheers,
Hymee.