Axial Flow Supercharger
02-28-2006, 10:47 PM
#2901
Registered
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.
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.
Last edited by rotarygod; 02-28-2006 at 10:57 PM.
02-28-2006, 10:53 PM
#2902
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.
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.
Last edited by Richard Paul; 03-01-2006 at 12:29 AM.
03-01-2006, 01:52 AM
#2903
Originally Posted by rotarygod
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.
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.
Last edited by Hymee; 03-01-2006 at 01:57 AM.
03-01-2006, 03:20 AM
#2904
Int'l Man of Mystery
Join Date: Jan 2004
Location: Central Florida
Posts: 3,651
Likes: 0
Received 0 Likes
on
0 Posts
^^ 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).
... yep... just checked MNAO's website...
212 hp 1.3-liter RENESIS 2-rotor, 4-intake-port, rotary engine
232 hp 1.3-liter RENESIS 2-rotor, 6-intake-port, rotary engine
232 hp 1.3-liter RENESIS 2-rotor, 6-intake-port, rotary engine
Anyway... by your figures Hymee, the RX-8 is making the power that mazda claims (now).
03-01-2006, 10:22 AM
#2906
Registered User
Join Date: Feb 2006
Posts: 8
Likes: 0
Received 0 Likes
on
0 Posts
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?
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?
03-01-2006, 11:41 AM
#2909
Originally Posted by Hymee
MAF readings I've taken are about 220 g/s at max power.
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.
03-01-2006, 03:44 PM
#2912
Bummed, but bring on OU!
Originally Posted by Japan8
And it looks like the new 6-speed AT still has the 4 port motor...
03-01-2006, 08:29 PM
#2913
Int'l Man of Mystery
Join Date: Jan 2004
Location: Central Florida
Posts: 3,651
Likes: 0
Received 0 Likes
on
0 Posts
^^ 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...
03-01-2006, 08:46 PM
#2916
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.
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.
03-01-2006, 09:18 PM
#2918
Administrator
Originally Posted by Japan8
^^ 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...
03-01-2006, 09:29 PM
#2920
Shifty Bastard.
Join Date: Feb 2004
Location: Melbourne, Australia.
Posts: 4,835
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by RotaryNoob
Speaking of axial flow... How many more years until it's ready?
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.
03-01-2006, 09:47 PM
#2924
Int'l Man of Mystery
Join Date: Jan 2004
Location: Central Florida
Posts: 3,651
Likes: 0
Received 0 Likes
on
0 Posts
^^ 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...
03-01-2006, 10:53 PM
#2925
Originally Posted by Japan8
^^ 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...
Cheers,
Hymee.