Supercharger performance
03-21-2007, 05:31 PM
#151
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Originally Posted by Brettus
I'm not looking for the ultimate drag racing machine , but something that will put a stock STI or EVO to the sword seems about right for this car . Lets say around 270 - 300 whp . At this level it seems that you are not having to upgrade every other system (spark,fuel,brakes,drivetrain etc ) on the car . As soon as you start with doing all that stuff you are getting into some big $ and you have to ask why you didn't just go out & buy a M3 - maybe a 2nd hand Porsche 911 .
So the question I would like to ask is :
What FI system will be the easiest to install with closest to OEM like reliability in the 270-300 whp range ?
I'm less concerned with the characteristics of the power curve because
I always knew the 8 was a torqueless wonder & still love it . But anything that delivers 270-300 peak is going to be quick enough for me & not be over the top for type of driving I enjoy.
So the question I would like to ask is :
What FI system will be the easiest to install with closest to OEM like reliability in the 270-300 whp range ?
I'm less concerned with the characteristics of the power curve because
I always knew the 8 was a torqueless wonder & still love it . But anything that delivers 270-300 peak is going to be quick enough for me & not be over the top for type of driving I enjoy.
Now saying that, just get the Greddy turbo and be done with it. Get the e-manage setup properly like MM does it and get it tuned. For the price and what you are looking to get out of your car, it's going to be the option that most closely meets everything you want.
03-21-2007, 05:48 PM
#153
Originally Posted by rotarygod
The RX-8 is not a torqueless wonder. Far from it.
03-21-2007, 08:29 PM
#154
How about this opinion; in order to maintain OEM-like reliability(the 2004 model's problems notwithstanding) one must keep their "boost" level, however achieved, at a level of +50 h.p. or things will become complicated by the need for external ignition controls. That would harken back to RG's assertion that the GReddy kit, properly tuned, would fit that bill perfectly. On the other hand, if you are happy with the 8's performance on the road course but would like a little kick for the drags, nitrous keeps the reliability, affordability, and performance all in balance. This gets away from the original topic, though, and brings us back to the matter of personal preference.
03-21-2007, 08:49 PM
#155
You can get close to 100 whp gains with the greddy kit, and you don't need ignition or fuel pump modifications to keep it safe. Just a good tune, and maybe a catless midpipe.
03-21-2007, 09:59 PM
#156
the local rotrex dealer just told me a rotrex c30-94 would be the best choice for a rx-8. to deliver 0.33 kg/s at 10psi.
I find it hard to belive it is suitable since the supercharger is so small. it would produce about 1-2psi boost at ~4000rpm
MM: long ago in a thread far, far, away : you believed the renesis would flow 324cfm (23.6lbs) which is only 0.17kg/s. does this still hold true? It seems like I'm over-estimating the flow requirements substantially.
comments welcome before I do something stupid like going out and buying a rotrex :D
I find it hard to belive it is suitable since the supercharger is so small. it would produce about 1-2psi boost at ~4000rpm
MM: long ago in a thread far, far, away : you believed the renesis would flow 324cfm (23.6lbs) which is only 0.17kg/s. does this still hold true? It seems like I'm over-estimating the flow requirements substantially.
comments welcome before I do something stupid like going out and buying a rotrex :D
03-21-2007, 10:45 PM
#157
Even better is this thread:
https://www.rx8club.com/series-i-tech-garage-22/rotary-math-106294/
That is my "Rotary Math" thread where I not only explain the formulas, I provide a FREE pair of Excel spreadsheets that calculate flow under every possible combination and the required injector mapping.
https://www.rx8club.com/series-i-tech-garage-22/rotary-math-106294/
That is my "Rotary Math" thread where I not only explain the formulas, I provide a FREE pair of Excel spreadsheets that calculate flow under every possible combination and the required injector mapping.
03-21-2007, 11:52 PM
#158
yeah I think I'm getting the math now. still don't like using VE's over 100%.
you linked this site and it is great! he seems to use the density ratio to compensate for the heat and compressor efficiency. I reckon this is the way to go. I think I have all the info now to put the puzzle together.
you linked this site and it is great! he seems to use the density ratio to compensate for the heat and compressor efficiency. I reckon this is the way to go. I think I have all the info now to put the puzzle together.
03-22-2007, 12:24 AM
#159
A supercharger/turbocharger is just a way to increase the VE above N/A. That is all it does.
Just like I tell people to compute fuel with pulse width instead of duty cycle, I suggest that you get accustomed to computing flow as a function of effective VE.
Just like I tell people to compute fuel with pulse width instead of duty cycle, I suggest that you get accustomed to computing flow as a function of effective VE.
03-22-2007, 12:51 AM
#160
if you use VE =PR then the result doesn't seem accurate. for the PR 1.7 = 170% VE the vol flow would be 629cfm about twice what you calculate (324cfm). I'm obviously doing something wrong with the formula since I can't get close to your value with your spreedsheet.
if I take into account compressor and intercooler efficiency and use the d.r instead of VE then I get the same flow you quote 23lbs.
if I take into account compressor and intercooler efficiency and use the d.r instead of VE then I get the same flow you quote 23lbs.
Last edited by rotarenvy; 03-22-2007 at 01:25 AM.
03-22-2007, 01:16 AM
#161
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One thing ive been seeing in the turboed engines that have been sent to Pettit to be rebuilt is there tends to be uneven were next to the exaust port were the apex seal runs on the steel housings. Weve seen it in three sofar. It tends to were a deep groove and cause major engine failer. Im woundering what might be the cause. My only thought is heat since theres no signs of detonation. Can turbos be holding the heat in because of back preassure or somthing in relation. Weve torn down Cams engine many times to inspect and havent seen this not to say it isnt possible with a S/C.
03-22-2007, 01:47 AM
#166
If heat is causing the wear on turbo kits...and we make the assumption (which I hate doing) that its a greddy...then could we could postulate that moving the turbo up to the "bling" position in front of the engine on top may alleviate this issue somewhat?
Certainly heat is still going to be an issue as you have higher temps due to FI anyway and the heat between the turbo and exhaust port will still exist...however perhaps the "bling" position has an advantage afterall...
You know a few years ago I was messing w/ stirling coolers (btw: our new thermal imaging cams use stirling cryo-coolers...tiny and chill to subzero C really fast) and totally toyed with the idea of using one driven by heat to chill an air-water intercooler...perhaps all this heat could be put to some good use haa haa...its the middle of the night so whatever...
*side note*
I think I have figured out how/where MM gets his sweet *** avatars from...he's always up at wacky hours...as am I...and he seems to have an unlimited supply of MM-Babes...he works for the pr0n industry I'm almost sure of it...haaa
Certainly heat is still going to be an issue as you have higher temps due to FI anyway and the heat between the turbo and exhaust port will still exist...however perhaps the "bling" position has an advantage afterall...
You know a few years ago I was messing w/ stirling coolers (btw: our new thermal imaging cams use stirling cryo-coolers...tiny and chill to subzero C really fast) and totally toyed with the idea of using one driven by heat to chill an air-water intercooler...perhaps all this heat could be put to some good use haa haa...its the middle of the night so whatever...
*side note*
I think I have figured out how/where MM gets his sweet *** avatars from...he's always up at wacky hours...as am I...and he seems to have an unlimited supply of MM-Babes...he works for the pr0n industry I'm almost sure of it...haaa
Last edited by eviltwinkie; 03-22-2007 at 01:52 AM.
03-22-2007, 02:02 AM
#174
Anyone notice any significant wear on the older 13b in the same areas? Since we dont have ready access to a S/C ren w/ longterm wear I would be hestitant to jump to a conclusion that its a turbo only possible issue.
The way I see it...and I could be mostly possibly wrong is that we have a "hot" side and a "cold" side to the rotary. The side being injected w/ fuel+air is going to be cooler than the side which is responsible for dumpin the exhaust. Its not going to be a huge diff but none the less there should be a difference. The point being perhaps when they moved the position of the exhaust ports...what we are seeing is an unintended consequence due to the increase in temps caused by FI...all that heat screaming to get out and simply heating up that area over time regardless of whats attached to the end...its simply a design issue which never accounted for FI applications and therefore never really considered the implications of additional heat and how it affects the "hot" side over time...
the gasses ARE trying to escape via an almost 90 degree exit afterall...not usually the most efficient...hot gas slamming up against barriers are certainly going to transfer heat along the way...
if i keep this up...I'm totally gonna get flamed...watch...haa
The way I see it...and I could be mostly possibly wrong is that we have a "hot" side and a "cold" side to the rotary. The side being injected w/ fuel+air is going to be cooler than the side which is responsible for dumpin the exhaust. Its not going to be a huge diff but none the less there should be a difference. The point being perhaps when they moved the position of the exhaust ports...what we are seeing is an unintended consequence due to the increase in temps caused by FI...all that heat screaming to get out and simply heating up that area over time regardless of whats attached to the end...its simply a design issue which never accounted for FI applications and therefore never really considered the implications of additional heat and how it affects the "hot" side over time...
the gasses ARE trying to escape via an almost 90 degree exit afterall...not usually the most efficient...hot gas slamming up against barriers are certainly going to transfer heat along the way...
if i keep this up...I'm totally gonna get flamed...watch...haa
Last edited by eviltwinkie; 03-22-2007 at 02:07 AM. Reason: Elaboration