Twin Charging....with one unit?
02-26-2009, 08:23 PM
#26
I've always thought of fun on the street dealing directly with low end grunt. You don't have to race the engine to go places. While turbochargers have proven themselves to be better at flowing air and especially with peak horsepower and torque numbers, I'm still seriously considering a supercharger for powerband reasons (my own opinion and wants, don't start with the hate mail).
In my eyes, racing is more focused on peak figures. You could be waiting for boost till 5000 RPM, you're not going to really notice it on the track since you're going to be above those RPM's anway. A fun street car makes power everywhere. Maybe not as much power, but more spread out. And isn't that the definition of what a supercharger does?
In my eyes, racing is more focused on peak figures. You could be waiting for boost till 5000 RPM, you're not going to really notice it on the track since you're going to be above those RPM's anway. A fun street car makes power everywhere. Maybe not as much power, but more spread out. And isn't that the definition of what a supercharger does?
02-26-2009, 09:44 PM
#27
/\ horses for courses .
The CF supercharger will definately not give you low down grunt but a twin screw or roots type will .
Then again , a small turbo will give you even more low down grunt than a SC but will run out of puff up top and a large turbo will give you the reverse .
Some say the 3071 give you the best of both worlds so it can be possible to have your cake and eat it too - but even with that there will be compromises.
So you have to think about what you want to do with the car
The CF supercharger will definately not give you low down grunt but a twin screw or roots type will .
Then again , a small turbo will give you even more low down grunt than a SC but will run out of puff up top and a large turbo will give you the reverse .
Some say the 3071 give you the best of both worlds so it can be possible to have your cake and eat it too - but even with that there will be compromises.
So you have to think about what you want to do with the car
02-27-2009, 02:40 AM
#31
^I've always been pretty against the centrifugal supercharger on high revving small engines and I've never had any issues being vocal against it for exactly the reasons you stated.
However since I love to experiment and try things, even things I don't think will work good, I am rethinking my position on them and would actually be curious to try one out or at least drive one. I still can't think of a reason to use a centrifugal on a rotary as opposed to other options but I'd really like to know what the fun factor is like. I've been staring at centrifugal maps lately and have found a couple that might work nicely on a rotary. I've got a few ideas about how to deal with the low end but unfortunately it all revolves around a 13B and not a Renesis due to the exhaust tuning benefits. I may pick one up someday and play with it on my RX-7 just for knowledge reasons. We'll see...
However since I love to experiment and try things, even things I don't think will work good, I am rethinking my position on them and would actually be curious to try one out or at least drive one. I still can't think of a reason to use a centrifugal on a rotary as opposed to other options but I'd really like to know what the fun factor is like. I've been staring at centrifugal maps lately and have found a couple that might work nicely on a rotary. I've got a few ideas about how to deal with the low end but unfortunately it all revolves around a 13B and not a Renesis due to the exhaust tuning benefits. I may pick one up someday and play with it on my RX-7 just for knowledge reasons. We'll see...
i never thought i would have seen this post.. buying in to lots of lotto tomorrow!
fred, is that you or have you been troll jacked?
beers
02-27-2009, 08:33 AM
#32
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/\ horses for courses .
The CF supercharger will definately not give you low down grunt but a twin screw or roots type will .
Then again , a small turbo will give you even more low down grunt than a SC but will run out of puff up top and a large turbo will give you the reverse .
Some say the 3071 give you the best of both worlds so it can be possible to have your cake and eat it too - but even with that there will be compromises.
So you have to think about what you want to do with the car
The CF supercharger will definately not give you low down grunt but a twin screw or roots type will .
Then again , a small turbo will give you even more low down grunt than a SC but will run out of puff up top and a large turbo will give you the reverse .
Some say the 3071 give you the best of both worlds so it can be possible to have your cake and eat it too - but even with that there will be compromises.
So you have to think about what you want to do with the car
02-27-2009, 08:34 AM
#33
Registered
My personal opinion is that Hymee still has the ultimate setup.
Swoope: Don't think I am a supporter of centrifugals. Like I said, I still can't find a reason to use one over the other options (except the Greddy turbo). However, I've gone from total centrifugal hater to someone that is a bit more curious about them. Mostly from a research standpoint. I figure it's probably best to badmouth something after you've verified it sucks!
Swoope: Don't think I am a supporter of centrifugals. Like I said, I still can't find a reason to use one over the other options (except the Greddy turbo). However, I've gone from total centrifugal hater to someone that is a bit more curious about them. Mostly from a research standpoint. I figure it's probably best to badmouth something after you've verified it sucks!
02-27-2009, 10:59 AM
#34
RotoRocks Powered
That's very true, still only belt driven. I'm looking towards belt driven for the lower RPM range, then when the exhaust is doing more work, it takes over for the higher RPM range...
Unless a centrifugal can hold it's power well up into an RPM range *let's just say 7-8k RPMs for S&Gs*
Unless a centrifugal can hold it's power well up into an RPM range *let's just say 7-8k RPMs for S&Gs*
When the blower is out of it's efficiency range you don't get more power out of the blower by spinning it faster, you get hotter charge.
Your best bet would be to implement the variable ratio gearing mechanism of some sort, which would keep the blower spinning at the most efficient speed regardless of the engine RPM.
02-27-2009, 04:05 PM
#35
My personal opinion is that Hymee still has the ultimate setup.
Swoope: Don't think I am a supporter of centrifugals. Like I said, I still can't find a reason to use one over the other options (except the Greddy turbo). However, I've gone from total centrifugal hater to someone that is a bit more curious about them. Mostly from a research standpoint. I figure it's probably best to badmouth something after you've verified it sucks!
Swoope: Don't think I am a supporter of centrifugals. Like I said, I still can't find a reason to use one over the other options (except the Greddy turbo). However, I've gone from total centrifugal hater to someone that is a bit more curious about them. Mostly from a research standpoint. I figure it's probably best to badmouth something after you've verified it sucks!
The Hymee is definitly on my list. More expensive than the Pettit kit, but it looks to be made of better quality parts. I still have a lot to learn about the Hymee kit though. I've tried to contact him but haven't been successful. Hymee has claimed a 340 rwhp run on pump gas, but has also claimed using stock components like the fuel injectors...??? I always thought it was common knowledge that the RX8's fuel injectors could not push more than 300 rwhp. Also wondering if his kit utilizes headers or not. Trying to figure out why his kit gives such marginal gains over the Pettit kit (I've seen videos of Pettit RX8's reaching ~330 rwhp, but with the use of headers, upgraded injectors, better pulley, etc). A larger displacement supercharger perhaps? But I have a very hard time believing he achieved 340 rwhp on stock injectors. But hey, what do I know right?
02-27-2009, 05:41 PM
#38
Ugh. Was worried about that. I noticed he never specified bhp or whp. My fault for assuming. Interesting though. That puts it on par with the stage II Pettit kit as far as peak horsepower goes. I doubt the flow charts would be much different either. It seems the Hymee kit is more expensive and supposedly better build quality, but at the same time I've read through a lot of Pettit owner's posts. The durability and quality of it seems tried and true.
02-27-2009, 06:03 PM
#41
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Could it be done with a one way bearing on the belt pulley, in a snese it would be like an RC car transmission. So at low rpm the belt will spin faster than the exhaust gas would and cause the belt to generate boost. At higher rpm the exhaust gas would cause the turbine to spin faster than the belt, but the one way bearing would allow the belt to "disengage" from the turbine shaft and spin on its own.
02-28-2009, 05:14 AM
#42
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Could it be done with a one way bearing on the belt pulley, in a snese it would be like an RC car transmission. So at low rpm the belt will spin faster than the exhaust gas would and cause the belt to generate boost. At higher rpm the exhaust gas would cause the turbine to spin faster than the belt, but the one way bearing would allow the belt to "disengage" from the turbine shaft and spin on its own.
Even if you found a clutch system, the problem is you would still need a gearbox to step up the speed of the pulley to spin the turbo fast enough. And even when the clutch disengages to allow the turbo to freespin there is still a gearbox load on your belt system leeching power. That gearbox would be eating a TON of power for this kind of application. What the OP is essentially talking about here is a centrifugal superchager crossed with a turbo. A Centrifugal SC in the first place is just a turbo with a belt driven gearbox in place of the hot side. Putting the hotside back in the system just means you have two drive systems for the same job. The problem here is that both a centri and a turbo make boost in similar ranges... To spin the turbo fast enoguh in low RPM by belt would require a gearbox with a significantly higher step up than standard Centri setup. This would require a TON of hp jsut to turn the gearbox in a powerband where the Renesis doesnt make any HP in the first place. And not only that, but requiring such power from the belt at such low RPMs would mean rediculous belt slip problems. You'd need to start with an 8/10 rib setup or even a full on COG belt setup just to make it spin. =/
Last edited by Mawnee; 03-01-2009 at 10:24 PM.
03-28-2009, 11:43 AM
#43
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Using exhaust gasses to pick up the load won't do you any good.
When the blower is out of it's efficiency range you don't get more power out of the blower by spinning it faster, you get hotter charge.
Your best bet would be to implement the variable ratio gearing mechanism of some sort, which would keep the blower spinning at the most efficient speed regardless of the engine RPM.
When the blower is out of it's efficiency range you don't get more power out of the blower by spinning it faster, you get hotter charge.
Your best bet would be to implement the variable ratio gearing mechanism of some sort, which would keep the blower spinning at the most efficient speed regardless of the engine RPM.
Variable Geometry Turbocharger
Last I looked into these there aren't many models that offered high enough boost/flow rates for my MR2 dream car setup so it was scrapped. I believe that VWs still use basically the same style of turbo although I believe they are dubbed VATN turbos.
How does variable turbine geometry work?
Last edited by Zeon; 03-28-2009 at 11:46 AM. Reason: Added another explanation with fun pictures.
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