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?

 

/\ 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

 

Is anyone on the site running with a large turbo with lag past 3000?

 

yes - lots
many of the 'bigger' turboed 8's dont get going till 5000 rpm

 

Oh really? I thought mostly everyone was running the 3071 from MM....

 

what chew talkin about willis???

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

 

I think it's a great street turbo. Kind of like the RX6 turbo for the FDs. But for racing, I'd hope the end user would choose a T4 turbine to open up the top end of the power band.

 

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!

 

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.

 

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?

 

/\ you fell for it .....

have another look - it's called crank horsepower

 

This time next week, the Hymee SC will be high on my shopping list, the MM turbo's just not working for me.....

S

 

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.

 

Por que no?

 

tell him to shove it up his *** next to the coils

seriuosly though - an upgraded greddy with a few special tweaks would not dissapoint you either....

 

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.

 

I have experience with such locking "clutch" bearings in a heavy machinery setting and they dont last long even in low horsepower and no heat situations. Eventually they wear the shaft they ride on and stop locking or blow the needle bearings they use and lock up on the shaft permanently. I wouldnt trust them with my engine =/


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. =/

 

Is this kind of what you are talking about Rotorocks?
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?