Twin Charging....with one unit?
 

OK, this is coming from two guys bored at work....

We know that Twin Charging is having a turbo and supercharger in the car at the same time, to mitigate each others weakness. Well, the one thing I was thinking, would there be a way to attach a belt from the drive train to the turbo, to spin it like a Supercharger, but then after XXX RPMs, the belt stops working, and thus the turbo kicks in with the exhaust gas....

I know it's just a little vague and not very detailed, I'm just curious if it has been done/can be done. I honestly don't see why it COULDN'T, but I'm hardly an engineer for these things...

I believe there was an MR2 from the factory with this system and a mini. It's kind of costly but I think the downside would be weight.

its POSSIBLE! ive seen it just not on our cars, on an M3....i have pics but my damn batteries are dead....

supercharger from 1k rpm up to 3k, then turbo kicks in, ABSOLUTELY NO lag

I'm not 100% sure on the weight. You're not really adding much to the turbo. A belt + whatever mechanism to stop the belt from spinning the turbo at 3k RPMs or whatever, and that's it. Maybe an extra 10 - 30 lbs?

I son't see it working quite that way as the belt would have to be turning really really fast unless there was a gearing system associated with it. However something very similar has been done. Look up "compond turbocharging". It's not done for power though. It's done for efficiency.

I don't think twin charging or even twin turbocharging is useful for the RX8. The 13B pumps out enough exhaust to fully spool up even the MazdaManiac and Esmeril turbo by 4K RPM. Even in 6th gear on the highway at 60 you'll start making boost the milisecond you put your foot down. 4K sounds like a lot to some people but the engine redlines at 9K, so you'll still be in boost the majority of your gear.

I think twin charging is like those cars that can run on water. Its POSSBIBLE, but not very cost-effective or practical =/

not quite - it even takes a little time to spool up the Greddy .....

This is a compound turbo system that is on one of our New Holland Tractors.

"Exclusive turbo compounding on the 485-hp T9050 boosts power and fuel economy while reducing noise. Exhaust gases are “recycled” through a second power turbine to generate even more power."
It mainly gives an 8% increase in fuel efficiency.

http://www.newholland.com/FILES/tbl_...T9000Turbo.jpg

But you can see how it is done.

Sounds like it would just need some kind of one way bearing on the pulley so that it could spool with engine rev's, then once exhaust built up that could take over and drive the turbine.

I dont know the technicalities of it, but if its true, I agree with what Red Rex is saying. $k RPM isnt too high in our motors range to be spooling up. Even in first gear you dont stay belof 4k RPM too long, and out of first gear you can always be in that range when you need to be.

I have the GT3071R and it spools up really fast, you can hardly notice the lag

Here is a vid i did yesterday which shows the spool up of my greddy from 3000 rpm then 5500 rpm at gear change

http://www.youtube.com/watch?v=3T2Bcl6ftFo

This discussion wasn't really gearing at me doing it to my car or anything, it was just a general idea for any engine/car.

What about looking at how a Supercharger does it...wouldn't there be a way to do it much the same way? Or would the turbo still not be spinning fast enough with such a small pulley..?

/\ they already make such a thing - its called a centrifugal supercharger .....

see link

http://www.mazdatrix.com/8forcedinduction.htm

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*

Interesting... but what would stop the belt from working, if it's connected to the drivetrain... it would always be working.

a clutch system like on LSD but opposite. probably a weighted system, where springs put tention on a central shaft attached to the pully. Then as speeds increase centrifigal force pushes the weights agienst the springs and releases tension from the pully shaft. the problem is the turbo would need to be perfectly sized to not try and outspin the engine till after a certian RPM. The best concept of this i can think of is the Brain Yo-Yo (dont pretend you dont know)

A more expensive way would to have a tourqe converter like structure on the pully, where the belt will drive it in one direction, but once the turbo starts spooling the turbine can speed up past the speed of the pully. Kind of like the caps on medicine bottles, except powered by oil and not gears.

See below...

That's actually some good ideas. I'd like to see what some other people can think of. The clutch system seems pretty good, if we can get it correctly. And the size of the turbo was something I was worried about also. Maybe a specific size of a turbo can come with XX size pulley...

Has anyone ever heard of a centrifigul supercharged paired to a larger turbocharger? The only twin chargers I've ever heard of used a traditional roots-type blower feeding air until the turbo was spooled up. Or why not throw all reason and practicality out of the window and shoot for a twin-centrifigul supercharger system?

As someone that has owned a Procharged(centrifugal) car. Um why bother ?
On my vette with the usual related mods the car made more than enough power to roast 1st-3rd gears and never felt like I needed more low end in higher gears. Infact..I got sick of rebuilding it every other weekend after once again decimating my driveline. Never an engine problem..just everythign from the flywheel back :eyetwitch

Centrifugals really are only useful on V8s with the low rpm power to spare anyway(to cover what the gearbox takes). And the delay on the power ramping up(which isnt as much as people are led to believe) is just an opportunity to find some sort of traction. On our engines I cant see a centri being practical at all. It would hurt the daily driving power more than would be justified by the performance gains.
Even with a dual forced induction application like is being suggested you would just be worsening our already poor fuel effeciency just to get back to the numbers a single turbo system would make. Not to mention all the extra moving parts to maintain. It is an interesting idea to process just for kicks....but from a performance or practicallity standpoint I just dont think it would be worth it. =/

^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...

I've actually reversed my thought on this also...within the next year I'll probably be throwing one together piece by piece to mount on my RX-8. But for my driving style and where I want the power, really just for track days, I have little issue having to wait until 5500rpms to start making meaningful boost. Only been within the past year that I've begun to change my mind on the issue. And packaging should be simple for one in comparison to a positive displacement unit.

Yea for the sake of experimentation I have the same mindset. Infact wayyyyy back when i was kneedeep into building my custom procharger setup for my vette, I even asked a similar question to this thread on the corvette forums. I posed whether using a procharger to drive a turbo was possible..... For the record...its possible....but VERY ineffecient :lol:

I think they would be great for a solid reliable race setup but a turbo that gets boost from 3000 rpm onwards is more of a blast on the street ...

Yeah, turbos are always tempting, and my previous RX-7s were both turbocharged and a blast...

I know for a fact that even a carburated roots supercharged 13B that puts out a measely 210 hp is fun on the street!

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 :beer:

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 ass next to the coils :lol:

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?