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.



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

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

 

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!