Nope, not the same. To run the same PR on both turbos, the secondary turbo needs to run a lot more boost. In my case, 13 psi on the first stage and 28 psi on the second stage results in PRs of 1.9 and 2.0, respectively, for a total of 41 psi and 3.8:1. Inlet pressure is routed to the top of the gate, so the small turbo boost goes up in step with the larger turbo as it spools. The only "odd" thing is that 19 psi springs get me 28 psi, and it's not creep. It's dead flat at all rpms, and stays at 28 no matter what the big turbo is making, so it's real. I haven't come up with an explanation for that yet. Probably because it's a good thing, I wanted 27 psi springs, and they don't make them.

 

Ohhhh right. so do you set the smaller turbo gates (2 x 44s in your case) to 13psi? if so how do you get the smaller turbo to always be boosting? surely once the big turbo is spooled up and the setup is compounding, the smaller turbos 'gates would open and let the big turbo do all the work?..... is this not the case?

Cheers

Chris.

 

Other way around, the small turbo's gates are at 28 psi, the large turbo is at 13. The small turbo spools to 28 psi and the gates open. As the large turbo spools any boost it makes goes to the top ports of the small turbo's WGs increasing that spring pressure (28) 1:1 with big turbo boost, much like your fuel pressure regulator does. 28+13=41 psi on the springs alone. If the small turbo's gates opened and the big turbo did all the work it would no longer be a compound turbo system.

 

right. That makes sense kevin. I have seen some setups, i think on a supra, that just let the little turbo free wheel once it was spooled up. But i guess you setup enables you to take advantage of the higher lbs per min of air the larger turbo can move without over boosting it. What are the intake temps like? How do they compare to your old setup? I guess you could always add a little meth after the big turbo to kill intake temps. How do you think it world work at lower boost levels? Cheers chris

 

Yeah, if it bypasses the small turbo, it's sequential.

Intake temps were exactly the same as the single turbo at the same boost. This is post IC, but my FMIC is pretty inefficient at this level, so an increase would have shown up. Not sure how it would work at lower boost levels, I can't go below 40. There is another guy with a 16g/60-1 setup on a 2g running lower boost, his data looked good.

Interstage cooling should be big, but I'm not sure how I want to go about it. If I stay with a (much better) FMIC though, the effect may be minimal as far as power goes. Maybe some gains in drive pressure, spool, and turbo life.

 

Kevin,

I have been YouTube'ing compound boosted setup and im have seen alot of guys running turbos fed be large ish centrifugal blowers. any idea how these setups work? There dosen't look to be any vavle inbetween the SC and the turbo.

I guess the SC will just act like its feeding a larger engine than its actually bolted onto wont it? Could this be a good idea for an EVO? obviously you would need to make sure you have ALOT of wastegate but could it work? What would be the disadvantages of this over a compound setup?

Also thought you might like to see what Norris Design is bringiong out. think they will be using a positive displacement blower and turbo. from what Simon has said they will be running a bypass vavle so once the turbo is spooled it will be boosting the engine not the SC, much like the VW setup.

Ill post the link later.

cheers

Chris.

 

There is some good info on this topic on D S M tuners.

 

any chance of posting some links mate? always a very intresting subject to look into.

 

I'm not sure how the guys with SCs do it, but I personally wouldn't bother with anything but a compound type setup. It's simple and it works. The problem I see with the SCs though is efficiency, compounding the compressors compounds the inefficiencies.

 

ok, so the next logical step here is to see someone attempt a compound set up on an evo...

i know we are all dying to see this.

has anyone thought about using one of those electric blowers before the compressor in order to keep the turbo spooled up?

 

i have thought about this one quite alot. packaging is going to be a total Nightmare! the easiest way i can see of doing it is small high presure turbo mounted low down (pos oiling issues) behind the half sized rad. this should give you plenty of room for a nice good flow exhast manifold. a very large wastegater could then be mounted of this manifold before turbo. this would then combine with the exhaust form the small turbo and come up and into a larger turbo mounted in a similar spot to where the Forward facing trubos guys put their turbos.

as for the cold side, well a filter might be hard to fit on the big turbo. but from there the boosted air would go across towars the drives side of the engine bay and then curve down into the small turbo. From there the air would have to bee routed nice and low back accross the fornt of the car to the intercooler.

Alternatively you could pipe the air form the large turbo through thr intercooler and into the smaller turbo. This would give you some interstage cooling. Then you would ahve to run a air to water charge cooler somewhere (pos in the cabin) for the smaller turbo. and then to the intake mainfold.

Or if you wanted it simpler you could try and do a rear mounted setup. not sure just how effective this would be but poss worth a shot!

Chris.

 

Great info on compound turbocharging.

http://www.dsmtuners.com/forums/cust...bo-set-up.html

 

good luck. sounds good in theory.

 

If you're refering to compound turbocharging, it sounds good in practice too.

 

Indeed.