The first turbo is the first of the two to see exhaust gas so the second turbo can only push as much air as the gate on the first allows it.

 

Its an internal wastegate so the air is gonna go through the same exhaust regardless.

thewird

 

Your right, so the control method must be the the second turbo can only be compounded as much as the gate on the first allows. It seems the boost logic kit uses two seperate manifolds and wastegates so they must go a different route.

 

it would also make the exhaust note a lil quieter. i have talked to lots of guys on the cummins fourms about this. they are big into it. from my under standing the small turbo X the big turbos boost by 4. its how the yuse to get 200 psi on tractor pullin trucks.. it might be the other way around but i think one of them times the other by 4 and they spool very fast

 

Why hasn't anyone mentioned this idea before lol?

thewird

 

every1 i brought this up to said it was a waste of time.. i wanted to do it so i could drive my very loud car in the street lol plus the boost was a good side effect

the guy i was talking to about it on the cummins site told me he thought it would work very well on a rotary. he just needed maps of the turbo i wanted to run so he could tell me the other turbo to use.. then every1 i told or asked about it in the rotary world told me to now waste my money. so i never got back in touch with the guy

 

I think there is enough room for a smaller and larger turbo. Pretty interesting concept. I think running fairly large exhaust housings with a smaller compressor and larger compressor would be ideal. This would help keep back pressure down as well as heat retention. I wondered how the first turbo didn't overspin as well but the internal wastegate on the first turbo would be simplest. You would definately want the second turbo to receive all the exhaust energy. So a dumped gate on the first turbo would be a no go. I'm going to try this one day. Shouldn't be too expensive for someone good at fabricating. Just some extra flanges, oil lines, plumbing, and turbo. You could also compound 2 turbos of the same size but this wouldn't be as ideal.

 

Um, how is this different from the factory sequential twin turbos (other than the size of the turbos)?

 

Almost everything. The way it's run, the way it works, and the results. Its two different ways to attack the same problem. Compound turbocharging is from what i've read a better way to do it. With compound turbos the first turbo's "downpipe" feeds into the exhaust inlet of the second turbo. The boost pressure of the second turbo feeds into the inlet of the first turbo. This compounds the boost, or multiplies it. Gives faster spool up while retaining the effects of a huge single turbo. Imagine the power of a t78 with spool similar to stock.

 

Sequential twin-turbo

Sequential twin-turbo refers to a set up in which the motor utilizes one turbocharger for lower engine speeds, and a second or both turbochargers at higher engine speeds. During low to mid engine speeds, when available spent exhaust energy is minimal, only one relatively small turbocharger, the primary turbocharger, is active. During this period, all of the engine's exhaust energy is directed to the primary turbocharger only, lowering the boost threshold, minimizing turbo lag, increasing power output at low engine speeds and providing the benefits of a small turbo. Towards the end of this cycle, the secondary turbocharger is partially activated (both compressor and turbine flow) in order to pre-spool the secondary turbocharger prior to its full utilization. Once a preset engine speed or boost pressure is attained, valves controlling compressor and turbine flow through the secondary turbocharger are opened completely (the primary turbocharger is deactivated at this point in some applications, such as the third generation Mazda RX-7). At this point the engine is functioning in a full twin-turbocharger form (or as in the RX-7 with a single large turbo), providing the benefits associated with a large turbo, including maximum power output, without the disadvantages such as increased turbo lag.

and we have been over what compounding is so that is the difference..

but incase you didint read it small turbo get exhast and flows into the larger turbos exhaust the larger turbos air flows into the small turbos air intake. just like the pic shows

cheers patrick

 

No. GT35 is to big for the first turbo. It would defete the whole point of a compound system on a two rotor.

-J

 

There are a few ways around this

-J

 

Actually if its routed correctly the second turbo will see exactly the same amount of exhaust gases as the first turbo. It would receive the gases that pass through the turbo as well as the gases that are routed past the first wastegate. The second turbo would then have its own wastegate to control how much boost it makes. On super high boost applications the second turbo probably doesn't even have a wastegate. But on our application it should have one.

 

Better get some garden hose and a more pumps to keep it from getting hungry...

 

-12 is way bigger then garden hose garden hose is around -10

 

I'd rather see the twin method that Opel used on their Astra diesel concept. It's ingenious and simple. It's both series and parallel with only 2 valves. This is the way to do it. Do a search online for Opel twin turbo and check out the diagram.

 

Wow! http://www.gre6.com/ansize

Fuel Supply Hose:


Opel Twin turbo.

 

i bet with decent fabricating skills you could even make the above setup with dual scroll turbos.
what setup would be best for a rotary engine is the biggest question.. that is, if you are looking for a big/small turbo combination.

 

The setup posted by Nick_d_TII is the same as the one in the picture except there is a check-valve to reroute the air from the big turbo more directly to the engine. I think a secondary wastegate is required for the big turbo for our application in addition to the internal wastegate on the small turbo. Internal on the small turbo because it simplifies things quite a bit and we need as much space as we can get. Do they make internal wastegates for the likes of the GT42R's? Cause that would simplify it even more.

thewird

 

Internal gates tend to be smaller so it may not be enough to have both internal gated. An external gate right between the exhaust outlet of one and the inlet of the other wouldn't be hard to do. I rather like open vented wastegates so mine would just dump right there.

 

What I'm wondering is if MAP based tuning would work since the airflow at different PSi levels will change depending if the big turbo is pushing air or not.

Who's gonna be the first to try this

thewird

 

I would think that that you would want to put a LARGE external wastegate on the first turbo(routed to the second turbo). Our engines need to breath espically with boost at high RPM. Think of the EMP before the first turbo if there was just an internal gate...

 

I would think a MAP based system would still work. The stock twins flow different amounts at the same PSI, and it would be similar with this setup. Early RPMs would be tuning mainly the smaller turbo, then the higher RPMs would have the big turbo. And the smaller turbo would be around 10 psi and lower, with the big turbo more at 10-30 psi or whatever. Plus all MAP based systems have different flows at different PSI, for instance, I can still boost 10 psi at half throttle, but the airflow is less then at full throttle, course maybe this is where TPS tuning adjustments come in, it's hard to tell on the PFC what the TPS settings actually do, and one of them has no adjustments even made. The other I "think" is for sudden throttle movements.

I agree back pressure is something to consider in a rotary especially. Internal gate is definitely simpler, and if they can be made large enough wouldn't be an issue. Otherwise rerouting an external gate is doable just more work and space required.

One thing too is that the smaller turbo can be even smaller then a typical "fast spooling turbo" because its expected RPM range is much shorter due to the larger turbo coming online at 4 or 5k, AND the larger turbo will spool even faster then normal due to the increased power and exhaust output from the smaller turbo. So you could then use an even bigger turbo and have even higher power potential, or just reap the benefit of the much improved midrange power from the large turbo coming on sooner. It's a win win situation.

 

Nope, that is not the defitnition of a compound turbo.

"Many people erroneously refer to these type of turbocharger arrangements as "compounds". They are nothing of the sort. By definition, turbo-compounds pass the exhaust gases though a turbine, that is true, but the shaft power from the turbo is coupled directly to the crankshaft through reduction gears and supplements the crank brake work. "


http://www.rotaryeng.net/sum-turbo-comp.html


BTW: The Opel twin turbo system that was mentioned earlier would be a wicked setup!!

 

With a bit of work i see no reason a 13b couldent be sporting something like this. BTW I think there is plenty of room, you just have to think verticaly stacking.