This system also has a prespool. It's just controlled differently.

The exhaust bypass valve acts as the prespool. It slowly begins to direct exhaust towards the 2nd turbo, but the intake air control valve prevents any surges in the system by not opening the intake air from that turbo to mix in just yet with the intake air from the 1st turbo.

See here's our mess....

We have the Prespooler that prespools the 2nd turbo, then we got the turbo control actuator which allows even more exhaust to get to the 2nd turbo just like Toyot'a exhaust bypass valve. Our charge relief and charge control is what lets the spooled air from the 2nd turbo get out just like Toyota's intake air control valve. Problem is our turbo control needs vacuum AND pressure to operate. It seems as if Toyota's system only requires pressure to operate. Which makes sense since all you see under boost is pressure.

Their system is just....well.....more efficient. They got less stuff doing the same amount of work AND to top it off, they have superior stock turbos.

This is why everything becomes a cluster **** when we start modding and no one wants to deal with it. The preespool is the main reason why we see those 4500rpm spikes with an open exhaust. The presool starts to prespool TOO much causing the spike in transition. Most people don't know what all they have to do is simply readjust the prespool flap.

 

Flybye, do you have dimensions for the supra turbos off hand? What do they equate to size wise? Who makes them?

 

I have no clue
I still have no clue
That's another great question

LOL I'm helpfull today
Eggnog kicking in

A little thread over on the Supra forum might help, though.

Or email Jim Swantko He's a pretty knowledgeable guy. I bet Jimlab might have an answer as well.

 

well........from waht i can tell the supra's system doesn't redirect the exhaust gases from the 2nd turbo to the first turbo.

Looks like it just dumps it farther down stream.

this would increase lag a bit more

so with the supra's setup it's not rpm based - so the 2nd turbo would come on when ever a certain boost level is achieved.

this would be a great benifit to modified exhaust/intake and allow that transition to occur several hundred rpms eariler in some cases.

you wouldn't have a surge or spike either.

hmmm.....well i dont' know....i'm just try'n to be a devils advocate but can't find a reson the rx-7's is better.

i know......all those plastics parts are better for heat soak and breaking?

 

Assuming both systems are well designed and of equal quality with similar high end flow expectations a twin turbo system will have better response, spool faster, better cooling, last longer and essentially the same high end flow. If you're looking for performance a twin turbo system is essentially always going to be better.

The drawback is the twin systems will be more complicated, cost more and take up more space. Most of it's just basic common sense physics stuff. I'm not talking about the OEM or even modified OEM turbos compared to single turbos btw.

Kevin T. Wyum

Happy Holidays

 

My bad...props to Porsche then

 

there is a twin T25bb out there some where (i have seen the one for dave's MS car)

 

Seems to me that when the supra runs on it's primary, because it doesn't redirect the secondary's exhaust and just dumps it, there's probably a significant difference in exhaust backpressure.. How healthy would that be on a rotary? (running uber-lean on the rear rotor?) Or does the fact that it's all plumbed into the same exhaust system keep the backpressure similar.

I'd assume that a LOT of thinking went into sizing the exhaust bypass valve on the secondary to minimize these effects.

I still don't understand why this type of system is any better than parallel since it doesn't use exhaust from the entire engine to drive the primary turbo in low-pressure mode.

 

In my endeavor to figure out if this is even a possibility for our cars, I found two pictures of a set of supra turbos. Could someone assist me in opening them up.

 

.

 

The plumbing is going to be the interesting part. The exhaust manifolds will need to be connected before the turbos as well as after to allow the second turbo to turn on and off. Think of it as an express lane for higher boost.

The description for these turbos stated that they can be run safely at 1.2 bar.

I am going to take measurements of the stock manifold and engine compartment space tonight.

 

Theirs are more like a two single turbos, instead of one set housing and turbos that we have.

the overall difference that I can see is that we use 5 solenoids, and they use 4 solenoids.
The one solenoid missing is Charge Relief Valve. This is valve is what we use to bleed pressure from 2nd turbo to intake box.
On the Supra diagram, they don't care about bleeding this into intake box, they just keep it into the engine intake. Look for the little loop on the second intake valve in the Supra diagram.

So in fact theirs runs like our non-seq. Ya?