Twin Turbo (1 big & 1 small) Lag Elimination

[stevechumo]

Folks,

I'm thinking of a twin turbo system with a large T70 and a small T25. The purpose of the system is to eliminate tubo lag if using only a single T70. The power goal will be the same as with only a single T70. By adding a small T25, the T25 will spool quicker and will flow the air quicker to the engine, which eliminates turbo lag, while the T70 is still building up boost. In this case, the t70 will build up boost slower than if it's in the system by itself. So once the exhaust pressure reached a certain point, the T70 will fully kick in and take over the T25. My thought is: will the T25 will be damaged, or will there be any other problems?

This turbo system is more simpler than a sequential system, but will it work?

I don't draw very good with the Microsoft Paint, but you can get my idea.

 

[cribbj]

Steve, I see two problems with this:

1) The T25 may be OK down low, but its turbine isn't going to take well to being oversped, nor is its compressor going to be in the map anymore at higher boost pressures & flows. There'll be a lot of heat generated there.

2) Once the T70 is up and "on boost", the T25 won't be able to "buck" it and the resulting strain of the exhaust trying to turn the T25's turbine one way, while the compressor trying to turn the other may cause some shaft problems.

If you could isolate the T25's compressor with a big reed valve, similar to the TT Supra setup, and isolate its turbine once the T70 is up on boost, this might work.

Alternatively, you could just spool that big T70 with a little shot of NOS....

 

[Lextreme II]

I was thinking the same thing few years ago. Here is an article on it http://www.lextreme.com/sstt.html

 

[DHBomber]

Why not just get twin properly sized turbos?

 

[Zuffen]

Porsche did a similar thing on the 959.

They fed the exhaust through the smaller turbo and used a flapper valve to direct the exhaust through the larger turbo as revs built up.

This gave them quick spool but a solid top end.

Try researching the Porsche set up.

I wouldn't think it would be too hard to replicate.

 

[Lextreme II]

JBrady and I have few phone conversations about this. He has some crazy ideas. Perhaps he will jump in someday.....

 

[stevechumo]

Or do you think an external wastegate installed in the smaller turbo pipe will make the whole system work? When the exhaust gas pressure in the smaller turbo pipe reaches a certain psi, this wastegate will work as the flapper valve and vent the excess exhaust gas out. But instead of venting this gas down to the muffler, it's redirected to the larger turbo pipe, and not the main pipe. So the smaller turbo T25 won't be choked, while the larger turbo will still have full exhaust pressure. If it works, then the Porche might copy from us...:006:

The reason I don't want the twin system (if this design works) is because the twin turbos might still have some little lagging. Each in the twin has to be larger than a T25 to create the same power as the T70. If this design works, there'll be no lagging whatsoever.

 

[DHBomber]

I can see what you're saying and it sounds like a killer combo. The reason why I asked was because a twin T28RS combo (with my expert calculations hahaonder: ) will start spooling pretty early (10+lb at around 2500, already boosting at 2000) and have the capacity to make around 500hp. I guess if you're trying to take advantage of the t70's extra airflow than that's a different story. Sequential TT?

 

[cribbj]

Steve, I still think you'll need to isolate the compressor side of the smaller turbo with a flapper check or an IACV (Intake Air Control Valve) like Toyota did with the TT system on the Supra. They put theirs on the #2 turbo to keep it from being damaged by back flow from the #1, however I think this would still work for you if you moved the IACV to the #1 side.

I drew a schematic of this system back in 2001, and I think David has it posted here: http://www.lextreme.com/sqtt.html

 

[JustenGT8]

Too much effort for little or no real world gain. If you really want killer throttle response down low then just keep the comp ratio high. My GT30 equiv twins produce 13psi at 2500rpm and ample poke below that...if anything i have too good a response and really need to get my traction control setup working.

If you are really set on a twin setup then a roots style Supercharger for low rpm respones with a large turbo for top end is the way to go.

 

[turboandrew]

I agree 100% with JustenGT8. If you really want to spool a very large turbo well, go with a compound charging, using a positive displacement supercharger (roots, or better yet, twin screw) and a large turbo. The turbo will blow through the supercharger, and there will not be any issues with this.

 

[stevechumo]

I agree 100% with JustenGT8. If you really want to spool a very large turbo well, go with a compound charging, using a positive displacement supercharger (roots, or better yet, twin screw) and a large turbo. The turbo will blow through the supercharger, and there will not be any issues with this.

Some peole have used a small Nos spray to help spooling the big turbo. And if with a supercharger (root type only) and a turbo, it'll be too hot for the combustion chamber. I haven't seen this, but I think detonation might come next. Also, it's a lot more complicated than a simple twin turbo system.

 

[JustenGT8]

I run a simple twin turbo....what you propose is NOT simple. Syncronising turbo repsonse is such a fashion is far more compicated than the predictable response of a roots style turbo.

Toyota (2JZ), Subaru (TT liberty) and Mazda (13BTT) as the most common examples have similar setups (use staged turbos of similar size though) and all have horrible torque curves and commonly experience all sorts of reliability issues. If the factories can't get it right not much chance ofd a custom setup coming together well eh?

I have designed a SC/turbo setup with the two systems running separate intakes...no temp or det issues then, not that i think this is a major prob anyways.

 

[DHBomber]

Ha ha, oddly enough, I loved my tt setup (FD full boost @2500 = a rotary that can actually pull up a hill without downshifting). I prefer it over my friends rx-6 setup... although there is quite a bit more power up top. Anyways, fuel mapping and turbo control will definately be tricky... here's how the 7 does it anyway.

 

[turboandrew]

twin sequential turbo setups are very complicated. Getting that 2nd turbo to "join the party" is very difficult. In fact, I have never seen it done sucessfully by a DIY'er, and the factory systems have their quirks and reliability issues. That's why I suggested a compound, not sequential (there is a huge difference in these types of systems) system with one supercharger and one turbo charger. Using a water-to-air intercooler after the supercharger will solve any air temp issues.

So, to be clear, the setup would be air-filter->turbo->[optional intercooler]->supercharger->required-intercooler->engine-intake. Having a positive displacement supercharger like a roots blower or a twinscrew will make the engine act "bigger" when seen from he point of view of the turbo -it will be injesting air at a much higher CFM, and it's exhaust energy will be much higher. For example, in very rough estimates, a 4.0l 1UZ running a roots 112 at 0.5 bar would be much like a 6.0l motor, in terms of intake CFM and exhaust energy. A turbo which would normally be too laggy for a 1UZ without the supercharger, but sized quite well for a 6.0l motor, would probably go quite well with a 1UZ+roots at 0.5 bar boost. And there's no fancy flapper doors or extra wastgates to make this work. The turbo blows into the supercharger, which blows into the engine. The supercharger will never "limit" the turbo, because its CFM is always higher than the engine, hence the term "positive displacement supercharger". I guess the downside here is that you need a supercharger intake manifiold and turbo headers. I still think that's a lot less hassle then designing and executing a sucessful twin sequential turbo system.

 

[skid]

one supercharger and one turbo charger.

I was wondering how long it would be before someone suggested this. How about properly matched twin turbos for the high end to come on boost just before the 112 runs out of puff??

I don't really care for bling, as long as something goes ok it's fine by me. However.... wouldn't it look the bollocks!

M

 

[sefo]

hey guys just an idea, on the large aftermarket turbos (gt3540 ect) they run a twin scroll design on the turbine housing, has anyone tried setting one up on a actuated slide setup that blocks one scroll off at idle and as boost increases, the pressure on the compresser side opens an actuator to feed the second scroll much the same way a wastegate works?????? this would allow a good response with good top end flow.