Different size turbos on a twin turbo setup?

[chaz_r33_gtr]

This occured to me whilst I was fallin asleep the other night (sad i know!) whas anyone ever tried using 2 differing size turbos with a custom manifold

e.g. use 4 cylinders to drive a large turbo and 2 to drive a smaller turbo, assuming you could use 2 boost controllers to controll each turbos wastgates so that the small one only boosts to say a bar and the larger turbo can boost to 2bar say. It would seem you would get the best of both worlds with virtually no turbo lag..

Would this be possible?

[Listerofsmeg]

isnt what you are refering to just a variation of a sequential turbo set up a-la RX7 or supra?

[chaz_r33_gtr]

aye it does sound like the same a the sequentail setup on supras now i looked that up LOL!. Anyone ever tried this on a GTR tho?

[andyneed4speed]

You need brakes not more bloody power

[Raiju]

The Rx7 is a slightly different concept. The turbos are fed off all cylinders, having a buttterfly flap that switches between the two turbos varying the amount of exhaust flow to each one, thus spooling up the smaller turbo first, and then switching to push exhaust gas to the larger rear turbo. You can't run different sized turbos on individual or pairs of cylinders as the exhaust pulses will not be matched which will cause huge problems.

It is possible to run a sequential setup, but the gains would be negligable compared to the costs involved.

[Lith]

Yeah its sortof along the lines of a sequential setup you are describing there but basically don't do it - as you need to even up the pressures etc.

You must remember that turbos aren't trying to feed the engine specifically, all they are doing is pushing air away from themselves - where it goes is the path of least resistance.If you have both feeding the same intake path and one can flow more than the other one then the air flow might decide the other turbo is the easiest path to follow out than the engine and start causing it to stall.

[SkylineUSA]

Huge headache to setup, that is why you always see Supra's with singles when upgrading for more power.

[kingsley]

Originally Posted by chaz_r33_gtr

This occured to me whilst I was fallin asleep the other night (sad i know!) whas anyone ever tried using 2 differing size turbos with a custom manifold

e.g. use 4 cylinders to drive a large turbo and 2 to drive a smaller turbo, assuming you could use 2 boost controllers to controll each turbos wastgates so that the small one only boosts to say a bar and the larger turbo can boost to 2bar say. It would seem you would get the best of both worlds with virtually no turbo lag..

Would this be possible?

Sounds like a recipe for disaster to me. Even if you did get one spooling before the other, you'd have to install one way valves else the boost the earlier-spooling one produces will just try to reverse down the other turbo.

Also, the engine won't be particularly balanced as you'd have two cylinders producing different power to the other 4, and probably having to run a differerent mixture and ignition timing due to different exhaust restrictions.

If you look at the system on the Supra it's quite complex. I don't know much about that system but I gather it causes quite a bit of back pressure which then meant that Toyota had to put mild exhaust cams on to prevent reversion, which are presumably the main 2 reasons why people remove this setup when trying to get big power out of Supras.

[SkylineUSA]

RPM window with N2O, or a 2 step.

A 2 step is kind of harsh on a turbo though.