Twin Tubo Setup

[SLY-25T]

Possibly a stupid question and could get flamed but was thinking about it the other day. Had a quick search and nothing turned up.

Question is.....

Would a twin turbo setup work with one turbo being larger than the other? Not over the top larger. Just a setup like a smaller turbo for the quick response and midrange, and a slightly larger one for mid and top end. Or would this system just fail? Has anyone ever tried?

Preparing to get flamed...

[rtune]

Possibly a stupid question and could get flamed but was thinking about it the other day. Had a quick search and nothing turned up.

Question is.....

Would a twin turbo setup work with one turbo being larger than the other? Not over the top larger. Just a setup like a smaller turbo for the quick response and midrange, and a slightly larger one for mid and top end. Or would this system just fail? Has anyone ever tried?

Preparing to get flamed...

you're talking about a sequential setup, which is used by RX7 and Supras.. supposedly it is complex and prone to problems and issues to do with the cut-over from the smaller to larger turbo, but is clearly going to be a superior system to a single or a twin if it works smoothly.

for rb26 being a straight six, you've got 3 cylinders pumping one turbo and 3 cylinders pumping the other. There is no plumbing or off the shelf parts for sequential, the system a controlling ECU would have to be created off a drawing board.

If you stuck a smaller turbo on one half of the engine and a larger one on the other then the larger one would never get into its efficiency range, and the smaller one would be overwhelmed before redline. The end result - even if the two turbos were only slightly different - would be inferior to twins of the same size.

[SLY-25T]

Thanks Moneypit. I've heard of the sequential setup but never actually understood what it meant. So basically, it's not viable as the money-power ratio would be severly one sided due to custom fabrications and 'one-off' pieces (including ECU).

I would have thought though that it wouldn't really make a diff that only 3 cylinders are pumping each turbo as once the smaller turbo begins to spool, more air is being pushed through and could spin the larger one fairly easily? Works in my head but might not in real life. lol

[Lithium]

I would have thought though that it wouldn't really make a diff that only 3 cylinders are pumping each turbo as once the smaller turbo begins to spool, more air is being pushed through and could spin the larger one fairly easily? Works in my head but might not in real life. lol

Thats pretty much correct, as on the pushing turbo side of things that is pretty much what RB26s have - except the two turbos are of course the same size. The trouble with having two different sized turbos is that they will pump air at quite different speeds and efficiencies, and the airflow will naturally try and follow the easiest path.

When the smaller turbo starts spooling up better than the bigger one there is nothing (assuming you just bolt everything up with no funky valving etc to control where the turbos push their compressed air) from stopping the smaller one from forcing its air back through the bigger turbo which is not yet pushing as much boost through it. You could possibly run the risk of the first turbo actually fighting the bigger turbo, depending on how its done. Same goes the other way, when the smaller turbo can't force any more air and as such beyond its efficiency - the bigger turbo could potentially start forcing air down its throat the wrong way. I can imagine it getting all kinds of nasty...

[SLY-25T]

Hmmm in saying that, do you think that there could be some sort of switch on/off built into the computer system? In order to shut off the larger turbo through 0-3500rpm, then turn it on 3500-7/8000rpm and vice cersa for the smaller? Sounds stupid and i figure it would be hard to simply turn on and off a turbo but interesting to know.

Also Lithium, assuming the motor was built with (im guessing) some type of valve variation, eg say a VVTi system with its own maps for valve timing for each turbo. would this work? Or am I simply making stuff up in my head? lol

[Lithium]

Hmmm in saying that, do you think that there could be some sort of switch on/off built into the computer system? In order to shut off the larger turbo through 0-3500rpm, then turn it on 3500-7/8000rpm and vice cersa for the smaller? Sounds stupid and i figure it would be hard to simply turn on and off a turbo but interesting to know.

Think about how you would mechanically do that... it sounds like you understand basically how a turbo works. Its a mechanical thing, for an ECU to "turn it off" it'd have to redirect exhaust/intake flow which regardless of how you look at it is going to be complicated and potentially wasteful as well.

Also Lithium, assuming the motor was built with (im guessing) some type of valve variation, eg say a VVTi system with its own maps for valve timing for each turbo. would this work? Or am I simply making stuff up in my head? lol

Its not going to change the fact that two different turbos feeding into the same engine are going to fight each other. All the turbos know is they are compressing air - all the engine does is breathe in the air from its source. I'm not sure the extent of your understanding of the whole system but think about it this way:

If you have a hose attached to a pressure gauge and you blow into it, it shows you can blow a maximum of 2psi - and you get a mate with a big set of lungs to try the same trick... turns out he can blow 5psi! What if you get two straws and attach them to the same gauge and both blow into it? It won't read 5+psi, its more likely you'll have air trying to force itself back down your throat and you will let go of the hose before you burst stuff. With a car, the engine is the same as the gauge - it won't bleed off the extra, it will just take more pressure - changing its valve timing will just change how it uses the air you are forcing at it. As far as the turbos are concerned, they can't "back off" if it has more pressure than it can blow against - it will surge/stall as the pressure gets blown back down its throat.

Not sure if that'll help? Sequential twin turbos tend to use a complicated bunch of valves etc to bypass airflow etc in such a way as to allow progress flow to the engine but they are invariably quite complicated to work with and are prone to misbehave and cause huge problems. With a turbo setup there is no beating a nicely matched turbo/engine combination with good tuning etc. If its too laggy, get a smaller turbo or a bigger engine

[SLY-25T]

lol that is a good way to explain it. I have a basic understanding of how an engine works but don't know the finer details. Thanks for the explanation Lith. I now understand what you were saying about them fighting each other.

[WRRR]

http://autospeed.com/cms/A_110964/article.html

Have read here. I know its a Benz oiler but has some pretty trick ideas for a sequential.

[SLY-25T]

Interesting setup. Thanks for that WRRR

[VB-]

ok, just to clarify a few things, as there seems to be alot of missimformation in here.

1. supras, and i think RX-7's (not 100% sure on the latter) use two turbos of the same size. with the supras, they use a series of valves and piping for sequential opertaion, ie: all the exhaust gas is directed through one turbo to spool it, then spread between the two at higher rpm, so they both make boost.

RX-7's do some wierd shit where two compressors share one turbine, never really looked into it. i like pistons rings, inside the motor, not apex seals spat out the side of them *if there are any rotor fans on here, i do understand them better than that, and yes i know they last if built right*

what your talking about, could be done with either valves and piping, or in a compound setup, as they do on diesel's. compound is where the bigger turbo will feed the smaller turbo on the compressor side, and vice versa on the exhaust side. thats how most have been setup that i've seen, although there may be variations on what gets fed by what.

compound would be easier to setup IMO, as the only real bypasses or wastegates for exhaust gas, typically dont see bypasses on the inlet side.

either way, both would involve alot of time and money as no-one has an off the shelf kit for skylines. one has recently come about for supras, from boost logic.

keep in mind, you will spend alot more than the value of your car to get it going right....

[paulr33]

a good example of a car with a bi turbo setup, that one is small, one large is the subura liberty B4

it has a small turbo, and a big turbo (also the subaru legacy GT is the same) and has valves that open/close

it has a big gap in its power band during changeover

[VB-]

just like supras ^.

thats another thing to consider, if the factory cant get it right, what chance do you have?

[Lithium]

Yeah I couldn't remember off hand which had offset side turbos or otherwise - I was more focussing on the complexity of whats involved with them. An interesting device which has emerged in the aftermarket is the "Spool Valve" which Forced Performance have released which they have made wild claims as to the potential of.

It is a "device" which goes between an exhaust manifold for a single entry turbo and a twin entry turbo which shuts off one of the turbine scrolls until a set pressure level is reached - which apparently hugely improves spool with minimal cost to top end flow. I am a bit of a critic of it but I still prefer the idea of it to a sequential twin turbo setup, however I don't know what longevity would be like with it.

[JMW]

If your looking at a twin set up for an RB25, Give Tangles from the SA forum a PM and he'll give you a run down on the set up he's got planned for his Stagea.

[joeyjoejoejuniorshabadoo]

just like supras ^.

thats another thing to consider, if the factory cant get it right, what chance do you have?

nail on the head there ben

[Tangles]

decided not to go twin due to the costs

but quite simple twin turbo of the same-size would only require the custom top mount manifold

you could run internal or external wastegate

and plumb the front dump into the rear dump.

same for air intake and intercooler intake - use two Y pipes to join the 2into1

$400 usd for rb25 twin manifold with or without wastegate pipe

twin hks gt2530's would be 2grand second hand, and the pipe work (3x Y bends for intake and exhaust to go 2-into-1) would be say $500 for custom work

decided to give my turbo gear to ATS Adelaide Turbo Services, that was a highflow, plus housings plus new 16g/td05h wheels, new bb pack, etc

they are crediting me for the parts as they can stock & resell, making me new lines and a GT3071r garrett ball bearing with nissan 6bolt exhaust housing for 2k