The Rig

iTrader: (13)

my mate has a skyline, single turbo, he wants to go to the r34 twin turbo, we got yaking on how the 2 turbos work, i thought the 1st turbo was tiny and that gave you the quick turbo at low revs then the bigger 2nd turbo took over at high revs, he reckons the one turbo helps the spin up of the 2nd turbo to spin quicker at low revs ?

are we both wrong ?

cheers

Shardlow

im no expert, but i thought what you said was correct? smaller turbo that almost spins constantly to keep the larger turbo moving reducing lag! could be wrong but sounds right!

GC8

Some cars have sequential turbos with a small quick spooling turbine handing over to a larger turbine at higher revs (with an infuriating gap in the middle); this is intended to make the car more 'drivable'. Others have one turbo per bank of cylinders, like later 6-cylinder Porsche tubrocharged engines. The notion that the fist turbines job is to spool up the larger turbine is absolute bollocks!

edmy716

the gtr skyline has two turbos each feeding 3cylinders
or people put a mahassive single that feeds all 6

TimmyboyWRX

yeah the RX7 had the twin turbo setup sequentially, i.e the little one spooling first and the larger later on to reduce lag.

People to build those with single turbos too to increase power.

didnt realise the skyline had a seperate turbo for 3 cylinders, always assumed it was the same as the RX ,learn summit new everyday

4stringMike

I'm not sure about Skylines, but I had a Supra twin turbo for a while, which has two turbos of the same size.

The way I understood it to work was that the first turbo spools up almost straight away (at like 1500 rpm) and therefore provides a reasonable amount of boost immedietely, then the second turbo (of the same size) spools up at something like 4000 rpm and ALSO provides boost, that's to say, at this point in the rev range BOTH turbos are working.

Like I say, thats how Supra's work AFAIK, but I know other cars have a small turbo and a big one, as said.


Mike

hades

Some of the slightly older Legacy's had twin turbos (one smaller and one bigger), with a lovely "characterful" dip in the torque curve somewhere around 3500-4000rpm IIRC when the changeover happens. If done well enough, you could potentially map round this and massively reduce/remove the hole

Izzy

The twin turbos on the RB26 engine of the Skyline GTRs are both the same & spool up at the same time working together. "Factory" boost is around 0.7 bar, but are safely capable of upto 1 bar pressure. They have ceramic spindles that can break at higher boost pressures than this, unless you have either the Nismo "N1" type which have steel internals, or aftermarket units. The twins are used to develop a decent amount of boost quickly without much lag. Larger "singles" can generate higher boost for big bhp but at the expense of lag.

I've not had any 1st hand experience of Supras, but I believe their turbos are sequential, with one spooling up before the second.

ScoobyDoo555

I thought that my twin turbos were sequential, but I'm not sure now. Just know that I've got two 'kin turbos, and a shed load of torque


Dan
(Audi S4 V6 2.7Litre Bi-Turbo)

Beef

Usually with V-configuration engines, a twin turbo setup has each turbo being 'driven' by 1 bank. Sometimes the outlet from each turbo will only go to 1 bank (sometimes the same bank it's fed from, sometimes the 'opposite' bank), and sometimes both banks will feed into 1 common inlet.

Usually with inline engines, a parellel twin turbo setup has each turbo driven by half the cylinders, and then both turbos feed into a common inlet (this is how the Skyline RB26 works).

With sequential turbo setups, it's practically always the case that both turbos are the same size (only exception I can think of is the new BMW engines). What happens in the case of the Supra 2JZ is that no.1 turbo is always 'online', which results in positive boost from tickover, and maximum boost from no.1 is usually achieved by 2,000rpm or so. In the case of the 2JZ, at about 3,500 or so some of the exhaust gas from no.1 is 'bled' off to no.2 to 'prespool' it, getting it up to speed by 4,000rpm when the system changes to 'parallel' mode, that being both turbos blowing at the same time. In this case, all 6 cylinders power firstly turbo no.1, then both turbos.

The reason for both turbos being the same size is that, if they're not, then it's easy for imbalances to occur, and for the larger of the turbos to end up forcing air backwards through the smaller turbo! From a quick bit of reading with regards to the BMW system, apparently the smaller turbo is used on it's own very low down in the rev range, with a brief transition period, then the bigger turbo on it's own up to redline. This is only what I've picked up though, so for the BMW system I could be completely wrong.

In terms of 'lag' (late spool is what people usually mean), a parallel twin turbo setup has about the same amount as a single turbo of the same amount of airflow - the reason for changing to single turbo setups is often because it's cheaper to buy one larger single turbo, and less complex to install. In the case of the Supra 2JZ, it's very difficult (basically, impossible) to upgrade the factory sequential setup, so the whole system is junked in favour of a more modern single turbo system.

Bi turbo and twin turbo are interchangable terms.

Beef

The only cars I know of to use sequential systems are the Supra, RX-7 and the new BMW's. A quick google says that the 959 had them too (never knew that).

Edit: Sorry, the Legacy did too apparently - again, didn't know that. Surprising given that it's a flat! Mind you, in terms of packaging, it's probably easier to achieve than on a V-engine.

Beef

Doh, and if I'd not missed this post first time I'd have seen that the Legacy has it too! I personally love the 'hole', it's like a brief lessening in the storm, before it comes back with even more force, and you can feel the surge building up through the whole car. It only lasts a fraction of a second anyway!

chris_c201

Some interesting reading here !

every1sgottablue1

So how do the Bugattis FOUR turbos work?

RedScoob

They're a quad cam V12 aren't they??? I think it's 2 pairs of sequential twins, one for each bank. What a bonkers car.

Beef

The EB110, or the Veyron? Although it must be said that I'm pretty darn sure it's just a big parallel system.

rasonline

Yep. The factory boost is set at 0.75bar.
The R34 GTR standard turbo can safely run 1,2bar whereas the R32 and R33 can only run up to 1bar. Common aftermarket turbo for GTR is the HKS2530s or the GT-SS which have similar spool up to stock turbos.

Running sequential turbos reduces the turbo lag. They are both the same size turbos though. For high power applications, the twin-turbo setup is a pain the a$$ to tune. A large big single is much easier and less costly.

There is also something called turbo shuffle which occurs when one turbo tends to "dominate" the other.. but that is another story altogether!