Twin Turbo

[Titas]

If you have a twin turbo car, can you have one normal turbo and one smaller quick spool turbo? I've always wanted to know.

 

[obi_waynne]

It depends on the setup really. If they are sequential then yes and this is quite a normal way to go. If they come on in parallel I don't see much point in doing this as the big turbo will be pulling exhaust flow to spool up at the detriment of the smaller one. With a progressive boost controller and clever actuator you could probably setup a sequential turbo setup anyway.

What engine is this question for then?

 

[SLEEPER]

If it is a twin turbo set up where they are not sequential but come in together then the turbos have to be the same size in fact they really should be identical.

If they were not wayne is spot on it would never work.

The point of a non sequential twin turbo is that the spool up is so much quicker in practice so power comes in much earlier than it would with a larger single turbo.
the .
You also dont get the flat spot that sequential set ups can get just before the bigger tubos comes in.

There is alway a trade off of course two small turbos will not usually produce the same top end power of a bigger single turbo which come in later .

It depends on the engine but on my engine (oversize RB26) a single turbo would not be the best bet unless you wanted 700bhp - but all engines are different .

 

[T9 man]

@ Sleeper, may I ask what exactly is the power of your engine with it's trick bits? from the snippets I have been able to piece together from some of your previous posts, it sounds like quite a monster you have there

 

[SLEEPER]

That is just over 500 at the hubs not flywheel as on that dyno you take the wheels off and bolt the hubs to the machine ( so it is much more accurate as well ) It made 606 atf on a dyno measuring atf

In fact it demonstartes what I was refferring to - a single turbo Rb26 would not be on full boost by 4500 let alone be producing maximim torque.

Things may change (i hope ) Im redesigning the intake system at the moment with a custom cold box fed direct through the vents in the Nismo front .

May not make much difference on a dyno but should do when driving especially in the summer

 

[T9 man]

Very impressive! I would like to see your induction mod when it's finished! I have a cold feed supply fitted to mine which seems to work quite well.

 

[HDi fun]

If you have a twin turbo car, can you have one normal turbo and one smaller quick spool turbo? I've always wanted to know.

For sequential systems this is the standard setup. Some V6 engines (Peugeot's 2.7 HDi unit is a good example) use two turbos, one to force-feed each bank of 3 cylinders.

 

[Titas]

I was just talking any engine in general. Ever since I read a book about Turbos, i've wanted to know if it could be done. Thanks for all the info, cars are the only thing i enjoy learning about.

 

[carnutter]

Several manufacturers have this sequential, twin turbo set up eg. Supra, Liberty B4.

They use a smaller turbo for bottm end response and when the revs reach a certain point, the bigger turbo takes over for better top end response.

Worked well in the Supra but not so well in the Liberty.

 

[SLEEPER]

The reason it works much better in a supra is its a 3 litre

This means that the turbos spool up much quicker so its easier to get the bigger turbo to come in earlier.

 

[carnutter]

The larger capacity engine does help. However, the Supra just had a better set up, with less of a torque hole between the handover from the small to larger turbo charger.

Here's a good comparison between the set ups in both cars:

http://www.autospeed.com/cms/A_109201/article.html

http://www.autospeed.com/cms/A_1229/article.html

And an excerpt from the B4 article:

"During the transitional phase - where the secondary turbocharger is starting to pump in addition to the primary unit - there's an ugly 'hole' in the torque delivery. Under full throttle, a significant dip in manifold pressure identifies the 4000-4500 rpm transition; we measured a full 0.25-0.3 Bar boost pressure dip.

It's enough for first-time passengers to ask if there's an engine problem...."

 

[SLEEPER]

The size of the engine does a lot more than help - its critical to spool up time.
Even boring out from my RB26 by 100cc made a big difference to when the power comes in.

This is particually important when running sequential turbos .
Because there needs to be a reasonable difference in turbo size for the system to be worth even considering it is harder to get the turbos working together smoothly.

On a supra it is not that the set up is better in itself . It is simply that the larger capacity of the 3 litre engine allows that better set up to work.