Twin turbos. Couple quick questions.

[IsaacHayes]

Twin turbos. Say you went that route on say a GM V6. One per bank of exhaust. Smaller so it could spool. What is the advantage? Is it quicker spooling but still able to boost as much as a single larger turbo? If not, then what's the advantage?

Not really intersted in turbo feeding another turbo, as all I can see that is to get tremendous amounts of boost and air flow that a single turbo wouldn't be ablet to do or spool soon enough right?

[Joseph Upson]

In my case it's a matter of what I have available mainly, then efficiency and novelty. I don't have a single turbo big enough to feed my engine but I have two T3s with .60 compressor wheels and .48 turbine housings so if you look at it from an efficiency point if you can get closer to your required exhaust flow with the sum of two turbine housings as opposed to one the twins would be better. If you are sophisticated enough to build a sequential setup then dual is better than single as Porche has demonstrated. I have enough turbo for 15 psi @ 6600 rpm before I have to go up one size in the turbine housing on the 3500.

Since I'm only aiming for 10psi I'll have low exhaust back pressure which should work well with the overlap in my cam regrind. From what I have read cam overlap is not a problem with a blown engine as long as it is properly placed. High exhaust pressure with overlap causes reversion and low back pressure and overlap with high boost can blow the fuel charge into the exhaust. So you have to keep a balance, since my back pressure will be low I can have overlap similar to what you might see in natural aspiration, I asked for a cam grind for higher rpm ~2500-6500 rpm.

I also like the idea of an integral wastegate which the .80 turbine housing does not have, and that's crucial because external wastegates cost as much as a turbo in some instances. This will be my fourth twin setup coming up and I believe by far the most successful since I'll be investing in the required equipment to do a good job of tuning, Emulator, Wideband O2, & EGT sensor to eliminate guestimating.

[Nightingale]

I've heard that twins are more streetable because you can have to smaller turbos that will spool quicker. You can still have a very streetable single turbo setup if you know what your doing though. I guess the main reason for single turbos is just ease of installation and less cost in plumbing.

[nocutt]

Twin turbos. Say you went that route on say a GM V6. One per bank of exhaust. Smaller so it could spool. What is the advantage? Is it quicker spooling but still able to boost as much as a single larger turbo? If not, then what's the advantage?...

Questions you will have to contend with...
* Race car or streetable?
* What platform...FWD or RWD?

On the street, with a FWD car you might aSS well kiss your tires goodbye...quick spool for the most part equal to no traction. Also, a single will almost always win at the top...street applications.
Now on a race car, eg drag...twins can be "oversized" (turbine), there is really no clear cut advantage over a single in this arena...as long as space is not at a premium.
Compromises and balance...

[IsaacHayes]

Street car. FWD/RWD don't matter, just wondering. A roots blower on FWD would have *similar* problems for launching...

So mainly quicker spool times. Size each turbo for half your engine displacment huh?

What about a turbo feeding a turbo? Was I correct on that?

[RacerX11]

A roots blower on FWD would have *similar* problems for launching...

A roots blown engine will have a much more linear power deliver, making it much easier to launch than a high-HP turbo.

[tejohnson]

Twin for a staged application... One for quick spool, the other for higher boost. Manage the wastegates independently depending if you are on the track, or on the street...

Course, a single turbo does the job just fine...

[IsaacHayes]

racer: Ah, I guess with a blower it makes near max boost from idle, but you can feather the throttle, but with a turbo even if you are feathering, the boost may all of a sudded just hit you. *wham* there it is kind of unexpectedly. I hadn't thought about that.

Todd: Hmm so have 2 turbos one bigger on one bank, one smaller right? Interesting!

I always thought if I had a turbo car I'd have a bunch of "boost controllers" made with a line of switches on the dash where I could go from low, med, high boost for mileage, launching, low octane fuel/etc. Start with 2psi, flip a switch once I'm rolling to bump it up/etc. 3 stages would be nice. You could even put a window switch on them if you wanted for launching...

[RedZMonte]

Look at a 3000GT VR4 Setup. That is the way to go. you want 2 equal sized turbos for equil back pressure on both banks. uneven backpressure will cause 1 bank to run leaner then the other (not good) and makes it impossable to tune. As for streetable/race it all depends on the turbo sizes. Small turbo's will spool fast and large turbo's spool slow. Keep in mind you may have 2 small turbo's but you are also only running 3 cyl. to each turbo so you have less flow then a single with all 6 cyls pushing it. Unless you have 2 VERY small turbo's you shouldnt have traction issues.

As for the 2 turbo's, 1 feeding the other it wouldn't do you any good, you are still only able to push so much air out of the smaller turbo so that will restrict you. This setup is used on a older RX7 and if you look, most of thoes guys switch to a larger single turbo. If you size it right a good single turbo will get you MUCH further then a twin setup. MUCH MUCH less headaches as well!

With an automatic trans also keep in mind, you only have to spool it once. Once its spooled it is allways spooled untill you let off. From a roll my car kicks ass! At sea level i have no doubt it will spool faster then it does up here in colorado 5000ft alt. I have NO power from a stop, compared to MN where i bought the car where it burns the tires on command.

S

[IsaacHayes]

ya I'm not a fan of un balanced things. But I swear the grand nationals i've seen, had the turbo on just one exhaust bank!!! Am I wrong on that??

Autos would be good with turbo since it has a stall.

[Zboy]

Yes, GN's had a single turbo but there is an exhaust cross over pipe connecting both exhaust banks.

[nocutt]

Street car. FWD/RWD don't matter, just wondering. A roots blower on FWD would have *similar* problems for launching...

On the contrary it matters big time...I understand you are just using theoretical scenarios but when it comes down to were the 'rubber meets the road' you have to take account of the platform...lol, just been a realist that's all

...So mainly quicker spool times.

...that's about it...


Also there are three main ways to do twin turbos, I am only commenting on the language used "What about a turbo feeding a turbo?" for clarity I think for the most part we are talking twins as in two turbos per bank, then sequential where the exhaust is what feeds the other, then staged or compound where the intake feeds the other...

[IsaacHayes]

Zboy, ah, it must have a pipe going around the back that connects that I didn't see.

nocutt, thanks, I was unclear on what to call the setups. "for clarity I think for the most part we are talking twins as in two turbos per bank" So would that then be quad turbo? lol, just caught a typo. Sequential I understand, but the staged/compound, what's the benefit there?

[nocutt]

Zboy, ah, it must have a pipe going around the back that connects that I didn't see.

nocutt, thanks, I was unclear on what to call the setups. "for clarity I think for the most part we are talking twins as in two turbos per bank" So would that then be quad turbo? lol, just caught a typo. Sequential I understand, but the staged/compound, what's the benefit there?

Lol...in a situation with two turbos, then primarily for attaining very high pressure ratios...secondarily lag is also minimized...not 'really' a good app for gasoline street engines...

[IsaacHayes]

Right, I've only heard of those used in crazy drag machines.