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Okay, so I was just wondering how a parallel twin turbo setup would run if one turbo was marginally smaller, and the other a bit bigger. Would there be any issues/problems? I've looked on google, and nothing really answered my question. Thanks. (By the way, I know a fair bit about turbos, not too much of a noob on them.)

It would run fine, a few factory set ups use this. The idea is that the smaller one spools first down low and then the big one gets going up top. While you still get points for the sexy factor a "modern" single turbo for most applications is in all honesty just as good.

Oh yeah, definitely, the sexy factor would play in very nice. However, in a case of where say, a MK3 supra, had a 2JZ swapped in, and was a daily/track fun car, I would personally want minimum lag so that I don't have oversteer on mid corner or corner exit. I might not seem to know what I'm talking about, but in words that you and others could understand, I don't want a single turbo that's has much or even some lag. I know SOME lag will be always there, but I would like to minimize the lag as much as possible. I know this is all a pipe dream to me, but I still like to think about it...

So new and modern turbos (I'm guessing like ball bearing, and billet compressor wheels, and such.) are just as good eh.. Well, I guess I'd have to research even more (that's pretty much all I've been doing since I got my laptop in the hospital). Thanks Sideways.

wouldnt this be called a compound setup? or did i not read something right?

This post has been edited by Sensation! on Nov 10 2010, 03:27 PM

Isn't a compound setup a complex turbo system where one turbo "feeds" the other bigger turbo..? I don't THINK what I'm talking about is a compound turbo, I'm just talking about a genuine parallel twin turbo system, with one turbo being smaller and the other bigger, to fill out the powerband a bit more.
EDIT: I looked up compound turbo kits on google, and that's definitely not it.
This is a compound turbo setup.

Image size reduced, original size: 800 x 600. Click here to view the image in its original dimension.

This is what I'm talking about. Imagine this on a V8, but one turbo is smaller than the opposite bank.

EDIT2: Hey guys, is it me or are those turbos different sizes

This post has been edited by chillined on Nov 10 2010, 03:58 PM

Isn't it called a "sequential" twin turbo setup (at least that's what I remember BMW calling it)? But yea, the setup works pretty well in BMW's twin turbo setup, but BMW has gone back to using single turbo setups for most of their inline-6 applications. Off the top of my head, the only car with a sequential twin turbo inline-6 setup from BMW is the 335is.

I think sequential turbo systems spool one turbo first (which is smaller) and then a valve or system lets the excess or opens up exhaust flow to the second bigger turbo. I'm just talking about a parallel turbo system with different turbo sizes, and no complex system to open valves and such. And I think you forgot MKIV Toyota Supra, I believe that Nissan Skyline GT-R had a seq. turbo system too. The BMW 135i's also have the same engine as the 335i (By the way, have you ever rode in a BMW 335i? They're awesome). I know the Mazda RX-7 (FD) also had one, but that's rotary... And there's a lot more that I can't think of right now.

This post has been edited by chillined on Nov 10 2010, 04:00 PM

Oh, ok, you're right. I got what you were saying a little confused. Sorry 'bout the mix up.

Man, no problem at all, it's not like I took offense to what you said haha Thanks for putting in your input though

The question I have, is how are you planning to deal with the flow differential? You have more air coming from one side than the other, because one turbo is moving more air. Where's the air going to go? Best case, into the motor. Worst, (and IMO more likely if you're trying to use the system for worthwhile gains over a single or compound setup) back out the compressor housing of the other turbo. It'll balance when the larger turbo spools, then once it gets into it's efficiency range it'll outflow the other turbo and reverse the situation. You'd have a constant compressor surge and less air going into the motor than out through the opposing turbo, which is now as a result trying to force the exhaust from that bank back into the motor.

The solution? There is none. It simply would not work. Cool idea, but that's why they use a compound setup that does the same thing in effect, but in serial instead of parallel.

This post has been edited by cmspaz on Nov 10 2010, 04:30 PM

So you're telling me, that once the smaller turbo stops flowing at it's optimum efficiency/bigger turbo spools INTO its optimum efficiency, the compressed air will go through piping, and where it joins with the other turbo's piping, and out through the smaller turbo's compressor housing, in the opposite intended way? What's forcing the air back to the other smaller turbo..? Uhm... This does not make any sense to me. If the two turbos were running on separate cylinders, and both pipings, coming out of the compressor housing, joined right before the intercooler, how would the larger turbo's air ignore the flow of the piping/intercooler, and OPPOSE the already flowing air from the smaller turbo and go out the smaller turbo's inlet hole..? Expand on this cmspaz. I'm not disagreeing with you, I just need a clearer explanation.

This post has been edited by chillined on Nov 10 2010, 04:46 PM

Because it's not psi vs psi, it's cfm vs cfm (cubic feet per minute).

You're taking a smaller turbo, which while capable of filling the piping with the same psi as the larger turbo (instantaneously), cannot move the same amount of air. It's the same reason you can run less boost on a larger turbo and make more power. The smaller turbo will also drop boost over time (I make 25psi at 3600rpm, by redline it tapers to 20), and the larger turbo will be capable of making more. You'll be limited at the tapered boost level of the smaller turbo at best, and even so, you're still moving more air through one pipe than the other.

So PSI is Pressure, and CFM is flow right? So what you're talking to say is that smaller turbos can pressurize the intake system, but cannot flow the same amount of air as the bigger turbo? So if the size difference wasn't big, would it still work? And how could a person figure out the limit of size difference or flow stats so that the smaller turbo doesn't surge..?

Hey guys, I just looked up on google "different size turbos" instead of "Different size turbos parallel twin turbo setup" and this popped up.
http://www.3si.org/forum/f35/two-different...598/index3.html
The user Phalse has claimed to use a 13g with a 9b for his 3000GT/Stealth (Which I believe has a non-sequential turbo system from factory).

So I think this can be done, but the difference can't be REDICULOUS, say like a GT12, and a GT42 Nevermind, anythings possible, and it makes sense. Thanks guys.
EDIT: By the way, not a double post, Sideways deleted his post.

This post has been edited by chillined on Nov 10 2010, 08:43 PM

Single turbo is all you need. Get the right geometry for your horsepower goals and be satisfied with it. You need to match the turbo to the engine. You want the smallest turbo that will meet your goal, so you can minimize lag. I've got a T4 frame .58 exhaust housing turbo on my 6er, and even tuned to 10psi, the lag is almost imperceptible. On throttle, and within a second, you're on boost.

Although this is a general question, as I never really specified that I will be getting these turbos or anything, it's just an idea lingering in my head. And I do realize that a single "will be all I need" but the fact is, I won't like that "within a second" trigger of boost. What I'm just trying to figure out is how I can reduce the action of "off and on" with a proper turbo system.

I wonder how he did with that 17g... Because the fact of the matter is that the 9b and the 13g are still both TD04-based turbos, and are both relatively small.

Supercharger and a turbo? It's been done. Most famously on the Lancia Delta S4 group b rally car. And here's one for you, you know you can get a smart blowoff valve that retains pressure in your intake system upstream of your throttlebody. That way you don't vent off all the pressure you have between shifts.

So long as you have a turbocharger, you will suffer from at least a little turbo lag. Nature of the beast.

This post has been edited by Cactus on Nov 10 2010, 09:55 PM

It doesn't matter because of the size. No matter how big the difference is, the fact is that the engine will always have negative pressure to be filled.

That setup also has a problem, or should I say problems. Placement of a supercharger, and a turbocharger is definitely tricky and piping would be a nightmare. And that's a way of hooking certain blow off valves that have the option of recirculating the air back.
Oh and if anyone wants to see a really cool thing that has been proven to work, look up the SP Engineering Quick Spool Valve. Neat thing, that.


This post has been edited by chillined on Nov 10 2010, 10:11 PM

It's not exactly black and white like ( pressure vs. flow ), but the second statement is more of why it would not work.

Yeah, I don't think I'll run boost levels like the EVO guys

Was talking about this with a buddy of mine last night who knows nothin about turbos. Basically I explained it to him like this...

You got your two turbos, one off a VW, saya K03. It's small. Then you've got, say a Holset HX83(I went the biggest I could think of, haha). Gigantic. Both running 6psi. Think of the size of the piping in the turbo, while the pressure is the same, the volume is completely different, and the HX83 is pumping a LOT more air through it than the K03, even though they're running the same psi.

I am not even sure if I should touch this at all.

It'll just be a waste of my time, and no one will be any smarter.

He was wondering why a motor like a 454 would make so much power off so little boost, while a smaller motor(such as a 2.0l) would need a hell of a lost more boost to make just decent power.

This post has been edited by MattW on Nov 11 2010, 11:50 PM

Not touching that one either, not even with a 20 foot pole.