combining boost adds up?

[I Hate Import Cars]

I'm not having this issue or anything, I am just very curious about this. Let me say first though that I would appreciate it if people who don't KNOW what they're talking about would politely keep their fucking traps shut. K? thanks. :) Anyway, so here's my question. On a twin turbo setup, where both turbos are set up exactly identical, (size, inlet, dump size, ect...) and say you're running 12 psi of boost, and they both feed into a common plenum manifold, you don't end up with 24 psi right? So then what's the point of having 2? Is it purely to be able to flow a larger volume of air? I understand why you do sequential twins, as far as one to spool quick and one to spool high, but why do it with identical turbos? Just wondering...

[FabricatorX]

A twin setup theoretically can move more cfm at a lower rpm than a single, but a large single can, once again theoretically, flow more cfm in the higher rpm range than twins, hence the ridiculous power spike most see. Other than that, a lot has to do with packaging as well.

[Tage]

Dude, as a V8 guys you should know the answer to this one! :)

Besides a sequential setup (like you already pointed out the benefits of a small a large turbo), this would be extremely rare thing in a 4 cylinder application. Twin turbos are more typical in a V6 or V8 configuration where there are two separate exhaust manifolds and logistics of single turbo manifold aren't very practical so you simply have two identical turbos with one on each side of the engine.

I've heard of some of the supercars with V12's having FOUR turbos! I'd imagine they could get away with just two turbos with 6 cylinders feeding each manifold but when you have enough money to afford a car that comes with a V12 what the hell right? Plus like the other guy mentioned in theory with more but slightly smaller turbos you should be able to get more boost at a lower RPM.

[I Hate Import Cars]

HAHA! Ya, the V-8=2 exhaust maifolds scenario had crossed my mind in all this wondering, and that definately makes sense, I was just wondering if there was any reason to do that OTHER than the fact that running a single turbo on a V motor would involve a lot more fabrication, which would involve a lot more money being spent, which involves, well, life sucking. So I guess that answers it. Speaking of fabricating, I've got to make a phone call! By the way, have you EVER seen a twin turbo setup on a 4 cylinder?

[I Hate Import Cars]

Now, NEXT question. On a sequential twin setup, is there some sort of a valve or something that closes off the inlet from the bigger turbo until it's time? I know just how stupid that sounds, but I don't understand how the boost from the smaller one spooling up quicker that the big one doesn't backfeed through the inlet for the big one and A)lose boost pressure and 2)further inhibit the big one from spooling. If anyone is up for tackling THAT one, I'd love you forever!

[Tage]

Now, NEXT question. On a sequential twin setup, is there some sort of a valve or something that closes off the inlet from the bigger turbo until it's time? I know just how stupid that sounds, but I don't understand how the boost from the smaller one spooling up quicker that the big one doesn't backfeed through the inlet for the big one and A)lose boost pressure and 2)further inhibit the big one from spooling. If anyone is up for tackling THAT one, I'd love you forever!

Not sure on the valve setup. I think there's a couple different systems out there but if I was to do it on a "V" engine I'd personally have a smal turbo and a big turbo. The answer to your question is a physics saying that air (or water or electricity) will follow the path of least resistance. In other words if you've got two turbos both producing boost (one with a lot more volume than the other) and forcing that pressurized air into the engine I don't see where the big turbo would ever have an easier time pumping the air backwards through the smaller turbo vs going through the inakte manifold, etc. I think there would be a point where the big turbo will loose effeciency but I don't see where it would be possible to go backwards through the turbo. Here's where some fancy throttle plates would be pretty trick through for max efficiency (i.e. Separate the boost side of each turbo at the appropriate time).

[fivesfe]

i didnt read the replies.

to the original question, Say you have 2 identical turbo's with their wastegates both set at 12 psi, you will only get 12 psi of boost. Reason being that your wastegates are both using the same pressure source and they will both open up once they see 12 pounds of boost.

never really dealt with twin turbo's, i can see the advantages of having one big turbo and a small one so you dont have to wait for power.

eh hope this helps.

[FabricatorX]

http://render2.snapfish.com/render2/is=Yup6aQQ%7C%3Dup6RKKt%3AxxWtUq4Pl-ofrj%3DQofrj7t%3DzrRfDUX%3AeQaQxg%3Dr%3F87KR6xqpxQ Q0PxQoaxGn0xv8uOc5xQQQJPooaJe0GPqpfVtB%3F*KUp7BHSH qqy7XH6gXPaJ%7CRup6lQQ%7C/of=50,590,442

I dont know how a sequential works however.

[fivesfe]

http://render2.snapfish.com/render2/is=Yup6aQQ%7C%3Dup6RKKt%3AxxWtUq4Pl-ofrj%3DQofrj7t%3DzrRfDUX%3AeQaQxg%3Dr%3F87KR6xqpxQ Q0PxQoaxGn0xv8uOc5xQQQJPooaJe0GPqpfVtB%3F*KUp7BHSH qqy7XH6gXPaJ%7CRup6lQQ%7C/of=50,590,442

I dont know how a sequential works however.

looks neat, but seems impractical. wouldnt it be cheaper to go with one big turbo in the long run?

whats up with the green names?

[FabricatorX]

looks neat, but seems impractical. wouldnt it be cheaper to go with one big turbo in the long run?

whats up with the green names?

green names? hunh?

It is more practical to go with a single, but you know; whatever the customer pays for the customer wants!

[crx3]

Back to the first question, manifold pressure is the same no matter where you measure it. So pressure measured anywhere between either turbo compressor and the intake will always be the same. Imagine a bottle of compressed air, the pressure is the same at the top of the bottle as it is the bottom, if gravity is not a factor. If gravity is a factor, then the pressure at the bottom of the bottom will be slightly greater due to the force of gravity. This will be true even if one wastegate was set at 12 PSI and the other at 6 PSI, whatever pressure is present in the manifold, or pipes will be equally distributed throughout the common chamber. Pressure increases and pressure drops occur if pipes change diameter, or if cooling occurs, as in intercooling, but in a simple closed system as in your question, pressure is always equal within that system.

Equal sized twin turbos (300ZX, 3000 GT) are a convienent, although expensive way to package the turbo sytem in "V" engines, with the added benefit of reduced turbo lag for the amount of total CFM delivered. Sequential turbo systems (Supra, RX-7) are intended to maximized performance while minimizing turbo lag. The new BMW 3 series has a twin turbo setup on a straight 6 motor. It packages well with two small turbos hugging the block, and has very little lag. It will be interesting to see if people hot rod this car with a new manifold and a bigger single turbo.

Your example of 12PSI + 12PSI = 24 PSI is probably possible with compound compression. Compound boost occurs when the outlet of the 1st compressor (SC or Turbo) is fed directly into the inlet of an additional compressor. This is common on industrial diesels, and has been used in racing cars and racing motorcycles for decades. The "Meguiars Car Wax" show car Integra Type-R has a turbo and roots supercharger in a compound boost configuration. HKS sold a turbo kit for the MK1 MR2 S/C that retained the S/C and doubled that cars WHP. Bob Norwood built a Mk2 MR2 that used a Lexus V6 with TRD (Eaton) S/C and a turbo. It was featured as multi-part article in turbo magazine and was very interesting. I remember Norwood explaining that at high boost, the S/C acted like a big cam, and took the load off of the turbo compressor by sucking boost and forcing it into the engine. This is only possible with a mechanically driven, positive displacement pump like a Roots blower. Freewheeling compressers (turbo) can slow down if the work required to move the compressed air is greater than the energy derived from the exhaust flow through the turbine. VW is selling the world's first production twin-charged engine in Europe. The VW "TSI" engine is 1.4 liters and makes 170 HP and 170 Ft/Lbs. It has a very linear power band and gets good fuel mileage. The economy is due to the abundant power not requiring much gas pedal for very long, and after you lift off the trottle, it's a frugal 1.4 liter. Saab now builds a V6 with a single turbo fed by 3 cylinders, which supplies boost to all 6 cylinders. The asymmetric turbo-charged 3.0-liter V6 is the first single-bank turbo-charger application in production. You wonder why someone didn't think of it earlier. As you see, there are many ways to boost a motor, and lots of configurations. Most of them were pioneered in the old days for WW2 fighters, or old school race cars. Mercedes had twin-charged grand prix car in the 30's that made 35 PSI.

[rexnaz]

good read

[I Hate Import Cars]

Back to the first question, manifold pressure is the same no matter where you measure it. So pressure measured anywhere between either turbo compressor and the intake will always be the same. Imagine a bottle of compressed air, the pressure is the same at the top of the bottle as it is the bottom, if gravity is not a factor. If gravity is a factor, then the pressure at the bottom of the bottom will be slightly greater due to the force of gravity. This will be true even if one wastegate was set at 12 PSI and the other at 6 PSI, whatever pressure is present in the manifold, or pipes will be equally distributed throughout the common chamber. Pressure increases and pressure drops occur if pipes change diameter, or if cooling occurs, as in intercooling, but in a simple closed system as in your question, pressure is always equal within that system.

Equal sized twin turbos (300ZX, 3000 GT) are a convienent, anthough expensive way to package the turbo sytem in "V" engines, with the added benefit of reduced turbo lag for the amount of total CFM delivered. Sequential turbo systems (Supra, RX-7) are intended to maximized performance while minimizing turbo lag. The new BMW 3 series has a twin turbo setup on a straight 6 motor. It packages well with two small turbos hugging the block, and has very little lag. It will be interesting to see if people hot rod this car with a new manifold and a bigger single turbo.

Your example of 12PSI + 12PSI = 24 PSI is probably possible with compound compression. Compound boost occurs when the outlet of the 1st compressor (SC or Turbo) is fed directly into the inlet of an additional compressor. This is common on industrial diesels, and has been used in racing cars and racing motorcycles for decades. The "Meguiars Car Wax" show car Integra Type-R has a turbo and roots supercharger in a compound boost configuration. HKS sold a turbo kit for the MK1 MR2 S/C that retained the S/C and doubled that cars WHP. Bob Norwood built a Mk2 MR2 that used a Lexus V6 with TRD (Eaton) S/C and a turbo. It was featured as multi-part article in turbo magazine and was very interesting. I remember Norwood explaining that at high boost, the S/C acted like a big cam, and look the load off of the turbo compressor by sucking boost and forcing it into the engine. This is only possible with a mechanically driven, positive displacement pump like a Roots blower. Freewheeling compressers (turbo) can slow down if the work required to move the compressed air is greater than the energy derived from the exhaust flow throught the turbine. VW is selling the world's first production twin-charged engine in Europe. The VW "TSI" engine is 1.4 liters and makes 170 HP and 170 Ft/Lbs. It has a very linear power band and gets good fuel mileage. The economy is due to the abundant power not requiring much gas pedal for very long, and after you lift off the trottle, it's a frugal 1.4 liter. Saab now builds a V6 with a single turbo fed by 3 cylinders, which supplies boost to all 6 cylinders. The asymmetric turbo-charged 3.0-liter V6 is the first single-bank turbo-charger application in production. You wonder why someone didn't think of it earlier. As you see, there are many ways to boost a motor, and lots of configurations. Most of them were pioneered in the old days for WW2 fighters, or old school race cars. Mercedes had twin-charged grand prix car in the 30's that made 35 PSI..

Wow. Well look at you, Mr. Smarty Pants! I'm just kidding. That was the most addictive post I've ever read! Can I put you in my pocket? Or even my brain? I KNOW that I missed at least half ofthe info you gave me, and I still feel 10x more informed on the subject. So thanks for your answer. And, while I appreciate your enthusiasm, you just completely shattered any hope or intentions I had of one day building a forced induction motor. Just when I thought I was starting to get a grasp on that whole FI deal, you come through and blow my mind.

Cliff's notes;

You answered my questions and then some.

You shattered my FI dreams.

[crx3]

Forced induction doesn't have to be complicated, but it can be. Don't give up on building a FI motor. The main considerations are 1) What are your goals with the car? 2) What motor/transmission/chassis will you use to acheive that goal? 3) How much work are you willing to put into the car? 4) How much are you willing to spend? When I first got into Hondas in the early 90's I was living in Houston, TX. I knew a guy with a CRX that had an LS swap, a T3 turbo, a rising rate fuel pressure regulator, and an extra fuel pump. That car ran 12's on the stock ECU. No built motor, no standalone ECU. The turbo and intercooler were factory car parts that he found in the junkyard, and he made his own "log cabin" exhaust manifold. I saw him beat John Hennessey (Hennessey Motor Sports) in a brand new Viper GTS on the street. After John caught up he demanded a rematch, and the outcome was the same. John then demanded that he pull over and show him the motor. I don't know what Hennessey expected to see under the hood, but his blank stare was something I'll always remember. Nothing but an LS, and rusty manifold and turbo. Back in those days the DOHC VTEC B series was a new exotic thing and folks hadn't started to boost them or build them all-motor. Some people were spraying them, and the eventual outcome was a busted shortblock. I'm almost sure that's how the LS/VTEC came into being. The GS-R was new and expensive to buy, but the LS was available cheap and had been around since '90. The David Vs. Goliath, Import Vs. Domestic battle is what got this whole scene going the way it did. Although I think it really has already peaked, it is still strong enough and look at the cars that are coming off of the assembly lines today. Who would have ever thought that major manufacturers from around the world would be selling 400 and 500 HP cars to the public. There is a variety of turbo and HO V8 cars to be had in the marketplace, and I think that the sport compact scene is responsible for a lot of it. The competition from Japan inspired the domestics to up the ante. I know, because I had an '82 Mustang GT with the HO 5.0 and it only had 158 HP. I don't think that Ford and Chevy would have really cared much if the 300ZX Turbo, Supra Turbo, and Mitsubishi Starion ESI-R hadn't hit the market in the 80's.

It is now possible to buy a car thats already fast enough if thats the way you want to go. If you plan to build your own, then it's all up to you. I've had a variety of cars in my 28 years of driving. V8's, V6's, L6's, L4's N/A, Turbo, and Supercharged. So if you can answer the 4 questions presented above, and set realistic goals, then go fo it. I currently drive a moderately powered supercharged DOHC VTEC CR-X del Sol. I could get twice the HP by switching to a nice turbo setup, but the car would probably be too fast for me, break parts, and I'd end up in Jail or dead (sorry but that's the truth). A track only car would be great, but thats almost like having a boat, and then you need the trailer and tow vehicle. The main point of advise is keep it simple, and don't reinvent the wheel.

[FabricatorX]

you sir, have alot to say.

[locash]

Wow, someone either likes to type, or cut and paste! :)

I hope he didn't shatter your dreams of FI, you own a Honda, do a decent single turbo setup and be happy. Before you make any more bets with your buddies though, talk to me, I'll steer you in the right direction. :)

[I Hate Import Cars]

Wow, someone either likes to type, or cut and paste! :)

I hope he didn't shatter your dreams of FI, you own a Honda, do a decent single turbo setup and be happy. Before you make any more bets with your buddies though, talk to me, I'll steer you in the right direction. :)

ASSHOLE! I know, you're right. I dissappoint myself. :( "Next time" right....ya right. "next time" it'll have 8 pistons and 2 turbos. Wanna tune it? ;) By the way, I got the answer to that 2nd question, and I feel like quite the retard. APPARENTLY in a sequential twin setup, the small turbo doesn't even feed into the manifold! the discharge side of the small turbo feeds directly into the "exhast" side of the big turbo to spool IT faster. so the big turbo is the only one pressurizing the manifold. Is that right? Is that crazy? I think both! It works like the gear reduction boxes in a VW Type 3, if anyone knows what I mean. My mind, has been blown.

[FabricatorX]

haha I know I know, it's ok!