Twin turbocharging Vs. single turbocharging.

[Hypsi87]

If you are too lazy to read long posts... Then you don't need to be driving a car let alone racing one.

OK, I was asked to post this because since I picked up that block, I have been serouisly thinking about going to twin turbocharging.

Now first I was like most the skepical about twin turbos because I used to feel that it was not worth the money. I also used to think that the only reason people used twin turbocharging is for better spool up because eveyone knows that two smaller turbos will spin up faster than one big one.

First thing I realized.

The whole deal about smaller twin turbos will spin up faster than a single is pretty much not true (assuming we are talking about having the turbochargers hooked up in parallel) is wrong. Think about it, on a v type engine with a single turbo, you route the exaust from one side of the engine,have it flow into a crossover pipe, that pipe connects to the other header. So all the cylinders (6 on my setup) are driving the turbine. Well on a twin turbo setup, you would have a smaller number of cylinders driving one turbo (for my setup, I would be using 3 cylinders per turbocharger. So, with a single turbocharger, you are getting massive ammounts of exhaust and heat through the turbine (Remember heat drives a turbocharger more than pressure.) Then on a twin setup, you have a smaller turbo, you have a smaller turbo being driven by half the exhaust heat and pressure.

Where I find the big advatage to twin turbocharging is not in airflow or manifold pressure or spool up time. It's in Exhaust pressure.

OK, lets get one thing out of the way, Turbochargers are NOT free horsepower. There is only one way to acheive free power out of ANY forced induction system, and that is intercooling.

Where the power loss is at is Exhaust back pressure. Now I know you all know that a turbocharger does put backpressure on the Exhaust system, but do you know how much pressure??

You would think that if you have 15 PSI of boost, then you would have 15 PSI of backpressure (get out what you put in right?)

General rule of thumb.... For every pound of boost you run, you will have 1.5-2 times that ammount of exhaust backpressure before the turbo. so you run 15 PSI, your going to have 30 PSI of backpressure. 20 PSI, 40 PSI in the exhaust. That is alot of damn pressure people. I know that sounds crazy and your probabally thinking "Oh BS, if that was the case, the exhaust would rush right back into the cylinder as soon as the piston stopped pushing it out of the cylinder." Well that would be true... BUT why do you think a cam that is designed for turbocharging has NO overlap in it?

Now going back to the way a single turbo setup Exhaust system is setup. the mainfold, over to the other manifold through a crossover pipe and in the turbine housing out the down pipe. That is a lot of piping with a lot of pressure. Then after it goes through the turbine, ALL the exhaust has to go though a single downpipe increasing the backpressure.

NOW on a twin setup, you have a shorter heads, two 3 inch downpipes, since it is a smaller turbocharger you can run a bigger A/R exhaust housing and decrease turbine housing backpressure (If you run dual ball bearing turbos, then you can run a HUGE A/R housing and have a real open turbine housing.) There are a few other things that reduce the pressure. Now I am not saying that you will completely get rid of the back pressure, you don't want to. Exhaust heat does most of the work but pressure does it's fair share as well.

Now lets go back to this turbo cam deal. A cam that has been ground for a turbo car is not designed to make power. For example, if you took a Buick Stage 2 272 cubic inch Bush grand national engine that made 600 HP naturally asperated, take the cam out of it, and put a cam in it designed to be on a turbocharged car, your power would drop so fast it would not be funny. If you can decrease the exhaust backpressure, you can start running a cam that is more ground for power and less ground for turbocharger ( I know that is not techincal but, I don't have the numbers in front of me)

Turbo cost also is a myth... Have you guys priced a PT-88 or larger large frame turbocharger???? Compared to a pair of TE-44's or TE-60s?? Now with a twin setup, you have more fabercation time and work in it but there are two things that ultimatly equal power. Money and Work.

Thourun, This is pretty much the short version of what I found

DISCLAIMER: This is research based on my Grand National. Different cars will be different in some certian aspects but, it all applies to evey type of turbocharged car.

[clawhammer]

Good write-up. The cost part is not clear to me. So it is cheaper for a twin-turbo than a single turbo (when talking about large turbos)?
Are you staying with a single turbo, or going twin?

[-Josh-]

That was a good read. HRM had a good article on a Twin turbo Viper, the guy switched from s/c to TT.... Also a good article to read if you're wondering what type of FI to use.

[CivRacer95]

Well, now I can tell my mommy that I learned something very interesting at school today. Thanks Hypsi, I think I'll book mark this page for future reference . L8...

[Zgringo]

Mr. Hypsi87, very good post, and your talking about something I was involved in at the University of Utah.
Some of the most heated arguements have been about turbo supercharging. The big myth you keep hearing is turbocharging is free HP cause it uses waisted heat and exhaust gas to make boost, whereas the centrifical, roots and screw type supercharger use the engine to drive them and consume large amounts of engine power to operate.
Lets establish two facts here. Fact one, the auto engine hates heat. Fact two, the auto engine hates exhaust backpressure.
Under controlled testing we installed different turbos on a engine with means of cooling the exhaust before it entered the turbo, in other words a cool exhaust. The difference between driving the turbo with hot exhaust and cooled exhaust was ZIP, nada.
The big difference was with cooler exhaust the turbos ran much cooler and the discharge air on the compressor was denser or more oxygen bearing air.
We went one step further and took a V8 and drove it with another engine making the engine a compressor. To that we installed a turbo to the exhaust side of this (engine) compressor and drove the turbo with nothing more than compressed air.
Everyone knows by installing a free flowing exhaust and headers you can gain 10-50HP on a stock engine. Now as you pointed out turbo's create back pressure. Your figures of 1.5-2 is alittle low, but close enough for the kinds girls I go with. This back pressure robs the engine of power. How much? depends on how much pressure you want to make. To compress air it takes power. I don't care what you use, to compress 10 lbs of air takes a given amount of power to make 10 lbs of compressed air.
Now a guy with this knowledge in Orem, Utah named Rick Squires (STS Turbo) and has developed a remote mounted turbo system, taking the turbo's to the next level. Being the turbo run cooler the discharge air is cooler (denser), cooler oil returning to the engine, much simpler mounting, and tests have proven more efficient than engine mounted turbos and less heat in the engine bay.
Old myths are nothing but old news, and those looking to get the most out of there cars don't need myths, but facts.

[drftk1d]

the advantage in parallel twin turbos is not that they spool faster, but can use both to create more boost vs a single. give me more time to think about why that is and i'll get back to you, okay?

[Zgringo]

Originally Posted by drftk1d

the advantage in parallel twin turbos is not that they spool faster, but can use both to create more boost vs a single. give me more time to think about why that is and i'll get back to you, okay?

Smaller turbo's have less weight to move so easer to spin, the same reason we use lighter flywheels, lighter crank pulleys, lighter anything thats in motion. It takes less power to accellerate or put in motion. The size of the compressor and how fast it spins within it's envelop determines how much boost you'll create.

[TheStang00]

so how much hp loss is there with a turbo compared to a S/C?

[Zgringo]

Originally Posted by TheStang00

so how much hp loss is there with a turbo compared to a S/C?

There is no loss as their all making power. As for the amount of power needed to compress air depends on how efficient the compressor is.
The most efficient compressor is the screw type supercharger and the topend turbo's real close.
Thats why Carrol Shelby chose to use the screw type supercharger on the new Shelby GT500 Mustang, as has Jag, Nissan and other car mfg's.

[TheStang00]

thats very interesting, i was always under the impression that turbocharging was better because it didnt eat up horsepower like a supercharger does

[Hypsi87]

Originally Posted by Zgringo

Mr. Hypsi87, very good post, and your talking about something I was involved in at the University of Utah.
Some of the most heated arguements have been about turbo supercharging. The big myth you keep hearing is turbocharging is free HP cause it uses waisted heat and exhaust gas to make boost, whereas the centrifical, roots and screw type supercharger use the engine to drive them and consume large amounts of engine power to operate.
Lets establish two facts here. Fact one, the auto engine hates heat. Fact two, the auto engine hates exhaust backpressure.
Under controlled testing we installed different turbos on a engine with means of cooling the exhaust before it entered the turbo, in other words a cool exhaust. The difference between driving the turbo with hot exhaust and cooled exhaust was ZIP, nada.
The big difference was with cooler exhaust the turbos ran much cooler and the discharge air on the compressor was denser or more oxygen bearing air.
We went one step further and took a V8 and drove it with another engine making the engine a compressor. To that we installed a turbo to the exhaust side of this (engine) compressor and drove the turbo with nothing more than compressed air.
Everyone knows by installing a free flowing exhaust and headers you can gain 10-50HP on a stock engine. Now as you pointed out turbo's create back pressure. Your figures of 1.5-2 is alittle low, but close enough for the kinds girls I go with. This back pressure robs the engine of power. How much? depends on how much pressure you want to make. To compress air it takes power. I don't care what you use, to compress 10 lbs of air takes a given amount of power to make 10 lbs of compressed air.
Now a guy with this knowledge in Orem, Utah named Rick Squires (STS Turbo) and has developed a remote mounted turbo system, taking the turbo's to the next level. Being the turbo run cooler the discharge air is cooler (denser), cooler oil returning to the engine, much simpler mounting, and tests have proven more efficient than engine mounted turbos and less heat in the engine bay.
Old myths are nothing but old news, and those looking to get the most out of there cars don't need myths, but facts.

On the Grand Nationals, we found that it was 1.5-2 lbs of pressure per lbs of boost.

NOW today in lab, I had a pressure gage hooked up to intake pressure and a pressure gauge hooked up to the manifold before the turbocharger (3126 CATERPILLAR diesel) and exhaust pressure was about 10 in/HG lower than boost at 90% load factor. The diesels have exhaust housings with such big AR's that they are not effected as much.


As far as you guys driving a turbocharger with cooled exhaust... I am confused. On my car and alot of other turbo cars that I have been around. The colder the exhaust the lazier the turbocharger was. Not that I am doubeting you, just not understanding.

[Zgringo]

Mr.Hipsi87, I love it when talking to people that are intellange enough to ask when they don't understand. I see someone with enough wisdom to look at things in a different way.

As to answer your question. From this point on everything is example only.
When the A/F (air/fuel) mixture fires it makes a great amount of pressure in the combustion chamber and drives the piston down. When the exhaust valve opens some of this unburnt mixture enters the exhaust manifold and is still burning and expanding creating more pressure. So what we have is the volume of the engine plus the unburnt fuel burning and expanding creating pressure on the turbine wheel.
Because of ignition timing and cam duration on most engines what we have is a engine with about 90% efficiency or a engine putting unburnt fuel into the exhaust.
Not really a big problem cause by supercharging a engine to say 14.7psi we can make a 300ci engine think it's a 600ci engine, but we still have the unburnt fuel problem.
We can't advance the timing much or we run into detonation problems, but we've eliminated the unburnt fuel problem. To eliminate the detonation problem if we install a water/alky injection system we'll not only cool the combustion chamber temps. but we'll also raise the octane level of the fuel so we can run more timing and thus eliminate the unburnt fuel problem and make more power as were putting more power into the engine than the exhaust. Also by making more power were making more pressure in the exhaust without the hi temp. thus driving the turbine with more power.
I suggest you read all you can about water/alky injection you can and kill all the myths about it at the same time.
And if you are really serious about this I'll tell you about making 1,000HP per liter engine displacement.
Snow has some pretty good info on water/alky injection.

http://www.snowperformance.net/

[Neutrino]

Zgringo i have to say that as Hpsi I'm very surprised by those results.

by cooling the exaust down the presure diference between the two sides of the tubine will decrease, or if you prefer to see it in terms of kinetic energy by cooling down the gass you are robing it of its potential energy which would normally be transfered to the turbine blades.


Also about STS turbo, i have to admit I was a bit cinical about its remote turbo systems. However it seems they do seem to work quite well. However I'm still firmly convinced that the best placement for the turbo is close to the exaust ports where the exaust gas has the highest kinetic energy.

Also my gym trainer who is also a major car freak like me happens to know the STS guy, and from my last talk to him it sounded like even STS agrees with me about the proper placement of a turbo, and their remote systems are more of a "next best thing" for convenience. Of course this is more of a hear say so i might have the wrong impression.

However I can talk to my trainer to ask him directly this question or me and Polygon can drive up there and talk to them directly.

[Zgringo]

Lets try this heat cold thing a different way. Take a turbo and on the engine exhaust side apply 1000F and on the discharge side apply dryice -180F. Well it spin?

Now take a Ingersoll Rand compressor and apply 150psi to the engine exhaust side (inlet) of the turbine. Well it spin?

The pressure differencial between the intake side and outlet side will determine the amount power the turbine potential well be.

Have your gym teacher talk to Rick Squires, owner at STS turbo and I don't think he'll say it's "the next best thing". If you'd like I could get Rick on here or maybe email me his thought's on this so I could post them here.

If you read my post I say the unburnt gas coming out of the engine is still expanding creating more pressure.

Read what a few experts have to say:

<DIV><DIV>Kenny Duttweiler - Duttweiler Performance, Inc.
(Longtime "Turbo God" Kenny Duttweiler has a well-established reputation as the finest turbo tuner in all of drag racing.)</DIV><DIV>"Squires Turbo Systems' remote-mounted turbos have solved all of the problems associated with traditional engine-mounted turbo systems. The intense underhood heat a turbo generates has been eliminated and you no longer need to punch a hole in your oil pan or cut up the front of the vehicle for an intercooler. Emissions should be really good too with mounting the turbocharger after the catalytic converter."</DIV><DIV>Joe Pettit - Editor of Sport Truck Magazine
(Joe recently installed our system on a Chevy 4.8L Silverado - details are in the October 2004 issue of Sport Truck magazine.)</DIV><DIV>"When we first saw this turbo system at last year's SEMA Show, we were very skeptical about throttle response. We thought that with the turbo so far away from the combustion chamber, the system would be lazy with a lot of turbo lag. But after driving the system on other trucks as well as on this install, we find the lag not excessive in the least; it is very near what you find on factory turbo systems."
</DIV><DIV>"So if you're looking for a power adder for your sport truck, we recommend you take a look at the STS remote mount turbocharger system." </DIV><DIV>Evan Griffey - Editor of Turbo and High Tech Peformance Magazine
(Evan's 3 page article on STS appears in the October 2004 issue of the magazine)</DIV><DIV>"The velocity of exhaust gas and the fact that the STS design features a good deal of straight pipe, coupled with what exhaust gas does when it enters a turbo, should help negate any "lag" in the system."

</DIV><DIV>"We commend Squires Turbo Systems for the innovation and integrity of the concept it put forth, and we also appreciate the enormous potential it represents."</DIV><DIV>Patrick McCarthy, instructor at ESPN's

Here's somemore to read about STS

http://www.ststurbo.com/testimonials

[Neutrino]

Originally Posted by Zgringo

Lets try this heat cold thing a different way. Take a turbo and on the engine exhaust side apply 1000F and on the discharge side apply dryice -180F. Well it spin?

Now take a Ingersoll Rand compressor and apply 150psi to the engine exhaust side (inlet) of the turbine. Well it spin?

The pressure differencial between the intake side and outlet side will determine the amount power the turbine potential well be.

notice in my post that i did specifically mentioned that the turbine is spun by the pressure difference.


So there is no contradiction between us. My point was however that by cooling the exaust before it hits the turbine you lower the initial presure.

About my STS comment as i said previously It was only hear say so I might have gotten the wrong impresion. That is why i might just pay them a visit this weekend to talk to them directly to find out more info. My trainer speaks quite well of them so it sounds like they have a very good company. However i would still like a few more details about their remote turbo systems.


About the original question Hpsi my opinion is to go twin turbo since from my knowledge its more efficient to have the turbo close to the exaust ports rather than have it at the end of a maze of tubes.