Turbo question
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,469
Likes: 6
From: Winchester Ontario
Turbo question
If one was to run a single turbo at 10 psi, compared to a twin turbo setup at 10 psi, what would be the power differences?
Would the twin turbo's double the power output or come close to it?
Basically, single turbo vs. twin turbo at same psi power output differences?
Would the twin turbo's double the power output or come close to it?
Basically, single turbo vs. twin turbo at same psi power output differences?
Melting Slicks
Joined: Jan 2002
Posts: 3,293
Likes: 79
From: Jackson MI
Ummmm, no, two turbos do not make double the horsepower.
The amount of airflow is what determines the horsepower. In the end one engine at 10psi will make exactly the same horsepower(gross) as a single turbo, twin turbo, or supercharger given the same air density.
The only thing that changes is the parasitic losses of the air supply method. The supercharger will have alot since it is belt driven, then the single turbo, then the twin setup.
With a twin setup you have less exhaust pressure. Using two 2.5" down pipes vs one 3.5" down pipe you have more exhaust flow with the two smaller pipes.
The other advantage is that twin setups typically have a better spool. It takes less power to spin two smaller turbos than a single turbo. The turbos also usually sit closer to the exhaust ports than a single, giving them faster spool.
Of course all of this hinges on picking the correct single or twin setup.
Its also cooler to say twin turbo, than just turbocharged. However, as Sir Mix-a-lot implies, any turbo setup is sexy.
The amount of airflow is what determines the horsepower. In the end one engine at 10psi will make exactly the same horsepower(gross) as a single turbo, twin turbo, or supercharger given the same air density.
The only thing that changes is the parasitic losses of the air supply method. The supercharger will have alot since it is belt driven, then the single turbo, then the twin setup.
With a twin setup you have less exhaust pressure. Using two 2.5" down pipes vs one 3.5" down pipe you have more exhaust flow with the two smaller pipes.
The other advantage is that twin setups typically have a better spool. It takes less power to spin two smaller turbos than a single turbo. The turbos also usually sit closer to the exhaust ports than a single, giving them faster spool.
Of course all of this hinges on picking the correct single or twin setup.
Its also cooler to say twin turbo, than just turbocharged. However, as Sir Mix-a-lot implies, any turbo setup is sexy.
Melting Slicks
Joined: Mar 2001
Posts: 2,149
Likes: 302
From: Timra, Sweden
If everything else is equal then a single turbo should make a bit more power because a bigger turbo is usually has a higher efficiency than a small one.
The problem is that not everythig else is equal.
It is more difficult to make good equal length exhaust headers for a single turbo.
Usually twins will spool quicker, but once the boost is there a big single will make more power at the same boost level. That is because a single big turbo does not require quite as high exhaust pressure to maintain boost.
Airflow is power.
Both boost, air temperature, exhaust pressure and exhaust temperature will affect airflow thru the engine.
If we look at a simple case with only one turbo. Changing only the turbine (exhaust) side of turbo will affect engine performance. With a smaller turbine the turbo will spool sooner and make more power early. At higher RPM exhaust pressure will increase and that will reduce maximum power compared to a turbo with a biger turbine.
It is not as simple as comparing single turbo / twin turbo. It is impossible to say that one is better than the other.
I built a single turbo for a few resons.
* Only one oil supply.
* Only one oil return.
* Only one wastegate.
* Only one turbo. ($$ instead of $$$$)
* I had room for big single where the A/C compressor was.
The problem is that not everythig else is equal.
It is more difficult to make good equal length exhaust headers for a single turbo.
Usually twins will spool quicker, but once the boost is there a big single will make more power at the same boost level. That is because a single big turbo does not require quite as high exhaust pressure to maintain boost.
Airflow is power.
Both boost, air temperature, exhaust pressure and exhaust temperature will affect airflow thru the engine.
If we look at a simple case with only one turbo. Changing only the turbine (exhaust) side of turbo will affect engine performance. With a smaller turbine the turbo will spool sooner and make more power early. At higher RPM exhaust pressure will increase and that will reduce maximum power compared to a turbo with a biger turbine.
It is not as simple as comparing single turbo / twin turbo. It is impossible to say that one is better than the other.
I built a single turbo for a few resons.
* Only one oil supply.
* Only one oil return.
* Only one wastegate.
* Only one turbo. ($$ instead of $$$$)
* I had room for big single where the A/C compressor was.
Last edited by JoBy; Sep 29, 2008 at 08:53 AM.
Advanced
Joined: Nov 2006
Posts: 61
Likes: 0
From: Elburn IL
If you are going build an all out motor and try to get every ounce of HP out of the engine, the twin turbo setup will make a slightly more power due the fact that you will have less exhaust back pressure in the exhaust manifolds. For example, in my 87 SBC Trans Am, I had a single 76mm turbo with a P trim .96 A/R exhaust housing. The car ran great little doggy on spool up but all around it was fine. Then I went a twin turbo setup with two 60-1 Turbonetics turbos with a P trim .59 A/R exhaust housing. The spool up is great and the top end is even better because the back pressure in the exhaust housing is much less. I had an exhaust housing that had an A/R of .96 then I replaced it with two .59a/r that was equivalent having a 1.18 A/R housing so the back pressure was reduced and therefore the motor made a little more power.
If I could do it all over again, I would just stick with a good single turbo setup and be done with it. The cost verses the gain is not worth it for our street cars
Just my $.02
Prasad
If I could do it all over again, I would just stick with a good single turbo setup and be done with it. The cost verses the gain is not worth it for our street cars
Just my $.02
Prasad
Melting Slicks
Joined: Jun 1999
Posts: 2,872
Likes: 3
From: Wilmington NC
Wicked V6,
Some of the points you made can be addressed on the single turbo setup by doing a few things.. one is the P-trim turbine wheel is old technology, and the wheel itself is quite small for a single turbo application on a 355cid engine. newer wheels such as the precision GTS, turbonetics MPS, turbonetics F-trim, etc.. are larger wheels in diameter and in depth allowing more flow capacity then the tiny P-trim wheel all the while improving spool characteristics. the turbine Aspect Ratio A/R can also be increased on most of the newer wheels as well to allow further better flow characteristics. if lower boost is desired then sizing the wastegate properly to flow enough exhaust bypassing the turbocharger will also increase horsepower and reduce backpressure creating a better pressure ratio between preturbo exhaust and inlet boost pressure which equates to higher efficiency in power making potential.
I agree with you on the twins being more expensive, but they may have a slight advantage over a single in the fact that there is less travel between the head port and turbine inlet for each side. the pro's and cons on a fun street car are relatively mild and if one is looking to go turbo... either will bring a pleasant grin to the face!
Chris
Some of the points you made can be addressed on the single turbo setup by doing a few things.. one is the P-trim turbine wheel is old technology, and the wheel itself is quite small for a single turbo application on a 355cid engine. newer wheels such as the precision GTS, turbonetics MPS, turbonetics F-trim, etc.. are larger wheels in diameter and in depth allowing more flow capacity then the tiny P-trim wheel all the while improving spool characteristics. the turbine Aspect Ratio A/R can also be increased on most of the newer wheels as well to allow further better flow characteristics. if lower boost is desired then sizing the wastegate properly to flow enough exhaust bypassing the turbocharger will also increase horsepower and reduce backpressure creating a better pressure ratio between preturbo exhaust and inlet boost pressure which equates to higher efficiency in power making potential.
I agree with you on the twins being more expensive, but they may have a slight advantage over a single in the fact that there is less travel between the head port and turbine inlet for each side. the pro's and cons on a fun street car are relatively mild and if one is looking to go turbo... either will bring a pleasant grin to the face!
Chris
Instructor
Joined: Sep 2008
Posts: 136
Likes: 0
From: DFW TX
Thank GOD I am finally around people that know more than me about turbo systems.
I was getting tired of being the "turbo expert" when I am clearly not.
From personal experience. If yuo want all out power go for single. If you want faster power with a more broad range go twin. And if you want a nice streetable package. Go sequential. Sure you'll shock the hell out of the big turbo, but who doesn't want to spool a GT35 @ 2000 RPMS.
I was getting tired of being the "turbo expert" when I am clearly not.
From personal experience. If yuo want all out power go for single. If you want faster power with a more broad range go twin. And if you want a nice streetable package. Go sequential. Sure you'll shock the hell out of the big turbo, but who doesn't want to spool a GT35 @ 2000 RPMS.
