would 14psi on single turbo make more hp than 14psi on twin turbo?
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dominican boost junkie
Joined: May 2008
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From: Dominican Republic
would 14psi on single turbo make more hp than 14psi on twin turbo?
would 14psi on single turbo make more hp than 14psi on twin turbo? Isn't 14psi the same regardless of the turbo? why?
Example 14psi on stock twins makes 315whp
14psi on a 60-1 t04s turbo makes 400whp
what is the difference? turbo efficiently? fuel? air flow?
Example 14psi on stock twins makes 315whp
14psi on a 60-1 t04s turbo makes 400whp
what is the difference? turbo efficiently? fuel? air flow?
Joined: Oct 2001
Posts: 6,279
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From: Florence, Alabama
everything else won't be equal. the OEM twins cavitate at 14 psi superheating the air so you won't get the same amount of oxygen molecules per volume into the motor.
while it would be possible to improve this a bit w water injected pre compressor if you did the same thing w the single it would retain it's advantage.
also, there are mechanical problems (bearings) if you run the twins at 14 very long.
hc
while it would be possible to improve this a bit w water injected pre compressor if you did the same thing w the single it would retain it's advantage.
also, there are mechanical problems (bearings) if you run the twins at 14 very long.
hc
Newbie
Joined: Apr 2007
Posts: 2
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From: USA
wow, this is only the 999,999,999th time this question has been asked
Think of it this way...
You have two balloons...
1.) Small Balloon
2.) One Large Balloon
You need to fill them with enough air to provide equal amounts of pressure, we'll just use 14psi for example.
Now, granted you could do this - lets release the air out of the balloons simultaneously and determine which balloon will produce a higher amount of air flow as air exits.
I don't know if what I said makes any sense... but maybe you'll get it.
Think of it this way...
You have two balloons...
1.) Small Balloon
2.) One Large Balloon
You need to fill them with enough air to provide equal amounts of pressure, we'll just use 14psi for example.
Now, granted you could do this - lets release the air out of the balloons simultaneously and determine which balloon will produce a higher amount of air flow as air exits.
I don't know if what I said makes any sense... but maybe you'll get it.
Banned. I got OWNED!!!
Joined: Apr 2004
Posts: 478
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From: Menasha, WI
What are your goals?
Stock twins vs. single or two smaller aftermarket turbos vs. single? It all depends....
Howards twin T04 setup obviously outperforms the stock twin setup
As others have said, 14 psi will yeild different results depending on setup. A larger turbo will flow more air (lbs/min) than a smaller turbo at the same psi, hence the difference in power.
In comparison to the two setups you mentioned, our GT4202 made 450ish at 14 psi. The powerband is also shifted depending on the turbo... if you want to make 400-450 hp, dont go with a GT42, there are a number of smaller turbos that'll get you there easily with a much better powerband. Think about the cost and complexity of running two smaller turbos vs. a single as well...manifolds, downpipes...etc.
Stock twins vs. single or two smaller aftermarket turbos vs. single? It all depends....
Howards twin T04 setup obviously outperforms the stock twin setup
As others have said, 14 psi will yeild different results depending on setup. A larger turbo will flow more air (lbs/min) than a smaller turbo at the same psi, hence the difference in power.
In comparison to the two setups you mentioned, our GT4202 made 450ish at 14 psi. The powerband is also shifted depending on the turbo... if you want to make 400-450 hp, dont go with a GT42, there are a number of smaller turbos that'll get you there easily with a much better powerband. Think about the cost and complexity of running two smaller turbos vs. a single as well...manifolds, downpipes...etc.
Last edited by SENZA PARI; Dec 12, 2008 at 06:54 PM.
There was a good thread (argument) on this topic a while back:
https://www.rx7club.com/3rd-gen-archives-73/why-bigger-turbos-make-more-hp-same-psi-645551/
https://www.rx7club.com/3rd-gen-archives-73/why-bigger-turbos-make-more-hp-same-psi-645551/
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A side note about how efficiency/back pressure/flow affects tuning.
Both twokrx7 and I noticed that when we went to single turbos from our highly modded twins, we ended up retarding timing more for low boost than for high boost to keep knock low.
Both twokrx7 and I noticed that when we went to single turbos from our highly modded twins, we ended up retarding timing more for low boost than for high boost to keep knock low.
always modding
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From: on a tiny island in the middle of a sea
was this due to more airflow at the low boost areas? (i.e. effeciency)
or due to colder charge temps equating to denser air?
or was there something else involved?
Rotorhead
Joined: Feb 2001
Posts: 9,136
Likes: 39
From: Charlottesville, Virginia, USA
Fuel is a separate issue and has nothing to do with the turbocharger itself.
Airflow is only important up to the point that the engine is not starving for air. If you think about it, once you have filled an engine rotor space with 40 cubic inches of fuel/air mixture (more or less), where would any extra air go? The primary reasons rotary engines seem to need more air than their piston counterparts are:
- Rotary engines fire all of their displacement each output shaft revolution like a 2-stroke piston engine as opposed to half the displacement like a 4-stroke piston engine. Therefore, with everything else being equal, a 1.3L rotary engine would probably use a turbo that is advertised for a 2.6L 4-stroke piston engine. It is actually the 4-stroke piston engine that has the misleading displacement rating, but we live in a world of 4-stroke piston engines, so that is considered the norm by advertisers.
- Rotary engines are high-rpm engines. The flow rate of an engine is based on displacement * rpm. Ignoring other variables like volumetric efficiency, a 2.6L 4-stroke piston engine that redlines at 5,500rpm would flow ((2.6L / 2) * 5,500) = 7,150L/min while a 1.3L rotary engine that redlines at 8,000rpm would flow (1.3L * 8,000) = 10,400L/min. As you can see, a turbo rated for a generic 2.6L 4-stroke piston engine may choke your rotary engine.
However, the single turbo would hopefully have better stats than the twins. Then again, a lot of people tend to buy a cheapie Ebay T3 Honda-sized turbo and then wonder why their engine makes less power with their new 'single'.
You have two balloons...
1.) Small Balloon
2.) One Large Balloon
You need to fill them with enough air to provide equal amounts of pressure, we'll just use 14psi for example.
Now, granted you could do this - lets release the air out of the balloons simultaneously and determine which balloon will produce a higher amount of air flow as air exits.
I don't know if what I said makes any sense... but maybe you'll get it.
1.) Small Balloon
2.) One Large Balloon
You need to fill them with enough air to provide equal amounts of pressure, we'll just use 14psi for example.
Now, granted you could do this - lets release the air out of the balloons simultaneously and determine which balloon will produce a higher amount of air flow as air exits.
I don't know if what I said makes any sense... but maybe you'll get it.
Additionally, your example is flawed because it assumes the model of a jet engine as opposed to a positive displacement internal combustion engine. The extra air volume does no good if the engine can not process it.
Last edited by Evil Aviator; Dec 21, 2008 at 04:23 PM.
The primary difference is turbo efficiency. A larger turbo will tend to have a higher compressor efficiency at higher boost levels and airflow rates. Higher compressor efficiency means that the turbo will heat the air less during compression so the air will have more density at a given pressure. Besides size, better engineering can increase efficiency. Also, a single drive turbine tends to be more efficient than two drive turbines, especially if the two turbines use a convoluted manifold that splits up the exhaust pulses and causes a lot of turbulence.
Fuel is a separate issue and has nothing to do with the turbocharger itself.
Airflow is only important up to the point that the engine is not starving for air. If you think about it, once you have filled an engine rotor space with 40 cubic inches of fuel/air mixture (more or less), where would any extra air go? The primary reasons rotary engines seem to need more air than their piston counterparts are:
- Rotary engines fire all of their displacement each output shaft revolution like a 2-stroke piston engine as opposed to half the displacement like a 4-stroke piston engine. Therefore, with everything else being equal, a 1.3L rotary engine would probably use a turbo that is advertised for a 2.6L 4-stroke piston engine. It is actually the 4-stroke piston engine that has the misleading displacement rating, but we live in a world of 4-stroke piston engines, so that is considered the norm by advertisers.
- Rotary engines are high-rpm engines. The flow rate of an engine is based on displacement * rpm. Ignoring other variables like volumetric efficiency, a 2.6L 4-stroke piston engine that redlines at 5,500rpm would flow ((2.6L / 2) * 5,500) = 7,150L/min while a 1.3L rotary engine that redlines at 8,000rpm would flow (1.3L * 8,000) = 10,400L/min. As you can see, a turbo rated for a generic 2.6L 4-stroke piston engine may choke your rotary engine.
What is sad is that he is right and you don't get it despite having 'engineering' in your user profile.
However, the single turbo would hopefully have better stats than the twins. Then again, a lot of people tend to buy a cheapie Ebay T3 Honda-sized turbo and then wonder why their engine makes less power with their new 'single'.
Doh, somebody forgot to factor in surface tension.
Additionally, your example is flawed because it assumes the model of a jet engine as opposed to a positive displacement internal combustion engine. The extra air volume does no good if the engine can not process it.
Fuel is a separate issue and has nothing to do with the turbocharger itself.
Airflow is only important up to the point that the engine is not starving for air. If you think about it, once you have filled an engine rotor space with 40 cubic inches of fuel/air mixture (more or less), where would any extra air go? The primary reasons rotary engines seem to need more air than their piston counterparts are:
- Rotary engines fire all of their displacement each output shaft revolution like a 2-stroke piston engine as opposed to half the displacement like a 4-stroke piston engine. Therefore, with everything else being equal, a 1.3L rotary engine would probably use a turbo that is advertised for a 2.6L 4-stroke piston engine. It is actually the 4-stroke piston engine that has the misleading displacement rating, but we live in a world of 4-stroke piston engines, so that is considered the norm by advertisers.
- Rotary engines are high-rpm engines. The flow rate of an engine is based on displacement * rpm. Ignoring other variables like volumetric efficiency, a 2.6L 4-stroke piston engine that redlines at 5,500rpm would flow ((2.6L / 2) * 5,500) = 7,150L/min while a 1.3L rotary engine that redlines at 8,000rpm would flow (1.3L * 8,000) = 10,400L/min. As you can see, a turbo rated for a generic 2.6L 4-stroke piston engine may choke your rotary engine.
What is sad is that he is right and you don't get it despite having 'engineering' in your user profile.
However, the single turbo would hopefully have better stats than the twins. Then again, a lot of people tend to buy a cheapie Ebay T3 Honda-sized turbo and then wonder why their engine makes less power with their new 'single'.
Doh, somebody forgot to factor in surface tension.
Additionally, your example is flawed because it assumes the model of a jet engine as opposed to a positive displacement internal combustion engine. The extra air volume does no good if the engine can not process it.
Let me get this straight.....You're telling me that everything else being equel on said engine, a 60mm compressor will make the exact same power as an 80mm compressor at a given psi?
-J
Last edited by Gorilla RE; Dec 21, 2008 at 04:47 PM.
Rotorhead
Joined: Feb 2001
Posts: 9,136
Likes: 39
From: Charlottesville, Virginia, USA
Yes, but the qualification assumes that the critical stats are also equal between the turbos (same compressor efficiency, same turbine efficiency, etc.). A smaller compressor could actually produce more power than a larger compressor at a given pressure and flow rate.
PSI is a measure of pressure not volume, 14 psi through 2.5 inch tubing versus 3 inch tubing is still in fact 14 psi, but the volume of air will be greater in the 3 inch tubing. So if a single turbo can pull in a larger volume of air at 14 psi, wether it be through a larger compressor wheel or by it running at a higher RPM, in theory you will make more power because you will be putting a larger volume of air through the motor.
Yes, but the qualification assumes that the critical stats are also equal between the turbos (same compressor efficiency, same turbine efficiency, etc.). A smaller compressor could actually produce more power than a larger compressor at a given pressure and flow rate.
-J
Full Member
Joined: Apr 2003
Posts: 72
Likes: 0
From: Scotland, Allover the road
My short answer is you will make more on a single at the same pressure than on twins... people often jump into comparing comp maps and forget the gains made by opening up the exhaust path. In theory you could make the same power on twins, however the practical reality of a single turbo is better conditions for making the power the first place..
but at 14psi why bother with the hassle and expense of fitting a single unless the twins are shot
but at 14psi why bother with the hassle and expense of fitting a single unless the twins are shot
^All the reason I need
My short answer is you will make more on a single at the same pressure than on twins... people often jump into comparing comp maps and forget the gains made by opening up the exhaust path. In theory you could make the same power on twins, however the practical reality of a single turbo is better conditions for making the power the first place..
but at 14psi why bother with the hassle and expense of fitting a single unless the twins are shot
but at 14psi why bother with the hassle and expense of fitting a single unless the twins are shot
P.S. ErnieT hit the nail on the head........But I know all ya'll know what the hell you're talking about already so no need for me to point this out.
-J
Last edited by Gorilla RE; Dec 23, 2008 at 06:10 PM.
Joined: May 2005
Posts: 2,745
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From: North Bay, Ontario
+1. The only realistic constant between two setups at an exact same PR and RPM is Volumetric Efficiency. If you maintain VE, at the same RPM, all else is constant including IAT`s, and same PR (1.95 - 14psi), a well-picked single will out-flow the stock twins. And yes, we`re talking compressor maps here, because CFM (as Ernie pointed out) is the only important difference in this scenario for horsepower (even though most well-picked singles will produce less heat then the stockers, thats not the point here)
