Physics Question: Bigger turbo with a given tubing diameter and psi = more power?

[disciplekyst]

Here we go guys,

As i'm gathering information on turbo setups, I realize that people often say that, with a given tubing diameter and same psi, you get more power from a bigger turbo.

Well i can understand that a bigger turbo can push more psi and make more power---> but without going with bigger intercooler pipes, I just can't see why it could produce more horsepower with the same amount of psi than say a my little 14b? It's just not logical to me.

Please, you little Einstein, explain this strange phenomenon!

 

[1gentalonfan]

its the same principle as say for plumbing. the water flowing through not only has a pressure but a flow rate which is key to more hp with the turbo. theres a few other things too but they dont apply enough here to matter just because your pushing 15 psi doesnt mean you pushing a lot of cfm. and yes bigger piping to an extent thats bent smoother will help with a bigger turbo but the bigger turbo that car flow more is key.

 

[timloomis]

It's not about psi really, it's cfm (cubic feet per minute). The bigger turbo can push more air at the same psi. Like if you have a big air compressor and a little air compressor. Both are set at 90psi for an air ratchet. Now which one runs that ratchet better?

 

[Spln_Hrd]

The air ratchet thing is irrelevent because it would not be able to keep the same pressure if it could not produce the same cfm that the ratchet was consuming.

Alot of it has to do with the exhaust side actually, with a more effecient turbocharger there will be less exhaust pressure on the turbine to create the same boost pressure or cfm so then the exhaust can leave the cylinders easier and draw in more air during the next combustion cycle. There is a good article on this by a forcedperformance employee.

 

[timloomis]

Its very relevent. The smaller compressor doesn't have enough cfm to drive the ratchet. The bigger compressor has more cfm going through the hose at the same psi as the smaller one. The turbine has a lot to do with it too, but putting a td06 on a 14b isn't going to make it push as much cfm as a 20g. And with the intercooler pipes, breath through a straw then breath through a 2" pipe, which is easier. Same principal applies, it just makes the turbo's work easier which can make more power.

 

[1gentalonfan]

yes the exhaust side does help but if you have you have too big of a housing it doesnt spin the turbine and it all just flows around it, but yes its a physics principle with air or liquids that the total mass flowing to or through a specific point depends on flow rate, pressure and total resistance all together

 

[pboglio]

Here we go guys,

As i'm gathering information on turbo setups, I realize that people often say that, with a given tubing diameter and same psi, you get more power from a bigger turbo.

Well i can understand that a bigger turbo can push more psi and make more power---> but without going with bigger intercooler pipes, I just can't see why it could produce more horsepower with the same amount of psi than say a my little 14b? It's just not logical to me.

Please, you little Einstein, explain this strange phenomenon!

Say for instance your 14b taps out at 30 lb/min at 6000 rpm on 21 psi. Well, the engine theoretically can ingest 35 lb/min at 6000 rpm on 21 psi. For starters your 14b cannot even supply the motor with enough airflow at that boost level and rpm to fully satisfy the motor. This 5 lb/min deficit is what the bigger turbo takes advantage of. I pick 6000 rpm because this is generally where the TD05H turbine wheel restricts the motor in making peak power on the 6cm turbine housing.

Slap a 50 trim on there and it will easily supply the motor with what it demands, which is 35 lb/min at 6000 rpm on 21 psi and no more than that. The final trick is that the 50 trim also has a much freer flowing exhaust side which allows the motor to power peak at say 7000 rpms instead of 6000 rpm and produce 40 lb/min at 21 psi. Well now your talking a whopping 10 lb/min (100 h.p.) advantage over the 14b at the same 21 psi boost setting.

On the flip side, set the boost level to 9 psi and your 14b and 50 trim will produce roughly close to the same airflow or horsepower because the 14b can easily supply the motor to redline and the backpressure at such flowrates isn't high enough to rob the motor of power. Pretty much common sense.

Tube diameters don't really have anything to do with things if your talking about intercooler pipes. Now the turbo compressor inlet can limit a turbo if it was small enough to produce supersonic flow. This is the way turbo's are airflow restricted on WRC rally cars, different topic though.