Ok I've got a question for you turbo guys. I was talking to this guy at some company who's saying that they've got a turbo setup that "flows more air" yet produces 300hp at the same boost levels as stock on a '89-'91 TurboII motor. He's saying it's because it flows more air.

Now, I said "but the flow rates beyond the turbo outlet are all still the same as stock, so what does the flowrate out of the turbo matter if it's the same boost level?" He continued to swear that it made more power because it flows more air and whatever..

So my question is, is he right? I understand the whole firetruck hose vs garden hose concept, but if the stock turbo wasn't flowing enough air to begin with, then the boost levels would drop as airflow began to decrease along the way. Just because more air is available coming out of the turbo doesn't mean that all of that extra flow can reach the engine.

 

He is correct.. A turbo the flows more will make more power. (assuming sized right )


The air intake temp should also be lower on a turbo that flows more.




-Zach

 

One turbo pushing 15 PSI with a certain volume of air passing through could make more power than another turbo pushing the same PSI and just flowing a smaller volume of air.

More Air = More Power (and more fuel demands)

A large turbo pushing 7 PSI and pushing through (for example) 200cc/s of air would make close to as much power as a smaller turbo pushing 15 PSI pushin 200cc/s of air.
(Just an example)

If you increase the Turbo's PSI it will pass more air, creating more power (to the extent of the size of the air intake). Subsequently if the Air Intake is opened up the turbo (at Max PSI) would actually be able to more effieciently pass air through faster and in larger volumes, creating more power. (And this must be countered with fuel.)

Blah...I think that is how it goes.

 

hmm.. see I figured that since the PSI was the same before the engine, and the flow rates between the turbo and the engine are still the same, the flow rate of the turbo wouldn't matter, but I guess not. Is it more a matter of how much pressure it can SUSTAIN through the entire intake system between the turbo and the engine?

 

The larger turbo should be able to flow more CFM at X PSI. Since you're getting more airflow at X amount of boost you'll get more power.

 

different compressor wheels compress the air differently. The more oxygen you have compressed into a space the more power its going to produce.

STEPHEN

 

Don't forget the exhaust restriction factor. A small turbo has to spin faster to make the same PSI/CFM, so the turbine side will be more restrictive. (As i gather )

 

Your assumptions are wrong - that's where you're running into problems.&nbsp Pressure is just one dimesion of "boost".&nbsp You're totally ignoring the concept of "air flow" (which is measured in CFM or equivalent).&nbsp Think about it real hard...&nbsp You can have two volumes of air at the same pressures, but airflow is different.&nbsp One of the biggest myths of a turbo'd engine is that the engine is the restriction - this is wrong.&nbsp The restriction in the whole "system" is the turbocharger, not the engine - the choke-point of the whole "system" is the turbo, therefore, the turbo dictates airflow (potential).


-Ted

 

so then would a turbo that makes 8 psi and flows 800 cfm be more likely to cause detonation than a turbo that makes 8 psi and flows 400 cfm?

 

basically yes.....your fuel needs are really based on the amount of cfm and oxygen, not psi of boost. If you bolt up a T78 and run 14psi of boost you'd need way more fuel than if you ran 14psi of boost on the stock twins because the cfm difference.

Look at it like this.......take the seq system for example, 12psi of boost before transition when your running one turbo is a whole different animal than 12psi after the transition when your running 2 turbos. Your still running 12psi but your making way more power. Now of course there are other factors, ect ect ect but I'm sure you get the idea. With no more boost your hp jumps 100rwhp in like 500rpms.



STEPHEN

 

That's a good way of putting it

 

That's too general of a question to have a definite answer; there are too many variables that can change the answer very easily.&nbsp If all else is kept equal, the higher flowing turbo implies a larger compressor which would imply it would keep the intake charge cooler - so you actually go that backwards.&nbsp What is actually happening is the large flowing turbo is spinning a lot slower to produce the same amount of boost than the smaller flowing turbo.



-Ted

 

"Exhaust restriction factor"

The turbine side of the turbo would be the factor in this case. The less restrictive turbine will allow less exhaust gasses to be trapped into the intake cycle, allowing the enigine to ingest a fresher intake mixture.

 

volumetric efficiency

 

Yepper!

What is the figure bandied about for T2's, up to 50psi of pressure in the exhaust before the turbo?