Boost vs CFM

[freebird50]

Assuming boost is the same between two different supercharger head units on the same engine but one has a higher CFM than the other would there be any difference in horsepower and torque between them? How much does CFM matter I guess is what I'm asking. Say you had a Vortech S trim and a Vortech YSI B and both were pullied to provide the same boost would the bigger YSI blower make more power. Thanks.

 

[JAJ]

Assuming boost is the same between two different supercharger head units on the same engine but one has a higher CFM than the other would there be any difference in horsepower and torque between them? How much does CFM matter I guess is what I'm asking. Say you had a Vortech S trim and a Vortech YSI B and both were pullied to provide the same boost would the bigger YSI blower make more power. Thanks.

CFM is the determinant of horsepower. The airflow in pounds per hour determines how much fuel in pounds per hour the air can burn. Air flow determines fuel flow and the fuel flow determines the engine's power output. Simple as that.

"Boost", on the other hand, is a measure of inefficiency. It's better thought of as "backpressure". It's a measure of the resistance to flow caused by stuff obstructing the path the air takes through the engine. If two blowers are making the same backpressure on the same engine at the same RPM, and there's no change in the intake charge cooling, the two will make the same power at that RPM.

 

[robvas]

Depends on the efficiency of the blower in the range you are running it at. S trim is going to beat out a YSi at the low HP levels.

 

[DSG2003Mach1]

If two blowers are making the same backpressure on the same engine at the same RPM, and there's no change in the intake charge cooling, the two will make the same power at that RPM.

the variable being efficiency of the blower, one could take more power to spin than the other.



also to the OPs question in that case seems more like both blowers are moving the same cfm to achieve that same boost number so bigger blower is probably running a bigger blower pulley to achieve that same boost/power

 

[venom1997]

It could also depend on the efficiency of the engine for example a blower that produces 15 psi on a motor with stock heads then you port and polish or buy a new set of heads that flow more cfm the boost will actually drop to say 12 psi yet the motor will produce more power


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[venom1997]

I also have an example on my car I was making 9-10 psi of boost I removed the blower inlet made it bigger to flow more cfm and on the same pulley I made 12-13psi I had the opposite effect but it was crazy positive as it was an inlet restriction by opening up the inlet it cleared the restriction and stopped it from being choked that could also happen if you have plugged air filter or intake tubing to small it chokes the blower


Sent from my iPhone using svtperformance.com

 

[01yellercobra]

There are some videos on YouTube comparing the Whipple 2.3 to the 2.9. My buddy found them as he was researching going to a 2.9 from his 2.3. They kept the same boost level and the 2.9 still made more power. Something like 50hp. Even at the lower boost level it's pushing more air per revolution.

 

[Rb0891]

CFM is more air. More air is more power. Higher boost is just more heat.

 

[robvas]

One thing I remember guys saying about the YSi, how if you weren't running at least 20lbs (or whatever the 'magic' number was), the YSi wasn't worth it. I remember people saying that the blower didn't even "seal up" j til you got it hot enough and ran high enough pressures or something like that.

Was it ever proven or was it an old wives tale?

 

[03Sssnake]

There are some videos on YouTube comparing the Whipple 2.3 to the 2.9. My buddy found them as he was researching going to a 2.9 from his 2.3. They kept the same boost level and the 2.9 still made more power. Something like 50hp. Even at the lower boost level it's pushing more air per revolution.

Oh for sure with those types of blowers.. The bigger 2.9 will make more power even at the same boost level as the 2.3…

 

[freebird50]

This is good info and I appreciate all the replies. Thanks.

 

[freebird50]

One thing I remember guys saying about the YSi, how if you weren't running at least 20lbs (or whatever the 'magic' number was), the YSi wasn't worth it. I remember people saying that the blower didn't even "seal up" j til you got it hot enough and ran high enough pressures or something like that.

Was it ever proven or was it an old wives tale?

I have a t trim maxed out at 26 psi. Built short block and stock h/c/I. 98 cobra. 702rwhp. I think I'm spinning my t trim fast as it will go so wondering if switching to the YSI would be worth it.