ok, i had this conversation with this guy, and he thinks:

"The likely reason why the GT30R will make more power at 26psi is because of the following:

The Big 16G can't hold the boost in the high RPMs. If it can hold 26psi to redline, it will flow the same as the GT30R. But what you're forgetting is the guys with GT30Rs make lots of power at 26psi because they rev them high. 8k+ rpms, no? Do you think a Big 16G can hold 26psi to 8k+ rpms? No. That's why the bigger turbo makes more power. But if they both run the same amount of boost to redline, they will both flow the same amount of air."

i told him that:
"
) PSI IS NOT AIR FLOW! IT IS AIR PRESSURE
2) CFM IS VOLUME OF AIR GOING THROUGH A MEDIUM, OR AS WE USE IT AIR VOLUME.
3) VOLUME IS AMOUNT OF AIR IN A SPACE.
4) VOLUME RUNNING THROUGH A MOTOR AND TURBO SYSTEM CAN PRODUCE DIFFERENT PRESSURE IF THE FLOW HARDWARE IS LARGER.

yes, but what your forgetting is this: THE TURBO IS BEFORE AND AFTER THE MOTOR. AIR GOES FROM THE TURBO, INTO THE MOTOR, OUT THE MOTOR, INTO THE EXHAUST HOUSING OF THE TURBO. this is where the larger turbo making more cfm flows more air at the same psi. think about it. the motor is IN BETWEEN THE TURBO AS FAR AS AIR FLOW IS CONCERNED."

please comment so i can shut him up. i remember seeing thread slike this, but i cant find them. basically, i say larger turbo, more cfm, makes more power at same psi than smaller turbo with less cfm. he says any turbo at 18psi will make the same power BECAUSE its at the same pressure. anyone knows pressure does not mean air flow... excet him.

 

Just like the old analogy says..... an engine is just a giant air pump... the more air you can get into and out of it.... (mixed with the right amount of fuel of course) the more power you are going to make.

 

the larger the turbo, the more air it flows at the same psi. anyone disagree? some of these s4 guys are idiots.

 

this argument has been recorded a thousand times. Volume is the same for every single turbo at the same psi and the same RPM. Smaller turbos simply cannot flow enough at higher RPMS to match bigger ones. Bigger turbos are nice, espcially with high rpm's becuase they can still produce 20+ psi of boost where the 16G would fall on its face and produce less boost and almost become a flow restriction. Also, bigger turbos are more efficient so they heat up the air less at any given rpm, thus 20psi from a 16g and 20psi from a larger turbo at a certain rpm has differences in temperature which leads to density differences.

 

^^ I disagree! Nah, im j/k.....a larger turbo has more CFM, therefore is allowing for more air to be sucked in. A larger turbo typically has a larger housing in which it can hold more air, and a larger compressor wheel where it sucks in more air. It will make more HP at the same PSI versus the stock turbo, but there will be more turbo lag. I would think this would be a common sense thing.......bigger turbo = more HP! Ur buddy must be smoking the crack!

 

this argument has been discussed, but not with your conclusions. i need to find the lengthy thread. can anyont find them?

picture this:

august issue of scc: 700 whp supra @ 18 psi on bone stock motor.
-this is with a t77.
-a stock motor supra will hold 18psi to red line, and make about 350whp while doing it.

-the upgraded injectors and intercooler and management are not making the 400 whp difference here. that turbo flows 600 more cfm at 18psi than both stock supra turbos combined.

 

I agree with 2GDSM in a sense. The thing that affects the power levels is the efficiency of the turbo at a given psi. If a 16G and a 20G pushing 18 psi were both 70% efficient at 5000 RPMs on a given car, they would both make the exact same power. But because they have different efficiency values and ranges, that is what makes the difference.

 

ive been told a car pushing 12psi can make more power than one pushing 20 psi just depends on the flow rat eof the turbo or something like that...i mean hypothetically speaking a car w/ turbo "a" running 20 lbs and a lower cfm makes less power than the same car w/ turbo "b" pushing 12 psi and but a higher cfm rate

 

http://www.honda-tech.com/zerothread?id=1004578

 

exactly, cfm is the flow volume, hypothetically, 20 psi made efficently on a smaller turbo and a said rpm, can actually make less hp than 12 psi on a larger turbo if the cfm its putting out at 12 psi is more than what the 20psi turbo is doing. efficeincy can be measured by how hot the air its producing. so if they are both low enough, its not the efficeincy (although it does play a role) its the increased volume of air per psi that a larger turbo will flow.

its fact, larger turbos flow more cfm through a motor than a smaller turbo and the same boost... works the same at 5 psi, works the same at 20 psi. guys, this is how supras make 700+ whp at boost under 25 psi.

 

I looks like 2GDSM hit it on the nose, but I’ll explain it a little further.

At the same psi and same rpm a small turbo and a large turbo will move the same volume of air. The real issue is the density or mass of air being moved.

A larger turbo will move a larger mass of air than the small turbo at the same psi and rpm (yes and therefore still the same volume). This is because the larger turbo will be moving cooler air. Cooler air is denser than hotter air (check a chemistry book – cooler air means more air in the same space provided), therefore there is more oxygen contained in a cooler volume of air then a hotter volume of air of the same volume. More oxygen means more gas can be burned. If the optimum air/fuel mixture is 12:1, more gas will be added to the larger turbo’s air than the smaller turbo’s using the same 12:1 mix because the larger turbo is adding more air then the smaller turbo even though the volume is the same. More gas is more explosion is more power at same rpm, same psi, and same volume using the same mix ratio.

This is why it is not unusual to see a larger turbo at a lower psi making more power than a smaller turbo with a higher psi. The larger turbo is still moving more air. Of course there are many other issues in two turbos of the different sizes to consider, but thats another subject.