Ive been wondering about this for a while now and i just cant figure it out. How is 35 pounds of boost from... say a phat shaft 64 different than 35 pounds of boost from a stock hx35?

 

probably faster spool-up, the phat shaft probably has ball bearings so it'll last longer and not get so hot?

 

number here are theoretical, not fact

well due to the larger size from a phat shaft 35psi might mean 1000cfm
whereas 35psi from a stock hx35 is prolly only 600cfm.

this is why if you run a stock turbo and are spinning it to 40psi, you may have 350hp and EGT's can hit 1600+, but switch it out for a larger turbo, and you will make closer to 400hp, at only 35psi, with EGT's down around 1400.

its not the boost we are looking for, its the volume of air we can shove into the cylinder for a more complete burn, boost is only the measure of restriction.

 

....and the phat shafts are not ball bearing turbos.

 

A hx35 is most efficient around 20 psi and a 64 near 32 psi so the 64 would be producing cooler air.

--Or at least this is how I understand it

*Waiting to get slam dunked by a local turbo guru*

 

where's the sugar??

 

I ain't giving you no sugar!

 

You also can have two different turbos producing 35 psi at 600 cfm but one will be doing it more efficiently by doing it with less temperature rise, like 350 vs 425 degrees.

 

Now we're splittin hairs.. Efficiency is a tough one to put a number to.

 

I gotta see where this is going.

 

You're right- thats why they make maps to show levels off effeciency at different levels of boost and different volumes of air =P

 

There are also differences in drive pressure from one turbo to another. For optimal efficiency you want your turbo to produce more boost pressure than the pressure required to spin it. When a turbo is overdriven the charge air becomes very hot and the turbo produces lots of backpressure reducing the performance you're supposed to be achieving

 

Well you have to account for loss even with a good performance map. The best measurement would be to accurately account for the temperature and pressure rise across the compressor vs. theoretical. Most maps are just theoretical so you might have to fudge the numbers by up to 10%.. The same goes for the turbine side, pressure and temperature drop vs output speed.

 

This is th way i see it....

Cooler EGTS outta the Phat shaft and efficiency is all that it is...

Rick

 

Boost is how many punds of restriction you have. Your intake valves will only flow so much each time they open per pound of boost. So 35 psi is 35 psi no matter how you look at it.