VIN#Diesel

Not true. Look at a counterexample. If you changed all your intercooler piping down to 1 inch pipes you'd see the psi go way up. But you'd actually be flowing less air.

Your garden hose lets the water out at a higher psi than if you attached an adapter and let it flow through a fire hose. But the garden hose isn't letting any more volume of water flow. It's why placing your thumb over the end of the hose lets you shoot the water further. More psi from the small opening. But not more water.

Its the actual amount of air (CFM) that really matters, not the psi.

THURENfab.

I get the concept, but the intake charge temp is THAT much different changing out to a different turbo?

What are some numbers? Is there say, a 100 degree difference of the air coming out of the turbo, when comparing an aftermarket and stock turbo?

THURENfab.

If you would read and quoted my entire paragraph, you'd see that I was specifically saying that.......

It seems the only way to get more air in without changing anything in the intake path, is to increase PSI.

THURENfab.

Right, but if the intake path(porting, cam, intercooler, yada, yada) is not changed, how do you increase the CFM? My guess would be increasing the PSI????

dfer10

CFM. stock turbo flows less CFM than an aftermarket turbo, with a larger aftermarket turbo you can flow the same cfm of the stock turbo but at a lower psi so the more psi the more air(cfm) with an aftermarket setup. make sense? good.

cquestad

Sorry about the hijack...how are those bump stops coming? ;-)

I am having a hard time behaving in my truck thanks to you Don.

cquestad

BTW...Don you are correct.

If the restrictions stay the same (piping, intercooler, CAM, etc), more psi is more air...period. You have less boost with a larger turbo at cruise because the DRIVE PRESSURE is less...not because it is moving more air.

It is always a trade off...even with twins to some degree...just less. Just find the "range" you want to operate in...and do your best to match your airflow requirements.

THURENfab.

LOL!!

Ok, I'm going to come up with a scenario here for the people not getting my thinking..

Say you have the stock turbo, and this stock turbo is making 40psi trying to push air though a 1" hole. Now you have a BETTER turbo making 40psi against the same hole. HOW, please tell me, does this equal more CFM through the restriction/1" hole? More PSI would equal more CFM yes..

Surely once you open up the restriction(porting, intercooler, cam) the stock turbo can't keep up, but with stock components, is there something I'm missing besides the exhaust side efficiency?

Still curious about the charge temp of the stock turbo at 40psi vs a better turbo at 40psi..

10mm

The variables are the exhaust side of turbo and the temperature at which the compressor creates boost. The aftermarket turbo with a larger more efficient turbine will cause less restriction to the exhaust flow which will in turn allow better exhaust evacuation and less restriction to the intake air. At the same time that small stock compressor spinning at higher speeds will heat the air more for a given amount of flow and pressure than a larger or more efficient compressor would because it is having to force the same amount of air through a smaller housing and it is probably designed to produce lower boost levels. Basically the stock compressor and its housing are made so that the air has optimal flow up to a certain pressure, in order for the smaller blades to create the same pressure in the air they have to spin exponentially faster which causes more friction and thus more heat in the air. The larger turbo will operate at max efficiency at a higher pressure because the blades and housing are designed to compress the air more at lower rpm without adding a lot more friction and thus heat. Or at least that is how I understand it from perusing the interweb.

Disclaimer: The information above is worth exactly what you paid for it and I didn't stay at a Holiday Inn last night.

Jeff K

Its all about compressor efficiency. The stock turbo is way off its efficiency map at 40psi, so it is not just compressing the air, it is superheating it as well. The charge air temps will be sky high, which means less dense air. With a turbo that is properly sized to put out 40psi and still be within its compressor efficiency map, that same 40psi air will be much cooler and denser.

trik396

Plus at 40psi with your stocker, I don't even want to think about the drive pressure you're seeing... Those poor exhaust valves....
Plus that higher drive pressure is going to keep some more exhaust in the cylinder instead of it getting out thru the exhaust, which in turn is going to heat up your intake charge even more. Not good at all....

CButler610

Well, here is my little bit of input on this:

I think manifold pressure is being confused with the volume, or "weight" of air that a turbo can flow (cfm) or lbs./min.

Lets take one of these cute little handy pancake air compressors. Lets say we have a sandblast cabinet that requires 90 psi. No problem right??

Well, reading further, we see that this cabinet also requires 24 cfm @ 90 psi!! and our pancake compressor can only do about 7 cfm. The cabinet will run this little thing to death while providing very hot air. A nice screw compressor on the other hand will deliver HUGE amounts of relatively cool air at mega volume, all day and hardly even work.

The important thing to remember is we are dealing with a forced induction engine that relies on a large volume of air to work properly. It does not rely on absolute air pressure to do its work, or how smooth or large an intake tract is. So we can increase the amount of (work) by allowing a more efficient 'volume' of air into this pump, to a degree. Of course, at some point everything else will limit this fun, like heads, etc.

I can say there are members making some ridiculous numbers with many stock components, but they are ALL doing it with a non-stock turbo.

That said, the stock turbo is limiting........

XLR8R

The focus tends to be on the quantity of boost, (which - like EGTs, as opposed to combustion chamber surface temps - is merely an indication of engine operating envelope conditions) instead of the quality of boost.

The only thing the piston crowns respond to is how many molecules of fuel and AIR are combustively combining in the chamber. "Better" turbos can support higher combustion quantities of fuel because they are able to compress more molecules of air into the same volume - they do this largely due to more efficient compression (less thermal energy imparted to the pumped fluid).

There is a lower limit to charge-air temps, since the CTD produces it's highest BSFC between ~60-90*F, but any 'charger is going to heat the intake air well over ambient. However, even though the stock Holset can heat the air up over 350*F (due in part to the aftermarket-fueled 75psi TIP ), the OEM CAC does an excellent job by cooling the charge air down to a ~25*F differential before the airhorn.

Basically, anything that improves the effective VE of the engine will produce more power.

Anyhow, just like electricity, fluidics, or physics - thinking of "boost" in terms of discrete units (such as air molecules) - rather than current, flow or quantum strings can help in understanding the phenomenom.

THURENfab.

After thinking about this whole "turbo turbo thing" for a couple days, I think I'm starting to see that light, and this above quote seems to sum it up for me..

It would seem that if the compressor can keep up and supply the needed PSI, the exhast turnbine would be key. If the the exhast side between the turbo and engine an keep a low PSI, then the two forces(intake charge psi/exhaust psi) don't crash into each other in the combustion chamber. So, it would seem that with the same intake boost(or less), more power can be made by simply reducing the exhaust restriction by using a more efficient turbine..

D.Wiggs

Less turbo thinking...More Optimus Suspension making/shipping!!!