Help my feeble mind

So a larger turbo that flows more air would produce the same amount of air as a smaller turbo running more boost? A hill I drive often would provide enough of a load to get me to 15 lbs of boost w/ the stock turbo and 10 lbs with my current and am trying to understand the dynamics at play here. In my case the PS64 would be running in a less effecient range at the above boost levels than the Hx35 but to keep it simple:

Lets say turbo A flows 200 cfm and turbo B flows 400 cfm.
Airflow @ 20 lbs w/ turbo A = airflow @ 10 lbs on turbo B ???

And how about when the turbo is spooling and no boost is reading on the guage? I assume that the turbo needs to hits its efficency range before the party starts, but in lower rpms when the turbo is spooling w/ no boost reading, is it just hanging in the wind so to speak, or is it working at an inmeasurable degree?

Another sorta on the subject question: less boost = better mileage?

 

Boost is boost, but not all boost is the same temperature from turbo to turbo. Since the 35 you had is so much smaller in size, it spins easier and can produce more boost faster and easier at those speeds/loads.

In your hill scenerio, you were getting more air molecules in the cylinder with the 35 than with the 64 you are using now. On the other side of the engine ( the exhaust ) you are getting more air out with the 64 than you were with the 35 from the lower restriction of the turbine.

Don~

 

Boost is a measurment of restriction, turbos do nothing but move volume, they do not make pressure. The more efficient it is at moving volume the better. Ive seen back to back comparison at 13 psi between a stock Garrett and a Hybrid turbo was 50 h.p. at the same boost level. Now keep in mind when moving more volume you must have a IC and piping to utilize the flow. Generally the smaller turbo really starts to heat the air when running high RPM which reduces the amout of air entering the intake. Ive seen some turbos make 8 h.p. per psi and others make 50 h.p. per psi.

Of course the turbo is always spinning even when theres no boost and the reason is the engine is able to consumer the amount of air the turbocharger is moving so it makes no pressure as there is no restriction.

IMO opinion there is alot to be gained on the exhaust side of things from porting the head to the turbine housing. Getting the exhaust gasses out more efficiently will aid in spool as well as be able to get more cool clean air in the intake side.

 

Good stuff. Is it air mass that matters most?

So the reason you see the different cfm ratings on a turbo is its ability to produce boost without overheating, thus if turbo A runs 20 lbs of boost effeciently and turbo B runs 40 lbs of boost effeiciently then turbo B would have double the CFM capacity?

Maybe I should read a book =\

 

The ECM fuels according to 3 parameters - rpm, throttle position, and boost. So in general, with everything else being equal, yes, less boost usually means better mileage.

 

On the intake side of things, air mass is very important. You want a turbo which will produce the boost efficiently, with as little heat as possible. Boost = pressure, and pressure is determined by the number of molecules and heat. So you want less heat and more molecules in boost.

On the exhaust side of things you want as little drive (back) pressure as possible. Back pressure is mostly controlled by the exhaust housing size, but can be reduced by getting rid of other restrictions in the system. In general, what you look for is a turbo which produces the most amount of boost for the least amount of back pressure in the rpm range you want to use.

Then to complicate things, it all has to be balanced out with fueling, or you start getting problems like surging and barking.

On the subject of exhaust back pressure, what is the most restrictive part of the exhaust system? It turns out to be the turbo. On a turbo with a 12 cm exhaust housing, all the exhaust, which isn't wastegated, is passed through a hole about the size of a quarter. When you consider this, you can see what the relative lack of importance the size of the exhaust pipeing is, to the exhaust side. And yet, the post turbo exhaust system is almost always one of the first places many look at when trying to imporve performance.