So how dow you compare turbos?

They should be able to give you the flow rate numbers along with the intake and compressor sizes. If they cannot, just walk away and find someone who has an idea about what they are doing.

Remember, you can run into issues changing out, for example, a 300cfm # 20psi turbo setup with a 750cfm # 20 psi. By pushing more cfm you are leaning out the mixture and must compensate with higher fuel pressure, larger injectors, and/or EEC programming.

If the person cannot give the flow numbers and impeller/compressor sizing, like I said earlier, walk away.

 

Bigger may not always be better. As said above if it is pushing a lot more air you may have some problems.

 

Most turbo shops will give you the air flow measurements in Lbs per minute of airflow. Some will even you give you cubic feet per minute CFM. A turbo that will move 140 Lbs per minute will move 2000 CFM. Your engine should require 115-120 Lbs per minute.

What everybody calls a BW Stage 1 turbo for a CAT engine could be different. Everybody has a different interpetation of how to build a turbo for this engine and horsepower range.

The turbo you have shouldn't be much larger physically than the one you have now.

 

Are you certain about that. I've seen and talked to a diesel mechanic. You can burn out any engine by running too lean. If you understood what I wrote I was getting the point across that more CFM at a certain boost level is a lot more air into the engine. Also that any shop should give you all of the numbers, if they cannot then find another shop.

 

Yes, you can burn diesel engine only running too rich what means smoke and high EGTs. Gasoline is vice versa.

More CFM at same boost level is only possible if you do some changes to engine breathing ability, like porting, or turbocharger that has better boost/backpressure ratio, not all of these "upgrade" turbos have.

It's difficult to get airflow numbers and maps for turbochargers because manufacturers for some reason don't want to publish them. Garrett is easiest, some BW models quite easy, Holset most difficult. In Finland there's a turbo shop that can get all the information of modern Holsets, but none of the older like HT4.
Wheel sizes and housing numbers should be easy, if the shop can't give them, you are right, find another shop.

 

V8Lenny is on the right track. It's really hard to get a diesel to run in a lean condition. A diesel running lean is starved for fuel. Just like a plugged fuel filter, runs rough and no power.

Adding CFM without increasing boost pressure means that you will only flow as much air as the smallest choke point allows. Most upgrade turbo's also push more pressure, that gets you more air into the cylinder. The intake tube on a cummins ISX would be replaced on any truck I owned.