Replaced actuators.....now this...Need imput.

[hhow55]

(07-28-2016 )gearhead Wrote:  The key is good airflow not psi. If you can make 150lbs per min at 20psi and it takes me 30psi to make 150lbs per min you are way better off no matter what you are looking for. It is all about backpressure vs drive pressure. You don't want big wheels on a low hp fuel milage seeking engine. You need it to spool fairly quickly. The problem is that you need it to be in its peek range at about 1400 engine rpm at about 150 mg/str. This is your loaded fueling on flat ground so if you can make the right amount of air to fuel ratio with very little backpressure you will have it made. The problem with the vgt on the newer engines is they take off great. But when it comes time to being loaded your at 2:1 ratio and can be as high as 4:1. So the harder you push it its like someone sliding a steel plate over your exhaust manifold. This turbo works ok if you only haul 10'000 in the trailer. If you haul heavy like 40'000 to permit loads forget it. Once that little vgt hits 30psi you are 3:1. You can feel the engine struggling to go. I think if the exhust housing ar ratio was better it would reduce some of this backpressure. Part of the reason the turbos are built this way is because of egr and dpf. Look at the time line of cummins. They didn't use vgt until egr came along. Egr came about they needed a way to control backpressure to force the exhaust gas to go into the intake. So with all this being said in the wrong thread it all comes down to the engines intended use and gearing. This is why it is hard to map a turbo with one file for all trucks. The cm871 turbo on the cm2250 works very well for heavy haul but hauling light it may not be the best choice. There is so much math and thiery with turbos it is it's own science.

Such great info, Gearhead