There is absolutely nothing wrong with non vgt turbos at all, they do work, they have worked forever on dodges and duramax's for years, no taking away from that at all.
The one advantage to a vgt is that you can have a very tight housing for spool up, and then a loose housing once things start to get moving, so back pressure is diverted inside the turbine housing basically into the hot pipe and then into the big turbo, essentially acting as an external wastegate but electronically controlled by the computer. Im actually hoping to prove on my truck that the vgt turbine isn't the restriction causing high back pressure, but the atmospheric turbo is actually the limiting factor to back pressure like charles found on his truck. Since my truck has such a large turbine that i shouldnt have issues, this should be a good test. I plan on checking boost and back pressure between stages just to see what is going on exactly so i can tune the gate (if needed) properly. My last turbo set up didnt require a gate at all, and it runs the same turbine that max powers have making the same amount of boost, just for a reference. I was actually able to see the vgt duty cycle going up trying to compensate for the "low" back pressure the computer was seeing vs desired.
A non vgt set up on dodges and duramaxs seams to work well with just a small internal gate in the exhaust housing, several set ups come to mine with 62/80 combos, or 66/88 combos with a small 30mm (ish) internal wastegate, with no external gate. I think to a degree its pretty important to have at least an internal gate in a compound set up to help balance everything. Now of course perfect turbo sizing will go a long way but generally speaking a good spooling turbo wont have the right flow thru the turbine without some sort of wastegate, especially in a compound set up since the mass air flow of the engine is so greatly affected by the atmospheric turbo anyway.
Turbine efficiency, housing sizing and efficiency, ect go along way in this but alot of the same rules will still provide to be true.
So basically think of non vgt turbo with an internal gate is a sort of crude vgt, because thats pretty much what it is, the advantage tho is less moving parts that can fail, and more tuning ability because the gate can be controlled by the end user better than something that needs to be controlled by the tuner.
Dont want to de-rail aarons thread anymore so i think ill move alot of these posts to its own thread so we can continue to talk about this...
and there is no such thing as west coast air LOL
ostwhore:
