DPC Round Two: Going for Broke

Dzchey21 · May 19, 2014

madman1234509 said:
My twins make more boost then back pressure until about 35-40lbs

as they should be, back pressure isnt an evil thing like some people seam to think. It takes back pressure to make boost, the faster you can make back pressure the better, then once boost comes up divert it and try to make 1:1 at peak, even if its not perfect the closer the better.

bigrpowr said:
3 stages can work, and spoolup is instant at well over 1000hp , but i know in my application its was very hard to keep bp down AND keep the turbos from falling on their face thru the shifts.

The whole point of trippes really was to make big boost numbers and keep the pressure ratios happy and keep charge air temps down while making say 125 psi of boost, but as you found out you can make 900 plus with no where near the boost so why do it? Compounds work great under 100 psi, i could see if you were going for 1500 hp on fuel where tripple COMPOUNDS would be something to seriously consider. The big charger does suffer so too because it has to pass thru 2 turbines before it gets to the big turbo. So the air has been cooled, diverted ect before it ever gets there.

NathannialD · May 20, 2014

Dzchey21 said:
as they should be, back pressure isnt an evil thing like some people seam to think. It takes back pressure to make boost, the faster you can make back pressure the better, then once boost comes up divert it and try to make 1:1 at peak, even if its not perfect the closer the better.

The whole point of trippes really was to make big boost numbers and keep the pressure ratios happy and keep charge air temps down while making say 125 psi of boost, but as you found out you can make 900 plus with no where near the boost so why do it? Compounds work great under 100 psi, i could see if you were going for 1500 hp on fuel where tripple COMPOUNDS would be something to seriously consider. The big charger does suffer so too because it has to pass thru 2 turbines before it gets to the big turbo. So the air has been cooled, diverted ect before it ever gets there.

Getting exhaust to the atmo was never a problem..... Other factors aside we were always running it at its max safe rpm. The problem was keeping the Vgt happy

Dzchey21 · May 20, 2014

did you guys ever try to get the big turbo to do less work to see if drive pressure came down?

NathannialD · May 21, 2014

The atmo is not the restriction. But just to entertain you if we slowed it down power dropped off several hundred hp. Seems foolish to slow down the turbo the pushes the most cfm doesn't it?

Dzchey21 · May 21, 2014

im not saying it was im saying its creating such mass air flow into the engine that back pressure has to go up since you are cramming that much air in the cylinders even if the boost really isnt that high. I i was just wondering.

Wayne · May 22, 2014

Pressure in the combustion chamber from big cfm on the inlet? Yes. Once it leaves the head, the restriction is limited by turbine wheels and housings primarily. 3 compound turbos add 3 levels of back pressure. The gates should work great in theory, but having the vgt as the high pressure complicates things. A simpler version with all 3 conventional turbos might be easier to get going, but that's obviously not happening here.

For the simple concept of understanding the back pressure issue, imagine if all 3 turbos were superchargers instead, with big headers going into 4" dual exhaust. I can't see much back pressure building there. I imagine about 300 HP worth of parasitic draw, and crazy boost numbers if you could get a group of chargers to take the abuse and rpm's necessary to make it happen. I am by no means suggesting it's a good idea to try, only using it as an example of how I see the back pressure issue.