Well, folks, I'm back...you may remember my 2uzfe...TRD S/C, Garrett GT 42, 200 hp nitrous and alcohol injection....put it all back together and am still in the process of tuning....I recently took the S/C off to see if it was a restriction to the turbo (charging from the turbo through the S/C). I was getting almost instantaneous 20 lbs of boost with the S/C on, but it sure didn't feel like it, even not having the AFR right, It should have done better. After I took the S/C off, when I hit the correct AFR (around 10.8 to 11.3, that baby takes off like a rocket!!! This is a little 284 cu in in a truck that weighs 5240 lbs w/me in it. I have come to the conclusion that the S/C is not capable of keeping up with the turbo in my application. It doesn't do bad things to the motor, the S/C just doesn't spin fast enough to do anything with the turbo boost once it is spinning up. I suspect, that if I sized them right, it would work much better....the reasoning behind doing both of them was to do just what John said, low end umph (motor is only 8.6:1) until the turbo is spinning up. I won't put the S/C back on, but I will get an adjustable window switch for the nitrous and use it to get my bottom end going when I need to get up those steep on ramps. Will post some numbers once I finally get it tuned.
Wayne
Wayne, really surprised and sorry to hear about your setback. It sounds like your turbo might be coming in too early, and perhaps its A/R ratio is too small on the turbine side? These days we're all focused on reducing turbo lag, but for twincharging, you actually
want a lag monster for a turbo. Also, for the S/C, you might want to consider adjusting its pulley so you don't overspeed it up on top, and then just ensuring it's big enough to give the boost you want down low.
Have a look at this thread over on the engineering forum:
http://www.eng-tips.com/viewthread.cfm?qid=174690&page=1 ; you might consider joining and contacting member Warpspeed by PM and discussing your problem. He's pretty switched on about twin-charging :boggled:
Benji, what you're describing is the way the sequential twin turbo Supra is setup, and it's done with a combination of a one way reed valve and an intake control valve for the #2 turbo to put it in parallel with the #1. There's a schematic of this setup here:
http://www.lextreme.com/sqtt.html
Disregarding the exhaust side of the diagram, look how the two compressors of the turbos are piped together. The reed valve serves both as a one way valve, and also allows the #2 compressor to come online gradually without creating a pressure spike. It's not a full size valve, but it does allow the #2 to start flowing some air. Sometime after this, the intake control valve opens and that lets the full flow of the #2 compressor come in. This system works well because both turbos are sized identically, so they're both boosting to the same pressure and producing the same flow.
If you were putting the SC in parallel with the turbo, you'd probably want to size the SC for sufficient boost down low, then have the turbo come in as the SC is running out of steam, say between 4000-4500 RPM. This wouldn't be two stage compression any more, but two single stage compressors working in two different RPM bands.
You'd probably have to do this with twin TB's - one for each compressor system, and linked either with some sort of progressive linkage, or else a drive by wire system. You'd also have to ensure the compressor of the turbo would be big enough to handle the total airflow at the maximum boost pressure you want, and then size the turbine side for it to come in only from the mid to high RPM range. You might even want to include a clutch for the SC to drop it out of the system once the turbo is on boost. All this would be way cool, but way $$$$ too....
