Originally posted by StraightSix:
John, I'm sure you know much more about these engines than I do; I had been under the impression that the stock system directed all the exhaust through one turbine with a valve in the exhaust manifold in low-rpm operation; is this right?
Yes, The VSV's (variable something-or-other valves) are controlled to direct all the engine exhaust through one of the turbines when at low load or RPM. This significantly reduces boost lag. As the load and/or RPM increases is allows the second turbine to start seeing some exhaust flow.
Once you get to any significant RPM or Boost, both turbos are running wide open.
The most common mod on these cars is to simply replace both turbos with a big single turbo as stock long block can easily take 600+ HP without any problem. The lag is worse but not much.
For the F/PS class you would have to keep the twin turbo setup which would be hard since an upgraded twin turbo manifold is practically nonexistant. You would have to get one made. But, with two GT35R's or so, you can still get a reliable 700-800 to the wheels.
With the stock twins, you really are not going to see much more than 550-600 WHP and the backpressure will be sky high.
This is pretty much what I was going to do before the Honda deal got dropped in my lap. Except I was going to use the SC300 coupe body and put a big single turbo on it. Good for 750-800HP and run in F/BGC against a 200MPH record. I still might, I love the looks of the SC300.
