Quote: Originally Posted by
Checksum 
I ran a 11.56 open and a 11.7 closed. Same night, same tune, same 1.67 60'
Open I made 30psi, closed I only made 27-28. The only reason I closed it up was because at PIR you can't run past 10pm if you are above 90db... which I was closed too, but oh well. The reason 8 out of 10 of the fastest cars run a mid length system is because of twin scroll turbo's and their need for a little bit of back pressure to keep the pulses separate. Also, open raises your egt a lot... not sure why, but it does.
I think a reason people loose power on open dump with stock turbo is you are spinning the turbo up too soon. You get the spike sooner then with the stocker its all down hill. who knows.
Thanks Eric for the input but wanted to point out a few things.
You lost boost becaue why? Your tune was for the open cut out not closed (expecting this to drop your power levels and times at the track).
Now with that said a more equal compairison would have been to have a mid pipe dump system on your car tune it for that then open the dump. Then we could see that the dump kills some power.... get my point. The car was tuned for the open dump and when you close it you have to go through what? An exhaust system, if it had been a mid pipe dump system and it lost power, I would say "right on" because that would be real world testing. Maybe you are running a mid pipe dump system, no idea.
The twin scroll is true to a point. The standard non twin scroll turbos also respond very well to mid pipe dump systems. The SST really wakes up if you have a dump in the DP but you get ever better results if you put a mid pipe dump system on a car with one. I can not speak for all the different turbo set ups on the market just what I have worked with and what we have found with our set ups is that a mid pipe system works much better then a dump DP.
