What do you guys think the performance gain is when running open wastegate rather than running it back to the down pipe. I mean its sounds nutz to me but then again its erking when the chicks are like wtf your engine is breaking.

 

There's a few things to consider when doing this.

a. Has this been discussed already? Find out using the search function.
b. Where you route the w/g dump into the exhaust, and how smooth the merging of the w/g and exhaust is (no 90 degree bends).

I think the general consensus is "not much" power is lost. It's worth it to me to plumb the w/g into the exhaust....otherwise it sounds like a lawnmower on nitrous with no muffler. With it plumbed, all you get is that nice viscious turbo spool noise going on.

 

Other considerations:

Is the car driven on the street? If so venting the exhaust is illegal for several reasons.

Properly designed, I do not see why you would lose any power from doing the right thing and running the dumptube back into the exhaust. At least then you could take advantage of the scavenging effect, assuming your exhaust system is properly tuned.