[max boost]

Originally Posted by teknochild

how much then did it actually add?

never dynoed but the butt dyno says at least 50rwhp....

[max boost]

Originally Posted by catm3

There would be a pretty good gain, particularly with the Xede+ race map. Exhaust backpressure + turbo = bad.

The pressure differential helps spool the turbo up, so the cutouts will increase that differential. The difference would be very noticeable on a high-output setup like the C5 of Maxboost.

true

[BoostedBMW]

With all that rice debate crap aside as far as sound goes , those QTP units are total garbage. If you are interested in going with something like that then go with a VES system from ATP turbo. It has no crappy little motors that will burn out in a week or 10 seconds if you hold the toggle for too long (which you never know exactly when its fully open or closed), instead it uses a wastegate where you will give it a vac line and when you boost your car it will open the valve so you will have no exhaust when you need it. This is not for everyone, but if I was looking for an exhaust cutout this would definitely be what I would go with. Here is some more info on it...

http://www.atpturbo.com/root/releases/release091004.htm

[Ultimate Racing]

Allow me to throw in my 2 cents.

Electronic exhaust cut outs are prone to electrical failure, and leaks! We have played with these and the motors just don't last. The ones that lasted more than a season ended up leaking so much it just sounded like a rusted hole in the exhaust.

ATP's unit also does not work very well. First off it is the most overly built cut out I have ever seen. The thing must way a good 10 lbs. It's a good idea, but does not perform. You would think that it'd go wide open under boost (by the way is set at 15psi before it opens!) but in reality it actually only cracks open about 15-20% MAX. Again, it's a good idea, but it's very difficult to find an actuator with a good amount of arm travel to open a throttle plate fully, and close it.

Darryl

[Terry335]

I've always used manual cutouts in the past, but couldn't one rig up a couple of large wastegates on the down pipe? Seems like a reliable way to reduce backpressure under boost when wanted.

[Ultimate Racing]

Originally Posted by Terry Burger

I've always used manual cutouts in the past, but couldn't one rig up a couple of large wastegates on the down pipe? Seems like a reliable way to reduce backpressure under boost when wanted.

I've done this on my own car (non-BMW). It's expensive, but definitely works. I would say a tad bit laggier than a full exhaust though, as you're running through the stock cat-back until you reach wastegate spring pressure.

Darryl
www.ultimate-racing.com

[Corey]

Originally Posted by teknochild

i thought backpressure was never good for modern cars?

i wonder how fast you would get pulled over if you pulled this crap on the street

Back pressure itself really isn't good for any cars. In a turbocharged car the turbo causes a ton of backpressure as it is, when it comes to your exhaust bigger is better (reasonably speaking). For naturally aspirated cars it's a little more complicated. A properly sized exhaust will create a scavenging effect that is beneficial. You would lose it with an exhaust that's too large because the exhaust gas's velocity would fall, and one that's too small would simply restrict the engine. So you want to choose an exhaust that is properly sized so that it will keep the exhaust's velocity high with minimal restriction. Here's some more info if anyone is interested:

In most naturally aspirated applications, the intake valve is timed to open a few degrees before the piston reaches TDC on the exhaust stroke. When the piston reaches TDC, both exhaust and intake valves are open, which results in valve timing "overlap." The mild vacuum created by the pulse of exhaust gas exiting the exhaust manifold and header pipe will accelerate the air/fuel mixture entering the cylinder. This acceleration effect is called exhaust scavenging and is used to a great effect in naturally aspirated engine designs.

When choosing a performance header, it's important to understand that larger tube diameters are effective only if an engine is highly modified. Smaller tube diameters increase the scavenge effect at lower engine speeds by maintaining high exhaust gas velocities through the header pipe. Increasing the pipe size merely slows the exhaust gas flow, which reduces the mid-range scavenging effect.

from http://www.tomorrowstechnician.com/tt/tt020526.htm