Posted: Wed May 31, 2006 5:44 am
Excellent! I love it! Thanks...
We do hear back from tuners fairly often about how surprised they were after tuning cars with our downpipe on them. The divorced wastegate design works extremely well, and it's very apparent to tuners in the ease of tuning the boost control, the great boost/throttle response, and the very strong power/tq output. Most tuners say that tuning the boost curve via wastegate duty cycles throughout the powerband takes longer than tuning the A/F curves and the timing curves. With our downpipe there is just much less tinkering necessary as the atmosphere into which the wastegate vents is always constant. With a bellmouth, it's constantly changing with the amount of exhaust coming out of the turbine outlet, so the wastegate vents differently depending on load and rpm, etc. A couple tuners said it was like tuning with an MBC in terms of simplicity and awesome response. So.... we'll take it
^^^ before I move on, btw, if you read Corky Bell's book, Maximum Boost, he talks about wastegates and very bluntly mentions the power and tunability benefits of separating the wastegate gasses as much as possible. Our downpipe is pretty much the extent of what you can do with an internally-gated turbo. The place you don't want turbulence is right before or right after the turbine... so moving the WG pipe down towards the bottom of the downpipe is far enough down the exhaust stream that it doesn't affect the function of the turbo, turbine outlet, or wastegate at that point.
So ANYWAY... it sounds a lot like our existing downpipe would work and we'd just have to do a custom midpipe to work on the BC-BF Legacy and allow the use of a stock-length catback. We could also do a full-length downpipe if you guys decided you didn't want it modular. If people are on a budget, we can get it made with a bellmouth and full length at a very good price.
Basically, y'all will have to come to a general consensus on what style you would like. I would want to get my hands on a stock BC-BF downpipe with midpipe attached so we can make an accurate JIG from which to build the production ones.
Our WRX downpipe is available with an auxiliary O2 bung in it, but the stock WRX bung is in the midpipe by the cat. If you guys needed two in the downpipe and none in the midpipe, that's not a problem. It'll all just have to get figured out.
For simplicity's sake I'd almost just want to have a full length bellmouth made. We can get them in that style and thermal barrier coat them and have them at a very very competitive price. I do sort of feel that nearly everyone will have to get a custom catback made to flow the kind of exhaust you might be making (as I have done a couple times in my EJ20-swapped '98 Legacy GT) so having the downpipe/midpipe end exactly where the stock one does doesn't really seem like a big issue, honestly. Everyone's sure the WRX ones actually need to be changed beyond moving O2 bungs, etc?
Jeremy
btw -- this is how our downpipe seals up with nearly all of the bolt-on turbos for our cars. It's really the design if you want the least possible amount of turbulence behind the turbine outlet. This picture is a VF39 turbine housing and you're looking from the side where the downpipe would normally be... this is just a mock-up flange with no pipe attached. You can see why we go from 2.5" smoothly to 3"... 2.5" matches the curvature of bolt-on turbos perfectly and is much larger than the actual turbine diameter of even the largest stock-location turbos.
...and a picture from Hugh MacInnes' Turbochargers just cuz
