Do I have the right exhaust for my MY93 WRX? I have a full 3" bore system waiting to be fitted, I was told the system came off a 98 turbo but I dont know who makes it. The flange on the decat downpipe is half blanked, is this right?

 

Do you mean the section in front of the penny valve is a flat plate but open in front of the exhaust turbine wheel?
That is the design of some down pipes. They are OK for modest power applications.

 

Yeah that sounds about right, I wont be fitting it myself though so haven't looked at the turbo side. What is the penny valve for by the way?

 

Penny valve is the wastegate - used to bypass exhaust gasses away from the turbo once you've hit target boost. I anything but stock turbo I wouldn't recommend this half blanked d/p config - it *can* lead to boost creep in some applications.

Richard

 

Ok so not ideal but should be ok with my stock TD05 then yeah? What is boost creep?

 

Where there isn't a good enough flow path into and out of the wastegate so it struggles to open correctly, or stay open, leading to exhaust flow bypassing the wastegate, over-driving the turbine and overboosting.

 

Refering to the top pipe (decat):
My old 3'' (maybe 5 years + old) made 380 bhp on a slightly modded Sti v3.
Thisdesign is a bit of a half way house design not seen much now.
The Cat pipe is an equally old Jap pipe.
The cheap new de-cat's on ebay are blank waste gate (penny valve) as this design makes it much cheaper to make.

Graham

 

Thanks for your help

Mine basically looks like your decat pipe except that there is no oval cut through leading to the smaller pipe section welded on the side. I'm not looking for major power hikes, I'll be happy with just a small increase. I just wanted to be sure that having half the flange blanked wasn't going to damage the turbo in anyway. I got worried after I read an ad on ebay for a decat pipe that stated that a half blanked flange was designed for the non turbo car. I assumed that was wrong anyway though as I'd imagine the flange on a non turbo would be a different shape anyway.

 

The stock inpreza turbo flange is blank across the waste gate, and the Sti V3 makes 280 ish bhp with that design.

I would buy a true open kneck design in 2.5'' dia for a nice mild tune wit a good centre and back box. I read the Revolution design is sound and quiet to.

Graham