I used to have the HKS downpipe which if I recall was a 3 inch downpipe mated to the 2.5 inch stock catback (later partialy replaced with a 2.5 inch Prodrive axleback). I didn't have any problems with that setup.

I just ordered the Helix 3 inch downpipe and plan to mate with a 2.5 inch catback (again with the Prodrive axleback) on the STi. I don't expect any problems but I'll let you know if I do.

 

just because he upgrades his turbo doesn't mean he would have to sell them, but I do agree I think he should go with a utec, but thats just me, I like the extras from it and they arent that much more used, I got mine for $600 shipped

 

also does anyone know he quality of the hks downpipe bc its only like 200, would this work/fit on my 02 wrx with the borla 2.5" catback?

 

I've got a helix DP mated to a Apexi N1 which starts at 2.5 and turns into 3'', no problem. It's not really the pipe diameter its the flange size on the end of it. I'd just call someone that sells the DP you are looking into and ask them if they know if it will bolt up well with your catback. I personally wouldn't get a 2.5 if i had the choice, i thought mine was going to be a solid 3'' mandrel bent but it wasn't. Just depends how much you plan on doing to the car if it's even going to make a difference.

 

oh ya and will it be really loud?

 

Depends on the catback, i did my turboback and up-pipe all at once and it sounded mean and loud at first but now i think its just perfect. Its def. loud enough to be noticed, the sound is gorgeous, but i drive next to cops and they haven't said a thing so far. I think if you got the exhaust headers it would be pretty damn loud.

 

The HKS downpipe is great for the price but it's not an ideal design in theory. The problem with the downpipe is that it has a flat flange just like the OEM downpipe. Some people tend to make a big fuss over this but the reality is that you're not going to loose that much power if any using the stock TD04 or most of the VF series turbos with the HKS downpipe. The next best choice on a budget from what I found would be the Helix downpipe for under $300.00 shipped. The helix has a bellmouth design.

flat flange (HKS, stock, etc)


bell mouth (Helix, Invidia, TXS)


twin dump (Vishnu, Bosal, B&B, etc)

 

Actually, the header ive got didnt give it much volume... however, it did get louder with a bigger turbo believe it or not...

 

the header I think actually reduced some of the noise on mine, and its all but lost the burble (damn almost equal length, but thank you better response)

 

What headers did you two purchase if you don't mind me askin? I've seen some go from like 400-1500 bucks, the price range is insane in the membrane.