I've already got the 3" cat-back exhaust - and I intend to keep the stock 2.5" cat for the next year or two - so here's the downpipe question:

Is it a good idea to replace the stock downpipe with either a 2.75" or 3" downpipe since I'm keeping the stock 2.5" cat - or will this combination result in some undesired results?

And if it is a good move then what would be a better choice - the 2.75" or 3" downpipe (given the stock cat)?

RallySportDirect has a good deal with free shipping on a Perrin 3" downpipe, but Perrin recommends replacing a cross-brace as well for pipe clearance which brings the total cost up to ~$450 is this worth the gains of a 3" pipe (with a stock cat)?

 

I think you wouldnt have any problems. I think you would see a quicker turbo spool. Thats what i got out of mine. The stock cat should be fine. I dont think you should see any negative results. If you dont mind, why do you want to retain the stock cat?

 

I've only got 1500 miles on the car so I'm trying to keep the visible mods to a minimum to avoid warranty issues with the dealer - I don't really want to touch any of the smog equipment and risk a CEL or find out I've voided my warranty.

Although I do see that Buscher has a 3" downpipe (that they claim doesn't require replacing the cross-brace) with a 3" high-flow cat which would come out at about $450 plus shipping.....decisions, decisions....

 

I know this question is kind of off topic, but will the Buschur High Flow Cat bolt to a HKS Hi-Power Catback?

 

If you're not replacing the cat, I'd just wait. Things might match up, but they won't be 100% perfect.

 

I got an HKS downpipe(2.6") with stock cat and HKS hiper exhaust. quick turbo spool up than stock set-up.

 

If you're certain you're going to stick with the factory cat, I'd recommend going with a 2.5" Downpipe. We have a nice one in stock which will bolt to your stock cat. As well, we eliminate the factory donut gasket (big restriction there), and include a double braided stainless steel flex section. At $275, I think it's a great deal. Let me know if you're interested.

Darryl

 

Some tuners reccomend a 2.75 inch downpipe if you are sticking with the stock turbo. Faster turbo spool, good power gain, no loss of torque. Works is one of those tuners. I have their 2.75 inch downpipe. It bolts right up to the stock cat, works great.

 

Ditto. The HKS downpipe matches up w/ the stock cat perfectly. I measured the stock cat inlet diameter and it's right around 2.5-2.6". Can't beat the factory like fit and the high quality of the HKS parts.

 

i you should go with the 2.5in downpipe, so it's the same diameter as the stock cat