Guack007

I have the tanabe 2.75 in DP and 3in with higflow cat waiting to be installed/tuned by dynoflash I think it should prove to be a good compromise in low end TQ and smoothness/ vs higher peak HP.
I want some improved low end smooothness because its my daily driver and it makes the clutch easier to engage at low RPMs (less wear).

EvOLcHiN

Would a 3 inch high flow cat be bad in between the HKS dp and catback? (Since both are less than 3 inches?) Which cat would work best with the HKS exhaust parts? 3", <3", or stock?

NvsEvo

iTrader: (1)

Helix is the way to go for me...... very reliable and great power gains......and not to mention its very cheap comparing to other brand......my .02

marksae

iTrader: (12)

I just installed my HKS downpipe this past weekend. While the downpipe was off, I measured the inlet diameter of the stock cat and it's about 2.5", which matches the downpipe perfectly. I also have a hi-power cat-back. I believe HKS designed the downpipe to work perfectly with the stock cat. Some folks have used a 3" high-flow cat or test pipe and say it works fine. I don't like the idea of going from small to big and back to small. I like smooth transitions.

Ken8masters

Ultimate Racing makes a great cat delete pipe. They make a 3" and 2.5" pipe that gurantees no CEL. It works great. I installed mine with the CEL still on from a gutted stock cat O2 trigger and the CEL turned its self off after a few days. I went with the 3" test-pipe with 2 3" gaskets and it came out to about $102 shipped to Chicago. I highly reccomend this pipe if you're looking to get rid of your cat.

BTW, this is the pipe that Al had suggested for me.

RMR 3" DP, UR 3" test-pipe, RMR 3" cat-back, RMR cone, AMS MBC @ 20PSI (soon to be replaced by Hallman Evo MBC due to massive spiking), and of course DynoFlash. This little puppy moves out.

I'm a 3" fan all the way. I'll take all I can get at top end due to the lagg from AWD.

David Buschur

iTrader: (53)

Bottom line, 2.75 or 3" are both too big if you are going to run into the stock cat, a 2.5" high flow cat or a 2.5" offroad pipe. The flow is going to be hurt with either one. You CANNOT run a larger diameter tube into a smaller diameter tube without hurting flow on an exhaust system.

The cost of both of these that you have listed above are quite a bit more than the parts we offer, heavier and with our design I am sure ours flow more.

Check it out on our website,

David Buschur
www.buschurracing.com

trinydex

iTrader: (12)

it really depends on what your end goals are. a 3" isn't always gonna be the best. if you want mid range torque a smaller system will give you more exhaust gas velocity and give you more torque. only problem with that is... you only get the torque until the diameter of the pipe can no longer sustain flow at high velocity in which case you get back pressure and power loss.

think about it this way. a 2.75 pipe is optimized to flow high velocity at mid rpm ranges but at higher rpms will "choke" and cause backpressure and weak top end. a full 3 would shift this optimized range up, but at lower rpms you'll get less fast more "stagnant" flow, hence a loss in torque.

if you want a bigger turbo you'll want to go 3" but if you're sticking to stock the top end is gonna be capped by the exhaust housing of the turbo and not your exhaust system.

if you want a lil more punch out of the spool you can hollow out your cat to about 2.75 inches and you'll have a full 2.75 to 3" system.

i do believe you mean that the turbo is so inefficient that it creates all the backpresure necessary. and you are right and wrong. torque and power is realised not when there is back pressure, but when exhaust gas velocity is high. take dp off... your exhaust gas velocity will go to **** because it's blowing right into open atmosphere and there's nothing to direct flow or otherwise which will give you a late spool and late torque and late power although the peak might be really good.

however with a bigger exhaust system your spool will get better. and the same can't be said for a smaller system becuase the less back pressure you have the more low end flow can be evacuated.

also keep in mind that people like hks build their exhausts for people running close to stock and they also value low end torque more than peak power.

a mere 7 foot pounds of torque could be magnified by a lot if other supporting mods are taken into consideration... we all know that mods build off each other, you need an orchestra of mods to get a fine running car.

also people keep commenting on the o2 housing, keep in mind that the size of our o2 housing is also gonna be effected by the fact that we have an integral wastegate. and also going bigger without having a bigger exhaust housing is almost as useless as just taking your whole dpback exhaust off. the point of going large exhaust is to one increase spool and two stay efficient for your turbo, most aftermarket turbos have an external wastegate and that makes room for a properly 3" exhaust output, hence the benefit of 3"dp.

stock o2 housing sucks not because of hte nature of the o2 housing, in fact buschur said it's very well made, it sucks because the exhaust side of the turbo sucks too.

David Buschur

iTrader: (53)

I started a thread on EVOM that is covering some dyno work we are currently doing.

Keep an eye on it because I am going to do some 2.5 vs. 3" downpipe testing so I can end all this once and for all.

David Buschur
www.buschurracing.com

hi_nrg_fizzix

David,
Will you be conducting your test with a stock cat? It would be interesting to see stock cat vs. 3" high flow cat.

Dboey

Hi,

The outer diameter of the HKS downpipe is 65mm and the inner daimeter is 62mm. It work fine with stock O2 housing of 58mm. However, if you intend to upgrade your O2 housing/turbo outlet to a biiger diameter like 65mm or 76mm, then you will have to replace your HKS downpipe.

hkfeet

iTrader: (20)

I have a hks dp now and I like it very much compared to my old BB 3" dp. Im just going to stick with my 2.5" hfc/testpipe > hks catback setup until I reach the limits to my stock turbo or even adding the 10.5 hotside.

David Buschur

iTrader: (53)

We did the testing with the stock cat vs. the 3" cat also. It is in that thread.

David Buschur
www.buschurracing.com

radbrakes

Any droning noises after you installed ur HKS dp? I just installed mine...and I can hear it slightly on full boost.......and sometimes real quick at low rpms...