i am out of money. i just ordered my last piece, a random tech hi flow cat, to complete my exhaust setup. i did not make enough power with an HKS hipower and a stock cat on my greddy turbo, so i went back to my invidia and got this HFC.

i noticed an immediate difference with the invidia, but now the car is leaning out and needs to be retuned because it is holding boost much better. HOWEVER, upon installation of my HFC i realized that the cat piping is 70mm while the invidia is 60 (v1).

i am aware that stepping down is generally a no no, so now i ask whats better - stock cat to invidia, or the larger HFC? what do you think would be better for an FI car?

 

you should search greddy, a lot of the recent threads have ended up talking about exhaust/cat sizing. There are many setups that work, biggest problem is creating too much flow and experiencing boost creep since the kit is internally wastegated.

 

i have been keeping up with all the greddy creep issues.

so far it seems a 70mm catback with a test pipe is the absolute limit before creeping will occur, but i'm sure mileage will vary on that. i'm using a 60mm catback and a HFC, so i'm not worried about creeping.

my main concern is the sizing of my HFC - 70mm. i'm trying to see if having a 70mm hfc mated to a 60mm catback would be beneficial or a bust. if stepping down in piping size negates the performance advantages of a HFC in the first place, i'll take it off and sell it.

 

you are not going to loose performance.

 

in this case, i doubt having a 70mm HFC is going to be very bad. You are technically stepped up then down again, since the downpipe is smaller than 70mm. People are using a testpipe w/ hks exhaust, which is probably similar in flow to your 70mm HFC and 60mm catback.

 

i am just torn as to whether or not i should keep it on or sell it. if it doesnt prove useful i could certainly do without the extra noise!

 

well, the HFC with the invidia is going to make more power than the stock cat with invidia. The HFC isn't so big that the step down is going to make the car perform worse than the stock cat. Hope that helps your decision.

The difference in power from a stock cat to the HFC can only be measured by a dyno, so only you can find out if the difference is worth it. For example, if the HFC makes 10more whp than the stock cat, is it worth it to you, to have the extra noise for the extra 10whp? If not, sell the HFC, pocket the extra money, and have a quieter, less powerful car.

I had an 80mm catback on my car that was really loud, but i wanted a quieter car, so i put a 70mm catback. I'm making less horsepower now, but it's not a huge difference--the huge difference was in the sound levels since my ears don't ring anymore!

 

thanks very much for the well thought out response!

i'm not so concerned about a small power loss, i think i am just being overly cautious with my power expectations now. i dyno'd very low with my HKS catback (227 on the basemap, then 254 tuned) and i was only seeing like 6psi at redline. once i switched over to the invidia i noticed an IMMEDIATE difference in my boost curve, so i'm just trying to prepare for my next tuning session.

i think i'm going to have the car tuned with the HFC on... that way if i decide to take it off and run with the stock cat again the car will just richen up a little bit. thats certainly a safer scenario than getting the car tuned with the stock cat, and then having the car lean out and need to be tuned again if i throw the HFC back on.

thanks again

 

254 tuned w/ the hks isn't bad since the hks is such a restrictive system. that plan for dynoing w/ the HFC sounds good. post up and let us know the results.

 

254?? we have dyno many NA s2000 in the 210-220 range - this is FI - should it not be adding 85-100 hp for a turbo setup -