How much louder is a hi-flow cat than the regular stock cat?
 

I would like to upgrade to a hi-flow cat someday after getting the stock ECU replaced. Anybody have a good idea how much louder it is?

Thanks!

Depends on the CB you have it mounted with. It's definitely louder any way you look at it, but not obnoxiously loud like a MP. And not nearly as smelly, either. (of course, it won't have the top end of a MP, but I'd rather not have to put up with the smell of hydrocarbons)

dont mean to hijack the thread but isnt a high flow cat basicly a stock cat with bigger holes around it (i mean from the front and out the back, like a 3" pipe?)

I have an N-tech hi-flow cat. It was noticeably louder than my stock cat. But it was well worth it. You could really feel the hp that was freed up.

Now that I got that smog issue out of the way...I am going to try out a mid-pipe. I bought one off ebay and it arrived today. Woo-hoo. I'm kinda worried that my car is going to be obnoxiously loud. I'll report back.

no difference...a midpipe on the other hand...

I noticed a difference... a little more throaty and laoder at WOT.

Maybe in your case, but I noticed that the N-Tech hi-flo is definitely louder than the stock cat, especially when the secondary turbo came online. As jpandes states, it also resulted in a definite increase in power, especially in the midrange.

i've got the pettit high flow cat with an HKS high flow exhaust. with the exhaust and an open element intake, there was a HUGH power difference at mid and higher RPMs from stock!

the second turbo kicks in and the tires start spinnin! I LOVE IT!!

my 1st 3rd gen had a midpipe... LOUD... ANNOYING LOUD!

HF cat is perfect on the sound level with a straight through exhaust (HKS)...

final conclusion...sounds mean as hell but is bearable to drive... no stink too!

Mine was a good bit louder than stock but not like a midpipe. It depends on your other mods though. I have before/after dyno graphs on my site. They were done within an hour of each other. I got 10 hp across the board.

I have down pipe, high flow, and Racing Beat cat-back. In my efforts to pass emissions I put the stock cat back on and OMG is it quieter!!! Noise volume at idle sounds just like stock and getting on it is not a whole lot louder. The stock cat makes things about 1/2 the volume as with the high flow. It feels seriously slower too, I bet I lost 25 HP by going back to the stock cat.

My car definitely got louder but it wasn't too bad. I had the M2 dualtip exhaust which is pretty quiet to begin with. I don't think it makes the car obnoxious. And as mentioned above it made a noticeable difference in power. Overall I think it is worth the little bit of extra noise.

ITS SMELLIER! you have to love that lawnmower odor.

I have a downpipe, RB dual tip exhaust with a power FC. If I put a midpipe on myself should I have the PFC tuned again? Will it run rich?

Thanks,
Joseph
'94 Black & Tan (Soon to be Black & Black)

Guys, is that true? Does a hi-flow cat cause odor? I thought just midpipes would cause odor. With my DP and mufferless catback I don't smell anything, and that's with the car sitting up on jacks running in my garage.

Will adding a hi-flow to this setup make my car smell?

Thanks for the replies!

I had the bonez hiflow cat from rp and it didn't smell any more or sound any louder than my stock one. Maybe a bit at WOT. Well at first there was a sulfur or firecracker like smell (like any new exhaust component). My resonated midpipe is hell. My neighbor came over one night to complain that she could smell exhaust coming into her house. I smell like exhaust anywhere I go. The bumper is covered in soot. I don't have an airpump though so...

what are the options for HF cats? i know of n-tech, and pettit.... .are there others?

also who likes what cat better, and any oppinions on what works "best" thanks

I know the boyz at Gotham Racing (www.gothamracing.com) also have one for sale.

I just bought the Gotham Racing one & have a couple of quetions. Will it work with a stock catback? & will I need to get an upgraded ECU to use it with my Apexi intake & M2 downpipe?

You probably will go over 10 psi with that setup, which mean either a boost controller or an upgraded ECU, yes.

Only on start/warm-up, otherwise it functions just like the stock cat once the catalyzer has "lit off". Once you get rid of the pre-cat, you will always get some odor on startup, stock main cat or not.

Thanks for the replies!

It's strange though, I can detect no noticable "exhaust" smell on startup with my DP on there, and this is with the car in the garage, too. Hmm, that's a good thing anyway so never mind... :)

gentleman, will a high-flow cat still allow for passage of emissions (as an approximate statement across all states).

also, can I have suggestions on the most economical brand/piece. For once I am strapped for $$, but since my car is being done now I may throw this in if it will pass emissions and not cost much.

Well, I have a mild streetport, DP, and straight pipe. Stock muffler.


It really is not THAT loud at WOT. IT has a nice deep thoathy rumble but when I stand behind the car when it's idleing... Good lord lord! The freaking fumes coming out of that thing makes my eyes water.

I think that the loudness depends on your cat-back.

A high flow will pass emissions. I have just in the last few days been struggling with emissions and swapped out my high flow for the stock. It made no noticable difference in tested emissions, only difference was sound and about 25HP.

Most HF cats should be very comparable in both price and performance. Get whatever is cheapest as long as it isnt some off the wall brand you find on ebay for $20 because then it probably wont fit right.

Thank you for the info Tom