Exactly, sound difference is AMAZING (depending on catback) I heard an FD with a pettit high flow cat and an HKS high flow (straight through) exhaust that sounded awsome. Not discustingly loud like my midpipe!

 

I dynoed my car with a mid pipe and with a HFC , I ended up with just over 30 HP difference, 34 to be exact. As I said, the sound is not an issue.

In the morning when I start my car the smell is pretty bad, I cant deny that.

 

that much of a power difference from high flow cat to a midpipe... was that wheel hp? also what kind of high flow cat were you using?

 

That HP difference sounds like he was using a Midas HF cat, either that or it is a 1000 HP car. Heck, on a stock or near sock car you dont get anywhere near 30rwhp difference going from stock cat to MP. Your test HF must have been seriously plugged up.

 

It was an rx7fashion Highflow cat. Ok, it was 32 HP, I feel so cheap now. Here is my thread from like forever ago.

https://www.rx7club.com/showthread.p...highlight=dyno

 

No, it was less than 4 months old. Its not plugged up. with the HFC I made 266 rwhp @ 12 psi.

 

An FD with any CB will be fairly quiet at idle. At idle, it doesnt matter what is in front of it.

The volume comes when you accelerate. A midpipe will be very loud regardless of which CB you use. A resonated MP will help a little, but it will still be very loud. If you don't want a loud car, don't get a midpipe. Simple as that!

 

Try 25 to 30 rwhp. I dynoed one. It had a 3 month old Bonez hiflow vs a borla and we saw a 31 rwhp difference. There was nothing wrong with the hi-flow cat, it was working perfect at the time. You will see a drop in hp down lower though, but the car will be faster overall.

 

I have the RB catback, and the RX7 Store Resonated Midpipe. I think this is about the best you can do with respect to sound. That is, short of keeping it stock.

When I switched out from a straight midpipe to the Rx7 store one, I got a 20DB drop in sound. Here is the link to the thread.

https://www.rx7club.com/showthread.p...hreadid=242372

The only thing you will probably never get rid of is the smell. If you have a sensitive nose, keep the cat.

And Tom I do not know where you got your information, but a resonated midpipe, will drop you only 2-4RWHP, if any. A high flow cat, will drop you upwards of 25-35 RWHP. Thats a proven fact.

 

I could have sworn I read numerous dyno comparisons between high flow cats and mid pipes that showed only single digit HP differences. I guess I was just remembering something wrong.

 

maybe it was highflow cat VS stock muffler. I think the difference is minimal there.

Also, if you have a restrictive intake and stock precat and or stock catback, I think the midpipe would give very little if any HP increase.

 

i never thought that a high flow cat lost that much over a midpipe... well so long pettit hi flow... i will probably buy the rx7 store resonated midpipe, is that a good choice? i dont mind a loud exhaust i just dont like droning when you are cruising or driving normal.. i have a blitz nur spec exhaust..

 

My 2 cents:
A friends FD with a large streetport, downpipe, midpipe, and racing beat dual tip catback is much quieter than my FD with a small streetport, downpipe, stock cat (with 80K miles), and the newer M2 Dual tip catback.

Any thoughts on this?

Petros

 

Don't mess around with the resonated midpipe. Go all the way, and use the straight-through midpipe

I estimate ~30 hp increase going from HFC to straight-throught MP (conservative estimate). When the motor is in vacuum, the sound is not bad at all, get on the boost, and it is deafening, no doubt

 

His may be quieter at idle. No way it's quieter when accelerating.

 

Adam,

I know you know Tyler (rynberg). He has been in my car many, many times. Ask him how quit my car is accelerating. Under 4500 RPM I notice no difference in sound between my HFC or MID PIPE.

 

zerobanger do you have a straight midpipe?

 

its not resonated. just a standard M2/Rx-7fasion midpipe. As for its sexual preference I never asked, none of my business.

 

I didn't know that you knew that I know Tyler. Now I know. Does Tyler know anything about these cars??

We know that restriction in an exhaust system increases with flow. At idle, very little air is passing thru the system, so it doesn't get "backed up". As we increase flow, restrictive elements become much more important. At under 4500 rpm, restriction may not be that different in a high flow cat than a midpipe. That may be why you can't notice much difference in volume. I would bet that the difference is more apparent to someone behind the car, rather than in it.

It sounds like the difference over 4500 rpm is significant. That's what I would expect.

 

At WOT his car is extremely loud. At idle and maybe even just cruising, he is noticably quieter.

Petros

 

Zero's car is a bit louder at idle than mine -- from OUTSIDE the car. Inside, it doesn't seem significantly louder. The same goes for under 4500 rpm driving. I would say that his car is a bit louder on the inside than mine after 4500 rpm. It's definitely louder above 4500 rpm on the OUTSIDE of the car.... However, I'm still running the stock cat and not a hi-flow.

Also, the tuning of the car does have an effect on exhaust tone and loudness. Cars with slightly different timing/air fuel mixtures will sound different from each other, even with the exact same exhaust components.

 

Bingo . A member on the board. (cant remember his moniker) ran his 7 on a dyno with the HF, and with just a straight pipe, and this is exactly what happens.

With a cat you actually pick up torque down low, but lose horsepower up top. With a straight pipe though, he gained 40HP at the upper RPM's.

 

#3 is what I run with.

I was running a straight mid-pipe but it was too loud. i.e. the neighbors were complaining.

Adding the Borla XR-1 16 inch oval sportsman made a noticeable difference at idle, light throttle.

WOT is a bit quieter, but still loud enough to make people swerve away if I am next to them and stomp on the throttle.

thesaint

p.s. as stated, if things are quiet your catback is restrictive, or your reference for what is quiet is much louder than what the majority consider quiet