I currently have a full 4" exhaust system w/ randomtech high flow cat and wastegate dump....needless to say, it's quite loud. I am planning on redoing my turbo/manifold/wastegate setup and was going to keep the 4" downpipe, but do a 3.5" downpipe back and plumb the wastegates back in. However, after piecing together all the components for my new exhaust system I am finding that it is going to cost way more than I anticipated.

Has anyone ever had both a 3.5" and 4" exhaust on their RX-7 and can comment on the difference in volume between the two? If the difference isn't that great, I may just keep the 4" system, install a resonator, and plumb the wastegates.

 

When I had PFS build my current exhaust (it's 4" from the turbo back) I had initially asked for 3.5" piping. When I told Ray that I wanted the 3.5" exhaust because of the noise level he told me that there wasn't a significant difference between a 3.5" and 4" exhaust.

Now, he could have just been saying that in order to make the sale, but it could also be very true.

Unfortunately that is the only suggestion/advice I can offer, since I've never owned a 3.5" exhaust myself, only 3" exhausts and my 4" one.

 

https://www.rx7club.com/2nd-generati...3/#post6361193

 

The muffler itself will make the most impact. Listen to how often you can hear all those straight-pipe Honda's with 2-1/2" piping with a fart can. It's very hard to get a well performing exhaust system without shelling out a bit of money. Listen to factory LS9 Corvettes, they move like no other and still sound great!

 

Anyone have a recommendation for a good 4" muffler and resonator then?

Think I might keep my cat...add a resonator...and replace the muffler.

 

I am running a 4in DP/MP to a modified RB Y pipe to RB mufflers (I own a FC). I suggest leaving it as it is, but replace the catback with a SMB muffler of 3.5in or maybe even a RB 3 in. So my muffler recomendation would be:

SMB (what RB uses), if not, Borla worked pretty good on my previous exhaust.

 

I like my 4" multi-core Borla mufflers.

thewird

 

Is this what you have?

XR-1® Multi-core Racing Mufflers - BORLA® - The World's Most Winning Exhaust

 

Thats exactly what I had on my previous exhaust. I had a XR1 OVAL Borla as a silencer, and a single chinese catback. The borla works pretty good, but it was still loud. Loud enough to attract cops...

Got tired of dealing with the cops, and went with smaller mufflers.

 

That's because you used a cheapie as your catback. I made the same mistake originally. I had the 4" oval in the midsection and a 4 lbs $200 titanium muffler in the rear to save weight. It was loud at high RPM and it droned. I then added the 4" round canister to the back as well and now its perfect. I left the raw tip, its not great, but its not terrible looks wise...



thewird

 

So you are running two oval 4" XR-1 multi-cores? In that picture, your rear muffler looks round.

Also, for the record...I think the raw tip looks awesome.

 

I ment to say round oops. Oval in the mid section and round at the back.

thewird

 

Awesome thanks. I'm not sure if I can fit the oval in my mid section with my randomtech cat...if I can't I'll just have to find another shorter resonator or something.

 

Yah, its pretty damn big, takes up the whole space. How is that Random cat anyway? I always considered trying one of their race ones lol.

thewird

 

thewird, you have a video of your setup i want to hear it if you do? i am also setting up a going with a 4" exhaust i just would like to keep it quiet as possible also.

 

They're may be a video of it somewhere taken by someone but I don't know where lol. I've already sold a bunch of things (PowerFC, spark plugs, map sensor etc.) from my car since I'm going 20b so I can't fire it up and make a vid or I would.

thewird

 

Sorry, for the delayed response.

The Randomtech cat is nice. It isn't very big and and seems to flow very well (didn't quiet down my car at all). The biggest difference I have seen is that it doesn't smell as bad.

Also, can you get a picture of the underside of your car with the oval muffler? I really think I may try and go this route.

 

The aftermarket cats aren't ment to quiet the car down. Only the stock one does that. Car has been parked in my driveway since spring. I will take a picture when I finally move it to pull the engine.

thewird

 

I can post up some video of mine later if you'd like. I know I have some from when i was running an open wastegate (way too loud), I'm pretty sure i have some after it was recirculated too..

 

Cool that would be nice if you could put up a sound clip.

Thewird, going 20b huh. What subframe are you using? I've herd most put the nose much heavier .

 

.

 

I checked and I only have a sound clip of when I still had an open wastegate

This video is with a 4" MP and Catback, it also had two mufflers (one in MP, one in catback) in the 4" section. I still had a 3" DP with the open wastegate. I swapped to a 4" DP with the wastegate recirculated. The sound under partial throttle is the same for both, but obviously once the wastegate opens the video is MUCH louder than what you would expect. I would take another sound clip of my car now but it's down for a rebuild

Here ya go:

 

thanks for the vid. that is actually quieter then my car as it sits right now. i have a 3.5" dp , 3" mid with a magnaflow straight through muffler and a 3" mangaflow titanium cat back. so i am also on 2 mufflers.

the mufflers you have on the 4" are the straight through?

heres a vid of my current setup also with open gate which is going to be shut once i go 4" and have that extra flow.

 

I'm fairly certain you were also running more boost than me in your video though, I figure that (WG noise) may account for the difference in volume??

I think so, I can stick my head down there this weekend and confirm that though.

Yeah, having the open wastegate is fun for a little while, but I got tired of needing to carry a pair of shooting ears in my car all the time

 

Rotary's are just plain loud unless you restrict the heck out of em'. I gave up trying to slience my 7, besides it sounds great at full boost!