Is 3.5" exhaust much quieter than 4"?
10-24-12, 05:24 PM
#1
Is 3.5" exhaust much quieter than 4"?
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.
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.
10-24-12, 05:31 PM
#2
F'n Newbie...
iTrader: (6)
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.
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.
10-24-12, 10:19 PM
#3
https://www.rx7club.com/2nd-generati...3/#post6361193
pipe dia is the easiest way to dictate pitch. what you really need to do is increase the volume of the pipe to slow down the air and sound traveling through it. the thickness of the pipe also plays a part in tone and volume. the thicker the pipe the less it will vibrate. this will send more of a crisp tone out the tip. the thinner the pipe, the more it will vibrate and dissapate the sound through the the system.
TR
TR
10-25-12, 10:44 AM
#4
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!
10-25-12, 01:38 PM
#6
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.
SMB (what RB uses), if not, Borla worked pretty good on my previous exhaust.
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10-26-12, 06:22 AM
#8
10-26-12, 06:43 AM
#9
Got tired of dealing with the cops, and went with smaller mufflers.
10-26-12, 12:03 PM
#10
thewird
10-26-12, 12:26 PM
#11
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" oval to the back as well and now its perfect. I left the raw tip, its not great, but its not terrible looks wise...
thewird
thewird
Also, for the record...I think the raw tip looks awesome.
10-26-12, 05:10 PM
#16
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
thewird
11-01-12, 01:41 PM
#17
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.
11-02-12, 07:27 AM
#19
F'n Newbie...
iTrader: (6)
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..
11-02-12, 11:41 AM
#22
F'n Newbie...
iTrader: (6)
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:
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:
11-02-12, 01:25 PM
#23
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:
PFS Fenda's RX-7 dyno run - YouTube
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:
PFS Fenda's RX-7 dyno run - YouTube
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.
11-02-12, 04:21 PM
#24
F'n Newbie...
iTrader: (6)
Originally Posted by smg944
the mufflers you have on the 4" are the straight through?
Originally Posted by smg944
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.
