Unbearably loud exhaust above 2.5k

[cw72]

I'm having a really odd problem but it's driving me nuts. So much so that highway driving is pretty much a no go because I'll go deaf.

Its a little difficult to explain so bear with me.

Bronco specs:
1990 Mustang 5.0/stock c4 w/rebuild/stock D20/4.56/40s

Driveability is fine, no other noises or problems as far as I can tell. Only code I get from the ECU is about it not being able to read the fuel pump because there's an aftermarket pump on the frame rail that's wired into a relay controlled by the key. (the fuel pump never ever stops running if the ignition is on, but I don't think that's causing any of this, its just a little annoying) and the c4 leaks, I think its from the gear selector.

It has a brand new Magnaflow Super Turbo on it, ruling out any muffler problems.

Main problem is the very loud air whooshing sound coming from the exhaust, it comes from the rear where the pipe exits. It starts around 2500 and really starts to get bad at 3k. Shouting at your passenger right next to you with the windows up and top on loud.

Also if I'm cruising at hwy speeds and put the pedal to the floor, the whoosh gets even louder but I hardly gain any speed, and the tach doesn't move any higher. (aftermarket sunpro)


I'm not sure if I'm looking at a motor problem here, transmission power delivery, or what but I'm completely stumped at this point. On the verge of taking it to a mustang performance shop to take a look at it. I bought the truck a few years ago and haven't had this problem until probably last summer or so.


Turning to you guys for a hand, I'm stumped. If anyone is near Denver and wants to hear it for themselves I'd be glad to drive it over for a listen.


Thanks in advance

[crawlercreations]

Is this a 2 into 1 type of muffler? I had the same thing with my 2 into 1 but I knew exactly what it was.... The single pipe exiting the muffler is too small. I had used what I had laying around for it which was 2" pipe. It screamed. Just a ton of wind/air rushing noise like you're describing. I changed it to 2.5" pipe and it's great now. Completely fixed the issue.

[cw72]

nope its 1 in 1 out. however its a 3" exit thats been necked down to a 2.5 tailpipe.

[crawlercreations]

nope its 1 in 1 out. however its a 3" exit thats been necked down to a 2.5 tailpipe.

That is likely your issue. 3" down to 2.5" is too big of a jump in size.

[cw72]

I wonder why it didn't do it before, unless I'm not remembering correctly.

Anybody have an exhaust bender?

[ZOSO]

Do you have a cat? I had that on my 79 and the cat was plugged.

[cw72]

So uh, I figured it out. Crawler got me thinking about the exhaust size and I went out to the truck to double check. Noticed for one that the clamp between the muffler/tailpipe was loose so I got that tightened up and when I went to the back of the truck I noticed that I had smashed the snot out of the tailpipe at the end. Grabbed a pipe wrench and went to work to make it sort of round again, and voila, she's way quieter.

Lesson for the day, don't turn your tailpipe into a kazoo and it won't make all that noise. I can't believe I didn't notice that before.

[Jesus_man]

That would do it! I would think 2.5 is plenty adequate for most SBF's.

I finally got tired of my exhaust getting smashed and ran it up high and thru the body to exit.

[Stubborn3]

That would do it! I would think 2.5 is plenty adequate for most SBF's.

I finally got tired of my exhaust getting smashed and ran it up high and thru the body to exit.

Not to hijack but I’d love to see how you did that as I’m considering I think something similar

[Jesus_man]

I don't have many great pictures, but here is a link for when it was installed after I put in my Atlas.

The drivers side comes off the shorty headers and goes forward and under the engine where there is a relief in the oil pan. Then it turns and goes towards the rear on the passenger side, grabbing the passenger side, then thru a Moroso Spiral Flow muffler, and then turns 90 out the side of the body.

Look at the last few pics on this page for an idea:
http://s8.photobucket.com/user/jesus_ma ... t=2&page=2

I had some of these exhaust rings made to make a clean exit from the body:
https://i8.photobucket.com/albums/a39/j ... 160093.jpg

I could take better pics if you want a better look.