Inliners International Forums General Discussion Engines exhaust note

I'm running a mildly hopped up 250 with a T-5 in a '52 chev H.T. I have headers running into 2inch pipe to flow master 50's.
My problem is a thrumming sound that permiates the car when I shift to 5th gear at highway speeds. This drone is very annoying on long trips. I'm thinking of going to a quieter muffler. I've been reading a lot of previous posts that mention an H pipe. Could this cure my problem?
If not, could anyone suggest a good quieter muffler?
Thanks, Al

Where does your exhaust exit. Under the car?
An "H" pipe will help.
It seems to me for the most part,Flomasters are not really quiet mufflers.
If you want a really quiet muffler,some sort of Hemi long type muffler. Not sure of the brands.
Just remember ,the longer the muffler,usually will be the quiter muffler.

MBHD

The exhaust exits at the rear bumper. I've heard of Magna Flow mufflers. Are they any quieter?
Thanks, Al

Those are pretty loud also.
Try the "H" pipe,& if it's still loud,then change your mufflers.
I remember in an old Clifford catalog,basically saying,it will be too loud running dual exhaust on the street w/turbo type mufflers.
Stating to be quiter,you should run a single exhaust system.
But if you are insisting running dual exhaust,use a Hemi long type muffler.

My 250 6 w/Clifford dual 2" exhaust and turbo mufflers was pretty loud also.

MBHD

Hi, Al. I've been running a Flowmaster 50 series, 2" inlet and outlet, on my Nissan truck with Pacesetter headers and it's so quiet I can hardly hear the exhaust note unless I have a window down. It sounds like you might have some exhaust vibration being transmitted into the car body or frame. Is your whole exhaust system isolated from the body or chassis? If there's a solid connection anywhere (i.e.,exhaust pipe welded to any part of the frame or floor pan), it transmits sound waves directly into the car interior and will darn near drive you nuts. Make sure that all of your exhaust system is isolated with rubber hangers and that there's no metat to metal contact anywhere. An H pipe certainly won't hurt, and might even give you a smidge more torque.

Al, I'm glad you asked this question!! I too have the same dilemma. But it started out with glasspacks. Now I have two Thrush Turbos (Cheapies) and it quieted it down tremendously. But my dilemma is it doesn't sound like I want it to. I was hoping to put in the Flowmaster 50s (knowing they are quieter than the 40s) but now maybe not. I know you like the sound your exhaust gives, but just too loud inside, right? Just curious, how well insulated is your interior? I was thinking of redoing mine to see if it would help. Just a thought.

The longer MAgnaFlow mufflers are very quiet. Wen we did dyno testing of mufflers and found that the Maganflow mufflers also increased some HP. When we put the Flowmasters on we lost HP. They just do a beter job of marketing. Last year I called Flowmaster to get the CFM rating on their mufflers and they told me "that they don't rate them that way", I am not sure what other way would be relevant. Maybe they have changed since, but I have never checked. Tom Hand wrote a book on building Pontiac's for the street and strip. Great book. He also tested 54 different mufflers on the flow bench, engine stand (with professional noise measurements) and at the drag strip. He found the Flowmasters one of the least desirable mufflers available. Kinda backs up my experience on the dyno.

If you are just trying to eliminate the drone at cruise and like the sound you have now here are a few things you can try.

Make sure the trunk seals well, any holes in the floor or leaks in the trunk lid gasket will make the drone louder.

If you don't have sound deadening, get some (I have been using the foil faced bubble wrap from Home Depot and Lowes, cheap, better stuff is available, but I gotta start somewhere and for what it costs it works good enough).

If all that is good, try a different exhaust tip. We have pencil tips on one of our cars (FWIW 2 1/4") and we had to extend the pipe quite a ways past the back of the car to eliminate a resonance like you describe (you could try the same). A friend has a similar setup with what I call meat grinder megs. They are straight till about the last inch or so then flare out like the 'meat grinder' velocity stacks. It seems to do a better job getting the noise away from the car.

You could try a small glaspack just forward of the bumper as a resonator.

The H pipe will make it quieter, it will also take some of the rasp and rap away and make more of a gurgling sound.

I have Dynomax super turbo mufflers on my A with a bent 8 in it (OT I know) they are quiet at cruise and have a nice tone when you blip the throttle (or are screaming up through the gears) and don't drone. We mounted them as far back in the pipe as we could.

Are you sure it's exhaust drone? I have a friend that chased an 'exhaust resonance' problem for over a year, before he figured out it was the intake that was droning (not too likely in what you describe, but woth checking out).


This is not conclusive or end all be all, and I'm no acoustical engineer. It's just stuff I have tried or seen/helped friends try.

Thanks for all your help so far. Yes I like the sound it gives going up and down through the gears but hate the drone at cruising speeds.
My car has some sound proofing under the rear seat and on the separater panel between the rear seat and the trunk. The trunk has new weather seals but no sound proofing on the floor. There is no extra sound proofing on the cabin floor and kickboard except for the carpeting and underlay. The exhaust is hung with rubber hangers and is not touching anything.
The note about a possible intake problem is interesting. I previously ran a Clifford four barrel intake which seemed much quieter than the Offy that I'm running now.
In any event, you all have given me some very good ideas to try.
I will post as I try the things you suggested.
Thanks again, Al

What kind of air filter are you running? I have a differernt friend (than the one that chased the opposite end of the car) that was trying to hop up a 6.2 diesel, he made a flat plate to replace his factory air filter lid. Turns out there is a harmonic (on the 6.2 anyway) right where it cruises that made the new lid reverberate loud enough I could hear it from behind his truck on the freeway. Yours doesn't sound like it's this loud but a different type of air filter might help (if it's the problem).

I'm running a pretty small air filter...a doughnut shape 6 and a half inches across, and about 4 inches high. This could be part of the problem.
I just ordered 2 Magnaflow mufflers. They are 18 inches long and 24 inches overall. These are the longest I could get that accepts a 2 inch pipe. They should fit as my Flowmasters are 17inches long and 23 inches overall. I hope that I will loose the drone. If not, I will try the H pipe. When they are installed in about 2 weeks, I will post again with the results.
Thanks, Al

I'd try some soumd deadener on the floor. I sounds like its some type of harmonics and floor sheet metal is vibrating somehow.

If the problem is only at cruising speed in 5th its because the engine revs are at the right frequency to set up a resonance in the exhaust. If so you should find that it will be the same in any gear a those revs with a constant throttle, but because you are accelerating though the band in the lower gears it is not a issue. Adding a couple of resanators will most likly help if not fix the ploblem. Take a look under any car on the street you will see two mufflers, usually the last one is a resonator to fix this same problem.

Pete

Well I finally swapped out my Flowmaster 50's for Magnaflows part #11254. Big difference. The exhaust note is more mellow, but I still get that unmistakable 6 cylinder bark. I no longer get the drone at highway speeds in 5th.
I'll miss the rumble at idle and the heavy rap on excelleration, but I will not miss the drone.
In my opinion, the Magnaflow is much more suited to a daily driver. The Flowmasters were a lot of fun but the noise drove me crazy after a while.
Al

Somebody needs to write a book about this stuff, but maybe it's too complicated and the people who know consider it a trade secret. I travel and rent cars a lot. It amazes me the difference between manufacturers. Some (like Dodge) seem to be able to make the base engine sound really good (even if it doesn't go) and others (like Ford), must save the good vibes for top end mustangs. I know BMW actually has some one in charge of "sounds" and is responsible for everything form the exhaust note to the "thunk" when you close the door. It seems like a lot can be done if you just keep trying.

Leif