what makes an exhaust sound raspy?

[EuphoriousCntrl]

Serious question for everybody, I've been wondering if anyone knew what makes the raspy sound on exhaust. Whether startup, warming up, or just all the time. Is there certain physics behind the workings of this? Also, is there ways to fix this without replacing the stock exhaust? I'm just trying to understand why the hell this sound appears on many exhaust. TIY.

[Bears]

Good question... something I've always wondered as well Anybody?

[Chinny4290]

I would think it'd be from vibrations from different areas of the exhaust system, as if something's loose...what do you mean by raspy?

[RedBaron328]

I would assume that it just has to do with the flow of the piping. I believe it's UUC who offers the RASP-X which is an X pipe that eliminates the raspy sound from the S54. Maybe someone knows more and can add to this?

[BMWdisease]

Different exhausts can mask the level of “raspiness” , but one of the main causes of the “raspy” sound itself is the “profile” of the cam(s) – lift, duration and overlap. In general, the more aggressive the cams, the more “rasp”.

[EuphoriousCntrl]

i should have specificied that I'm really directing this towards all aftermarket exhaust, not stock. so in comparison to the post above, a lot of cheap honda ricers do not have aggressive cams so i feel like its more than that. also, how can we fix issues with raspy exhaust even if they're good named products?

[CMailco]

i should have specificied that I'm really directing this towards all aftermarket exhaust, not stock. so in comparison to the post above, a lot of cheap honda ricers do not have aggressive cams so i feel like its more than that. also, how can we fix issues with raspy exhaust even if they're good named products?

Because it is difficult to design an exhaust system that will attenuate frequencies across a broad spectrum. In the majority of aftermarket systems, the primary goal is to reduce losses. Tuning out some frequencies takes a back seat to performance. Then again, some are very poorly designed but "look" nice. Reactive type mufflers (e.g. the type of design that has the best low frequency attenuation) generally suffers from the highest insertion losses. It takes a lot of development time to build one that will cancel those unpleasant frequencies at a low loss.

It's always a trade-off. Removing the 1/4 wave side-branch resonators that many cars employ from the factory only exacerbates the problem. You're left scratching your head wondering... where did all these ugly sounds come from. Ironically enough, the resonator was there for a reason. Remove it and you need to attenuate those frequencies in other ways or just live with them.

-Chuck

[EuphoriousCntrl]

so are there other resonators that can be swapped to attenuate specific frequencies? in that case it sounds like fooling around with different brands is the best way to make a plausible fix on an already installed muffler and piping. however will be a costly and timely job to pursue unless the manufacturers can give information as to what the input/output levels and basic frequency ranges are. then again I was the one who asked the question originally so please tell me if i am wrong.

[DU09]

Resonators are a good way of getting rid of rhasp period, magnaflow makes some good one. I have a system with no resonotars and a high flow cat and when its cold its rhaspy as crap, but when its warm it sounds bitching haha. I do plan on ditching the cat for an x-pipe and resonators though.

[CMailco]

EC,

The best advice I can give you is this....

Don't use a "straight through", absorbtion type, muffler at the back. Find a good reactive type muffler to use. Also, use the largest case size that will fit.

Use a resonator and place it near stock location or just after the merge (y-pipe) or in pairs after a crossover (x or H pipe). Resonators are absorbtion type and they are designed to cancel higher frequency noise. Works very well with a reactive type muffler out back. Also use a resonator that is near the same length as stock. If none came stock, use the longest possible.

If the exhaust system employs a 1/4 wave side-branch resonator, do not remove it. They do not adversely affect exhaust flow in any way. It's ok to replace it with another resonator but most importantly, the branch should remain as close as possible to it's original length.

Can you delete a resonator and tune out those frequencies? Of course it's possible... how much R&D time/money do you have??

Of course, keep in mind that what works best for designing an exhaust system that meets dB requirements and some level of refinement vs what works best for overall engine power are often not the same. It can be done but there's a lot of computer simulation, R&D prototypes, etc., that get that job done.

I don't know of all the big German exhaust makers but Corsa makes a very good system that IMO does a lot of what we're talking about. I'm sure some of the others are just as good though.

Best regards,
Chuck

[DU09]

I agree with everything you say except dont use a straight through muffler, magnaflow mufflers (straight through ) + inline 6 = pure sux.

[deadbird]

does the diameter of the pipe have something to do with it as well? i've noticed the smaller exhaust tubing generates a more raspy sound than the larger tubing.

[moroza]

I've noticed that cars with no resonators sound really raspy. Ergo, a bigger (longer? wider?) resonator should cut that down.

[EuphoriousCntrl]

Haha, many good points. Kinda sucks now because I'm sitting here with 2.5" piping all the way to my magnaflow (straight through). Sounds like a long ass resonator is my only option other than swapping out the muffler. It's definitely too open for the little displacement I have.

[HBpredhunter]

im running a 24" resonator on a 3" exhaust with a small dynatech split flow rear muffler. and my car rasps more than a e46m3 with SS race catback.

im gonna swap out rear mufflers for a larger magnaflow and see if its cuts the sound a little. i love the rasp, just too loud.

[White94RX]

what makes a car sound raspy? a Honda engine with a cat back exhaust on it. Now that's raspy.

When I put my GReddy cat-back on my RX-7 I was scared of it being too loud, or obnoxious and raspy. But, I was pleasantly surprised when I got a smooth deep tone, with NO raspiness. Now, if I took off the cat converter, that'd be a whole different story.

[CMailco]

deadbird,

A smaller pipe has a different tuning frequency. Average flow velocity is higher, avg. temperatures are higher and pressure waves move at higher speeds than in a larger area pipe. However, all other things equal, dB levels are usually higher from a larger diameter pipe although some frequencies may come across "stronger" in the smaller? Very possible.

For more info search out helmholtz pipe tuning. You'll likely find more information than you care to read.

EC,

A resonator definitely won't hurt the situation. Larger pipes need even more consideration. Larger cases and/or reactive noise cancellation would be a plus for sound quality.

-Chuck

[EuphoriousCntrl]

here it is on a really good day. http://www.youtube.com/watch?v=hGaNXOe1YQc

just got into an accident today where i pretty much lost the face to my car. smashed the hood, nose panel crushed to the radiator which crushed the fan and is up against the engine block. $400 ellipsoids with halos smashed to pieces along with the corner lights. fender crush on both sides. maybe intake crushed too. only thing left PERFECTLY untouched is the m3 bumper, plate and fog lights. looks like a new resonator along with many other things is tacked onto the to do list for this summer. thanks for all the input guys.

[EuphoriousCntrl]