What causes RASP?

[PewterBird]

I had to replace my cat, because it was so clogged, my car would hardly shift outta first.

So now, its all good, but now I have awefull rasp. It sounds great up untill 4000 rpms and i get a kazoo sound. My question is what part of a exhuast system makes rasp?

My theory is that since ricers like the sound they put a huge diameter tip on a small pipe. The dramatic change in diameter makes rasp.

Since this new exhuast system is kinda peiced together and not planned for. I have all stock pipes.

3in Cat ---> 2.25I-pipe---> 2.5 Dynomax Super Turbo---> 2.25 tailpipes ----> 3.5 X 18 Long Slash tip rolled lip tips.

I am guessing that 2.25 pipe has to go.

[Camarorulz]

The 3800 makes rasp lol. Very few have gotten rid of it completely. That's a lot of variation in your exhaust diameters, go with a full 3" system, or at least 2.5"

[Ian]

what causes rasp?

the lack of two extra cylinders.

rasp is most exhaust on v6's.

popping is too little backpressure.

[PewterBird]

<blockquote>quote:</font><hr>Originally posted by Camarorulz:
The 3800 makes rasp lol. Very few have gotten rid of it completely. That's a lot of variation in your exhaust diameters, go with a full 3" system, or at least 2.5"<hr></blockquote>

I do plan on changing out the I pipe and the tailpipes. to 2.75. So even though it will vary, it will only vary in the muffler, where I beleive the .25 difference is negligable, because the caverns inside are larger anyhow.

<blockquote>quote:</font><hr>Originally posted by Ian:
what causes rasp?

the lack of two extra cylinders.

rasp is most exhaust on v6's.

popping is too little backpressure.<hr></blockquote>

Yes, you are right the lack of two extra cyclinders is more prone to rasp. But I don't think most people are gonna do a swap, just to get rid of rasp. ;)

I had a 92 3.1 that had zero rasp, but it was a complete 2.5 mandral bent from the collector all the way out the tips. I have also heard nice 6 cyclinder import that had no rasp. So I know there is an answer.

I want to narrow it down to what exactly influences the sound, so people can design their systems better.

I am looking for more of a technical answer, I know some people on here have taken or are studying fluid dynamics. Rather than a bunch of people chime it with, "You need a V8" or "The 3.8 will never sound like V8" lets get technical.

To help with the description, this rasp occurs for just a second right as the Rpms start to drop after a rev at about 4500. Sounds almost like a rattling licence plate + a kazoo.

BTW: It did get better when it started to warm up. It also still needs to break in.

[ October 08, 2003: Message edited by: PewterBird ]</p>

[toast]

Also i have found that rasp is more prone with stock exhaust manifolds. Usally headers and a full 3inch system drones out the rasp completly. But because it is a V6 is not the cause on why it rasp because i have heard plenty of V8, even LS1s, that rasp and sound terrable up high. Of couse the LS1 sounds gay no matter what rpm it is at. ;)

[Ted]

I don't think I ever heard a perfectly good 4cyl or 6cyl in my life (except for some GNs and a few other really nicely done cars). Any 4cyl is gonna make rasp, most 6cyls make rasp. This is just life. There are ways to hide it, some expose it. The way the engines were designed, it's in their nature. Like toast said, you can get headers and such a free flowing exhaust that will cover up the raspy sound. Other then that, we have to learn to accept this.

[Lord_Verminaard]

I have to disagree. I had a 91 Beretta with the 3.1 with a full 2.5" exhaust, catco converter, and edelbrock RPM muffler. Even with the stock restrictive manifolds and unequal crossover pipes it sounded real mean. Rumbled very well at low RPM's and actually got quieter at higher RPM's. No rasp at all. It was one of the best sounding exhausts I've ever heard on ANY car.

My Camaro's exhaust note is funny. It's all stock, but like someone else said, if I rev it up a little more than usual while going through the gears, it almost sounds like a "snort" during shifts when the RPM's drop. [img]smile.gif[/img] I dont think I've ever heard any other type of car doing that before.

Brendan
2000 L36 M49

[Loochy88]

so v6's are a little raspy/ricy. who cares. it will never sound like an 8. Maybe close, but not exactly. If you want v8 sound get a v8. i actually like how my v6 sounds

[98v6]

<blockquote>quote:</font><hr> popping is too little backpressure. <hr></blockquote>

i have to disagree, i had a stock exhaust with a cutout right before the muffler, sounded ricey and popped on deceleration due to the extra backpressure from the muffler. popping is caused by a low pressure area and a high pressure area, it might flow fine through acceleration but exhaust gas backtracks after you get off it and this is what causes popping. i put a dynomax dual outlet muffler on it and it cured both, popping and rasp, still somewhat raspy but NOTHING like it was before...

[PewterBird]

<blockquote>quote:</font><hr>Originally posted by Lord_Verminaard:
I have to disagree. I had a 91 Beretta with the 3.1 with a full 2.5" exhaust, catco converter, and edelbrock RPM muffler. Even with the stock restrictive manifolds and unequal crossover pipes it sounded real mean. Rumbled very well at low RPM's and actually got quieter at higher RPM's. No rasp at all. It was one of the best sounding exhausts I've ever heard on ANY car.

Brendan
2000 L36 M49<hr></blockquote>

I think it has something to do with that motor, cause my 3.1 sounded awesome.

<blockquote>quote:</font><hr>Originally posted by Loochy88:
so v6's are a little raspy/ricy. who cares. it will never sound like an 8. Maybe close, but not exactly. If you want v8 sound get a v8. i actually like how my v6 sounds<hr></blockquote>

I care, You are right it will never be an 8. But I don't want a V8 sound. I don't want rasp.

Rasp is getting less and less, as the new cat breaks in.

Besides NOT being a V8, what mechanicly about the V6 or the exhaust componets makes rasp?

[ October 08, 2003: Message edited by: PewterBird ]</p>

[toast]

<blockquote>quote:</font><hr>Originally posted by Lord_Verminaard:
I have to disagree. I had a 91 Beretta with the 3.1 with a full 2.5" exhaust, catco converter, and edelbrock RPM muffler. Even with the stock restrictive manifolds and unequal crossover pipes it sounded real mean. Rumbled very well at low RPM's and actually got quieter at higher RPM's. No rasp at all. It was one of the best sounding exhausts I've ever heard on ANY car.

My Camaro's exhaust note is funny. It's all stock, but like someone else said, if I rev it up a little more than usual while going through the gears, it almost sounds like a "snort" during shifts when the RPM's drop. [img]smile.gif[/img] I dont think I've ever heard any other type of car doing that before.

Brendan
2000 L36 M49<hr></blockquote>

Well the older 60 degree V6s (2.8,3.1) that were used in the FWD cars have a crossover pipe that blends the left bank with the right bank and then exits into one pipe. I believe that is why they sound that way. Personally i am not a fan of the way the old FWD 60 degrees sound, too much like a boat motor to me. Also that type of manifold does dentin the sound when the rpms are rasied. My brother's old 2.8 sound pretty good at idle but anything above that it sound like a boat. My camaro sound a whole lot better even tho i do eve his idle note.