Rocktagon

iTrader: (1)

I have LT OBX Headers and an ORY going into an LM catback. This produced an ugly amount of Rasp in certain RPM ranges but I loved the way it idled and at WOT. Couldn't stand the rasp though so took it to the shop and had them replace the LM resonator with a high spiral flow bullet muffler where the Y meets the I pipe. This killed 85-90% of the rasp but it's still there taunting me at certain times, ugh. Also, it got a little quieter which I have mixed feelings about.

My question: There is one small resonator (I have no cats) that each header dumps into, is it possible that these are the culprit instead and not the LM Resonator? If so what will replacing each of them with just a straight section of pipe do soundwise? Or is there something else I'm missing, perhaps I never needed the muffler to begin with? I just want all of the rasp gone and if it gets a little louder once more that's fine.

SSCamaro99_3

iTrader: (1)

I am not familiar with the OBX system. If you do not have a good Y merge, that can help. Rasp sems to nbe persistent in any Y setup for these cars, to some extent. A lot of muffler can cover it most of the way up. The only solution that will completely eliminate all rasp is duals.

jimmyblue

iTrader: (11)

It's my belief that rasp has two possible sources.
One is loose or flexible metal, which can resonate
at particular RPM. This can be the walls of a resonator,
muffler baffles, etc. With the exhaust here consisting
of pretty much just pipe of various diameters, I think
this is probably not it.

The other source is "sharps" in the gas stream, which
can make like a dog-whistle and add high frequency
noise to the exhaust. When I was running gutted
cats, I found them raspy but dressing the edges
that are presented by the flanges and hogging off
some pipe ends that stuck into the stream, made a
fair bit of difference (leaving however the ~2500RPM
drone, where the hollow shell does act as a resonator.
Same thing on Y-merges, I've seen come craptastic
fit-ups where one side of the Y stuck 1/2" into the
other side, raw sharp edge.

If you wouldn't want to drag baby skin across it, then
grind it off, is a good rule of thumb.

Rocktagon

iTrader: (1)

Before this I was running only the LM cat back with stock manifolds and stock Y or mid pipe with gutted out stock cats. And honestly it sounded awesome, there was no rasp AT ALL. However there was some drone. The hollow cat shells make sense for that. I'm just baffled how that stock setup didn't have these issues. I would like to go back to that roar I had just minus the rasp. Do you think adding some high flow cats and yanking the muffler for straight pipe would help or would it just quiet it down more?
Now, True duals: I am open to that idea too. So with that do you go X or H pipe? Muffler no mufflers? There won't be rasp if I have an open system with dials?
I greatly appreciate your guys input. Paying for exhaust work and taking the gamble of liking the sound afterwards is something that the pocket book won't allow. Lol

HCI2000SS

iTrader: (2)

Yeah I don't know how you stand that setup to be honest lol. I have the same basic setup with higher compression with my heads and cam, and it's horrible at certain rpm's. Im looking at doing a Flowmaster merge pipe, and a Magnaflow 14419 muffler in place of the LM 1

Rocktagon

iTrader: (1)

Yeah that old setup had some drone but atleast it didn't sound like a raspy old farm truck. And it screamed at WOT, which was fun. I'm seriously thinking about duals now to fix what's going on. Anyone know of some kits or do I need to have an exhaust shop make something?

justin hover

I had switched from lm1 to duals...The rasp had pissed me off, plus I've always had interest in duals. I like loud but the lm1 was almost embarassing blasting through town with the rasp.
Look at texas speed true dual system. Alot of us run it. Kooks also has a stainless over the axle version for 3x the price. Or if you now anything about exhaust setups, it's just as easy to buy the pipes/mufflers separate and have a good shop fab it up. Either way you can't go wrong with duals...best sounding exhaust hands down...and not a hint of rasp. Most go with an x pipe.

SSCamaro99_3

iTrader: (1)

Over the years I have had:

LMI with stock manifolds/stock catted Y = sounded great
LMI with stick manifolds/catless SLP Y = sounded great
LMI with LT/ORY = rasp arrived in full force. Once you start really moving exhaust gas and shoving into the same pipe (especially with a bad merge) you get pulses bouncing around and weird harmonics.

LT/X/Duals = truly a thing of beauty

If you want to stay with the LMI a Y with a good merge and some high flow pup cats will probably clean off as much of the rasp as possible.

Rocktagon

iTrader: (1)

Cool, I want to get away from the LM now. For the cars with the duals are they dumped or do you have em out the back? For a do it yourselfer it seems dumping it right before the rear axle (like the Texas speed one I found) is an easy garage project. I bet that setup is loud as Hell though. It only has two skinny resonators right before the tips. If its not much louder than a LM with gutted cats I'm cool with that. This is a TA so the rear bumper would look a little empty though..

Z28SteveA4

iTrader: (16)

yeah dude longtubes with aftermarket y-pipe and a lm exhasut is nothing but rasp! So nasty to me. You have to ditch the lm or go dual like you were saying

Full-Force

iTrader: (11)

A bone stock exhaust has rasp. Its such a tuned sound that it sounds like a deep flutter. When you start removing baffling it becomes a high pitch and more pronounced flutter.

I build exhaust for these cars. Y pipes, duals, every damn thing and its inherent with these cars when you run straight pipes. These bullets and resonators are not real mufflers.

I can build a set of duals (a tsp rumbler x copy) and dump it and you dont hear rasp. Its deep as a bigblock. I can build a y pipe with a 4" outlet and bullet dumped and it sounds the same.

Now I can take that set of duals and extend the pipes all the way out to the bumper and it wll have rasp like a bitch. I can show anyone in person

99wssixm6

iTrader: (3)

So is there a set up that is for sale currently that has zero to little rasp.

sscamaro you mentioned that lt x duals sounds the best. Please give examples of what we can buy to replicate this.

Thank You

Z28SteveA4

iTrader: (16)

i have ZERO rasp with my borla. I absolutely hate rasp and there is none here

SSCamaro99_3

iTrader: (1)

I have Jet-Hot LT's/Hedman X-pipe/Dynomax (Ithink they are the 12 inch bullets/ dumped at the axle. It is just as loud as the LT/ORY/LMI, but it does not annoy anyone becasue it doesn't sound like ****, the sound is crisp deep and clean. You can move through the 2300-3000 rpm range without your car soundin like it is recovering from a bender and 2AM all you can eat buffet at Taco Bell.

z28SSilvest

OP I'm having a lot of rasp as well with my Borla. I think the best way to get rid of it is to just do duals, especially if you are running longtube headers.

99wssixm6

iTrader: (3)

I think you'll find the general conciseness on this forum to be that rasp is caused by cat deletes and the y pipe merger style. I have personally found that the cat delete to be the main contributing factor and have learned now that the y merger is very important as well.

That is one reason other than different set ups that we have conflicting opnions from z28ssilvest and z28stevea4 Steve has a catted y...

Just a few thoughts on the topic. I started a thread in this section that had alot of discussion in regards to the y-pipe. Its called something like elimination of rasp

BlueBird346

iTrader: (13)

I agree, some of it has to do with the tailpipes. I had a Texas Speed Rumbler, it had some serious rasp wit the longtubes/ORY. I cut the over the axle section off and welded a turndown and a hanger on the end of the bullet, and that alone cut the rasp in half.

There was still rasp due to the garbage y-pipe but it sounded much better.