Lately I have been getting lots of messages on how to eliminate rasp with PCDs on exhaust systems other than stock. As most of you know a Magnaflow 10426 will remove most if not all rasps on a stock exhaust system. What about ATLP, XLR8 and custom setups. My answer has always been add a resonator larger than the 10426. I am sorry for such a terribly vague answer.

I believe we should take a somewhat scientific approach to solving this problem other then guessing. I have been pretty busy lately. However I figure I would throw this info out there and the community could work on it together. Maybe even having other manufactures make PCDs compatible exhausts.

My theory is that increasing internal volume to an exhaust system will reduce the amount of rasp. In order to tests this theory we must calculate the internal volume of a systems without rasp and try to match our target system to the same internal volume using resonators.

Formulas
Volume of cylinder = Pi(r^2)h
Pi = 3.14
R = (circumference/Pi)/2

To keep things simple lets solve everything as if it was a cylinder. That way we can easily measure the circumference of our mufflers and resonators.

Volume of O.E resonator
h=16.75”
Circumference = 15”
r = ((15/3.14)/2)) = 2.38”
A= 3.14*(2.38^2)*16.75 = 300.40 in^3

Volume of O.E mid muffler
h=6.5”
Circumference = 28”
r = ((28/3.14)/2)) = 4.46”
A= 3.14*(4.46^2)*6.5 = 406in^3

Volume of O.E muffler
h=11.25”
Circumference = 28”
r = ((28/3.14)/2)) = 4.46”
A= 3.14*(4.46^2)*11.25 = 702.67in^3

Volume of O.E 2.25” tubing
h= 64.5”
r = 2.25/2 = 1.125”
A= 3.14*(1.125^2)*64.5 = 256.33in^3

Volume of O.E 2.0” tubing
h=54”
r = 2/2 = 1”
A= 3.14*(1^2)*54 = 169.56^3


Volume of Magnaflow 10426
h=18”
Circumference = 13”
r = ((28/3.14)/2)) = 2.07”
A= 3.14*(2.07^2)*18 = 242.18in^3

Total volume of O.E exhaust + Magnaflow 10426
300.40+406+(702.67*2)+256.33+169.56+242.18 = 2779.81in^3

I have been getting lots of emails about ATLP exhaust systems lately. Assuming they are using the same volume mufflers as stock and the system is nonresonated. Right now these are just estimates.

Volume of ATLP muffler
h=11.25”
Circumference = 28”
r = ((28/3.14)/2)) = 4.46”
A= 3.14*(4.46^2)*11.25 = 702.67in^3

Volume of ATLP 2.5” tubing
h=64.5 + 23.25 (length of deleted resonators) = 87.75”
r = 2.5/2 = 1.25”
A= 3.14*(1.25^2)*87.75 = 430.52in^3

Volume of ATLP 2.25” tubing
h= 54”
r = 2.25/2 = 1.125”
A= 3.14*(1.125^2)*54 = 214.60in^3

Total volume of ATLP exhaust
(702.67*2)+430.52+214.6 = 2050.46in^3

Now that we know the internal volume of the exhaust that does not rasps and the exhaust that rasps. We can calculate the difference and choose a resonator.

Difference = 2779.8 – 2050.46 = 729.34in^3

We need to add ~3 times the volume of the Magnaflow 10426 used on the stock exhaust to kill the rasp on the ATLP system. Let’s looks at some resonators from the Magnaflow site.


http://www.magnaflow.com/02product/universalmuffler.asp




736in^3




508.7in^3



395.6in^3


With the constant of PCDs we can conclude that the Magnaflow 12640 would be the best choice in reducing PCD rasp on a generic nonresonated exhaust system. Again the numbers from the ATLP system were estimated. Hopefully this information can help some of you tame the beast. If someone is bored can they please check my math it has been a while.

 

interesting approach Richie...I like it.

I have your v3 pcds/v3 jpipe and xlr8 quads with the magnaflow 10426 welded on.

most of the rasp is gone...I may get a teeny tiny amount shifting from 2nd-3rd around 3500rpms...but it's not bad at all. as I told you before, I do want to install a larger one to quiet the exhaust overall and decrease the minor rasp.

i think I'll go with the 12640 like you mentioned...I've had my eye on that one for a while anyway

 

I have ATLP V2 exhaust that sounds like absolute crap over 3k rpm's after PCD's were installed 3 nights ago. I just ordered this, so I will report back once I have it welded in.

Richie- Thanks for the quick response to my email!

 

Nice thread Richie. I've gotten numerous PMs asking which size resonator to use with 'X' exhaust as well. I've been through so many exhausts I almost PM'd myself one time LOL. I was/am always happy to help a fellow member out, but this seems to be a better approach. I would usually take an educated guess when considering what size piping and mufflers would be used to come up with the best size resonator. I would calculate the internal volume of each muffler, then what resonator I think would quiet it best depending on what they wanted. I used my exhaust as a "benchmark" (mine is loud but with very, very minimal rasp). So if someone wanted it relatively quiet, I'd recommend a larger resonator than mine, and so far so good! I think most were happy which made me happy!!

This is definitely a better approach though as I did not get into this much depth. I'd definitely agree with you and say Magnaflow probably has the best selection of straight through resonators. I'd also recommend the Vibrant line (ultra quiet) and Aero Turbine AR25/AR30. They are much smaller, but apparently do a really good job at suppressing the exhaust as well.

Btw I'm still open to help anyone that needs a second opinion I enjoy it.

 

How about with hfpc's? Any rasp with those?

Even with no rasp what size resonator to tame a custom 2.5" exhaust to near factory...... assuming that the mufflers themselves are as quiet as stock.

 

..... I'm wanting aftermarket perf with close to stock sound.... Any suggestions? Doesn't have to sound like a tl per say but close to a stock car and I'm not referring to a sprint cup stock car, lol

 

I'd go with with the last picture that Richie has (12616) and a pair of Vibrant Streetpower mufflers. That should give you a relatively aggressive note at WOT, but tame around town. If you really want a "stock" sounding exhaust, I'd go with the middle resonator. The largest (12640) will be overkill I think.

 

i threw a vibrant resonator on my ATLP base exhaust.
btw my entire setup is comptech supercharger, rv6-p hfpcs, atlp j-pipe + high flow cats

 

According to our previous calculations you are missing a mid muffler and you need to add a resonator to get to the sweet spot of 2779.81in^3.

Volume of O.E mid muffler
h=6.5”
Circumference = 28”
r = ((28/3.14)/2)) = 4.46”
A= 3.14*(4.46^2)*6.5 = 406in^3

Volume of Magnaflow 10426
h=18”
Circumference = 13”
r = ((28/3.14)/2)) = 2.07”
A= 3.14*(2.07^2)*18 = 242.18in^3

Volume increase needed to equal stock exhaust with Magnaflow 10426.
406+242.18 = 648.18in^3

This one might do the trick its a bit on the smaller size but we don't want to over do it and the next step up is too big.


508.7in^3

 

Why do we not want to over do it? What would change with a larger than needed resonator?

 

^^ You do want SOME sort of exhaust noise, right? You don't want to drive around in silence lol. Maybe you do. I think Richie suggested that because it would be the perfect mix of daily driveability and WOT ear sex.

 

ok, just curious, I thought maybe too big of a resonator would act as a pipe bomb and blow the car up!!! lol, jk, I was curious about the suggesting bc I would rather be sure to get rid of any rasp plus I would rather be too quiet than too loud..... I like the "stage 1" mod but not the "stage 2".....

 

sub'd....i will be doing my calculations

Thanks for the thread Rich

 

None what so ever. I have the RV-6 HFC's, ATLP V1 J pipe/race pipe, and Excelerate cat back and it sounds incredible. I do have the resonated version of the Excelerate, but it's a pretty tiny resonator; you really have to look closely to see it, as it just bulges out from the exhaust pipe ever so slightly.

I do have a bit of drone at times on the highway in 6th, but not too bad, and the exhaust sounds so damn good, I don't want to mess with it. I get compliments from a lot of people on the sound.

 

^^^ true...RASP comes in from a FREE FLOWING exhaust....the minute you have rasp you can almost be certain your exhaust is offering very little back pressure....

that is when the pulses start going ballistic in the pipe....

HFC's offer little backpressure at the start of the pulses journey....and hence "modify" the pulse frequency and hence no rasp....

EVERY EXHAUST ATLP/XLR8/RV6 have almost the same amount of sound suppressants (resonators/mufflers/etc) but the minute you put a jpipe + cat deletes in front of them, HELLO RASP !!! since all the exhaust are pretty free flowing....

Inaccurates 3" exhaust is raspy as fawk (how he describes it) but its the most free flowing exhaust i have seen....

 

That's pretty much why I went with the HFC's over the deletes. Sure, they give up a few horsepower to the PCD's, but IMO that's a small price to pay to not have the annoying rasp. I see the same scenario played out all the time. In the end, if you can't stand the rasp with the PCD's, you end up spending just as much, if not more money than the HFC's would've cost, trying to quell it with different resonators and you also end up negating at least part of the PCD's power advantage with a big resonator.

 

What are your mods? You won't have any rasp with the stock precats in place.

 

hell yeah, math and physics FTMFW

 

i just got a resonator welded and absolutely no rasp. i have rv6 pcd v3, xlr8 v2 jpipe, custom catback. i used the 10436 resonator. but every catback exhaust is different. 4" diameter, but the 6" one should work best. thanks for putting out that info richie

 

Will these Magnaflow #12640 and #10436 remove the rasps and eliminate the drones..

 

it will remove rasp. drone would probably depend on which catback system you have. i have a custom setup with spintech super pro street mufflers, the loudest ones they make. and i have crazy drone due to the design of the muffler, it has no packing, its more like a flowmaster but even louder. after i had the resonator welded on, all the drone seems to have moved to the rear of the car, pretty much from the mufflers. before that it felt like it was coming from the front/middle of the car. its a big improvement

 

I have installed RV6 V3 J-Pipe and Greddy EVO2 full catback recently. Now, I am catless and had mid-muffler deleted.

I love the power gains and loud throaty tones from the new exhaust, however, it has alot of drones inside the cabins and driving getting crazy...

The measurement of resonator from OEM exhaust are the following:

7" Round
Body Length = 18"
Overal Length = 24"
Pipe diameter = 2.5"

Among the Magnaflow resonators, which one is recommended - #12640, #10436 or 12646 ?

 

i would go with the biggest one, Magnaflow #12640. not sure if its going to get rid of the drone for the greddy evo. but it would definitely tame the beast without sacrificing flow. the way i see it, the greddy evo doesnt look like it would have much exhaust packing material, thats the downside of buying fart cannons . oval mufflers are the way to go if you want less drone. i would recommend magnaflow oval mufflers, and dynomax ultraflow. both mufflers have the straight thru design.

but definately get a magnaflow resonator welded, and let us know how it turns out.

 

Thanks for the suggestion.

I went shop around online for Magnaflow#12640 and the sale price is $92.69 + free Fedex shipping.

 

I agree withe the Aero Turbine AR25 it does a good job with jpipe and atlp exhaust theres a slight rasp between 3-4k @wot. But with precats forget its just way too raspy.
Adding a vibrant (ultra quiet) is overkill its way to quiet and its huge not recommend it if the car is slammed....lol

 

Anyone have installed this Magnaflow#12640? Will it fit under the TL's?

Has anyone tried this race muffler instead of cones to kill the rasps and drones?

 

^^^ just pray inaccurate doesnt see this

this design you will loose a ton of high end HP, but gain a little low end because of the back pressure !!! i dont recommend this....

 

Gimmicks abound (comment directed at the Twister muffler)

 

^^^ PHEW !!! thanks for the clarification Tim....you had me worried LOL....

 

I have confirmation from Magnaflow that #12640 will fit on 2004-2008 Acura TL's..

"I assumed this Magnaflow#12640 will fit on 2004-2008 Acura TL, am i right ? "

Yes it will work on your vehicle.

 

You also have to keep in mind the material that the resonator uses for packing material, as well as the internal construction. Steel wool, rock wool, fiber packing all eliminate different resonance frequencies. In addition to that, the way the inner core is perforated or louvered, or if it has a venturi/baffled system, all makes a difference in controlling rasp.

 

PROBLEM SOLVED !

I removed the Twister race muffler and replaced with Magnaflow#12640. This resonator eliminated the drones/rasps and quiet down the beast Greddy EVO2 catback..I'm very pleased with the outcome.. " Happy Wife..Happy Life.."

next mod: RV6 PCD (maybe)

 

Will 12640 work with the stock 2.25 exhaust? Right now I have v3 PCD - v3 jpipe - stock exhaust. I want to eliminate the rasp and only have one resonator, so I will be replacing the stock one with a larger one.

 

I have RV6 PCD and when I got the RV6 TD exhaust it took care of alot of the rasp as he has a resonator installed in the exhaust!!! to me I feel a slight rasp high in the rpm is what makes the sound sexy as fukkk!! but then again to each its own.....

Either great thread and for me Richie you built an amazing exhaust which goes perfect with the RV6 PCD's

 

Just to kill the rasps on your setup...below are your options:

Magnaflow#10435
Body Shape: 4in. Round
Inlet/Outlet Size: 2.25in./2.25in.
Body Length: 22in.
Overall Length: 28in.
Core Size: 2.5in.
Position: Center/Center

Magnaflow#10436
Body Shape: 4in. Round
Inlet/Outlet Size: 2.5in./2.5in.
Body Length: 22in.
Overall Length: 28in.
Core Size: 2.5in.
Position: Center/Center

Magnaflow#12640 might be overkill for you..unless if you are upgrading your stock exhaust to any aftermarket full catback..

 

Ok so now I'm a little concerned about raspyness flowing through my car since I just purchased the xlr8 resonated exaust, I have pcds and and jpipe already installed along with the magnaflow 10426 now am i gunna wanna add this resonater along to my already resonated exaust to clear all raspyness;? If someone could give me an answer before 3pm today that'd be greatly appreciated because I plan on getting the exaust installed around then and posting video clips

 

^its really a preference kinda thing.
since your exhaust already has a resonator, it might be already quiet.
who knows till you actually put it on

 

Yeah true, ill guess ill just find out when once its on the car..I'm just worried about it sounding real raspy but hopefully the resonated catback takes care of that

 

^^^ another thing you can do is wrap the exhaust....its takes the "tin can" noise out....give a tad bit deeper growl....

 

So i just got the exaust installed on my way back from work today and im pretty disappointed in how loud and raspy it is, other than the exaust tips i dont think i like anything else about it. I understand its not the exausts fault for sounding so loud and raspy because i do have pcds and a jpipe installed but at this point im not quite sure what to do with it weather or not i should sell it for to someone without pcds or add a resonater to tame the loudness and rasp..i took a quick video so i will try and upload that asap so everyone can check it out