Cherry6speed

I posted earlier about muffler resonance....I decided Maganflow needed to answer my question. I called 1-800-817-3930 and talked to Adam. I explained my (our) problem with muffler resonance on the C-4's and asked for his advice. 1st off, he explained that the lt-4 hot cam changed the stock sound waves and caused them to overlap and re-position themselves in the exhaust pipe thereby, creating resonance. In my case, and in most of yours, past the resonator. He suggested several methods to correct this: First, you need to find out "where" your sound waves are "building up" in the exhaust. One method he suggested is; to place masking tape along the length of straight pipe ahead of the Y and start the engine up. Where the tape peels off or starts to burn is: the "hot spot" This is exactly where, as he explained, the sound waves are building. The other method is; use a thermo-laser temperature gauge and point it at the exhaust pipe until you find the "hot spot." Next, you need to modify the hot spot by either bending the pipe-in (slightly) or placing a 3" muffler at the exact location. Magnaflow sells the 3" mufflers off their website [ http://www.magnaflow.com/01home.htm I haven't priced them. According to Adam, the slight bend would create some backpressure but it would correct the problem. He also recommended using the muffler/resonator at the location for zero performance loss. He explained the muffler would create an area of expansion and eliminate the resonance wave. I have no idea if this stuff will work or not but, Adam works for the factory and I told him there are a whole lot of guys in the forum that will benefit from this info and if it solves the problem, they would benefit too. I gave him the forum address and invited him to join the discussion. For those of you interested he said the Magnaflow mufflers part #15623 gave a 16.6hp gain over stock HP and torque gain is 13.4 .Peak power on stock LT-1 was @5,100 and torque came in @3,900. (This is off their dyno in-house) Pretty good info for a free call... Eh? I'll keep y'all posted if I burn myself huntin the hot spot.... Hey, I just want my cake and it it too :thumbs:


[Modified by RUBYREDVETTECARD, 9:30 PM 4/6/2004]

DON M

Thanks, good info. :flag

C10 JDR

Very interesting - keep us posted :cheers:

VR'92

:iagree:

LT-4 CE

When I bought mine last year, I found their tech to be the most helpful and human of all the companies I talked to. They actually knew about their product and did not simply read me the marketing text out of the catalog. That alone was almost enough to make me buy their product.

FWIW, the wave he refers to also used in race header technology. When I was drag racing with open headers, we used to bolt a piece of tubing the collector and run it a couple time. Where the paint started to fade or blister, we cut the tubing off. This was worth performance gain.

C10 JDR

This also implies, if I read it correctly, that any recommendations on resonance from other members are pretty useles unless they have the same cam, maybe same porting mods etc as oneself.

JAKE

So, what is the exact point are we looking for?

The forward-most point that the tape burns or the rearward most point?

Did he indicate how long the engine should run (I'm assuming at idle)? I guess if it runs long enough, the tape will burn off no matter where it's positioned.

Jake

Cherry6speed

Unless I misunderstood them entirely, the cause of resonance doesn't matter...they only explained why I have resonance. They in fact believe that their mufflers are accoustically designed to work with stock resonance waves and locations. Further, they explained the new Hemi-Dodge had a similar problem and that is how they solved-it. Locate the "hot-spot" and correct it. Adam futher mentioned a gear change would merely alter the "timing" of the resonance and do nothing to correct it. I have no idea if what they say is correct, But you have the phone number give them a call. I think you will find they are "very knowledgeable" and easy to talk to and definately respect our knowledge of our cars. :thumbs:

Cherry6speed

Jake, He said the tape will peel first @ the hottest point and that is your hot spot. Not very scientific. I plan on borrowing a temperature laser and get the exact spot marked. According to Adam that spot is exactly where the resonance is comming from. Sounded good to me. :seeya

rick lambert

I think that's great information and great customer service :thumbs: for the post and :cheers: here's to them :D

65Z01

With an L98 which has s single cat after the front Y followed by the rear Y, I wonder if the rear Y would get hot enough to use the masking tape method; here it might take the temp probe setup.

Also, I'm wondering if we couldn't benefit from wrapping the rear Y with some sound deadening material, since the resonance is originating in that area.

If the resonance wave is created in the rear Y (in some cases anyway) that may be the reason for some Ys being sold with that cross-over tube.

So, now I wonder if true duals with bullet cats may not eliminate the resonance problem.


[Modified by 65Z01, 6:37 PM 4/6/2004]

redfast

So, now I wonder if true duals with bullet cats may not eliminate the resonance problem.


[Modified by 65Z01, 6:37 PM 4/6/2004][/QUOTE]

No your right, I have the 2.5" true duels with the magnas. and the rear has the cross over. The exhaust is very loud and has alot of resonance, but I like it :thumbs:

LD85

My first test with the Vortech cones will be at the exit of my, Bullet muffler/entry to the y-pipe, so Iwill know something about that soon.



[Modified by ld85, 7:45 PM 4/6/2004]

Steve85

If the whole hot spot-muffler placement proves to be effective this will be some of the best information on this forum. Exhaust/noise/resonance is, week in week out, one of the hottest (sorry, most popular) topics.

JAKE

I'd sure like to know if those inserts work. Keep us posted.

Jake

h rocks

Locating the hot spots (by paint blitering, not tape) is how you locate the ideal positon where to put your crossover pipe.

LD85

Jake, I MAY try to put the cone into the y-pipe this weekend, I really wanted to wait until I got the car back from being tuned first.

Also, right now my car is totally acceptable to me, with very minimal resonance after putting in the bullte muffler.

I really believe the best place to put the cone is at each muffler inlet, based on what Magnaflow says, this would dissrupt the sound waves at the point where I HEAR the resonance. When I am in my car, it is obvious to me that the rear of the car is the point where the most noise comes from.

69mako

:withstupid: :steering:

dtorc4

IMHO, I think the best solution, if found to be the case, would be to find the hot spots in the rear Y, and have a crossover pipe welded between the Y at the hot spot points. It seems like the store-bought xover Ys may be of some help, esp. on a stock vehicle, but, like Adam said on the phone, changing the engine setup will change the resonant frequency (and therefore the location) of the sound wave in the pipe. If you give the sound waves some way to break up, then it should reduce the resonance.

tobijohn

Is there some sort of frequency "threshhold"? I ask because aren't the stock exhaust systems for both the LT1 and LT4 the same? Because of the differences between these two engines, doesn't that mean that their sound waves were different as well? Do stock LT4s have more resonance than stock LT1s because of those differences or are those differences not enough to push it over that resonance threshhold?


[Modified by tobijohn, 1:42 PM 4/7/2004]