It would be interesting to find out if this "flutter" is associated to engine displacement & muffler size. Do the members with big displacements encounter this noise (427+) ?
Is it only smaller (408-) that encounter it?
When I had the original VERY restrictive mufflers I did not have any "flutter" but as soon as I installed the S/S 2.5" mufflers I started getting it.
It's almost as if the flow capacity of the muffler is too much for the engine @ lower RPMS & you get a "sucking effect" that causes the fluttering.
I suspect that if I installed 2.5" turnouts the problem would go away--would look rediculous but might solve the problem. (not going to happen)

Not being a engineer & not knowing anything about expansion-contraction-heating-cooling-velocity of exhaust gasses this is my best shot at the problem.

I am sure that someone here is & can answer with a more accurate solution/cause/effect.

Craig

I have it now with a 600hp 482" s/o and 3" Classic Chambered exhaust.. I didn't have it before with the other 3" CC exhaust. The other set flowed as much as this set.. I'm not really complaining as I've grown used to it and others outside the car don't seem to hear it.

I have stainless steel glasspacks that I had Lucien Donofro of Arizona Exhaust make up for me about 7 years ago. 4" outer diameter, 3" inner diameter. Louvers facing backward. From the time I put them on I noticed a SIGNIFICANT increase in power, but upon any deceleration of engine RPM, you get the sound like papper fluttering in the wind at the outlets.


Who cares.


.

I keep waiting for the final solution on this thread, but it doesn't really sound like there is going to be one definative anwser.:CRY: I am running the same engine in my Spf that I took out of my E-Morrison, and the loss of power is really noticeable. I can't stand it any more, and ready to make a change just not sure what. I really only want to do this once. Where is anyone sourcing the different muffler choices?

I got my 3" core Cobra Pack mufflers from Eric at Classic Chambered, and I'm having Nick Acton from Acton Customs ("Mickmate" on Club Cobra) do the work to put them into the old sidepipes. The mufflers I took out were stock from Contemporary, and were about the most restrictive I have ever seen, they were much worse than I ever imagined.

Both Eric at Classic Chambered, and Nick Acton from Acton Customs are straight shooters and a pleasure to deal with. Stuff costs what they say it will cost, it looks the way they say it will look, it works the way they say it will work, and it shows up when they say it'll be there. You can't beat that. I highly recommend both!:)

767..

Thanks for the source on the mufflers. We can do all of the work in house, and I have a guy down the road from our shop that powdercoats all of our marine parts for us. I may watch this thread a little longer before pulling the trigger. Thanks to everyone for their input.

Hey Dean, Eric looked at your sketch and made these up from it. http://www.classicchambered.com/clas...cts.html#cobraKidding, but he has them in stock at the bottom of that page as a reducer. We took and cut out just the transition we needed to match diameters and put it on the end like this http://www.clubcobra.com/photopost/s...=65423&cat=500. We installed them in Dougs 3" and Karls 2.5". They make a really smooth radiused transition between the diameters so if the flutter is caused by reversion off the corners then this will fix it. Karls car will be running soon so we'll have some real feedback on whether it works. What was that about a lifetime beer supply................????????

I don't think powdercoat will handle the exhaust temperatures, I'm thinking you'll need ceramic. There's even a few good color choices for it, I listed the guy I use he has them on his site. Doug go to bed!

You have email!

Same here. Someone else mentioned that it sounds like paper flapping in the breeze. Great description for those that have not experienced this. There are a lot of annoying sounds that these cars can make (i.e. wind noise on the freeway is louder than any muffler). But the "flutter" is truly annoying and gets harder to live with the longer you have it. I suppose that exhaust pop from a Weber system is another of those sounds that others just deal with. Perhaps more period correct, too. :LOL:

Looking forward to reading the updates. Now I just need to find a beer truck idling next to a 7/11 that I can steal. :3DSMILE:

-Dean

put a straight pipe on that is long as possible and see if you get the flutter, if yes, starting cutting off inches at a time till it quits, this would be your optimum length.

even if it doesn't flutter, you could cut to see what would happen.

Aren't you describing the procedure for optimizing the torque curve just aft of a header collector? Old drag racing tuning trick. Not sure how lengthening or reducing the straight pipe affects harmonics? I should have paid more attention in HS physics class. :confused:

There is definitely some level of turbulence that is causing the flap. But, again, only on deceleration and usually more prevalent below 2,000 rpm. Might be air crashing together under engine braking?

-Dean

could you be thinking of crossover tube placement?

my jbl has the sound you're talking about also when cold sitting still, don't know if it is the cold clearance on the solid rollers or what. i think it is the sound of reversion though. here is some data from a program that figures the length of pipe, hth.

---- Primary Pipe's Harmonics ----
1st Harmonic = 131.8 inches long ... typically never used
2nd Harmonic = 50.0 inches long ... longest recommended
3rd Harmonic = 29.9 inches long ... highly recommended , best Torque Curve
4th Harmonic = 20.8 inches long ... shortest recommended
5th Harmonic = 15.7 inches long ... typically never used
6th Harmonic = 12.3 inches long ... typically never used
7th Harmonic = 10.0 inches long ... typically never used
8th Harmonic = 8.3 inches long ... typically never used

---- Collector's Harmonics (includes Intermediate, Muffler , TailPipe) ----
1st Harmonic = 137.5 inches long ... longest with Mufflers and TailPipes
2nd Harmonic = 68.7 inches long ... longest recommended with Mufflers
3rd Harmonic = 34.4 inches long ... more bottom-end Torque
4th Harmonic = 17.2 inches long ... highly recommended , best Torque Curve
5th Harmonic = 8.6 inches long ... reduced Torque , more top-end HP sometimes
6th Harmonic = 4.3 inches long ... reduced Torque , not recommended

Nick did my SPF
 

I have been looking for more Power from my FE and found alot more than I expected in the exhaust. I changed to a baseball roll thur. size from stock, Wow what a difference. Nick cut out the old muffler and welded in the new one. He sent it to the coater and everything went back together great

The sound is not bad until WOT then everyone runs for cover:LOL:

Vector1,

If you have the standard JBL headers and sidepipes they are:

Primaries:

3rd Harmonic = 31.6 inches long 1.75 Dia.

Collector:

3rd Harmonic = 33.6 inches long 3 inch Dia.

This was the best compromise that I could provide for the various 351 derivatives.

They are pretty close to your program numbers.

But of course not optimal.

Muffler replacement huge horsepower gains!
 

Why do some guys go to 3.5" internal perf tube or is that for eg 800hp over 7litre engines?

When we dynoed this 373 engine with smaller port inlet to suit the C3 heads we only lost 1bhp over the big manifold at 7000rpm, going by the dyno found there is no real point in going over 6800rpm, all this was done straight out of the tapered collector of 3" diameter going into the typical large silver 6 or 8" flexible ducting hoses so I dont know if going bigger than 3" internal mufflers would achieve much. Going by all the information on CC etc and my rpms it appears that 3" for my 600+hp engine would be adequate.

We have a 200bhp increase from 4000 - 5000 @ 520bhp I dont think I need anymore low to mid range hp by keeping my muffler size down.as its going to be hard to get this beast to hook up due to the lightweight I emagine we are still a liong way off having it mobile!

hello richard

i had no doubt that the headers were optimally designed. through the rpm band there is a point where the exhaust gets to be almost like a f1 shreek, even with ear plugs it is ear splitting, could be some other factors also.

from what i understand of the program optimum is usually within a couple inches either side when tuned on a dyno but not much difference in power. collector length followed by primary length then primary size would be order of importance if i remember correctly.

one problem with the jbl, i can't find enough twisties!:LOL:

Cobra owners of a flutter, flock together - or something like that.........

Undy, you ran the 3" inserts over the louvers? No wonder the exhaust was so LOUD!!! This may also have something to do with the "flutter" you guys are talking about, as Undy said he did not have any with the mufflers going with the grain. I recommend going into the louvers (against the grain) for max noise attenuation, but they will flow either way of course. From what I've heard from several customers, they are about 3-4 dBA's louder going over the louvers (or with the grain). There will be a little less drag, but I don't think there is a big trade-off.

Here's a video of Cobrapacks on a Viper....................I know you are Ford guys. Wait til the end, your Ford interest will be greatly redeemed, trust me!

Grab a coffee, beer, or Dr. Pepper - this is about 10 minutes of some VERY neat exhaust analysis. It's also a lesson on how to make a V-10 sound GOOD! Which mufflers sound best??? Enjoy:
http://www.pod9.com/ant/viper/exhaus...k_dyno_day.wmv

-Eric

Eric, The flutter occurs when the mufflers are installed as they are intended, for max sound attenuation. When I installed the inserts before, with the louvers being ineffective for max flow and minimal sound attenuation, there was no flutter. This flutter issue is very wide spread, not just your systems (no pot shotz at CC intended here at all, I've always been happy with your stuff and customer support).

You have any thoughts on this flutter issue??

Dave

I had this company make my stainless pipes. The 4" muffler body is, the muffler. No muffler breaking of the welds causing rattling. No glass packing to burn out.
No more cost of ceramic coating and constant polishing. The collector is a venturi with welded "stars" to aid with flow and fluttering. They are very highly polished. The cost is high but, they should last for many years vs. mild steel and re-coating them after a handful of years.

When I receive them, I plan of dyno testing these vs my old side pipes that are from Lone Stars kit. I can't wait to see and test them and find out how much HP/TQ I'll gain.

http://fireflyperformance.com/