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Straight through mufflers

General engine tech -- Drag Racing to Circle Track

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ptuomov
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Re: Straight through mufflers

Post by ptuomov » Mon Jun 29, 2020 5:01 pm

tjs44 wrote:
Mon Jun 29, 2020 3:03 pm
I dont care if i loose 50 HP if I can kill the drone.Car operates 99.9% of the time from off idle to 2500 max.Cruise either in 4th on the street of 5th on the freeway is at 2000.Tom
In my opinion, a key to eliminating the drone is to have many mufflers, many pipe sections of different length, and a crossover or two. None of these measures in my opinion mean that one has to increase back pressure or lose any power.

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Re: Straight through mufflers

Post by pdq67 » Mon Jun 29, 2020 9:18 pm

Travis,

Might butt end to end a couple or even three WDT smooth perforated inner pipe real glass packs to help quiet her down. And I did this way back when I had my 409 "W" engine in my car.

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Re: Straight through mufflers

Post by SpeierRacingHeads » Mon Jun 29, 2020 10:02 pm

Has anyone ever tried a Thrush Rattler?
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Re: Straight through mufflers

Post by econo racer » Tue Jun 30, 2020 5:04 am

I own a muffler shop and I can tell you this. In your case I would adapt down to a 3 inch muffler with 2-3 inch tailpipes using the Dynomax super turbo muffler. It will sound a little quiter but more grown man sound and it breathes very well. I am a very big fan of there mufflers. I have uncapped my car at the track and it ran no faster maybe.04 for weight. Try it you will like it. :D There quality too.

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Re: Straight through mufflers

Post by ptuomov » Tue Jun 30, 2020 7:58 am

econo racer wrote:
Tue Jun 30, 2020 5:04 am
I own a muffler shop and I can tell you this. In your case I would adapt down to a 3 inch muffler with 2-3 inch tailpipes using the Dynomax super turbo muffler. It will sound a little quiter but more grown man sound and it breathes very well. I am a very big fan of there mufflers. I have uncapped my car at the track and it ran no faster maybe.04 for weight. Try it you will like it. :D There quality too.
I think that stepping down the exhaust pipe size as the exhaust gas cools makes all the sense in the world. If one looks at new factory stock performance cars, they all seem to be stepping down the pipe size from the turbine outlet to tailpipe and put the mufflers at the rear bumper area. I think that one of the main advantages is that one can have a muffler with a small pipe inlet/outlet area divided by the muffler chamber cross-sectional area, which leads to good noise suppression.

We tried to guesstimate how much the exhaust gas cools as it gets further down from the engine in this thread:
viewtopic.php?f=1&t=49628&start=45#p662407

No idea how close we got. Our final guess was that if you start with 3.5" pipe at the turbine outlet, 2.5 meters (about 8 feet) down you can go to 3" pipe while maintaining the same exhaust gas velocity. After a cross-over in a cross-plane V8, one could probably go down even more without losses.

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Re: Straight through mufflers

Post by falcongeorge » Tue Jun 30, 2020 4:24 pm

x3 on the smaller tailpipes. Same size as the collectors up to the mufflers, smaller afterwards. My experience is, no loss with smaller tailpipes, and quieter. This is what I am running on my chevy II, 3" tubes, x-pipe and Ultraflows into 2.5" tailpipes over the axle. Easier packaging, quieter and virtually no performance loss as compared to 3" tailpipes or dumped in front of the axle. Heat is energy, large surface area of big pipes dissipates that heat faster, what happens after the mufflers is probably of little consequence, within reason.

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Re: Straight through mufflers

Post by enigma57 » Thu Jul 02, 2020 2:54 am

travis wrote:
Fri Jun 26, 2020 3:31 pm
I would imagine that would get highly annoying very quickly if you drive it much.

One thing that would probably help though would be pointing the exhaust straight out the back, with the tip sticking out just a bit. I’ve noticed on mine, even with the really loud mufflers, that pointing the turn downs out from under the truck instead of pointed at the ground makes a huge difference inside the cab. The sound waves bouncing off the ground and back up under the bed gives it a really bad resonance, even when using quieter mufflers
That's been my experience as well, Travis. In my state, exhaust must exit outside the vehicle. Cannot terminate under the vehicle. Must extend past rear bumper. Or at the very least, must terminate outside the vehicle but behind the passenger compartment.

Not sure how tight they are on enforcing that now of days but having had carbon monoxide poisoning back in the '70s I am very careful about that.

Was working on a construction job running pipe about 20 ft. above the concrete floor. Don't remember a thing except for coming to. Passed out, fell off the ladder and got lucky...... Landed in a big pile of cardboard boxes filled with insulation. Was taken to hospital. They did a blood test and found high levels of carbon monoxide. My old work car at the time was a '62 Chevy and it had an exhaust leak I wasn't aware of.

I do like turndowns like the MOPAR cop cars had in the mid-'70s. An inch or two past the rear bumper, though.

Best regards,

Harry

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Re: Straight through mufflers

Post by David Redszus » Thu Jul 02, 2020 10:58 am

Years ago, SCCA imposed a sound limit on all road racing cars.

In attempt to comply and to improve performance, we designed a straight through exhaust using no mufflers fitted to a BMW four cylinder race engine.

It was a combination design, consisting of both diffusion, and side resonant style chambers. It allowed the exhaust pipe to be at the optimum length for performance which was much shorter than the exit point required by the rules.

The design program incorporated;
exhaust pipe diam & length, resonator diam & length, outlet diam & length and EGT.
The output was sound attenuation (DbA) and frequency, both could be tuned by changing inputs slightly.

The technical discussion is covered by Blair in his Four Stroke book.

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Re: Straight through mufflers

Post by enigma57 » Thu Jul 02, 2020 2:40 pm

That sounds like an interesting design, David. Just for fun, I thought I would fabricate an exhaust system for the '57 incorporating chambered sections and add some side branch Helmholtz resonators for added sound attenuation. Its an experiment. Wanted to see if I could make such a system having no conventional mufflers work on a road car.

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Re: Straight through mufflers

Post by gmrocket » Thu Jul 02, 2020 5:50 pm

I had a customer who had the dreaded highway 60mph drone, it was worse after he switched to a manual 5 speed od trans which we thought had more to with how and where the muffs were mounted

Same engine I built for him, was much worse with manual than the auto ...OD was the worst, in 4th not so bad.

He was asking about a cam change and other stuff that didn’t make any sense to me.

His wife refused to ride with him,,she is a looker, so he had to fix his problem..he tried a few different hi flow mufflers that didn’t help.

In a desperate last ditch effort he got some red pack sound proofing that’s used in residential and wrapped his mufflers banded with some thin tin....what a difference! It was like he put on stock mufflers

After that be pulled up his carpet and installed sound deadener , the thin sticky tar stuff with a foil facin

It was amazing after....

So it seems like his was some kind of weird resonating thing going on between the floor boards and road making it hard to drive

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Re: Straight through mufflers

Post by SpeierRacingHeads » Thu Jul 02, 2020 6:53 pm

I wrapped my dynomax in the video I posted and it made a totally different muffler out of it.

I used 2" header wrap.
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Re: Straight through mufflers

Post by dave brode » Fri Jul 03, 2020 7:51 am

Travis,

I have a pu with a 10.3-1 CR 454.

3" duals, with X pipe above the driveshaft, exit at the roll pan. Fyi - there is no other good place for the X. The truck has the old coil spring control arms.

I have the ability to swap from one pair of 12" body Dynomax bullet race mufflers under the cab [LOUD] to three per side [really very quiet, almost no highway drone]. I have two bolt flanges right behind the differential. I have two different rear "tail pipe" sections, one pair are just tubing and turn downs, the other pair has two 12" bullets per side and turn downs [for a total of three per side].

Fyi I started the engine at different points as I build the exhaust. The X pipe after the pair under the cab reduced the noise quite a bit.

If I want it to be really loud, I remove the rear section all together and let it dump behind the differential.
Dave

p.s. - on a related note, it is quite amazing how 12 or 18" of length on the secondary / tail pipes effects the sound. I'm talking sound "good' or shitty", not decibels. [pipemax ideal and avoid length stuff here]
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Re: Straight through mufflers

Post by ptuomov » Fri Jul 03, 2020 11:16 am

gmrocket wrote:
Thu Jul 02, 2020 5:50 pm
I had a customer who had the dreaded highway 60mph drone, it was worse after he switched to a manual 5 speed od trans which we thought had more to with how and where the muffs were mounted. Same engine I built for him, was much worse with manual than the auto ...OD was the worst, in 4th not so bad. He was asking about a cam change and other stuff that didn’t make any sense to me. His wife refused to ride with him,,she is a looker, so he had to fix his problem..he tried a few different hi flow mufflers that didn’t help. In a desperate last ditch effort he got some red pack sound proofing that’s used in residential and wrapped his mufflers banded with some thin tin....what a difference! It was like he put on stock mufflers After that be pulled up his carpet and installed sound deadener , the thin sticky tar stuff with a foil facin It was amazing after.... So it seems like his was some kind of weird resonating thing going on between the floor boards and road making it hard to drive.
A thicker or multi-layer case for a muffler can be surprisingly helpful in reducing the radiated noise from the case:
viewtopic.php?f=1&t=49628&start=165#p670675

Here's some test results on muffler case radiated noise:
Image

Image

http://ijiset.com/vol2/v2s7/IJISET_V2_I6_64.pdf

The worst case scenario is when the exhaust pipe/muffler drones at the rpm at which the the cabin resonates. The cabin resonance is a huge issue, in old transaxle Porsches they had heavy weight damper to kill any driveline vibrations that were close to cabin and other natural resonances.

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Re: Straight through mufflers

Post by falcongeorge » Fri Jul 03, 2020 3:51 pm

SpeierRacingHeads wrote:
Thu Jul 02, 2020 6:53 pm
I wrapped my dynomax in the video I posted and it made a totally different muffler out of it.

I used 2" header wrap.
I am scared to use wrap on a street driven car. I used it on headers before, and it DRASTICALLY shortened their life. May not be as much of an issue on mufflers as they don't get as hot?

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