121 replies to this topic

[swast4]

Noise cancelling mufflers, that sounds interesting? How do I measure back pressure and its implications, can I pull an exhaust sensor out put a T in it and then a pressure gauge and exhaust sensor back in? The other thing is I could remove the twin tips and put a single 3.5" tip with a 73mm inner diameter. Sent from my LG-H815 using Tapatalk

[Jetpilot]

I swapped my tullet to a single tip, it didnt really seem to make much difference when on the go, it worked for static noise tests but still black flagged at stricter tracks.

 

Matt Bentley was working with flowmaster silencers if you want to take a look, but i have no idea how this affected flow rates and mapping.

 

My solution/bodge if you like was gut a std silencer, pretty much the biggest you can get in the space, make it straight through and then fire it out through the diffuser into the tarmac, it was considerably quieter than a tullet but never had a chance to test at the stricter tracks before i sold the car, you do have to alter a little pipework and cut a 3" hole through the diffuser but it seemed pointless having a car build for tracks days that you couldnt use on track days. If i had kept the car would have also swapped out the cat for a small resonator too, which would assist.

[CHILL Gone DUTCH]

I swapped my tullet to a single tip, it didnt really seem to make much difference when on the go, it worked for static noise tests but still black flagged at stricter tracks.

 

Matt Bentley was working with flowmaster silencers if you want to take a look, but i have no idea how this affected flow rates and mapping.

 

My solution/bodge if you like was gut a std silencer, pretty much the biggest you can get in the space, make it straight through and then fire it out through the diffuser into the tarmac, it was considerably quieter than a tullet but never had a chance to test at the stricter tracks before i sold the car, you do have to alter a little pipework and cut a 3" hole through the diffuser but it seemed pointless having a car build for tracks days that you couldnt use on track days. If i had kept the car would have also swapped out the cat for a small resonator too, which would assist.

 

My chamber is actually built in to the main box, really seems to do well and even when the box completely burnt up the packing i still didn't get kicked off the track at snet 

 

but my box is very very oversized 800mm wide with a 200mm empty chamber 

[swast4]

Thanks guys, I did see that empty chamber on your exhaust Chris and wondered what it was for.

Also I want convinced that the single tip made much difference

I think I've come up with another solution.
I've had a good rummage under the car and measured, prodded and felt all along my exhaust back box and tail pipe. I've decided I'm going to squeeze another 5"repackable silencer about 12"long.this is to go from the main box outlet to the tailpipes.
There is room behind the heat shield, a small amount of room between exhaust tail pipe and shield.
So this will involve moving the Offside exhaust bracket pin 15mm to move the exhaust on that side towards the engine.
Then the U bend on the outlet of the main can will have a 20mm straight section inserted to give me the clearance from the main can. Then the straight section from the U bend to the tail pipe will have the new Silencer put in it.
By moving the bracket back towards the car by 15mm will move the tail pipes in by 10mm, I will try and over come this when welding the tips back on. (I'm not doing the wising by the way).

This should give me 3 silencers all repackable with ZT1.
I remember Nevs investigation into exhausts that the more silencers the better, but not necessarily the length, so we will see.

The heat shield will need a bit of bashing to get the exhaust in but hopefully it will fit.

I have a couple of questions

The exhaust cans will be virtually touching each other, so you think I should wrap them with a thin exhaust wrap in these places to stop them resonating off each other.

I need to relocate one of the wide band exhaust sensors, can I fit it next to the other one on the U bend upstream of the main can, it will save me Re routing the wiring to the downpipe.

I Hope this works..........

Sent from my LG-H815 using Tapatalk

[CHILL Gone DUTCH]

YOU don't want the exhaust knocking against each other It will produce false knock to the knock sensor and pull the ignition

[vocky]

Having a single exit exhaust works well for track cars, just blank one side off rather than using just a single tip

[swast4]

Hi Chris, I didn't think of that, I'm going reassess my gaps. I'm off tomoz, looks like it's coming off again to measure measure measure. Hi Vocky, I was going to weld the tip but as jetpilot said its still going to fail the drive by and Donnington is one of my favourite tracks, which is strict. Sent from my LG-H815 using Tapatalk

[alexb]

Noise cancelling mufflers, that sounds interesting? How do I measure back pressure and its implications, can I pull an exhaust sensor out put a T in it and then a pressure gauge and exhaust sensor back in? The other thing is I could remove the twin tips and put a single 3.5" tip with a 73mm inner diameter. Sent from my LG-H815 using Tapatalk

 

The most common used trick for 'noise cancellation' in mufflers is using quarter wavelength cancellation. That's frequency dependent however and is usually just used to get rid of a persistent drone. Most OEM mufflers have such a resonator built in. I don't think it does much for you on track however, as you spend most of the time in higher RPM regions and the noise measurement is usually done when at higher RPM. Or perhaps if you tune it more towards the higher RPM (and temperature, as speed of sound is temperature dependent) range found on track. Even better, tune it for the RPM range you use where the dB meter of your favorite track is . 

 

Back pressure can be measured by using a normal pressure sensor, but at some distance from the hot exhaust. Temperature is easier, as you have sensors that go to 1000C or more. You can use the lambda sensor bung for both, but as far as I know you don't have combined T and p sensors for the exhaust.

 

As far as your three in a row plans go, yes, you will get rid of some dB. Question is how much, or rather, if it's enough. Issue with the absorption type of mufflers is that they're pretty good in keeping back pressure low, but bad in keeping noise down. Expansion chamber designs are more or less the reverse, but depend on chamber volume and entry and exit diameters a lot. In both cases you want the biggest volume muffler that still fits the available space. The standard VX turbo muffler is 68 cm long, 29 cm wide and 17 cm high. The available space allows for an even longer one, up to 75 or even 80 cm. Problem is that there are very little universal mufflers that have exits in the middle. Hence the Tullett solution of taking a round muffler with the extra bend to exit in the middle. If you want to stick to absorption, you could also take an oval one with an offset straight perforated pipe though the entire muffler, a 180 bend outside (non perforated if you want to avoid noise ) go back into the muffler with perforated pipe and bend 90 degrees to exit in the middle. Add some nice tips that don't use the quarter wavelength trick to amplify the noise at certain frequencies and you have something that is simple and might even work. More volume for the gas to expand in and more length of pipe for the absorption.

[CHILL Gone DUTCH]

My box Is 700 mm long and 7 " diameter

Edited by CHILL Gone DUTCH, 29 April 2018 - 07:22 PM.

[swast4]

Thanks Alex,
I was thinking of basing another exhaust like you said on an original back box and rip the inside out.

But for now I'm hoping for a result using the 3 boxes.

I've taken the exhaust off yet again and remeasured and I can definately fit another 5" silencer in, that is 11" long.

I just have to wait to get them made........ Hopefully they'll fit me in early next week.


Sent from my LG-H815 using Tapatalk

[FLD]

I have a decat silencer in mine. Helps a bit but I'd like more noise damping. I considered a third box like you but I'm not convinced it'll be that great. I'd look into a 3" miltek style box if I were going to do anything more.

[smiley]

Vocky's 2.5 inched NA miltek box is doing ok on 250hp not?

 

 

[swast4]

Hi FLD, Is the miltek design a baffled design? Is it on a 3 " Sent from my LG-H815 using Tapatalk

[FLD]

I believe milteks are 2.25 in and are a baffled design. A 3" version would need some R&D

[swast4]

Well I've managed to get my exhaust back with my 2 new repackable silencers. I've trial fitted it and marked up the tailpipe for correct fitment. I'm surprised how well it has fitted, I just need a slight mod to one of the hangers.

I'm dropping it off on Friday for final mod, then I'm fitting it on Wednesday so fingers crossed it's as quiet as a Tesla. Only joking but I do need it to pass Donnington drive by......

The lads said I could have put an expansion chamber in the main muffler which would help also, so a perf pipe with wadding say 25cm then an open chamber of 20cm, then a perf pipe again for 25cm with wadding. But since I've packed it already with new wadding I can't be bothered. I suppose this is a bit like tubular design, but they have the chamber at one end.
I remember Nevs, exhaust thread, where he had better results from each time it got to expand rather than the length of expansion.



Sent from my LG-H815 using Tapatalk

[swast4]

There was a trackday at Oulton Park today, so I thought I'd pop down and get sound tested and hopefully get to go out for 20 mins to do a drive by.

My static was 103db and they wouldn't let me out, as they had alot of people out. (it was 4pm and I know alot pack up by then, but rules is rules)

Did anyone know what that, would equate to on a drive by with a Harrop SC?

Adam


Sent from my LG-H815 using Tapatalk

[CHILL Gone DUTCH]

Mines 99 Db static and is normally ok on drivebys

But only just

[CHILL Gone DUTCH]

I have failed the driveby at Bedford after passing the static at 99 Db

[CHILL Gone DUTCH]

Think Bedford I s a 88 Db driveby

[swast4]

Cheers Chill,
Looks like I'm still going to struggle, I've got Donny on 18th of June which is 98db drive by, so will get a pair of bends made and point towards the track.
When you do your static test, do you do it at 4.5 or 5k?
Also have you got an enclosed air filter or cone type?

Sent from my LG-H815 using Tapatalk