|
|
Post by zoona on May 31, 2022 21:47:14 GMT
Made my exhaust. It has no resonator, and this back box. 3" tubing from the down pipe (which is 2.75") While it does sound glorious... It is offensively loud. Embarassingly loud. I need to make it quieter. It looks like this:  It has a vband connection, so i am thinking of getting "quieter" back box and simply replacing it. Then at least i have a loud version if i want to be a twat. There are so many to choose form that I a bit lost. There is quite a bit of space, so I could fit something quite big, but i need enough room to snake the pipe back for the exhuast tip, so i think it would have to be something like:  Any suggestions on back boxes? Or makes that you have used or sizes that you have used? Requirements are - Not to sound like a twat - 3" pipe, - mild steel - not stainless. - Preferably from here |
|
|
|
Post by warpspeed on Jun 1, 2022 1:05:18 GMT
A three inch straight through system is going to be pretty noisy and drone, as there is virtually no back pressure. All the exhaust pulses go straight through without much attenuation, and the whole system will resonate at some natural droning frequency. A totally silent exhaust requires a constant steady gas flow at the exit point without any pulsing at all, which is neither practical or really possible. Best compromise, and one that works is to have at the rear of the exhaust something that closes right down at small constant throttle opening, offering only slight extra pressure drop. The three inch pipe will have enough pipe volume that a restricted outlet at the rear will produce a more steady constant outlet flow and greatly reduce noise without adding much extra back pressure. When you floor it, the increased flow opens up the restriction still maintaining only a very small constant back pressure. The noise reduction will be substantial, and it will add very little extra back pressure when flat out. Only muffler on the market that I know of that has a spring loaded flap inside that does this is the Dynomax VT muffler. These all have 2.5 inches internal flow diameter, but can be bought with 2.0 inch, 2.5 inch, or 3.0 inch inlet and outlet stubs. Best results are with small capacity four cylinder engines with a LOT of pipe volume between the engine and rear mounted VT muffler. They don't work anywhere nearly as well on large capacity V8 engines, but for us, definitely can be pretty effective. www.jegs.com/p/Dynomax/Dynomax-VT-Mufflers/1316158/10002/-1 |
|
|
|
Post by zoona on Jun 1, 2022 1:12:07 GMT
watching the video... it seemed to suggest that at full throttle it opens up to be noisey. Which is sort of what I am trying to avoid.
Or am I completely missing the point?
|
|
|
|
Post by warpspeed on Jun 1, 2022 1:25:23 GMT
Typically with a big straight through system, most of the noise will be a very angry snarly idle, and an annoying constant drone at steady freeway speeds.
Sure its going to make more noise pedal to the metal, but any exhaust system does that.
If you want it quiet even flat out, put the factory exhaust back on !!
What the VT does, is remain quiet enough not to attract any attention when you are driving around at normal traffic speeds.
But flat out it will definitely be more noisy.
The idea that you can fit a three inch straight through that is going to be as quiet as the factory exhaust is just not possible.
|
|
|
|
Post by wannabe on Jun 1, 2022 9:23:30 GMT
The AK Automotive 'Race' system is very good in terms of only being a bit 'rorty' when under load - off throttle it is very quiet, remarkably so, and cruising is pretty civilised.
It is not cheap, however... lol
I need to see if I can get a video as the youtube ones are basically useless, haha.
|
|
|
|
Post by howardb66 on Jun 1, 2022 12:33:32 GMT
Would it be possible to add in a mid silencer? As warpspeed said, a straight through system is never going to be quiet. |
|
|
|
Post by atlex on Jun 1, 2022 14:14:42 GMT
I would try a bung.
|
|
|
|
Post by zoona on Jun 1, 2022 14:37:05 GMT
OK, so exhaust education required here... Like many things on this car, I have tried to do some reading/understanding, but mainly just dived in.
Straight through exhaust means using a silencer that isn't chambered?
Can I just use a bigger, chambered silencer to reduce the volume?
Or would a chambered silencer of a similar size make a decent difference?
I do have space to put something else in main pipe back from the front - but it is pretty tight, so it would need to be quite slim
My goal here is to reduce the overall max volume - at the moment it is obnoxious, and wouldn't pass a UK track day db level test.
I think they are a bit more lenient here, but if i saw/heard this car driving down the road, i would think the driver was a complete nob.
|
|
|
|
Post by Zed. on Jun 1, 2022 17:33:02 GMT
if i saw/heard this car driving down the road, i would think the driver was a complete nob. sayin nuffin   Rich. |
|
|
|
Post by zoona on Jun 1, 2022 18:53:45 GMT
if i saw/heard this car driving down the road, i would think the driver was a complete nob. sayin nuffin Rich. Maybe I should have been more specific about the noise being the cause of that... |
|
|
|
Post by Zed. on Jun 1, 2022 19:29:34 GMT
sayin nuffin   Rich. Maybe I should have been more specific about the noise being the cause of that...  Rich. |
|
|
|
Post by atlex on Jun 1, 2022 20:16:58 GMT
So the reason I say you should look at a bung is this. You've already got a turbo in the system. The turbo dampens the noise and pitch significantly. I happen to like the turbo + straight pipe sound. BWAAARP. Very Rallye.
I assume the exhaust is already mild steel, it should mellow a bit after more use also.
But a decent bung should kill the decibels without killing the performance.
Look at the ones M2 Motorsport sell.
|
|
|
|
Post by zoona on Jun 1, 2022 20:48:33 GMT
So the reason I say you should look at a bung is this. You've already got a turbo in the system. The turbo dampens the noise and pitch significantly. I happen to like the turbo + straight pipe sound. BWAAARP. Very Rallye. I assume the exhaust is already mild steel, it should mellow a bit after more use also. But a decent bung should kill the decibels without killing the performance. Look at the ones M2 Motorsport sell. Sorry, I missed your previous post. I think it appeared just before I pressed go on mine. I'll take a look |
|
|
|
Post by Zed. on Jun 1, 2022 22:33:25 GMT
So the reason I say you should look at a bung Must. Resist.  Rich. |
|
|
|
Post by warpspeed on Jun 1, 2022 22:52:39 GMT
The Supertrap rear muffler has been around for a very long time, and consists of a rear bung with removable baffles. You fit only as many baffles as you think you need to make the noise tolerable. Not familiar with the M2 motorsport bungs, but it sounds like something that works in a similar way.
The Dynomax VT does a similar thing but far more cleverly, because it self adjusts to close down when you are not trying very hard to go fast, and opens right up at full throttle.
I have been experimenting with these kinds of adjustable noise reducing systems for many years and my latest creation might be of interest to some of you. The basic idea is to have a large poppet valve, similar to a wastegate but MUCH larger.
It has a spring and a giant diaphragm actuator the same as a wastegate, but this is the mother of all wastegates in size.
Exhaust pressure from the front of the exhaust probably from the dump pipe area opens the poppet valve which is placed right at the rear of the exhaust system. Opening pressure is about 0.4psi and fully open at about 0.75psi
That is very low, but its enough to hugely reduce the noise level.
The current prototype uses a 2.5 inch poppet valve and a six inch actuating diaphragm. The poppet valve works within an exhaust turbine housing which flows in the reverse direction. Exhaust hits the poppet valve and spills out around the circumference. The exhaust turbine scroll gathers the exhaust which is connected to the exhaust tip.
Have not yet tried this particular prototype on the car yet, too many other projects on here at the moment.
This was very easy to make, it really needs a larger A/R housing with some serious porting, but what I have now will be good enough for some proof of concept testing.
This one is 2.5 inches and uses a GT35 housing. A 3.0 inch poppet valve and GT45 housing is another possibility.
From previous experiments along similar lines over the years, this should be the perfect quiet stealth exhaust system for high power on the street.
I do have some pictures of this, but unfortunately have no way of posting them.
|
|
le sigh