96 replies to this topic

[vocky]

Mine probably loses enough heat before it reaches the backbox so the packing has survived ... so far

[CHILL Gone DUTCH]

Your right I think it's going have to be sound cancelling or a baffled system with wadding which will cope with the heat and sound waves Or maybe both

Edited by CHILL Gone DUTCH, 17 November 2016 - 06:47 PM.

[Nev]

I've spent a lot of time head scratching about this issue as it affects me more than anyone and I want Nippers 5th exhaust to actually work, which is why I am doing the job myself and not using some off the shelf silencer.

 

BTW, there is 3 advantages (that strike me off the top of my head) to splitting the path of an exhaust (assuming you keep the twin pipework the same bore):

 

1. You halve the gas speed, which gives the gas twice the time to refract.

2. You union the gas flow at the exit out of phase (by having asymmetric length pipes), thus helping to reduce noise.

3. You can also use wave cancellation by facing both flows into the other (instead of point 2 above), but it could cause possible problems.

 

 

Edited by Nev, 17 November 2016 - 08:17 PM.

[anz3001]

I've spent a lot of time head scratching about this issue as it affects me more than anyone and I want Nippers 5th exhaust to actually work, which is why I am doing the job myself and not using some off the shelf silencer.

 

BTW, there is 3 advantages (that strike me off the top of my head) to splitting the path of an exhaust (assuming you keep the twin pipework the same bore):

 

1. You halve the gas speed, which gives the gas twice the time to refract.

2. You union the gas flow at the exit out of phase (by having asymmetric length pipes), thus helping to reduce noise.

3. You can also use wave cancellation by facing both flows into the other (instead of point 2 above), but it could cause possible problems.

 

 

 

The other side of that is if you split and use a smaller bore afterwards it allows for tighter pipework which potentially gives more usable space and a smaller bore in the box gives a larger area for silencing material.

 

3" into 2 x 2.25" works.

 

Do you have or are you keeping the heatshield? Have you explored bringing the front pipe down the centre in 3", split into 2.25" and run one to the left and one to the right using what we call wing boxes, in/out same side (like the 911) as large as can be procured.

[Nev]

 

I've spent a lot of time head scratching about this issue as it affects me more than anyone and I want Nippers 5th exhaust to actually work, which is why I am doing the job myself and not using some off the shelf silencer.

 

BTW, there is 3 advantages (that strike me off the top of my head) to splitting the path of an exhaust (assuming you keep the twin pipework the same bore):

 

1. You halve the gas speed, which gives the gas twice the time to refract.

2. You union the gas flow at the exit out of phase (by having asymmetric length pipes), thus helping to reduce noise.

3. You can also use wave cancellation by facing both flows into the other (instead of point 2 above), but it could cause possible problems.

 

 

 

The other side of that is if you split and use a smaller bore afterwards it allows for tighter pipework which potentially gives more usable space and a smaller bore in the box gives a larger area for silencing material.

 

3" into 2 x 2.25" works.

 

Do you have or are you keeping the heatshield? Have you explored bringing the front pipe down the centre in 3", split into 2.25" and run one to the left and one to the right using what we call wing boxes, in/out same side (like the 911) as large as can be procured.

 

 

Yea, I've thought about all of this over the last 3 or so years, there is nothing anyone has said yet that hasn't already struck me. Here is a photo of some of my sketches and ideas, I have considered just about everything and anything. I even considered a system that ran up the N/S chassis and exited out of near the front wheel arch (this had quite a lot of merit to it BTW).

 

 

The bare truth of the 2ubular system is that it is simply executed and shows no design initiative. This is probably fine for some people, though I have heard of people having problems getting on track with them (eg MaxR).

 

[The Batman]

Everyone is on 7" diameter which works for people under 300bhp For above that you need the 8" and gun silencer or cat this works perfectly If continue to get noise issues on track use a 90' bend and point to floor

Edited by The Batman, 17 November 2016 - 09:57 PM.

[CHILL Gone DUTCH]

Is mine a 8" joe ?

[Nev]

I spose you could even point it under the car towards the front for track testing!

 

For me, the noise issue is also about waking my neighbours up, so my idle and low RPM noise output needs to be really quiet if possible.

 

Here is one of my previous efforts, it only reduced noise by 2 dB, maybe with a downward pointing bend it might have managed 4 dB.

 

Edited by Nev, 17 November 2016 - 10:42 PM.

[The Batman]

I can't wait to see what this exhaust looks like. The pic above looks like something you stole out of your mums top drawer

[Nev]

The pic above looks like something you stole out of your mums top drawer

 

Actually I stole it from your mum's top drawer, whilst I was over there "rummaging around"!  

Edited by Nev, 17 November 2016 - 10:52 PM.

[Exmantaa]

An absorbtion type silencer only works in the middle and high frequency range, so whatever you design it will still have issues in the low ranges.

So to really make an efficient muffler you will need to combine this witn a reflection type (effective in low/mid range) or maybe use helmholtz part...

[Nev]

An absorbtion type silencer only works in the middle and high frequency range, so whatever you design it will still have issues in the low ranges.

So to really make an efficient muffler you will need to combine this witn a reflection type (effective in low/mid range) or maybe use helmholtz part...

 

Yep it may be the case, we shall see, I have lots of variants of pipes + bends + flaps to assemble, each one of which I'll test with the dB meter.

[siztenboots]

vacuum chamber around silencer (wacko)

[Arno]

Perhaps just as an example..

 

This is what the OEM Toyota Elise (111R) silencer looks like inside:

 

 

Most of the pipework on these is 2.25 to 2.5" and it's enough to get it to pass type approval noise regs with the 2ZZ-GE with and without SC.

 

As you can see it's pretty simple inside and doesn't even use that many chambers/baffles to cut the noise. And cutting the noise it does!

 

Also like most OEM silencers it's a double-skin design to cut much of the noise re-transmission to the outside because the outer skin on a silencer starts resonating so the noise then gets radiated out from the silencer body in quite a significant amount too,

 

Such chambered designs do make the exit point of the silencer fairly irrelevant and freely selectable, so you don't need external pipes/bends/etc.

 

The version mounted on the SC'ed Elises (220 and up) is pretty much identical. It just brings out the end pipe a little differently, but similar construction so for Lotus it seems to scale pretty well.

 

Anyway.. Just as a bit of background info..

 

Bye, Arno.

[Nev]

Thanks for the pics, can you just explain where the flow is on this thing please, so I can understand it. Ta.

 

[fezzasus]

In through top right pipe, which flows through the longest pipe at the top into the large open chamber second from left, this then flows into the shorter long pipe at the top which flows into the chamber second from right. This then flows through the mesh section into the tailpipe chamber.

 

The dimensions of the large open chamber and the pipelengths flowing into it will help reduce low pitch drone, while the dimensions of the mesh chamber close to the tailpipes will be used to attenuate high frequencies. 

Edited by fezzasus, 20 November 2016 - 01:24 PM.

[Nev]

k, thanks for that.

 

So am I right in thinking the 2 pipes that point fwd/bwd in the pics are the tailpipes that are ejecting gas rearward (towards the tarmac) ?

[Exmantaa]

Funny, was just looking to this same 111R exhaust pic yesterday.  

 

 

[fezzasus]

k, thanks for that.

 

So am I right in thinking the 2 pipes that point fwd/bwd in the pics are the tailpipes that are ejecting gas rearward (towards the tarmac) ?

 

Correct

[fezzasus]