Adding more quietness to the exhaust

[dnb]

I got a friend to make a new exhaust for my TVR Griffith. His work is exceptionally good, and I'm incredibly pleased with how things turned out, but the car still isn't quiet enough.

All noise measurements were made with the same meter using the "standard" trackday test of 45 degrees, 0.5m and 4000 RPM.

With the STANDARD silencer (but an interesting engine) with twin 2" compression bent tubes, it made 113.5 dBA

With the new Edelbrock SRT silencer and a much smoother flowing mandrell bent twin 2.5" tube system it is now a more reasonable 106.5dBA

However, the trackday noise limit I need to achieve is 105dB, but I would prefer something much closer to 98dBA so I can use it at Goodwood.

Short of welding plates across the back, are there any ideas?

Here's a couple of old pics. One with the old exhaust fitted, showing how little space there is to work with, and one with the tacked together new system.





Thanks![/img]

[V8Smudge]

Is there any way you can squeeze a couple of resonators into the angled section of the tailpipes, just to take the edge off the volume? A mate of mine is a Powerflow agent, he had to play around with silencers to get the exact exhaust noise that suited me, while being legal and bearable.

[Ian Anderson]

Put end turners on the tip off the exhaust and point one out each side of the car

They must test 0.5m 45 degrees from the outlet - that means the meter will only read one pipe at a time!

Were your readings taken inside the shop? If so the echo and other noise would have added to your number

I believe there is a specificationlike no wall or vertical obstruction within 30 m of the tail pipe

But where they find that space at Goodwood????

Ian

[kiwicar]

have you got a ballance pipe between the two sides of the exhaust? if not stick one in at the collectors, should be worth 3dB saving (and a few extra GGs), if you have a ballance pipe already try an X pipe connecting the sides it should be better by another 2 dB or so. You have the exhausts ending at the very back of the car, chop 8" off the tail pipes weld a pair of bends on cut so the gasses exit straight toward the ground, preferably tuck the pipes up under the rear valance if you can, either way have them stop a couple of inches before the rear line of the car, it should save about 6 maybe 8dB. If you still need more you could try a short cross box in that bit where the two tail pipes run parrelel to each other (effectivly a scilencer box constructed between the two pipes, with wadding inside and perforations into the box on the inside of the pipes)
Best regards
Mike

[dnb]

Noise measurements were done well in the clear. It's a damned noisy beast!

The problem with sideways facing pipes is that I risk failing drive-by noise tests. It's why TVR stopped doing side exit pipes on the Sagaris. Worth a try though!

There is limited space for additional resonators. The main problem is distance between the bodywork and the exhaust.

[dnb]

Didn't see your post Kiwicar!

The 2 manifolds merge at the front of the car into a 3" pipe. This turns backwards and splits into 2 again for the silencer. It probably classes as a X pipe. There's plenty of GGs so I must have done something right...

There's no rear valance to tuck the pipes behind unfortunately, but another good idea - I could add one.

There's no space for a cross box in the parallel section at the back. The rear diff cooling fins get in the way. There may be room for a pair of short cherry bomb style silencers in the 45 degree sections, but I am worried about pipe diameter and whether the cherry bombs will be effective - I don't really need to attenuate the high frequencies these things tend to remove.

Turning the pipes down would look a bit ugly, but it seems the best way so far. I could make them removable, so not too worried.

[ramon alban]

Short of welding plates across the back, are there any ideas?

You are very close with your desperate suggestion.

The propogation of exhaust noise is enhanced by resonation so if you can retune certain parts of the system to interfere with that, then the noise output can be changed.

Like Louis Armstrong muted his trumpet, you can quieten your exhaust with a couple of home-brew baffles something like this:



Read about mine here :

http://www.vintagemodelairplane.com/pag ... ust01.html

then go to the PDF available from that page to study my article how the RV8 exhaust system behaves and what your options might be.

Within its comprehensive analysis you will find various suggestions regarding the muting (or even the amplification) of noise.

Some may not be practical (for you) but understanding the exhaust process may lead you to resolving your problem.

Examples:

# revert to cast iron headers.

# exhaust wrap

# baffles as mentioned

# customised reflecting bombs

# you might also try clamping the twin pipes to each other where they run parallel to disrupt their individual resonance and kill any harmony,

Sadly though, because the most efficient exhaust of all is "no exhaust" anything you do to restrict or change the nature of the noise may also further reduce its efficiency and therfore cause loss of power.

It's a balancing act that has to be addressed depending upon the parameters of need versus the practicality of modification.

[V8Smudge]

There may be room for a pair of short cherry bomb style silencers in the 45 degree sections, but I am worried about pipe diameter and whether the cherry bombs will be effective - I don't really need to attenuate the high frequencies these things tend to remove.

This is the section I was on about, a resonator/silencer could definitely take the "bark" out of the system !

[dnb]

Ramon - super document. Thanks.

All, I will try to get some sound recordings of the car so you can hear the problem. It doesn't bark as such. Instead it sounds like a small angry thunderstorm.

Here's another pic of the exhaust at the workshop, 5 minutes before it was fitted to the car.


And while we're talking about noise, here's the engine bay - guess how loud the induction noise is Note that this pic doesn't show the cold air feed pipes etc. You can also see the interesting forward facing exhaust arrangements TVR thought were a good idea...


Thanks so far - I have some really good ideas to try out as soon as the snow goes away.

[kiwicar]

From what I remember Powerflow do some nice straight through short boxes, if you can fit one in the 45 deg section this may well do the job, I think you may have to do several things to fix this, bit should be possable.
A heat shield above the collectors , keeping the hot air away from the inlets would also get you a few HP more.
Best regards
Mike

[russell_ram]

In pipe baffles would get around your package/sapce issues - add as few or many as you need ?

http://www.summitracing.com/search/Depa ... Rank%7cAsc

Russ

[stevieturbo]

Surely there is room for some straight through "chery bomb" style silencers ?

There are lots of straight sections where they could be installed, and are available in a variety of lengths.

As a last resort, you could fit a couple of hi-flo cat's up front which would help reduce noise some too.


But there is a far more effective solution, and looks like plenty of room too.

Install a couple of turbochargers up front. They reduce exhaust noise a fair bit

[dnb]

Stevie - you suggest the very same solution as I did.

The result of implementing it would mean I would have an "accident" that would prevent me having more children. I see this as a bad thing.

BTW the shortest (stainless) cherrybomb I have found is 12" body and 16" overall. These just about fit in the rear 45 degree sections, but 12" overall would be much easier to fit keeping the pipe spacing looking standard. Any pointers?

[stevieturbo]

What style of silencer is the existing one ?

Isnt there room in the rear sections after the silencer ?

And possibly room at the tail section, or the straight between the bends ??


And length isnt an issue. Just buy a longer silencer and cut it to whatever length you need. It is just a round tube after all.
Magnaflow have a good range of round/oval stuff.

http://www.magnaflow.com/02product/univ ... hape=round

I would just go for the traditional straight through, perforated tube with packing style.

[dnb]

The original was an absorbtion silencer. This didn't work (even after I set fire to it and then repacked it)

I was reluctant to buy a silencer to chop it up (visions of the damned thing dropping apart or wadding tangling my grinder up ), but if you say it'll work, then I'll give it a go.

I replaced it with a funny magical reflection silencer. This did work, but not well enough. (7dB reduction over "standard")

The straight between the bends is 10" long (approx). I don't want the tail pipes spaced any further apart because this would spoil something else I am planning, and I am trying to keep things looking standard.

Straight after the silencer is a no-no. The tubes I have now only just fit between the chassis and diff. Making them thicker would result in them having to hang under the chassis, losing at least 3" of ground clearance. This is an unacceptable compromise because I couldn't get the car over the speed bumps near my house.

Tail section is possible, but the diameter can only really be increased to 3" without losing the clearance I need to get the car on my trailer. It has to be reversed on as it is (no clearance at the front either). The stainless cherry bombs I have found are all 4" diameter.

In short it looks easy, but has defeated me for ages now.