More Silent Silencer

[erictharg]

As I was right on the 105dB limit at Mallory I decided to find a better silencer. Ended up with a 5" dia re-packable one from Demon Tweeks. Need to cut and shut the link pipe as it will have to sit a bit lower than the skinny original. It's also a lot heavier - not good. But will give it a go. If effective I'll look for something more svelte when budget allows. Anyone else tried anything different in the silencer world?

[Mknight702]

What, pardon, can't hear you, speak up!

[erictharg]

Exactly. Earplugs recommended for longer journeys. New silencer now in place. Doesn't look too bad. Overall noise level not that different but it's killed some of the higher frequencies so should bring the DbA level down. I'll be very pi**ed off if it doesn't. Mission now to find something similar and a couple of kg lighter. That doesn't cost the earth...

[Mknight702]

Charles,

Do you run the perforated cone? I wondered how much difference that makes, thinking about a trackday but it has a 102db limit.

[Westfield 129]

I have been using stainless mufflers from Magnaflow. I purchase from www.justmagnaflow.com They are a warehouse distributor, and the pricing is very competitive.

The mufflers come in several lengths, in polished or unpolished stainless. They are straight through, and relatively light. The mufflers fit the car well, as they are not too big around.

I already have a substantial hearing loss, so I always protect my ears in any open car. I can't tell you how loud it is, but I can say that nobody has bothered me about the noise. 102db? Probably not that loud.

[erictharg]

Big, heavy, ugly silencer not the answer. No quieter. So spoke to the people who make the big ugly silencer and they tell what they do to take the edge off noise without adding too much back pressure. They add a couple or three little perforated half moon "deflectors" into the straight through tube in the muffler. Located at even intervals and spaced 180 deg from each other they just bounce enough of the gas into the wadding to make a real difference. Otherwise all that high velocity hot gas just goes the easy way out of the pipe, expending very little energy through the perforated tube into the wadding.
So, I did the mod on the original Westfield silencer, and re-packed with new wadding from DT. 101dBA. Brilliant. I have the small original light silencer and no noise problem. And no noticeable loss in power.
I will say that it's worth trying just re-packing your original silencer before doing anything more extreme. An hours job. Drill out a few rivets. Re-pack, and rivet back together.

[Westfield 129]

101db? That breaks every club racing noise barrier at every track here, and every noise law in all 50 states. Actually, that is hardly any muffling at all. 100db is "threshold of pain", and surly will leave permanent hearing damage with long exposure. Just how "loud" is "quiet" in the UK?

My "loud" Magnaflow does 89db, borderline for Laguna Seca. No measured loss of power. Considerably quieter.

[sgrant]

There are a wide variety of limits at UK trackdays, depending on how sensitive the local residents have become. Usually the car is either measured in the pits, before the trackday starts, about 1 meter away from the exhaust, at about 2/3rds of max revs ("it's an old engine, mate, only revs to 5500, honest"). This is how they do it at Brands Hatch, for instance. Otherwise, at places like Donnington there are microphones set up around the circuit and if you trip one, you are black flagged. The trick is to try to work out where they are and just back off around those locations.

The strictest circuit that I know is Goodwood, which is almost always 95db, except for a very few weekends a year (Festival of Speed, Goodwood revival, plus a handful the GRRC run a couple of trackdays a year).
I was at Brands last week and it was 102db and so there was a noticable lack of the usual exotica that normally turn up at GoldTrack days. The Porsche I shared a garage with had a ridiculous exhaust arrangement in order to meet the requirement.
Silverstone trackdays seem very varied, including quite a few that are unlimited. I've done a couple of unlimited days there and, not suprisingly, they are the days when the really lovely stuff comes out to play - including a 956 on one occasion. Last time I was there, an ex-Le Mans Porsche came up the hanger straight behind me and as it ripped past it was so loud that my hands involentarily came off the wheel and attempted to cover my ears (unsuccessfully, since I was wearing a helmet). The pain in my head as it went past was horrible!

My Caterham, at 4500rpm, with a mic 1meter away from the pipe, is 94db or so, according to the marshall last week. I'm pretty sure at anything under ~4000rpm my Westfield is much, much louder than the Caterham, but I'm not sure about at the top end - the k-series gets pretty feral as it gets close to the limiter. I've not taken my Westfield on a trackday yet, but I suspect I'd need to be on a 105db -limited day or some such to be safe. Obviously, given that there's an r-squared relationship between the measured sound level and the distance from the end of the exhaust to the measuring device, the key thing here in comparing noise levels is how they are being measured. I'd be suprised if your Westy is only 89db measured 1m away from the end of the pipe, at 4000rpm.

stephen

[Mknight702]

Westfield 129 wrote:> My "loud" Magnaflow does 89db, borderline for Laguna Seca. No
> measured loss of power. Considerably quieter.

[b]If[/b] I understand correctly, in the States you measure noise at 10 meters, some rough calculations show that the 105db at 1m is equivalent to 85db at 10m, so if that is correct your car at 89db would be too loud for all but the unrestricted (very few and expensive) trackdays in the UK.

[erictharg]

A bit like tons, and gallons, seems as if we do things a little differently. 105dBA is the norm for a road car based racer at most circuits, but if you are a "sports car" (in racing terms) you get the same 108dBA as the open wheel cars. As before, at 1 metre from tailpipe, and 45deg to the axis of the pipe.