Exhaust Baffles

Much interesting work took place at the weekend, I got some baffles off ebay (dB Killer) I think the ones I got were for a bike. My exhausts are 5" with a 3" ID baffle the full length of the side pipe. The plan is to stuff an extra baffle, intended for a puny 3" exhaust down the centre of the existing baffle. Others have then stuffed some stainless steel scouring pads from Tesco to further bring down the noise. We are taking a vaguely scientific approach and taking measurements of 1) original 2) extra baffles and 3) extra baffles + scouring pads.

These are the baffles:

and these are the sidepipes and existing baffles:

This is the new baffle wrapped in stainless scouring pads ready to be fitted. Looks a bit amateur (matches the rest of the car then!) but I'm well informed that it does actually work.

The weld at the end of the existing baffle is just visible and was removed with a dremel where it had penetrated through. This allowed the new extra baffle to slip in with a bit of help from Mr Wood and Mr Hammer. Then, out came the cobalt drill bits to drill through both baffles and fit a retaining screw.

End cap back on and job done.

Now as for the measured noise reduction, this post is a bit of a cheat as I did the passenger side exhaust on Monday night. On Sunday due to rain and the water pump deciding it was bored of keeping the water on the inside, we only added the extra baffle to the drivers side. The results were interesting though. With a calibrated sound meter (not a smart phone app!) with the original baffle we measured an average of 100dB (left and right) at tickover. The test in the IVA manual says the sound meter has to be 500mm away from the exhaust, level with the outlet at an angle of 45 degrees. The engine has to be at whatever rpm equates to 3/4 max engine power and the noise limit is 99dB. Until a couple of years ago it used to be 101dB. We had a guess that 3750 was probably about right for this, although its probably a little higher, more like 4250.

Anyways, 100dB at tickover. At 3750rpm the average was 115dB, which is very very loud. With the extra baffle in (drivers side only) it was 96dB at tickover and 106dB at 3750rpm, which is an impressive reduction considering the passenger exhaust is still on full loudness. I then baffled the passenger side and re-tested. Tickover was still 96dB and 3750rpm was 105dB. I think this was because when you do the noise test with sidepipes you are only "listening" to one side at a time so the combined effect of silencing both sides was a little disappointing.

The water pump is hopefully not much of a problem, it was spurting a bit of water and steam from the gasket on the cover plate on the back of the pump. I didn't have the correct imperial spanner (shame!) to nip up the fixings so an imperial spanner set is winging its way from ebay.

On a more general note, this could be a good solution for track days as apart from cleaning off the weld on the inside of the large baffle and drilling the hole for the fixing screw it only took about 15 mins, which included locating the correct tools which were scattered to the four corners of the garage. 

Most UK tracks have a drive-by noise limit measured trackside on a main straight. At Donnington this is 98dB and at Snetterton this is as low as 92dB! Snetterton specifies the measurement is taken 20m from the track. They also have static noise tests which for road cars will be 105dB at the very most on a "noisy" day and can sometimes be as low as 98dB.

To meet the IVA noise regulations in the end more severe baffling had to be added. These beauties were constructed by the chap I got my exhausts off. They started off life very similar to my motorcycle DB Killer baffles and were then bent to match the shape of the end of the exhaust itself. A blanking plate was then cut to match the exhaust outlet shape and welded on the end. A good dollop of fibreglass wadding was then wrapped round and the hole thing held on with a big jubilee clip to avoid having to drill extra holes in the exhaust.

This is it fitted to the car, a 5mm radius stainless wire was bent to match the shape of the exhaust exit and welded on which then meets the IVA requirement for sharp edges as the exhaust in its standard form with no rolled edge would have failed that.

This worked extremely well and got my static noise below 90dB and my 3/4 max revs was tested at 97dB on one side, 98dB on the other side so passed the IVA noise test with room to spare. Driving with these fitted caused noticeable reduction in power and rather disappointingly made the engine so quiet that the tyre noise was the loudest thing when cruising along and rather spoiled the experience.