I spent ages experimenting with different baffle designs before I landed on something acceptable, I found the motorcycle silencers too restrictive. That whooshing sound at the top end is caused by
too much restriction.
My silencer is basically a 4" SS reducer with 2.5" SS pipe that comes drilled with 3mm holes all over it, for this very purpose, that I cut, spread drilled/tapped so that it could be bolted on to the narrow end of the cone. The pipe is around 8" long and loosely wrapped with wadding. Overall, it is similar to the baffle in the link below although I polished the cone, which has a shallower angle than
that one, so mine looks nice :biggrin:. For all the agro I went through experimenting along with the cost, this would be a better solution and just wrap it with some (
glass) wadding. That's mine at the bottom.
I drilled a 4mm hole in the exhaust and then a corresponding 3.2mm hole in the baffle and tapped that to M4. The hardness of the SS means that although it's only 1.5mm thick there is enough to hold the baffle securely in place with one fastener. I used a SS hex dome head M4 screw cut so that only about <0.5mm protrudes inside the lip. I think those nut and bolt fittings look a bit crude, but that's just me.
I've tried different diameters and lengths of piping and hole sizes as well as tight/loose wrap and different types of absorber but in the end this works best for a balance of noise reduction while keeping the power. I have a ZeroSports 3" catless system with a 4" straight pipe on the end. The motorway drone is a major issue with me along with a nasty pulsing bass I had at around 1.5K that was really annoying and uncomfortable at urban speeds (
30 in 4th or 36mph in 4th).
If I pull the baffle, it is quicker but really noisy inside and out, as well as probably annoying everyone else so I think this is a good compromise. Final result is not as loud as some of the other lunatics around here but definitely UEL header/Scooby sound. It's kind of amusing seeing the young lads (
everyone below 30 is young to me) heads turn when they hear me coming and the odd look on their faces when it isn't the Impreza they expected, "
this is not the WRX you are looking for":starwars: :lol:.
4" Universal Exhaust Silencer Db Killer Fits Jap Box Baffle Bung | eBay