The monster is pretty much ready for the autocross season (starts sunday and it's snowing today!)
We have pretty strict noise limits locally (95 dB at 100') and I suspect I'll be there or a bit more.
Exhaust is currently headers-3" pipes-two series 40 Flowmaster mufflers. What should I add on the cheap to tone it down?
Maybe Cherry Bomb style mufflers, to act as a resonator. Should free flow enough. Maybe some turn downs.
Are there any straight sections of pipe that could easily be replaced with resonators or straight-through mufflers? If so, that's a good place to start. If space allows, you could also swap the FM40s for something quieter.
downturns on the exhaust?
I built a downturn for the Abomination. It's right at 99 dB as it sits. We have a couple of events that are 95dB.
I cut a piece of exhaust tube at a 45 and welded a plate over the end. Then I drilled a 2.25" hole in the bottom. That drops me to about 93 dB. It installs with a single screw in about 45 seconds. If I get called out, I slap it on in grid. I'm sure it costs me a little flow on the top end but not enough to worry about.
I'd do turn ups (turnips?). Aiming at the ground might help but my understanding is that there is a lot of resonance/reverb/?? off of the ground
also, what about supertrapps on the end?
+1 for turnips. Internet consensus says turn downs, but turnips are tasty.
In SD region we have a 93db limit, so you see a lot of creative exhaust systems. Keisel and his Sprite/FD were always dancing over the line.
Most popular is turn downs angled away from the db meters. Kinda defeats the spirit of the rule, but you gotta do what you gotta do to play.
Why not just have a separate set of bolt on mufflers. Bring the cheapo silent ones in the car, if needed, change them. It’s just autocross, so I can’t imagine a silent muffler is going to choke power badly enough to prohibit a good lap time. Certainly nothing a good driver couldnt overcome.
mad_machine said:also, what about supertrapps on the end?
They generally cost more HP than they are worth, with enough discs to retain decent power, they are loud and heavy.
They might be useful for 2-stroke bikes, but I'm not sure.
Trackmouse said:Why not just have a separate set of bolt on mufflers. Bring the cheapo silent ones in the car, if needed, change them. It’s just autocross, so I can’t imagine a silent muffler is going to choke power badly enough to prohibit a good lap time. Certainly nothing a good driver couldnt overcome.
Depending on the vehicle and class, the weight is sometimes a consideration. Personally I don't understand the desire for overly loud autocross cars, you're just trying to win trophies and dash plaques, so I tend to lean towards reasonably loud, but street legal exhaust systems and one should design around it.
I'd try a 90 pointed at different angles relative to the ground, I tried one pointed 45 to the ground that seemed to work well. Or heck if you have the room, try straight up!
Walker Dynomax stainless race muffler. Kick butt in glorious, throaty silence. Well. not really silence, but not douchebag loud.
let them complain then fix it later.
Why not add a Supertrapp? Do the job with little back pressure and removable if you want when not required to be that quiet.
wspohn said:Why not add a Supertrapp? Do the job with little back pressure and removable if you want when not required to be that quiet.
Because they actually add a E36 M3load of backpressure unless you run a ton of discs. And then they're said to be pretty darn loud.
rslifkin said:wspohn said:Why not add a Supertrapp? Do the job with little back pressure and removable if you want when not required to be that quiet.
Because they actually add a E36 M3load of backpressure unless you run a ton of discs. And then they're said to be pretty darn loud.
Yep, they really aren't that great a solution, either you have very few discs to keep it relatively quiet but your back pressure is pretty high and power output is lower or you have a ton of discs and its too damned loud but your power is there.
They might work well on 2-strokes, but I'm not sure they work all that well on 4-stroke motors.
Mostly the ones that are reasonably effective are the glasspacked ones and that's mostly from the glasspack aspect, in which case, add a cherry bomb for much less money.
The Spintech mufflers seemed like an interesting solution to investigate. It would be interesting to do some tests on some of the common (and not so common) solutions proposed to see what actually makes a measurable difference in power and sound levels.
Got room for a 1/4 wave resonance tube tuned to your peak power/noise rpm?
The one region I raced with had a stand set off to one side at the fastest part of the course with the decibel meter on it. Someone I knew simply slipped a 90 degree turndown over the end of their exhaust and then aimed it in the direction opposite the stand.
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