Exhaust Question

[Smoochy]

In the rule books while describing modifications to exhaust, the book always says something along the lines of, "exhaust will terminate behind the driver and be muffled." I was just wondering how strictly enforced that "must be muffled" part is. For example, if my exhaust was essentially a straight pipe all the way back, will that be frowned upon, and be grounds to not let me compete?

Thanks for any help.

[JimR]

Autocross depends on the courtesy of whatever entity is letting us use their site. Some events will read and sometimes enforce a set dB limit. We do not at our regional events, but we are mindful to not generate any cause for complaint at the college next door to our primary autocross site.

I don't know your specific application, but some sort of muffled exhaust is required.

[91talon]

I would thing that at MINIMUM, some sort of baffling system should be in place, but that is just me. Running just a straight pipe, on a non-FI car, doesn't really give that many benefits.

[Smoochy]

I would thing that at MINIMUM, some sort of baffling system should be in place, but that is just me. Running just a straight pipe, on a non-FI car, doesn't really give that many benefits.

I guess FI means something other than fuel injected? The main benefit for me is price. I'm looking at exhausts right now, and a exhaust system with a catted down pipe, muffled and baffled exhaust is about $600 more than the setup I was looking at.

[JimR]

By FI, he's talking forced induction. Turbos act as a bit of a sound dampener.

I'm guessing your car is something naturally aspirated? A straight-piped car is going to be painfully loud for you and everyone else, and be pull-over bait on the street.

Since the exhaust note is something you will be living with anytime the engine is running, doing it right the first time is worth the cost.

[Ironhead]

The main benefit for me is price. I'm looking at exhausts right now, and a exhaust system with a catted down pipe, muffled and baffled exhaust is about $600 more than the setup I was looking at.

*shrug* So don't buy a catted pipe if you live in an area where you can get away with such a thing.

I have an un/de-catted big ol' 'mericun V8 with headers and I don't think anyone could claim my car is too loud. I know for a fact that I'm less than 90dB at 50 ft with only a standard crossflow muffler. FWIW, a cat or cats can also perform a fair impersonation of a muffler in quieting the exhaust. Pre headers, my car had essentially a straight pipe (no muffler) back from the cats and it was far from loud then as well. It did have a pair of cats however.

As Jim pointed out, the important thing here is to muffle your car enough so that we are not a nuisance to our site neighbors and therefore to our site management.

Nuisance = complaints = lost site = no more events.

[Smoochy]

By FI, he's talking forced induction. Turbos act as a bit of a sound dampener.

I'm guessing your car is something naturally aspirated? A straight-piped car is going to be painfully loud for you and everyone else, and be pull-over bait on the street.

Since the exhaust note is something you will be living with anytime the engine is running, doing it right the first time is worth the cost.

Yeah it would be loud, but I like loud exhaust, and I seriously doubt it would be any louder than your typical Harley Davidson rider, or redneck diesel farm truck guy with crappy exhaust.

My car is turbo'd. It's an '05 WRX STi.

I'm just kicking around ideas for now, deciding which class I want to run. I'll probably show up to the first event stock to see what's going on before I try and mod at all.

[Bullitt2954]

Yeah it would be loud, but I like loud exhaust, and I seriously doubt it would be any louder than your typical Harley Davidson rider, or redneck diesel farm truck guy with crappy exhaust.

My car is turbo'd. It's an '05 WRX STi.

That sounds Unacceptably Loud. Both of those you held up as an example are targeted regularly by "The Man" because of obnoxious straight-pipes and deafening Jake-brakes (ever notice the noise-ordinance-signs at the city limits of most towns?), and both are completely clueless as to the reason for their targeting:

"It's harrassment I tellya's! HARRASSMENT!! They just Hate on me 'cuz Ima Cool, Yo! Lousy Stinkin' Pigs!"

(Just an FYI - I used to be "one of those guys")

[JimR]

The STi is a fairly popular autocross car, especially in a street tire class called "STU" that allows basic suspension and mild engine bolt-ons.

Bobby, one of our regulars, used to have a '04 STi campaigned in autocrosses at the National level, and it had an exhaust that dumped around the rear axle. It sounded fairly sedate at part throttle, and wasn't a nuisance at WOT. A N/A car couldn't get away with that. It didn't have a muffler, though it may have had a resonator and it definitely had a cat. STU requires a cat:

Any high flow catalytic converter(s) are allowed, but must attach within six inches of the original unit. Multiple catalytic converters may be replaced by a single unit. The inlet of the single replacement converter may be located no further downstream than 6" along the piping flow path from the original exit of the final OE converter.

A cat-back exhaust is legal in all the Solo classes. Check on the big Subaru forums and see what other autocrossers are running.

[FlatBlack]

A friend with a white bugeye WRX wagon is running without a muffler, and it isn't too loud.

I have a straight 6 with "straight pipe" coming about 7 feet off the turbo, and dumping at the diff. It doesn't get complained about [unlike a fellow autoXer in a black F-Body ], but is too loud for my tastes in a street-driven car. I will be going with a proper muffler soon, I just have to figure out some space restraints where the muffler would sit under my car.

If I were a STi owner, I would gut the cats and possibly drop the axle-back for events. It's not too loud, and should relieve plenty of unwanted backpressure. It also gives you the option of not looking like a jackass teenager while driving around [assuming you put the axle-back back on ]