I am not sure about Illinois law, but some states require that an exhaust not be louder than X amount of decibels. Therefore, you can have an aftermarket exhaust system but the decibels have to fall within a certain parameter set by the state. The decibel meter is simply placed within an X amount of feet from the exhaust pipe while the RPMs are raised to X amount. If the reading is higher than those set by the state, infraction. Illinois law, according to your first post, states that the exhaust cannot be modified in ANY way as to amplify the noise emitted from the exhaust system. You do not need a decibel meter to determine if an exhaust system is louder than stock.

 

Screw em, I am in Southern Illinois and i have straight pipes. Its loud and cops here give me a when i pass them.

 

dont flowmasters always say 50 state legal?

 

I am not so sure about that. I agree a decibel meter is needed to determine if the exhaust is louder than X amount. For standard noise level limitations, X amount is the same for all vehicles.

But according to Illinois law, the X amount decibel limitation is different for different makes/models of vehicles because the X amount is that of the particular vehicle with stock exhaust. Illinois does not say you can't use aftermarket exhaust, just that it can't be louder than stock. So what if it is 2 decibels louder than stock? It isn't like a police officer knows the X stock amount of decibels for every vehicle ever made and can tell by his calibrated ear whether or not it is louder than stock. Plus not all types of vehicles makes are the same in stock form. For example, my Mustang is louder in stock form than a 6 cylinder Mustang, and it is slightly louder than a automatic GT (different mufflers on automatic and manual GTs from the factory). And a GT500 is even louder in stock form. If a police officer assumes all Mustangs are the same in stock form and he heard a manual GT next to a 6 cylinder, he would be wrong to give the GT a ticket even if it is obviously louder.

Certainly if someone is running aftermarket exhaust with mufflers similar to straight pipes that would be a good indication that its louder than stock, but in other cases it may be difficult to tell.

 

Bottom line is that it doesn't take an idiot to decide if your aftermarket exhaust emits more sound than said stock muffler. Obviously performance cars have a different tone to them and are a little louder stock, but let's be realistic. If the exhaust only emits 2 measly more decibels than your stock exhaust did, most likely the chance of you getting pulled over are slim. Usually, and I say this while cringing cause I know how this scenario works, but a cop will not simply pull you over for having an exhaust on your truck. It usually takes another infraction (like speeding) to stop you and then things like illegal tint, exhaust, etc are added on top of the original infraction. Now if you're running straight pipes and can be heard from a mile away, yea you're probably going to get stopped either way.

 

It doesn't take an idiot to decide if your aftermarket exhaust emits more sound than said stock muffler only if it is extremely loud. Yet the Illinois law doesn't state "extremely loud", it states "louder than stock." So by the letter of the law the burden is upon law enforcement to prove it is louder than stock. How do they do this if they don't know how loud stock exhaust is in X decibels, or if they don't have a baseline for specific stock cars to use a decibel meter in comparison?

Why do you need a decibel meter to determine if the exhaust is louder than X amount of decibels when it is a fixed rate, yet you don't need a decibel meter to determine if it is louder than X amount when it is a variable rate dependent on the stock level of sound for said vehicle?

 

This is going nowhere...agree to diasgree

 

A Roush kit is completely legal since they're sold on Roush f150's. Buy one of their kits. Done.

 

Good call stealth.

 

Actually a Roush kit isn't stock exhaust unless he has a Roush F-150. Stock means what the vehicle came with when purchased new.

Just like I have FRPP GTA axle-backs on my Mustang GT (which come stock on Shelbys), but they aren't stock on mine and are louder than my stock ones were.

 

My conclusion is that these types of laws suck and that SEMA didn't do a good enough job lobbying.

Sure, some type of noise limit should exist but freer flowing exhaust systems offer better mileage and thus reduced polution too...maybe Al Gore can start to push free flow exhausts.

 

The Roush legal kit is just that, legal, no matter what f150 it's for.

I'm glad I live in Texas. We erase pinko politicians.

 

According to Illinois law (which is what this thread is about), if it is louder than the stock exhaust which came with said vehicle it is not legal.

 

I knew we were in the same thread for some reason. Let me rephrase. The Roush legal kit is just that, legal, no matter what f150 it's for.

 

The funny/ironic thing was that he (state trooper) said he has trucks that are and I quote "louder than loud." But since the trooper labled my buddies cavie as a "tuner" car, he pulled us over because his exhaust is loud (which it is loud (very loud)).

Zane