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I'm building a '67 Fairlane, 351W, long tube headers and trying to decide if I should bring the exhaust out behind the rear wheels or out under the rear bumper. I'm concerned that the side exit will be much louder and annoying. I don't want my "passenger" reminding me every ten miles that the car is loud. How much difference will it make?
 

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Well your already behind the axle so a foot or two of straight tubing is not going to make much difference.



I have almost all my exhaust systems(easily over a dozen built) kick out in front of the rear tires. This allows you to run as low as you want and tuck the exhaust above the frame rails to give a clean look letting you slam the frame against the ground(even if you do not intend to) without concern.

Most people will tell you doing this will make the thing loud. But only if it is done wrong. Running a loud muffler and tips pointing at the ground your going to have a loud exhaust.

I run cast manifolds(cheap, reliable, and some flow good) feeding 2 or 2.5" pipes depending on the engine and then a quiet muffler(s). The pipes will run the length of the transmission with the muffler being as far back as I can place it with the rear of the muffler being around 18" from the axle tube. If I have room for a free flowing cat or a cross over I use them where they fit if not I do not and just use a quieter muffler.

After the muffler I have the tubing angled so the tip is aimed at the inside of the rim or above the front of the tire. Your not aiming it at the caliper or rotor your aiming it at the inside of the rim or top of the tire. What this does is use that turbulent air as a wall to deaden the sound when your moving. It also has hot air rolling out your wheel wells which helps in the winter/can just look cool on some rides.


Now I like a quiet exhaust. Start the thing at 3am in town and not wake the neighbors quiet. You do loose a bit of performance in a muffler that will allow this. But, that's why I love V band clamps. You can easily slap a diffrent muffler (or section of pipe)with a V band clamp welded to the front for those weekend endovors then when your ready to go home(and things cool) bolt your quiet muffler up.
 

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1949 Ford Coupe RESURRECTION
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I found myself in the same conundrum but solved all issues by using a fairly quiet Dynomax Muffler along with electric cutouts. The only issue that I had to correct later was to relocate the butterfly valves for ground clearance. Here are two galleries of the initial install and then correcting what I did wrong. By the way it's only really noisy (which I love) when you drive along next to a solid wall next to you. And be sure to install a crossover pipe it Smooths the sound out quite a bit.
I know this is a matter of personal preference but I think the pipes coming out behind the rear wheels just simply looks better then in front of the wheels.



Video with the cutouts closed

Open
 

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I have Dynomax race bullet mufflers on my car and because of the narrowed rear and tire size, I'm not sure how someone would sneakl 3" pipe up and over the rear, and out the back, so I just decided to add turndowns and accept the fact that it's going to be loud.
 

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I do not like loud exhaust. A buddy's early 'Vette w/ sidepipes is to me like the worst thing, blat-blat-blat every time he steps on the gas a little bit... Just a personal opinion, not trying to start anything. W/ the "pro-street" (sigh) Challenger, 496" Hemi which can put out a volume of exhaust gasses, I still worked full pipes in with the chassis design and they go all the way out the back. Relatively small 3" pipes, 2 chamber Flowmasters between the ladder bars, you can have a conversation in the interior that has no sound-proofing. People in the car behind me probably hear it more. A downside is heat in the rear axle area, it gets bad in traffic and kills external fuel pumps. Right now the car sits apart, along w/ other work I will be switching to an in-tank pump.
 

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Actually once the vehicle is in motion the air behind the vehicle is turbulent and under less than atmospheric pressure. So bringing the exhaust pipes out under the rear bumper puts them at a low pressure area which reduces the amount of power the engine expends on having to push the exhaust out against atmospheric pressure.

Side pipes may look cool but unless you’re doing air flow analysis around the body of the vehicle the likelihood of having to push exhaust against an air flow that is higher than atmospheric pressure is a really high possibility.

Bogie
 

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1949 Ford Coupe RESURRECTION
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Bogie, I have always enjoyed and admired your knowledge and analytical approach to your answers/postings to help some of these guys out.. However, on this one I'm going to have to address what you said... the "vacuum" created in the airstream at the rear of a vehicle (unless you are getting close to supersonic.. hahahaha), could hardly be measured. The pistons/valves/exhaust pipes would never see the difference in the location of the exhaust tips... assuming the same number/radius/etc. of the turns and length..... But, you must understand.. that's just me...
 
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