What factors affect exhaust tone

[RPMS]

Hey, guys!

 

This is the first time I've welded up my own exhaust system, and I have a few questions:

 

1) How does pipe length/diameter affect the tone?

 

2) How does muffler placement (ie near the collectors, near the tailpipe, or somewhere in between) affect the tone?

 

3) How effective will an X-pipe be in mellowing out the tone?

 

Right now I've got 2 SpinTech low-profile Cruiser series mufflers, an X-pipe, fresh muffler bearings (the guy at the parts store said I needed new ones), enough 2 1/4" diameter pipe to plumb the system with duals from front to back, and PLENTY of acetylene!

 

So here I sit, DUNCE cap on my head. Who's willing to educate me?

[olie05]

I don't know anything about the first two, but I know that having an x-pipe will make the exhaust note lower in volume because the pressure waves have a chance to cancel each other out. I came up on this subject a few weeks ago when i was looking to buy real twice pipes for my 280. when you isolate the cylinders from one another it is much louder and chainsaw-like (hondas, for example) . I'm assuming you have a v-8... if that is the case, for sound, I would go with x-pipes. I don't konw how this affects performance but the twice pipes system for the l-28 is supposed to be the best flowing when taken straight from the headers as 3-2 and out. Hope that helps!

[Guest Nic-Rebel450CA]

Larger diameter typically will lower the tone and make more of a vroom than a pop.

Personally I prefer smaller pipes for more of a crackle.

 

Exhaust system length makes a difference as well. Shorty systems will typically resonate more and make more of a rumble (my preference for trucks, especially my truck). Longer systems have more length to balance the flow and smooth it out and will make for a more directional growl.

 

X-Pipe does help a little with tone, and also helps a little for performance. A properly installed x-pipe will help the exhaust system scavenge better. A good way to tell where to put an X-pipe or crossover pipe is to spraypaint your exhaust system. The paint will burn off down the system to a certain point. About 6 inches before that point is the optimal spot to put the crosspipe. (6 inches is a relative measure, I believe it would be about 1/10th of the way back up the pipe towards the head pipe, but the key is to have it where the exhaust is still plenty hot and will still have good velocity.)

 

Muffler placement makes a huge difference. The closer you get to the header the more even your exhaust will sound. Now, what I mean by even is how the exhaust will sound through the RPM range. If the muffler is at the very back of the exhaust system then the tone will sound much different throughout the range. (May sound lousy at low-power RPMs, but will sound very nice in the higher torque RPMS). If the muffler is closer to the header, the exhaust will sound much the same throughout the RPM range and will be much less likely to have any range that "doesnt sound good". If I remember correctly, having the muffler closer to the header also helps get the more distinct sound that will make the engine "sound like a Chevy" (or Ford or Dodge, etc) though the muffler selection has more of a bearing on this.

 

What type of sound do you want? Do you want crackle, growl, rumble, or vroom?

[RPMS]

What I WANT is a deep burble at idle, an even tone at cruise which is non-resonant and not fatiguing to the ear, and I want to sound like a Nascar racer at WOT! I know I can't have all three, but if I can have #1 and 2 I'll be happy.

 

As a benchmark, the best exhaust note I've ever heard is on a GT40 replica I heard on some british motoring show once. It sounded much more like a Ferrari than the Chevy engine it was. Absolutely erotic. The link is worth downloading just to hear that sound. It's a funny video, too!

 

http://www.racingflix.com/getvideo.asp?v=126&p=19

 

You need to register to download, but it's well worth the effort. Give it a listen and tell me what you think!

[RPMS]

Oh, LORD! I buttoned up my system this morning and took a test drive around the block. DRONE...Drone...drone. Idle is okay, if a bit louder than I wanted, but from idle to about 30 mph is punishing. It's resonating like crazy the whole way at about 80 hz or so. I haven't had a chance to test what it sounds like at WOT, but from 40-50 mph with moderate throttle opening, it sounds very nice and no-nonsense! I have no idea what it will sound like on the freeway. I'll find that out tomorrow I guess, when I debut the car 40 miles away.

 

I wanted something a bit, well, crisper. Not like cornflake crispy, but more like "frozen pizza baked on the center rack" crispy. The way I have it set up is with the X-pipe halfway back to the mufflers, and the mufflers about 12" in front of the bumper.

 

Would putting resonator tips behind the mufflers help cancel the drone?

[pparaska]

My experiences echo all that's been said so far.

 

My exhaust: http://home.comcast.net/~pparaska/exhaust.htm

 

Hooker block huggers (1-5/8" primary, 2.5" collector)

2.5" mandrel bent pipe throughout

Dr. Gas 2.5"x2.5" X-pipe just below the back of the trans

duals to the rear left side (2.5")

Two Dynomax Hemi Super Turbo mufflers (center in, side outlet) right at the bumper

 

It' idles with a low rumble (deep burble), not too loud, but not quiet.

 

At cruise, there is no drone, except down around 1700rpm, but I don't cruise there much. It has what I'd call an enjoyable, not-too-loud even tone.

 

At 1/2 to WOT in the 2500 rpm and above, it sounds like a lightly muffled NASCAR. That's the X-pipe.

 

Scott, this sounds like exactly what you want!

 

I need to get a digital capture of my exhaust.

[Guest BigWhyteDude]

i have seen an electricly controlled exaust valve that you mount before your mufler. its more of a Y where when you activate it it closes off the pipe to the muffler,but opens up at the other side of the valve to just strait pipes. see why i cal it a "Y" valve? Dont remember the technical name for it. pritty nifty little part though, i can't remember where i saw it at...... if you had one you could run a muffelled system for the street and on the other side run just strait pipes for the track. i think i saw it on horse power TV maybe?????

[Guest Nic-Rebel450CA]

Sure, you can have all three, but your muffler selection is going to be the biggest factor. I have never heard the mufflers you have, but they may work. I would say for the sound you want, you will want the mufflers close to the collectors and have a shorty pipe. (you may be able to use a full-length pipe, but not too sure about that). They key is going to be pipe diameter. You are probably going to need pipe smaller in diameter than what you have. At the very least you are going to want smaller tail pipe.

 

To find out the smallest pipe that you can use, you first need to find the max CFM that your heads flow at. A section of straight pipe will typically flow about 115CFM PSI. (115 cubic feet per minute per cubic inch). Now, keep in mind that a 1inch diameter is not 1 square in, and likewise with a 2inch diameter. The area of a circle is pi-R-squared. (pi times (radius x radius)).

 

I would also check to find out what the flow rate is of your mufflers as many times a drone sound comes from pipes that flow significantly more than the mufflers.

 

I will take a recording of the exhaust on my truck and you can see how close it is to what you want.

 

BTW, if you know the math then forgive the simplicity of my post, I just wanted to elaborate for those who may not be as into math.

 

The part that BigWhyteDude is talking about is normally called an "exhaust cutout valve" or something similar. I dont recall where to find the electronically controlled ones, but last time I checked they were about $150 each. You can buy cable controlled ones from most speed shops as well as JC Whitney for right around $40 each. I plan to use these on my truck to have a dual path exhaust system. I will have two mufflers with the cutout in the middle of the two. That way I can make it super quite when cruising down back roads or near cops, and then pop it open (but not uncapped) and have a nice loud exhaust without being uncapped.

[Sumo]

The resonators will help cut the drone but mainly the droning noise comes from the muffler choice. Maybe bigger resonators? Although i dont know if resonators cut into HP numbers.

[RPMS]

man, at this point, I don't really care if it cuts a bit into the performance! I know that sounds rather extreme position to take, but as it is I can't pull the car out at night for fear of waking up the neighbors! The car ain't no fun if I can't drive it!

 

Pete, your system does sound like mine, except that you're using even larger pipe to plumb it. It's too bad we can't just shrink and grow the diameter of our exhaust plumbing so we can hear the difference diameter makes. Your description of your exhaust note sounds like just what the doctor ordered. Maybe I'll have to invest in some Dynomax mufflers when I have more cash to throw at the problem.

 

Nic, SpinTech is an up and coming company who supplies a lot of racing organizations. I first heard them on a friend's Dodge R/T truck, and I thought they sounded great. Then he put a set on his Mustang GT, and again, the sound blew me away. The mufflers I got weren't the same as his, but I figured there would probably be some corporate identity to the sound (i.e. the "Flowmaster" sound) but apparently not. His cars burble menacingly, mine makes women and small children run for the hills shrieking in terror. Not quite the "low profile" sound I was looking for!

 

I'm going to try to get a recording of my car tomorrow so you can see what I'm dealing with. It's the first time I've tried something like this, so wish me luck. I look forward to hearing y'alls cars, too!

 

Scott

[RPMS]

Well, this morning I tried to record the exhaust on my laptop's built in microphone, and it completely overwhelmed the poor thing. Just left a mash of distorted sound that's pretty much incomprehensible.

 

I'll try to find a microphone somewhere and get a slightly better sound.

 

Scott

[pparaska]

Pete' date=' your system does sound like mine, except that you're using even larger pipe to plumb it. It's too bad we can't just shrink and grow the diameter of our exhaust plumbing so we can hear the difference diameter makes. Your description of your exhaust note sounds like just what the doctor ordered. Maybe I'll have to invest in some Dynomax mufflers when I have more cash to throw at the problem.[/quote']

 

Well, some people think it's loud. I think it's a bit louder than I like, but not hurtful.

 

His cars burble menacingly, mine makes women and small children run for the hills shrieking in terror.

 

And there's a problem with this? <BSEG>

[RPMS]

[quote="pparaskaAnd there's a problem with this? <BSEG>

 

The problem isn't that they run for the hills. It's the mess they leave behind when they wet their pants in terror!

 

I've been considering making a pair of slip-on reducers that go from 2 1/4 OD to 1 1/4 or so. That way I could burble my way out of the garage without offending the neighbors, and when I've made my escape I can jump out, toss the reducers in the hatch, and roar away in a cloud of hydrocarbon joy!