The Stovebolt Site Forums The Shop Area Engine Shop What causes distinctive sound of 235 with dual exhaust?

My dad is an old mechanic from the 50's 60's and tells me I should put dual exhaust on my 235. Does anyone know technically what exactly it is about the 235 design that causes this distinctive sound. He get's a twinkle in his eye when he describes it.

It has to do with the 120 degree pulsing or something, Hot rod Lincoln describes it better. However fond of a memory he has of it, reality is pretty obnoxious, I ended up with 4 mufflers. Even at that, the fentons, (If that is the style you are thinking of, there are others.) are of such nostalgic value that I don't know why anyone would use anything else, as they really don't provide much of a performance gain, and they look nice. My suspicion is that if you do it, you would be better off putting the mufflers way far back as you can get them. I have one set of cherry bomb type quite close to the manifold, with those alone, at about 2500 RPM the racket was absolutely horrid. So I got a set of 18" generic round tube magnaflows, and they ended up about 18-20" (maybe less, I don't feel like going and measuring right now) from the bumper. (AFTER the rearend, the only place I could put them given way the fella did my exhaust) It is actually a little bit too quiet now, but gives a significantly more pleasant sound. I have a feeling that I could just remove the forward mufflers and things would be just fine, but I don't know for sure. So if you do it let us know how the exhaust sounds vs muffler placement, as this has come up a couple of times.

virtually any inline six or v-6, or even opposed (Corvair-Porsche)six will sound the same with a 180 degree exhaust system. Thats when the first three cylinders of the firing order fire thru one pipe and the last three cylinders fire thru the other pipe, or in the case of a v-6 or opposed six when one whole bank fires thru one pipe and the other bank fires thru the other pipe. Once you hear it you'll recognize it.

Its easier to do on v-6s or opposed sixes since all you gotta do is just run one exhaust system (like the muffler shops do) down each side, on an inline you gotta "split" the manifold and run the dual side from the added outlet. Also on any of them you gotta keep the pipes separate--no crossover connection, no "H", or "X", or whatever alphabet soup style, or you wont get the desired sound.

Once you hear the sound you can pick out the sixes in traffic just by their exhaust note. Lots of Dodge pickups V6s get duals--if you hear the sound you quickly look for something that could be had with a six (and now-a-days its usually a pick up).

Muffler location has to do with the sharpness of the sound-long tailpipes from the muffler back is sharp; short tailpipes from the muffler back is duller sounding. (I think the longer pipe from the muffler lets the sound rattle around more before you get to hear it) Also the the muffler type itself makes quite a difference. The straight-thrus can be hard on law enforcement's ears. I've seen brand new straight thru glasspaks taken off a 283 v8 ('cause they were too quiet-factory style crossover pipe connecting the two banks) and put on a split manifold little 216 chevy and get written up on their maiden voyage (you gotta keep your foot outta it).

clear as mud?

Also remember that the six cylinder is producing fewer pulses per second for a given RPM. 75% as many. So a V8 winding up to 3600 RPM for a moderately aggressive shift is producing an exhaust note of 240 pulses per second (120 pps per side). The six, in the same scenario is producing an exhaust note of 180 pulses per second (90 pps per pipe). This can make the difference between the sound being perceived as a hum versus a buzz (rap). This can also make the six more likely to produce an annoying drone at cruise rpm. A crossover pipe tends to make both pipes produce the same, higher pitched sound, making it more hum-like.

Like edski says, you gotta control your foot when you're not in the proper, appreciative crowd.

regards,
Leon

Appreciative crowd....ha....screw the crowd.

This is an interesting topic to me, since I'm new to these stovebolts. I'm curious to see If I could hear the difference and wondering if I would like it better myself. I'm gonna have to pay more attention next car show I go to.

Simple answer is sound waves. Headers are suppose to have a collector that is of a certain length to take advantage of the sound waves to flow the exhaust. There is a math formula to figure the length of the collector or stinger on the old two cycles.

All of your post is spot on IMO with the exception of this part which I understand as being a bit different. The first unusual thing on the stovebolt head is that there are 6 cylinders but 4 ports exiting the head. 1 and 6 are separate but 2 and 3 share a common port as do 4 and 5.

With a firing order of 153624 and a split manifold or headers the following happens:

1-single port, front pipe
5-shared port, rear pipe
3-shared port, front pipe
6-single port, rear pipe
2-shared port, front pipe
4-shared port, rear pipe

Pulses alternate front/rear (aka right/left) every spark but also the port type changes every second pulse generating that unmistakable sound.

Let me share some of my experiances along those lines. With many six cylinder cars thru the years I have had the later series motors (194/292) that have the six separate exhaust ports, and when you run a set of tubing headers arranged such that the front three cylinders flow thru one exhaust pipe, and the last three cylinders flow thru the other exhaust pipe (both running mufflers), they, thru my ears, have sounded just like the 216/261 series motors.

I have run both "split manifolds" and tubing headers with stock, straight-thru glasspacks, straight-thru steelpacks, and oval glasspacks on the 216/261 series motors. On the 194/292 motors I have run "split manifolds" and tubing headers with straight-thru steelpacks, chambered mufflers, and Flowmasters. Other than the noise levels and tone qualities they all sounded out the same RAAAP as produced by the 216/261 series.

I think the above mentioned Dad had heard/remembered and coined that memory as the classic dual exhaust sound of a 235 because of the overwealming popularity of that motor series in those times. When I graduated in '63 at our high school no other six cylinder cars had "split manifolds" or even headers other than Chevy 216/261 motors, and with the popular straight-thru glasspacks, you would think they could break out windows with their RAAAP!

I feel any of the sixes with the same exhaust grouping will sound the same (other than tone qualities produced by different mufflers, and pipe lengths).

I have heard one Chevy 4.3 V6 pickup (2000 or so) that has not had the familiar RAAAP. it sounded so much like a V8 that I crawled under it in a suit to check it out, and then demanded to see under the hood and only found six spark plug holes plugged with six spark plugs. Those 90 degree sixes dont have the constant 120 degree firing pattern due to their 90 degree block design and their compensated crankpin offsets, yet Dodge V6s (with similar[?] crank/block situation) do sound "classic"--no answer for that. I have never heard a 60 degree V6 with duals either (like a Ford Ranger-or 2.6 S-10 Chevy)--they should sound "classic". Sorry to be so long winded, but I wanted to be as unconfusing as possible--probably failed.

As I am full of it today, let me comment to ol' North Texas Chapter Leon's post by saying.... My son has just gotten a '13 Camaro V8 stick car. The automatic V8 Camaros have D.O.D. (Displacement-on-Demand) GM's take of cutting down on the world's demand of fossil fuels.

When these automatic cars drop down to running on four cylinders their cars do have some annoying interior drone. Get this, GM added a capped "j"-pipe of a special length to the interior of their mufflers to tune out this drone!

The stick shift cars do not have D.O.D and do not ever run on four cylinders--thus no need for "tuned" mufflers. Who would have ever imagined that state of affairs--to save gasoline you gotta live with special mufflers--well you could put on some glasspacks and have a bi-lingual sounding vehicle so "in the times" in Texas!

To get an idea what its going to sound like, screw a 3 foot piece of pipe into your lawn mower where the muffler is now, then you will know.

The 180 degree headers for V8 engines sound like six cylinder cars due to firing order. On each bank, each cylinder fires one after another, no skips, the tubes look like a jungle gym under the car crossing everywhere. The idea is that as the first pulse hits the collector, it creates a vacuum pulling the next one out quicker, this then creates another pulse and vacuum and so on and on...... They work quite well on some cars, but sound just like six cylinder cars.

A well tuned header for the six cylinder with mild camshaft and low rpm would probably have about a 32" long x 1 1/4" diameter primary pipe, with a 2 1/4" diameter x 18" or so collector. Long pipes help low rpm torque, small diameter pipe keeps the gases moving quickly,. The collector size is determined by cubic inch and rpm. I have run a lot of computer simulations on dad's pro engine analyzer and each time come up with the long headers. The short cast headers do very little other then change noise levels.

Pipe diameter will change the noise levels some. Small pipe will RAP more, larger pipe will be deeper sounding.

Joe

Weren't some splits done as 4/2 as opposed to 3/3?

maybe, but I never heard them--but we did have a fellow with a '52 Pontiac straight eight that was split 5/3 and sounded so V8-like that he was always being picked on to race by other guys with V8s. The V8 thunder sound comes from a missing beat from each bank that happens to be in the other bank due to the way the crankshaft hooks all the cylinders together on a 90 degree V8--as Joe Hand said the indy cars have each pipe collecting four equally spaced cylinders (firing wise) all together (which necessatates grabbing the "missing" cylinder from the opposite bank and bringing it to fire out through the other pipe making the exhaust runners look like a "snake pit") Once in a blue moon you will find a V8 dirt track car with that kind of system and its sound is quite "buzzy" That kind of system, though having a higher power peak when done properly, makes for a less broad, and more peaky power band, more suited for a longer track than a short track where the motor speed will swing in and out of that peak.