I was wandering what size exhaust pipe people are using to run dual exhaust on a stock 225 2 barrel slant six.Some around here say I should go with a 2 inch and some say a 2 1/4 pipe.Any suggestions would be great.I am going off my stock manifold and splitting the single into duals.Thanks

Why do you want to add the expense and weight of dual exhaust? It gives you zero extra power over a well done single system. 2" is plenty for duals.

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Joshua

Canadians are new to the game.

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exoJjL

Anything over 1 7/8" at the rear will drone on the highway, no matter how good your muffler/s are. Duals will allow you to keep that small size. In addition to being quieter, the smaller size also keeps the velocity up in the tail pipe, which Joshua himself has told me is better.

I have used all sizes on mine, and know for a fact that the distance from the muffler to the end of the tail pipe is such that it sets up a very annoying standing wave in that rear section when size is increased. That was one of the first things I did to this car 21 years ago, was increase the tail pipe size to 2" with a stock muffler. It was quiet with the 1 7/8" pipe, and got very annoying when I stepped up the size. Now it is 2.25 duals, and I will eventually put 1 + 7/8 back on.

I just got back from a longish road trip with this car. After five hours on the road, you really want some quiet. I will use stock mufflers,and an X pipe. Other projects are ahead of that one though.

Sam

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Rather than 1 7/8 pipe, why not the 1/4 wave exhaust pipe.......

Example here:

http://www.kcsr.org/showthread.php?t=131893

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

That is fascinating. I did not understand the theory, or the actuall set up, but can see that this is something that can do the job of providing quiet without choking off the engine. It seems like maybe the best one of many devices that work with, and not against the complex forces at work inside the exhaust pipe of a reciprocating engine. I would like to read more about it.

How do we figure out what size, length,diameter and shape would work on a slant? Every time I ask that kind of question I get an answer which is a good one,but a bit impractical: Dyno testing. Is there a way of looking at products currently in operation on a similar sized engine that we could predictably apply to our engines? Maybe there is math that will accurately predict design. But the math they talked about in the forum post was a combination of too vague and maybe over my head technically.

I have gotten good suggestions from others about resonators and such, but am reluctant to spend big money for something that may not do the job. I have done that a few times already. The DB meter was good in the forum post link. That is testimony you can trust. "It is really quiet" is not. I was told by the dealer of the current mufflers on my car they "Are really quiet". They are not. Any more info on the quarter wave exhaust pipe? Must go to work, but might research more tonight.

OK so I read the thread again, and understand the principle, but the math was still over my head. Can anybody out there calculate the length pipe needed to cancel out the drone at 2300 RPM? That seems to be where my slants have gotten nasty.

Sam

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This is for a V8

http://www.performancetrucks.net/forums ... ne-489463/

Extracted from above use a /6 and 2300

Say your /6 truck resonates at 2300rpms, right at cruising speed. You'll need to find the frequency of the drone. Units here are pulses per second, or Hertz.

f = RPM * pulses/rev * (1/60)

f = 2300 rev/min * 3 pulses/rev * (1/60)

f = 115 pulses/second = 115Hz

At 2300rpms, your /6 fires 3 times per revolution. RPM is in minutes, so divide by 60 to reduce to seconds. Now you need to find the length of the wave at the frequency you just calculated. Wavelength is denoted by lambda (λ), units are meters.

λ = v/f = speed of sound / frequency

λ = (343m/s)/(115Hz)

λ = 2.983 meters = 117.5"

Divide by 4 for 1/4 wave = 29.38"

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Thanks. I could not have done that. Does this mean it will still drone at another Rpm with that length pipe?

I was interested in Joshua's earlier comment that a single exhaust could be just as efficient as duals. If an efficient single can still be quiet, I might do that. We have now discussed the resonator box and the 1/4 wave pipe. This is getting interesting, and worth thinking about. What other tricks are out there. There is Teds resonator before the muffler. I wonder if it is functioning like the resonator box?


Sam

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You need to be sure at what rpm the drone is.


The drone rpm is some function of the total exhaust pipe length.

Usually only happens at specific rpm range (2300 +- a 100 or so) and at multiples of the primary drone (4600).

There might be another drone rpm; you could just add another 1/4 wave pipe.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Just to reiterate, I installed two of "Ted's devices", 12" variety, made by Flow Master on my two inch duel system in front of OEM after market mufflers, all the drone is gone, nasty highs gone, general exhaust tone is on the mellow side, and quiet.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

What size pipes before and after mufflers. Is there any chance you could measure DB's at cruise? What rpm do you cruise at?

Thanks, Sam

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Bill, I just noticed you have already stated 2". Did you have that custom bent? Who was your supplier?

Sam

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That 2" duel system stem to stern was on car when I got it. Probably installed in early nineties by the guy that converted her into a drag queen with all the go fast stuff including a pair of turbo mufflers that were well past their prime when my middle aged tinnitus plagued ears had a few years behind the wheel.

The exhaust note was loud enough to require foam ear protection we had to use in the mill on trips over half an hour. The racket at typical slant drone rpm was unbearable to me, and anyone with an open car following behind as well when we would caravan to car shows...

The Music Master 2 1/2 watt Amplitude Modules radio was inaudible in any gear but park, as well were mechanical engine noises, rear end noise, brake noise, most rattles, and even the squeaking polyurethane UCA bushings.



Most of my two lane rural cruse is at speeds between 40 and 60 mph, or 2000 to 3000 rpm, so 50 mph is smack dab on the 2500 rpm drone tone.

As for DB's, I haven't any way to measure them. However The Music Master Am radio, when close enough to a station during daylight hours, can be heard at any speed below 65 mph at less than half volume, any faster and wind noise with top down is too much racket for hearing enjoyment. The most prominent noise now when under way is wind with top down or up, body rattles, some engine sound perhaps from fan, tire noise, and a strong low howl or growl when held at WOT with engine under load as secondaries open up around 3300 rpm to 6000 rpm. Exhaust sound is hardly noticeable when under way at any speed or rate of acceleration. Oh, those damn squeaking UCA bushings can now be heard when under way.

Bill

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Thanks Bill. There was a company in PA that custom bent 340 pipes for my 360 Dart. I wonder if they are still in business. I found them in Hemings back around '97. Several knowledgable folk have expresses the opinion that smaller pipes keep velocity up and are better for a smaller displacement engine.

Sam

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these are helmholtz resonators and they do work if you know the frequency you are trying to cancel. (the newer hondas have them from the factory to cut out some funny noises) The thing that can make them effect a wider frequency range is to put a larger volume at the end of them.