AFter reading this article sent to me by Joshua Skinner, I am wondering if we are making our exhaust pipes too large. What are your thoughts on this? This is not the first time I have been told this, but is the first time I have seen an educated, scientific defense of this idea.

http://www.popularhotrodding.com/engine ... 505em_exh/

I am not saying it is right. This is to start a dialogue about the idea. Those who are interested, please read and comment if you see either foul or fair here. Of course the subject is a 350 SBC so that may change things. I don't know.

Sam

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On my first Duster I had a 2-1/4" system made up for it when it was completely stock. It would actually collect water in the low spots, a good indicator that the exhaust was cooling off too fast from slow flow.

Also, I took it to the track a lot, and it was no faster with the bigger pipe than the stock system with the cat in it.

Bigger is not always better.

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Official Cookie and Mater Tormentor.

Would you believe that Neons come with 2 1/4" exhaust? It isn't too much for 132-150 hp, but many 225s don't make that much power so in many cases a larger pipe on a slant is a waste. My daily driver is stock with duals (into a single muffler) of about 2" and is rated at 240hp and it's just right. The engine is a system and needs to be treated as such.

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Joshua

I'm not really sure how much power my 225 makes, but I think I might have too much exhaust on it. It has a single 2.25" pipe with a 22" cherry bomb coming out in front of the passenger rear wheel. It sounds great under power and decent when idling, but when you come off the gas at speed it burbles and pops. On the other hand, I might just have an exhaust leak at the manifold.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

Thanks for the link to that article! It is a good one.

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Casually looking for a Clifford hyperpak intake for cheap.

great article, I learned a lot from it. thanks for posting it up

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1970 Barracuda 225 /6, 3spd on the floor, Blue/Blue

What are the secondary pipes?
Sam

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They are the pipes after the collectors on the headers...

Ahhhh... Sonic Turbo's. I remember them fondly. Had them on every one of my cars for a decade or so...

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vm

This article raises more questions than answers, however, it is a good discussion starter. I must run off to visit my Mom now, but will post my questions later. The general category of question is of course how do all these dimensions translate to a slant's need?


Sam

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One thing that will help is a smaller diameter tailpipe. On a low-medium performance build this will boost torque.

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Official Cookie and Mater Tormentor.

Sounds to me, just like all other decisions on our cars like cams, carbs, fuel delivery etc., is what are our plans with them... Slow stock cruisers? Or are you trying to get it to breath and haul some ass turning up some good RPMs?

I agree that going bigger on our slants is ALMOST pointless. However keep in mind that back in those days the engines were so damned restricted its not even funny.

However, if youve upped compression, done any kind of head work, larger cam, or anything on that level then YES go a little bigger. Even a stock 1bbl slant should have no less that 2" front to back IMO, especially on an application like mine thats a looong wagon. The big kicker is the manifolds, go big on the exhaust the piss-poor intake and exhaust will cause enough restriction that youll never lose power from "too large" of an exhaust. Hell Chrysler even caught on and did it themselves with the Hyper-Pak and Super Six combinations...

That being said, I love opinionated subjects... Theres really no one person who is correct except the guy that has every engine combo under the sun dyno-tuned to prove his/her theory

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"if it aint broke, fix it till it is"
78 Plymouth Volare Super Six wagon
89 Volkswagen Golf GTI 16v
92 Chevrolet K1500 5.7
98 Ford Escort ZX2 zetech

So here are s ome of the questions that are raised, and maybe answered and I missed it.
1. What is a resonator box?
2. How far back should one place an X or crossover? Did I miss that? How do you figure it?
3. Are flow figures published for mufflers these days?
4. If the most popular carbs for slants are in the 350 cfm range, is it safe to assume a muffler that flows 350 CFM is correct?
5. It seems the distance from secondary to exhaust pipe is the most critical as it effects the resonance characteristics, which I still do not get. I need to do more reading on that.
6. It seems as if keeping the flow speed high, and the back pressure low is the golden mean in mufflers. Which ones do that? There were lots of diagrams, but I was unsure of conclusions there.
7. Too big of a muffler (speaking physical size here) adds to noise, which I do not want, but adds nothing to power. How do you figure what is ideal for our slant.


This is just the beginning of the questions. I will read this more, and on a bigger screen than my iPad, and hope to gain more insight. I will say the guy who bent my down pipes for my Dutra Duals builds street rods for a living, and he looked at the 2.25 exhaust and said, "you will make more power with smaller exhaust pipes". I gave it no more thought until I read this web posting.

Sam

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1. It's not a resonator box. It's a pulse-wave termination box.
2. Requires testing, but general recommendations are given.
3. Not usually. The Sonic Turbo became the Dynomax Super Turbo, FYI.
4. 1.5 CFM intake flow per hp, 2.2 exhaust CFM.
5. It's about the pressure wave tuning.
6. Flow speed depends upon pipe size and gas volume, not on the muffler.
7. How did you come to this conclusion?

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Joshua

I thought I read number 7 in their text.

If guidelines are given for distance back, I missed it. I will read again. I remember guidelines for size, and my reading suggested a larger pipe than I would likely use for the exhaust pipes themselves, so was left scratching my head on that one.

The pressure wave tuning is over my head at this point. That seems like voodoo. I will read again, and perhaps do a search for more info.

True enough on number 6, however I do not think that negates my comment. Can't a muffler create unwanted back pressure, and still be big enough to flow more than the pipes?

I will do a search for pulse wave termination box I guess.

I am off to my weekly Friday night cruise-in.

Thanks for the comments, and the conversation of last week.

Sam

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