Vapor lock and New exhaust system – per spec?

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I’m replacing my exhaust on a ’34 836A, and likely using Dixie Exhaust Works.  I’ve read in the forum issues of vapor lock being more likely with the installation of the first of the three mufflers (resonator).  How critical is it to include all three mufflers, versus two?  Is it an originality question? a performance question? Any thoughts would be helpful.

-Matt

The spec I’ve found for a 1934 840 and 836A exhaust system is below.

This was a straight-through system, using three simple round mufflers of different lengths and 2t” tubing, with the exception.of the last section from the last muffler to the car rear, which was 2″. All mufflers were 6″ in diameter. The first, or shortest, muffler was located at the end of the first section from the engine under the engine side pan. The second was located with its rear end just ahead of the transmission cross member, and the third, or longest, was located with its front end at the rear of the transmission cross member. Mufflers and tubing material may be purchased from the Maremont Muffler Div. of the Maremont Corp., 168 N. Michigan Avenue, Chicago 1, Ill. The mufflers, called their “service mufflers” are as follows: Ist—U.T.34 6″ diam. x 14″ body length; 2nd—U.T.38 6″ diam. x 22″ body length; 3rd—U.T.48 6″ diam. x 29 3/4″ body length.

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The first muffler is located under the fuel pump and provides a measure of exhaust heat insulation to help prevent vapor lock.

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The original Pierce mufflers were “asbestos lagged” using a layer of asbestos inside to reduce heat transfer. I dont think available standard mufflers have any insulation, but I  believe the exceptions are straight through glass  packs that use internal glass or other fibers for sound absorption.  That is what I used for the short #1 under the fuel pump to provide a measure of insulation to reduce the fuel pump heating. The original multiple Pierce mufflers were straight through designs to minimize backpressure. I plan to add muffler wrap to the mufflers or under floor insulation as I found out years ago on another car that the wood flooring and carpet is not enough insulator without “asbestos lagging” on a hot day. My wife had to keep her feet off the floor because it got so hot.

Note that without asbestos lagging there is no such thing as an exact authentic replacement.

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I read that some new mufflers are filled with steel wool for sound deadening.  Is that what Waldon, etc. uses?  Is the first muffler built the same as the other two?

– great advice about floor board insulation

 

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Back in my power plant days, we used a woven fiberglass “fire blanket” material to good effect. We used this fireproof, flexible fabric to contain cutting flames, weld splatter, grinder sparks and dust during hot work. It was very effective as a safety product to protect from heat and debris.  We purchased it by the roll, but smaller quantities should be available. It was a white to gray color and had larger diameter threads. Knives or heavy shears will cut it to length and width, then it can be held in place with tie wires or metal straps. Check with a welding supply house for availability.  Consider a couple of layers as thermal insulation around the pipe and mufflers to keep heat away from your feet and fuel lines.  Herb.

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It was a few years ago when I was digging into this. I relied mainly on using the Summit Racing site that has a good search function for a lar ge vaeiety of mufflers. They often list the basic design type and I recall many were steel wool. At the risk of saying 200% of what I know, I think the glass packs and and other fibers such as steel are generally straight through and by themselves have limited sound absorption, popular with hot rudders. The Pierce mufflers were also straight through but were perforated tubes inside the outer tube. They were 3 differant lengths to attenuate different frequency ranges, the idea being to get effective sound absorption wi5h minimum back pressure. Many mufflers use internal baffles to get the sound absorption in a more compact unit with more back pressure.

I used a straight through for the #2 from Summit, but the only source I found at the time for the very long 3 ft last muffler was Waldron.They are custom built and at the time took something like 6 months to get.  Hopefully they are doing better now. Waldron had a choice of how much sound absorption, quiet or more hot rod. I chose the quiet since it is a Pierce, but in retrospect would have gone for the less quiet relying on the triple muffler concept to keep it quiet. I imagine the difference in the two sound absorptions is the amount of baffling being employed.

Another reason to use a muffler insulating wrap is Pierce often ran the fuel line down the same side as the exhaust,, sometimes on the inside of the frame rail, bad for vapor lock.

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Sounds like a Buick straight eight muffler to me…

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