Eighteen Year Old VOE Mufflers

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VOETOM

VOETOM

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Every now and then I get to brag about my Vacuum Operated Exhaust (VOE) mufflers I built (and am still building). I just got done with six pair for Pontiacs and I test them on my '69 340 Barracuda 340-S. While my set was off for testing these others, I shot a few photos of them to share.

These use a 4" diameter vacuum actuator, originally found on GM heat and AC systems. With an actuator this big, you can generate a lot of puling force, which allows you to use a strong spring to hold the muffler closed internally. They start to open at around 6" inches of mercury vacuum and are fully open by about 9.

These are made from 304 st. st. so they do not discolor too much .

The original 340 muffler has an 18" long body and they are 21.625" overall length, 2.25" in and out. These I built have a 19" body and they are about 22.5" overall length.

Sadly, they are not terribly high flowing, in fact, they flow about as bad as the typical old chambered mufflers most mustangs had on them. They do better than stock 340 versions but these are 2.5" in and out. However, they are very quiet when closed and very loud when open: as loud as the chambered mufflers but as quiet as the noise reduction systems the '70 340 Dusters used.

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This is a similar set, internally. Top set is closed, quiet, and bottom set is open, loud.

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Tom, does the reduced exhaust restriction cause a significant performance boost or a change to the air/fuel ratio?

Or, reading your earlier description, are there most beneficial for the great sound?
 
No to the first question and not likely to the second as they are no real different than a stock muffler swapping to typical chambered muffler.

A tougher and switchable sound is one reason and the lack of resonance is another and extreme silence when you want it is another.

There is 10 dBA difference between open and closed and that is a lot.
 
I have a GM style Hy-Cee fruit can hidden under the driver's side fender. It is evacuated by a one from the carburetor and has a check valve inline so it is "fully" evacuated at all times the engine is running. In the cigarette lighter area, I have the switch that looks like thelighter but pulls out only enough to change modes.
 
As a side note, Pontiac built approximately 233 GTOs from November 69 till Jan 1970 with this option. These cars are very rare and even more valuable with this functioning muffler option.

Here is a photo of the real things and these are worth thousands and thousands of dollars.

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Why such a short production run? Was Pontiac too close to the legal edge and had some regulatory agency drop the hammer on them?

Tom, until your posts about it, I knew nothing about Pontiac VOE. I thought I knew about most of the cool and quirky options from the first supercar era.
 
GM upper management stopped it due to some exhaust issues associated with Chevrolet leaving plugs out of trunk pans (so I am told) and PA prohibited the VOE GTO sales there.
 
I know that california required a different exhaust system in the late sixties. No chrome tips on rr's in Cali, tho stock everywhere else.
 
As far as automotive great ideas that go away and come back, this has to rate up there with the 58 Ford retractable.
In today's market, there are literally thousands of cars and trucks driving around with some type of 'push a button-quiet to loud' exhaust. The fact that the idea was put into production originally in 1970, essentially abandoned for 30 years and now more popular than ever, is pretty cool.
 
So true Chris! Every time I hear a new Mustang or a Challenger growling at me, I smile and remember how long ago that cool option got started and what company did it!
 
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