A NEW INSULATED MUFFLER SHIELD AND THE ARIES MUFFLER
A Combination That Beats the Heat (159 Degree Temperature Drop!)
by LESLIE PAM

Muffler Shield-- click on an image to see an enlarged view.

While cruising back from the National convention in Riverside, with the temperature well over 100 degrees, I noticed that my gas pedal foot was getting very hot, and I had to use the hand throttle to go the rest of the way. It made me wonder how many times we have heard that same complaint about hot feet from our front seat passenger, while cruising in the heat of a California summer. Like many others I have consideresd a number of solutions-- ranging from muffler shields and floorboard insulation to the firewall accessory manufactured to fit the Model A. While I have tried all or a combination of the above, in an attempt to make my driver's compartment as free from heat and noise as possible, I am going to restrict this article to our tests done on different mufflers and shields.

Bob Travis and Bob Moore volunteered their sedans, as Travis had the Aries muffler and Moore had a stock replacement muffler. Most of the tests were going to be done on Travis’ sedan, but I wanted a reading off of Moore’s stock muffler for comparison.

Both Bob Travis and Bob Moore had the commercially-available muffler shield already installed on their cars and I provided an alternate choice with a prototype of my newly-designed extreme-duty muffler shield. Having had a bracket failure on the currently-available shield, I had decided to improve on the design, and I conceived of creating the insulated shield which I subsequently built and am currently running on my own car. In the original shield, the sheet metal brackets which are made of the same gauge as the shield itself are spot welded and tend to crack, due to the flimsy nature of the design. If you have one of those on your car I would recommend checking for this problem, as Bob Travis’ shield had a serious crack in the rear bracket which I pointed out to him when we removed it for one of the tests. To eliminate this problem on the new shield, I am fabricating 1/8 inch steel brackets that are attached with 3/8 bolts. I also wanted to create a more efficient insulated shield by sandwiching a commercially-available heat-absorbing material between two pieces of sheet metal.

Test Devise
To get accurate readings on all the tests, I used a hand-held infrared thermometer, with a laser to pinpoint the exact spots we wanted to test. All measurements were made from six inches.

The Cars
Bob Travis’s sedan has an Aries muffler and a 160 degree thermostat, which kept the engine temperature at a constant 160 degrees. Bob Moore’s sedan has a stock muffler and no thermostat, so we used a towel over the radiator to keep his engine temp at 160 degrees. The temperatures were checked periodically with the infrared thermometer pointed to the center of the core.

Surprisingly, when we started measuring the temperature off the muffler, which was always done at the front and rear seams, we noticed that when the engine was cold, the temperature was hotter than when the engine warmed up. This is due to the effects of scavenging. When the hot exhaust gases come into contact with the cold manifold, exhaust pipe, and then muffler, the gases condense, slowing down the flow, hence the higher exhaust temperatures. After reaching operating temperatures, the scavenging effect produces a faster flow and less heat in your passenger compartment.

Bob Travis’ sedan measured 330 degrees at the front seam of the muffler with the engine cold and 207 degrees at the front seam when at 160 degrees operating temperature. Bob Moore’s sedan went from 394 degrees at the front seam with a cold engine to 289 degrees at the front seam when at 160 degree operating temperature. It is interesting to note the 82 degree differential between the Aries and the more common replacement muffler after the cars reached operating temperatures.

Test One
Bob Travis’s sedan with muffler temperature at front seam read 207 degrees and as expected with no muffler shield, 207 degrees from the top side coming into contact with the floor boards.

Test Two
Bob Travis’s sedan with commercially available muffler shield read 160 off shield coming off the front of the muffler, which is a reduction of 47 degrees less heat than is coming directly off the muffler.

Test Three
Bob Travis’s sedan with my extreme duty muffler shield read 130 off the shield coming off the front of the muffler, which is a reduction of 77 degrees less heat than is directly coming directly off the muffler.

What We Discovered
The Aries muffler runs 82 degrees cooler than the "other muffler". The extreme duty shield gives you an additional 30 degrees of reduction over the "other shield".

Overall reduction is 159 degrees with the extreme shield and Aries muffler combination. That is 159 degrees of heat reduction under the floorboards of your passenger’s feet.

What’s Next
Bob Travis’s sedan was also fitted with a special rubber pad with 1/8 inch aluminized material bonded to the backside that I designed to fit under the carpet and go up the entire firewall from inside the car. He will test this combination of extreme duty muffler shield and firewall kit throughout the year as we need to put this combination to the summer torture test. My own car has all of these modifications and while coming back from last years Zaca Lake trip with the temperature well over 105, my wife Ann never complained about her hot feet. Either Bob Travis or I will be carrying the infrared thermometer with us on club tours, so please ask us to check the temperature of your floorboards in the passenger area. Then decide if your passenger deserves the time and effort to do this improvement. And please don’t take our word for it; ask Joyce or Ann, our better halves.

[Bob Moore is president and Bob Travis is technical advisor to the Santa Anita A's Model A Ford Club, Arcadia, California.]

The "KOOL FEET" Muffler shield is available from Leslie Pam for $79.95.
Tel: 310-275-3836 • Email: LAKoolp@pacbell.net