Backpressure Comparison Chart
Muffler Type
Miles Per Hour
Engine RPM
Backpressure
$50 Facsimile
40
45
50
55
1500
1700
1900
2000
10
oz
32
oz
46
oz
54
oz
Early
Jobber
(no longer available)
40
45
50
55
1500
1700
1900
2000
2
oz
4
oz
10
oz
16
oz
Non-Tapered
4" Diameter
40
45
50
55
1500
1700
1900
2000
0
oz
6
oz
10
oz
16
oz
Aries
Reproduction
Tapered Muffler
40
45
50
55
1500
1700
1900
2000
0 oz
6 oz
12 oz
12 oz
The road tests were performed by Doug Windrem of Ontario, Canada. All tests were performed on a level road at an altitude of 1,000 feet. The temperature was 75¼ F. on a clear sunny day. The tests were actually performed using a 1928 Model A Phaeton. An extra length of special piping was installed between the exhaust manifold and the muffler to be tested (see photo). It was here that the back pressure gauge was attached. The mounting point of the tail pipe was also lowered so a correct fit could be maintained without leakage.
Two people rode in the car, one driving and one taking readings on both the "Snap On" brand tachometer and the pressure gauge. The pressure gauge is manufactured by O. T. C. Division, SPX Corporation, Owatonna, MN 55060, tool part #7215 and is specifically designed for testing back pressure on automobiles. The speedometer was also calibrated and tested over the test speeds and found to be accurate within one mile per hour.
