1928 Plymouth 1937 Plymouth Plymouth: The First Decade

Estimated 1933 Plymouth De Luxe Performance

Introduction

While the my car was disassembled I became curious as to how fast it should be when it was back together. I have not seen contemporary performance numbers based on actual road tests published by American magazines. Apparently that type of new car coverage came later.

There some numbers from British magazines but they are only valid for the car equipped with the small bore export motor and quite a different final drive ratio. [Motor 1933] states that the Chrysler Kew Six (basically a Plymouth) with a rear axle ratio of 4.875:1 was capable of achieving 56 MPH from a stand still in 21.4 seconds. It also lists a top speed of 70.87 MPH. But that engine was also about 13% smaller than the US version.

The AllPar - Chrysler, Plymouth, and Dodge car information web site has an article [AllPar 2001] that includes more British performance information from the era. As noted above, the United Kingdom version of the Plymouth differed mechanically from the US version, so it is not clear if this information is applicable. [AllPar 2001] cites Auto Guide as the original source of data. The values for Plymouth differ significantly from those reported by [Motor 1933]. In any case, there comparison of the 1933 Plymouth, Chevrolet and Ford shows:

  Ford V-8 Tudor Chevrolet Plymouth Six Coupe
0 to 40 (seconds) 12.4 17 11.9
0 to 60 (seconds) 29.7 39 29.0
Top Speed 83 MPH 65 MPH 85 MPH

Hewes 1942 pg93] lists the assumed acceleration values for passing maneuvers. Reformatting the numbers into a form more suited for this topic and doing some simple arithemtic we have:

Speed MPH Acceleration
MPH Per
Second
Estimated time to
accelerate 5
more MPH
(seconds)
Estimated time to
accelerate from
10 MPH
(seconds)
10 3.2 1.6 0
15 2.9 1.7 1.6
20 2.6 1.9 3.3
25 2.3 2.2 5.2
30 2.1 2.4 7.4
35 1.9 2.6 9.8
40 1.7 2.9 12.4
45 1.4 3.6 15.3
50 1.3 3.8 18.9
55 1.1 4.5 22.8
60 1.0 5.0 27.3
65     32.3

So the highway engineer of 1942 assumed that the average car would take nearly 12 minute to accelerate from 10 MPH to 60 MPH. If the 1933 Plymouth could accelerate from 0 to 60 MPH in 29 seconds as reported by [AllPar 2001] then it was a very good performer in its day.

A Computer Model

The above information I found long after becoming curious about this item. And being a programmer by trade and a mechanical engineer by education, I set up a simple numerical integration model and fed it some basic data regarding the vehicle characteristics. Naturally, as with all computer output, this is subject to the GIGO (Garbage In, Garbage Out) situation. A lot of simplifying assumptions were made.

Executive summary

Statistic: approximate value
0 to 60 Time: >18 seconds
1/4 Mile Time: >20 seconds
Top Speed: <77 mph

Now that the car is back together, I have not tried to push it yet and find out how accurate my estimates were. But based on casual about town driving and a couple of trips where I ventured on to the freeways at speeds of up to 60, I think the model was reasonably good. The top speed is probably about right. The acceleration numbers are probably optimistic.

Maybe some day I will get out with a stop watch and check the model for accuracy.

Model Inputs

Max Power 70 hp @3600 rpm Automotive Industries, November 12, 1932
Final Drive Ratios: High: 4.375:1 Owner's Manual
2nd: 6.78:1
Low: 12.29
Tires: 17x5.25 Owner's Manual
Weight: 2,700 pounds Automotive Industries, November 12 ,1932
Wind Resistance (typical) 40 hp @ 70mph Automobile Digest, February, 1935
Rolling Resistance (typical) 0.2 hp /mph Automobile Digest, February, 1935
Gas consumption (typical) >1 GPH per 10 hp Automobile Digest, February, 1935

Assuming a late 20's and early 30's L head motor design have similarly shaped horsepower curves, then using a curve for the Model A (from How to Restore Your Model A) and scaling it for the difference in peak power and the RPM at which the peak occurs:

Model A '33 Plymouth
RPM HP RPM HP
0 0 0 0
650 13 1064 23
1700 35 2782 61
2200 40 3600 70
3100 35 5073 61

Further assumptions: Weight of driver, fuel, etc of 300 pounds. Shift time of about two seconds (no synchromesh). No "red line" limit, shifting based only on horsepower. Acceleration run continued until no substantial increase in speed possible, that is until maximum vehicle speed is reached. Since a gasoline motor puts out no power at zero RPM, it is assumed that for road speeds that would require RPMs below 500 (idle) that the engine is running at 500 RPM and the clutch is acting as a 100% efficient torque converter.

Model Output

Time (sec) Speed (MPH) Distance (feet) Gear RPM HP
0 0.0 0.0 1 500 10.8
1 11.0 8.2 1 1645 35.9
2 21.7 32.3 1 3267 67.8
3 30.1 70.9 1 4528 65.9
4 33.2 118.6 2 2749 60.3
5 32.0 166.0 2 2654 58.2
6 33.5 212.9 2 2775 60.8
7 38.6 265.8 2 3198 67.5
8 43.2 325.9 2 3577 69.9
9 47.1 392.2 2 3904 69.3
10 50.4 463.8 2 4178 68.1
11 53.2 539.9 2 4411 66.9
12 55.6 619.8 2 4608 65.4
13 54.6 701.2 3 2920 63.4
14 52.7 779.9 3 2818 61.6
15 54.0 857.6 3 2887 62.8
16 56.1 938.4 3 3002 65.0
17 58.2 1022.2 3 3110 66.2
18 60.0 1108.9 3 3210 67.6
19 61.7 1198.3 3 3301 68.0
20 63.3 1290.0 3 3385 68.8
21 64.7 1383.9 3 3461 69.3
22 66.0 1479.8 3 3530 69.7
23 67.2 1577.5 3 3593 70.0
24 68.3 1676.9 3 3650 70.0
25 69.2 1777.7 3 3701 70.0
26 70.1 1879.9 3 3746 69.9
27 70.8 1983.2 3 3787 69.7
28 71.5 2087.6 3 3822 69.6
29 72.1 2192.9 3 3854 69.5
30 72.6 2299.0 3 3883 69.4
31 73.1 2405.9 3 3908 69.3
32 73.5 2513.4 3 3930 69.2
33 73.9 2621.5 3 3951 69.1
34 74.2 2730.1 3 3968 69.1
35 74.5 2839.2 3 3984 69.0
36 74.8 2949.8 3 3999 69.0
37 75.0 3059.6 3 4011 68.9
38 75.2 3169.8 3 4023 68.9
39 75.4 3280.3 3 4033 68.8
40 75.6 3391.1 3 4042 68.8
41 75.7 3502.0 3 4049 68.8
42 75.9 3613.2 3 4056 68.7
43 76.0 3724.6 3 4063 68.7
44 76.1 3836.1 3 4068 68.7
45 76.2 3947.7 3 4073 68.6
46 76.3 4059.5 3 4078 68.6
47 76.3 4171.4 3 4081 68.6
48 76.4 4283.4 3 4085 68.6
49 76.5 4395.5 3 4088 68.6
50 76.5 4507.7 3 4091 68.5
51 76.6 4619.9 3 4093 68.5
52 76.6 4732.2 3 4095 68.5
53 76.6 4844.6 3 4097 68.5
54 76.7 4957.0 3 4099 68.5
55 76.7 5069.5 3 4100 68.5
56 76.7 5182.0 3 4102 68.5
57 76.7 5294.5 3 4103 68.5

1933 Plymouth acceleration curve from computer model