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 ¹⁄₂ 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