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The Gentleman's Express: Tech-Tips from the JIOC

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The Pump Exposed

Author: Michael J Lotwis & C F F

The important difference between pumps is particularly related to the impeller blade number, shape and diameter. Chrysler has now crossreferenced all 361/383/400/440 water pumps down to only two part numbers, those for a/c and non-a/c vehicles. Note at this point that Chrysler’s reason for two pumps was simply to slow down the water flow in the a/c equipped vehicles. (This is another reason why one should not run an engine without a thermostat as it does act as a flow restrictor). Basically, all C-V8’s, Int I and II w/out a/c had pump #2808680, now pump #3780196. This has always been and still is the largest 4.50" dia 8-blade pump.

Most aftermarket suppliers, such as TRW, sell only the smaller dia pump with 8 smaller blades as an a/c pump. This is because when Chrysler first introduced the a/c pump, it came out with a 6 blade 3.75" dia pump #2808681. It later became #3683834 with the 1972 ‘H’ engines (larger bearing housing but still 6 blades). Then, due to a newer internal taper-design pump housing (identified by the water inlet on the right-side of the engine), Chrysler now changed #33683834 to #3780127. This is only 4.25" dia and with 8 small blades. This pump is exactly the same as most aftermarket companies provide for a/c equipped cars.

The problem however results from the difference in RADIATOR SIZE between Jensen and Chrysler vehicles. We can only surmise that Jensen’s stock 4-row core requires a more powerful pump to move a lot of water when at idle in traffic. A clue here was Jensen’s use of a special smaller diameter aluminum pump pulley #CT6882 on SP (sixpack) and 1972 ‘H’ engines. This could have been Jensen’s answer to get the 6-bladed a/c pump to move more water at idle. Note that it is not possible to install this single groove pulley on later 440’s because of their dual belt setup. This same theory can be accomplished by using the non a/c and larger 8-bladed pump #3780196 in all Jensens. Tests on many cars both in the U S and the U K confirm this to be true. Experience indicates that the worst possible pump for the street Jensen is the aftermarket 8-blade aluminum pump. Only use aftermarket pumps which match the Chrysler #3780196 part.

One such pump that appears to meet these requirements and provide additional performance is that available from TDB Automotive #FK/1679, developed for NASCAR and off-road racing. It has the diameter, the blade number, etc and is easily recognizable in the manner of the back-sweep and assembly of the blades, not the usual bentup ‘prongs’ of the standard units.

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Contents copyright 2008, 2009 - Jody F. Kerr

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