Difference between 40083 and 4657 fuel pumps??

[Dan B.]

I was wondering what the difference between these 2 fuel pumps is besides the location of the fuel inlets. Why was it necessary to have the 40083 pump for High performance (did it deliver more pressure?) and why did GM feel it was necessary to relocate the fuel inlet when the fuel supply line for all 327's is the same? Just something I've wondered about that I'd be interested in understanding better. Dan

[Dan B.]

Re: Difference between 40083 and 4657 fuel pumps??

If nobody knows, I'll try and find the answer and post it if there is any interest.

[Russ S.]

Re: Difference between 40083 and 4657 fuel pumps??

The 400083 used a stamped steel bottom cover instead of the cast one. I would assume because it was the high performance pump that it delivers more fuel.

[Dan D.]

Re: Difference between 40083 and 4657 fuel pumps??

I have seen 40083 pumps with the cast bottom and with the stamped steel. Believe is depends what year car it is.

I don't know what the difference is between 4657 and 40083 pumps is, but I would like to know. Why is the 40083 higher performance? Would think the 40083 has more fuel delivery. But how?

-Dan-

[Dan B.]

Re: Difference between 40083 and 4657 fuel pumps??

I did a little research and besides the difference in the bottom covers between the 2 pumps, I looked at some of the kits for both (which are not interchangeable) and the diaphragm spring appears heavier on the 40083 pump which may be an indicator of intended increased fuel delivery pressure. I don't know this for sure, but it seems plausible. However, the fuel pressure specs I find are very close or the same for both pumps depending on what application you look up and the 40083 pump works fine with the Carter carbs (lower HP) even though not correct in application. In short, I still can't see a reason for making 2 different pumps nor the need to relocate the fuel inlet. The differential seems too small to me.