Technical > Spud Miller's Cave

under driving a pump

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wideopen231:
Is anyone running a mech. pump with an under drive. I have a 7 GPM pump on the car now. NA 482 ci. Sin ce bypassing about half the fuel I was wondering about underdrive for pump bypass less and running at lower pump rpm has to be easier on the pump. Now how to figure fuel system. Using Spud's calculator. If use 10% drop in fuel flow I have chart that shows it looks like would expect. How accurate with a lot of assumed and no real flow bench info?

tcoupekyle:
I am also curious. I have a 110 pump and it’s just a bit much I think running a .160 pill.

wideopen231:
From what I can gather it runs pretty linearly. A 10% reduction in drive equals 10% fuel. Now that is generalization of about 10 pumps out of my Gorr sheets.  Hoping for input from anyone having done it real world not calculations .

 

slingshot383:
Anybody that flows pumps (or has a flow chart from a pump being flowed) you should be able to make easy calculations from it.  A flow chart will compare flow rate to rpm, so take your reduction percentage into rpm and match that to the graph and you'll have your new flow numbers.

wideopen231:
I have chart for one pump and total flow of other pump. Easy enough to know flow of one with full chart. Now that I have had 3 or 4 confirm that it changes same as drive change I know what one with just total flow number will do.

Have a fuel flow sensor for data logger coming and think I can convert it to use on home made flow bench. At least readings will be the same as what I get when it is on car since it essentially the same piece as long as rpm matches.

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