I've seen a couple posts lately about mechanical fuel pumps providing better fuel mileage for cruisers because they don't pump fuel at a constant rate like electric pumps do, but I don't get it. If the electric is really worse on mileage, where does the extra gas go? When your carb(s) float bowls are full, the doohickey closes and no more fuel gets pumped, so it should make ZERO difference. I'm currently running a mech pump on our Olds and am planning one for my Cad 390 powered hot rod, but had always planned to keep an electric pump in the trunk and wiring already in place in case the mech pump failed when I was hours from home. I don't really care about the mileage, as I stated in another thread, but I'm just curious how the hell this could be accurate...
Pumps and mileage? I don't see how the fuel pump on a carbureted car could influence mileage at all unless it either produced enough excess pressure to overwhelm the float valve OR it somehow restricted delivery to less than the capacity of the carb jets. Either condition would have to be minor, or engine would not even run.
The fuel pump only delivers to the carburetor what the carburetor asks of it. Or simply put, what your foot demands. Shouldn't be any difference in volume, only in pressure. And for most street engines the psi should be 7 or less. If you need more mpg, look elsewhere.
I've had both on my 400" SBC powered Stude, with T400 ******...and noticed NO difference in either...21 mpg at 70 per on the highway... However, if you're talking about the PRICE of gas over the last 10 years...I've noticed plenty...!!! (Yes, this is a sarcastic comment...!!!) R-
That's what I thought and I agree with you guys, I've just seen several posts where people claimed the opposite and wanted to make sure there wasn't something I was missing. As for mileage, like any other hot rodder, I'm interested in burning as much gas as possible. In a proper ratio with oxygen, of course...
I wouldn't be so quick to dismiss this claim. It's not fuel consumption by the engine but energy consumption by the accessories. An electric fuel pump runs continuously, the excess fuel is returned to the tank when fuel demands are low. The energy used by the electric pump is essentially wasted, since that same fuel will be pumped more than once. A mechanical pump on the other hand, is designed to provide fuel at a rate that is matched to the engine rpm, thus reducing the amount of wasted energy. My question would be though, which takes more energy to operate in the first place? Electric pumps are pretty efficient these days. I would guess if there is a difference one way or the other, it is insignificant.
Not all electric pumps have return lines to the tank. Some are just dead-headed. Even the mechanical pump in my 258-powered Jeep had a return line, which I removed. If anything, I'd expect the electric to return better mileage, because the engine doesn't have to work harder by pumping the mechanical pump back and forth all the time. (***uming you removed the mechanicial pump.) But, yes, any gain one way or the other would be minimal, and probably not measureable. Pete
Mechanical pumps are just as bad about wasted pumpage, they have to pump with every engine revolution as well, even if they're an internal deadhead pump without a return. Electric vs mechanical the electric almost always wins for efficiency. Water pumps, fuel pumps, etc. The alternator's just a more efficient way to generate energy off the spinning beast. Fuel pumps add a pound or two of moving m*** inside the motor. I don't think you'll ever see the difference tracking mileage at the pump with a notebook & calculator. But I bet there's a slight difference if you did a controlled experiment that measured specific fuel consumption.
Look at the name, look at the reply. There's your answer. A ton of you guys are just speculating, what if this - what if that and the answer has already been said. Same engine-same car-same results.
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