vac fuel pumps

[wolfgang]

Ahh, I understand you now. If the engine efficiency is equivalent (lbs fuel/HP/hour), then the pump(s) must be up to the fuel delivery task. It/they must deliver X pressure and X flow to accomplish the target HP - agreed.

Are you aware the efficiency of the diaphram fuel pump is affected by port timing? Be aware a vacuum pulse diaphram fuel pump designed to run with stock porting may not deliver the same performance in a port modified engine. For this reason all new mod engines should be instrumented until pressure and flow is proven.

Absolutely. And pressure as well as fuel flow increase with rpm. I am currently retrofitting two Merc double diaphragm pumps to my Force 4-cyl. One diaph. gets fed from a transfer port cover, the second diaph. from the tapped transfer port of another cylinder - sort of suck and blow (I figured). Each pump feeds its own twin throat OMC carb. I think plumbing both pumps into one manifold might lead to the pumps "hunting" i.e. the pressure pulses may double in intensity or cancel themselves out. What do you think?

[Tim Kurcz]

Hey Wolfgang,

You raise a good question about the possibility of pulse cancellation with alternating twin diaphram pumps. My guess is this is unlikely due to the baloon/dampening effect of rubber fuel hoses unless the lengths are perfectly the same.

My concern about independent fuel systems is if one goes south - you burn down a cylinder. Piping to a common manifold eliminates tuning issues and provide redundant supply.

Good luck with your project. Please post pics - sounds cool!

Tim

[wolfgang]

Hey Wolfgang,

You raise a good question about the possibility of pulse cancellation with alternating twin diaphram pumps. My guess is this is unlikely due to the baloon/dampening effect of rubber fuel hoses unless the lengths are perfectly the same.

My concern about independent fuel systems is if one goes south - you burn down a cylinder. Piping to a common manifold eliminates tuning issues and provide redundant supply.

Good luck with your project. Please post pics - sounds cool!

Tim

thanks Tim - on the strength of your experience I will install a manifold.