question for techies

[jeff miles]

do any of you guys know what the manifold depression (vacuum) is (lbs sq in or whatever)for a fuel injected 4L RV8? I am trying to find the range from tickover, thru constant cruise, to throttle wide open under full load. And if you do know, do you also know where I can get an adjustable pressure/vacuum switch that will work in that range.

Thanks

jeff

[nighthawk]

I've never measured a RV8 to check, but it shouldn't be much different to any other engine.

Vacuum is measured in "Hg or "water

Depending on the condition of the engine and it's state of tune, the Vac can vary especially if the cam has a large overlap.

Perfect vac is just under 30inches HG

An engine in a decent condition should be above 20" minimum, usually anywhere upto 26inches at idle

full throttle will be 0 inches as the throttle os fully open,

Only you and a gauge will be able to plot how the vacuum deminishes as the throttle is opened.

You'll notice a slightly higher vacuum on overrun too.

[GreenV8S]

Got various measurements on mine if that helps?

All with a fast road cam, normally aspirated:

Normal 900 rpm idle -7.5 psi.
600 rpm idle -4 psi.
2000 rpm fast idle -10 psi.
3000 rpm cruise conditions -7.5 psi.
full throttle 3000 rpm 0 psi.
full throttle 6000 rpm -1.5 psi.
3000 rpm throttle closed (engine braking) -14 psi.

With a stumpy cam fitted the manifold pressure at idle has dropped by several psi.

[jeff miles]

Thanks guys - that tells me what I needed to know

cheers

jeff