plumbing webers for vacume
- Thread starter Randy
- Start date
Vacuum for what Randy?
Bob
Bob
I've been toying with the same idea for a couple of things;
1) Central vacuum point to use for a vacuum advance distributor which would aid in starting and driveability.
2) Pulse dampening - a shared vacuum source would dampen out the intake pulses as well as reversion and make the carburetors less sensitive to same.
My ideas have only been on paper so far but hope to get to the point of execution in the coming year.
A Shared plenum that mounts between the carbs and the individual runners on the intake.
A network of 3/8" steel lines connecting to fittings underneath the intake manifold. Each fitting tapping into the floor of the intake runners just before the port connection to the cylinder head. The eight lines coming together via a log style manifold underneath the intake and a port from that coming through the valley of the intake to the outside world.
I think anything smaller than 3/8" may not be able to react quickly enough or have enough volume to make any/much difference..
Would like to hear what Jac and some of the others have to say on this...
1) Central vacuum point to use for a vacuum advance distributor which would aid in starting and driveability.
2) Pulse dampening - a shared vacuum source would dampen out the intake pulses as well as reversion and make the carburetors less sensitive to same.
My ideas have only been on paper so far but hope to get to the point of execution in the coming year.
A Shared plenum that mounts between the carbs and the individual runners on the intake.
A network of 3/8" steel lines connecting to fittings underneath the intake manifold. Each fitting tapping into the floor of the intake runners just before the port connection to the cylinder head. The eight lines coming together via a log style manifold underneath the intake and a port from that coming through the valley of the intake to the outside world.
I think anything smaller than 3/8" may not be able to react quickly enough or have enough volume to make any/much difference..
Would like to hear what Jac and some of the others have to say on this...
Terry Oxandale
Skinny Man
I remember a similar discussion years back as a means to overcome some of the inherent individual carb flow restrictions that a common plenum resolves.
The procomp weber manifold has a common plenum on the underside.
Bob
Bob
Without knowing WHY Randy ( OP ) requires the vac other than the -3 or -4 line size suggestion here goes..
Vacuum advance only- the - 3 lines into a common point prior to attaching to dizzy should be sufficient.
Vacuum advance plus brake booster, then something larger like 3/8" or more reqd, catch 22 here.. if you look at most factory 4bbl manifolds the brake booster line usually attaches to one single intake runner rather than a plenum, Ive been told in the past that the pulsations in the runner help trigger the one way valve in the booster can... make of that what you will...
All runners linked to a large plenum area on the underside, or paired, quaded to dampen pulsations and increase the effective carburettor size, Tom in Germany was looking into this prior to his accident using a 'Pro Comp' weber manifold that has a lower plenum after this fashion...one possible problem with that design might occur after a long period at cruise speed there could be considerable amounts of fuel that has dropped out of suspension puddled in the plenum... this would play hell with mixture when throttle opens up..
To sum up, I race cars- no vacuum advance or brake boosters needed
Vacuum advance only- the - 3 lines into a common point prior to attaching to dizzy should be sufficient.
Vacuum advance plus brake booster, then something larger like 3/8" or more reqd, catch 22 here.. if you look at most factory 4bbl manifolds the brake booster line usually attaches to one single intake runner rather than a plenum, Ive been told in the past that the pulsations in the runner help trigger the one way valve in the booster can... make of that what you will...
All runners linked to a large plenum area on the underside, or paired, quaded to dampen pulsations and increase the effective carburettor size, Tom in Germany was looking into this prior to his accident using a 'Pro Comp' weber manifold that has a lower plenum after this fashion...one possible problem with that design might occur after a long period at cruise speed there could be considerable amounts of fuel that has dropped out of suspension puddled in the plenum... this would play hell with mixture when throttle opens up..
To sum up, I race cars- no vacuum advance or brake boosters needed
I have a vacuum set up on my CAV, I run 4x48IDA, vac advance MSD billet distributor +6al box, Audi power brake booster, vacuum controls for heat and AC and it all works perfectly! It is setup with a box under the turkey tray that has 8X 3/16 rubber vacuum hoses- one from each runner under the throttle plates- to the "box", then one half inch i.d. rubber hose to feed booster and necc.vacuum controls for heat etc, one more take off for distributor. I was thinking about installing electric vacuum pump but found it unneccesary . I f any one wants pics of setup, email me with your email and I will gladly send pics, I cant figure out how to put them on this site!!!
You should also bear in mind that vacuum sourced from the plenum as described above has different values to that which would normally be sourced in the region of the throttle plate of a conventional carb for the distributor....
as such you may be getting more or less vacuum advance than you need under some engine operating conditions... best advice would be to disconnect/plug/disable the vac adv while partaking in events like track days, races etc
as such you may be getting more or less vacuum advance than you need under some engine operating conditions... best advice would be to disconnect/plug/disable the vac adv while partaking in events like track days, races etc
Pat Buckley
GT40s Supporter
I once used an electric pump and abandoned it because it was very noisy.
If your braking system is reliant on vac for the booster and considering cam spec can seriously affect vac it might be an idea to fit the diesel type alternators that come with a vac pump on the back. Plenty of range as far as output goes, they need an oil feed and dump tube back to the sump but are worth thinking about at the build stage.
Bob
Bob
