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Where can I get more intake vacumn? I installed 300zxt TB on my 78 280z and I'm not getting enough vacumn for my distributor. I by pass the vacumn canistor and put the hose straight from the TB. not still enough. Where else?
 

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The a/c and heater control use vacuum. During my '78's rebuild I replaced the vacuum controlled heater mess with one from a '77 (non vacuum controlled). Unless your car is stripped, like mine is, it will be a rather large task. Not sure how well the '78's heater system will work without the vacuum lines going to it. You could give it a try...What about the brake booster hose? Has anyone tried to run with out it? Just a thought...
 

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You may be trying to use the wrong vacuum port. The distributor uses PORTED vacuum which operates basically in reverse of manifold vac. Ported vac increases with rpm while manifold vac drops with rpm increase. If you attach to manifold vac outlet your timing will be advanced at idle and will drop like a rock when you crack the throttle, while ported vac will increase. If your throttle body doesn't have a ported vac outlet, you may need to go to a solid breaker plate in the dizzy and then have the distributor recurved and just run on mechanical advance.
 

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Perfect example of "upgrading" one part of a balanced system and upsetting the overall performance.

Anyone else remember the VW Bosch 009 dizzy that everyone tries to use? It's a mechanical advance unit only and people tried to use them in bugs and buses without adjusting the curves. Most of the have surging and lagging problems that the owners "just can't figure out" ... they never stop to think it's the dizzy that's designed for a Porsche turning 6,000 RPM instead of their grocery getter chugging along at 3,000.

ConorP
 

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why do you wnt more vacume to your distributor? the only reason for the vacume advance is for fuel economy at cruising speeds. if you are looking for something else, let us know.
 

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hey JohnH240, port vs. intake?

Hey JohnH240---I read your post (above) regarding "vacuum advance" by yo2001, and I was wondering if you could please answer something for me? In the past, I have read your answers/advice and have found you to be a most credible author. I was not aware of any distinction between "port-vacuum" vs. "manifold-vacuum." Having said that, where should my distributor advance vacuum line pug into? I have a 240 with a ZX power plant, ZX distributor 12-80E, 71 balance tube, N36 intake manifold (260Z), round top SU's and, headers (no smog pump, or a/c). Currently, I have the line plugged into the port present on the forward SU...is this correct?
Thanks---Jerry
 

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As I understand it you should have manifold vacuum going to a "T" connector and then to the "Vacuum Delay Valve" and then on to the Vacuum Advance on the Dizzy.

The Vacuum Delay Valve allows full flow one way and restricts the flow in the other way. This keeps the Vacuum Advance Unit operating smoothly as opposed to reacting quickly to sudden changes in manifold vacuum.

The base of the "T" goes to the Thermal Vacuum Control Valve. Until the engine coolant get to the proper temperature vacuum does not flow through this valve. When it does flow, vacuum is the applied to the carbon filter / fuel tank purge canister. This type of vacuum valve is referred to as "Ported Vacuum", the "port" opens or closes depending on what is being controlled.

There are many options for vacuum hose routing here depending on Fed U.S.A / California / Canada and transmission type etc.

In any event you should have at least 16 inches of vacuum at the "input" side of the Vacuum Delay Valve at idle (i.e. 700 RPM) and the gauge should be steady. When you open the throttle quickly the gauge should react quickly.

Put the vacuum gauge at the Vacuum Advance side of the valve and you should have the same 16 inches of vacuum at idle (i.e. 700 RPM) and the gauge should be steady. When you open the throttle quickly the gauge should react slowly.

Put a vacuum pump on the Vacuum Advance Unit and pump it down to 16 inches of vacuum. As you apply / release the pump vacuum your idle speed should change. If it does not you may have a defective vacuum / mechanical advance unit.

The vacuum hose routing, as far as I am concerned, is a very gray area here, based on Year, Make and Model BUT you should have direct manifold vacuum at the Vacuum Advance Unit.

Wayne Monteath
Masham, Quebec.
 
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