Vk HEI Dizzy conversion help.

[VK SL 3800]

Going to put a Vh HEI dizzy into my Vk to to finally put an end to crap timing woes with my EST system constantly trying to advance of the scale. have only 1 question:

Where do you run the the vacuum advance line to?

as i understand vh commies have a special port on the carb for it an vk's dont, can anyone point me in the right direction................... thanks

[vkberlina]

my site has hose diagrams,I woul put a T piece off the lines on the EGR system for the vac advance. that way it will only advance once the engine it up to temp.

scott

[VK SL 3800]

Thanks mate will do

[codfishface]

The VK carb does have the port, it's just blanked off from the factory.

I recently did the same conversion and was lucky enough to have some help from an old skool mechanic that works at the workshop that reconditions and re-graphs distributors.

I took my reco'd Varajet to him and he drilled the port out and placed a hose connection in the now un-blocked port.

It had been a while since he had done one, so I watched him compare the VK carb to a disassembled VH one. The hole for the vac port on the outside of the carb isn't blocked off, it's blanked inside the carb, so don't drill into the side of the carb hoping you'll jag it. The internal gallery turns 90 degrees upward about 1/2 inch into the body and that's where it is blanked off.

As far as taking the vac feed from the manifold, here's my take on it -

At idle, your in dash vac gauge will read 6~7 (10kPa).
At WOT, it will read 1 (10kPa).

As you open the throttle butterfly, the manifold breathes through it, so the vac pressure in the manifold drops.

This will mean at idle you have MAX vac advance on your timing and virtually NONE at full throttle. Arse-about-face.

The vac port on your carb is ABOVE the throttle butterfly. So -

At idle, it will have 0 to very little, vac pressure. ( It isn't being effected by the manifold pressure. The butterfly is closed, like a door, all the action is below it).

As you increase throttle, the butterfly/door opens, exposing the ported vac to more manifold pressure until WOT, when you will have full pressure, hence FULL vac advance.


As I said earlier, this is the way it makes sense to me. I know plenty of guys just hook up to the manifold and away they go.

Bosch no longer manufacture the Vac Advance units and the diaphragms perish. If you have one in good condition, look after it!

Hope this gets the brain working. Cheers!

[vkberlina]

Thats why i suggested the EGR vac as it opperated at the same time the vac advance does, plus only once the car is warmed up, so it will be ideal for the advance on thedizzy

cheers
Scott

[codfishface]

Yeah, I agree with you on that, Scott.

In my case, I no longer have the EGR or the TVS's in place. The Air Pump and piping are long gone as well.

I looked at using the EGR vac source until I had my carb modded/drilled.

[delcowizzid]

As far as taking the vac feed from the manifold, here's my take on it -

At idle, your in dash vac gauge will read 6~7 (10kPa).
At WOT, it will read 1 (10kPa).

As you open the throttle butterfly, the manifold breathes through it, so the vac pressure in the manifold drops.

This will mean at idle you have MAX vac advance on your timing and virtually NONE at full throttle. Arse-about-face.

that is exactly how its meant to work it pulls timing when theres no vacuam IE full throttle and increases timing at cruise

[codfishface]

Help me out here if you can delco, as I'm certainly a novice with these devices.

By saying "pulls timing" do you mean the vac advance unit retards the timing at full throttle?

At full throttle isn't the engine at max rpm, therefore needing max advance?

Once again, help me get my head around it.

Cheers.

[delcowizzid]

yes when it has vacuam it advances which is at closed throttle and cruise it has vacuam. at wot theres no vacuam and high load so the advance is retarded to stop pinging and so it makes power.the advance all gets pulled back and the counterweights do all the advanceing for wot they do the advance at every load situation as well just the vacuam advance mechanism changes the base advance and the weights do the curve of the advance

[codfishface]

Thank you for that.

My problem was, I was thinking in 3 stages. Base timing, then Centrifugal, then Vac.

It's all starting to make sense.

Ferk I love this place.

[ari666]

just to throw in a little more info, i know its not necessary cos all the correct points have been covered but FYI.

part throttle and deceleration is where you will see all your vac advance. so on freeways, cruising and coming to a stop in gear. should be up around the 20-25 inches mark. vac advance helps keep the car running cool and i have been told that it helps with fuel economy but i cant work out why cos' you get better fuel economy from retarded timng. maybe its because when your vac/mechanical advance are hooked up correctly you can run a lower base timing, i.e. 8 degrees rather than 12.