Vacuum advance on a 440 6 pack question

[ottawamerc]

Hi Guys

Well good news is she runs and sounds sweet Now I'm trying to set it up to get it somewhat stable so it will be able to break in.. Here's the numbers I have so far: idle set 940 rpm, manifold vacuum around 21"hg, initial timing set at 19*BTDC. with vacuum advance plugged.

Now when I reconnect the vacuum advance it advances a few degrees I believe that there should not be any vacuum here until the engine is at cruise, I have the hose connected at the center carb on the port on the mixture plate.

Thanks again guys. 

[firefighter3931]

I believe that there should not be any vacuum here until the engine is at cruise, I have the hose connected at the center carb on the port on the mixture plate.

Thanks again guys. 

On a 6 pack the vacuum line has to be connected to the metering block port/nipple and not at the baseplate. If the idle speed increases and the timing advances you are connected to manifold vacuum and not ported vacuum.

If this is a new build hopefully you broke the cam in properly 


Ron

[ottawamerc]

I believe that there should not be any vacuum here until the engine is at cruise, I have the hose connected at the center carb on the port on the mixture plate.

Thanks again guys. 

On a 6 pack the vacuum line has to be connected to the metering block port/nipple and not at the baseplate. If the idle speed increases and the timing advances you are connected to manifold vacuum and not ported vacuum.

If this is a new build hopefully you broke the cam in properly 


Ron

Thanks Ron

Yes it is connected to the metering block port, the secondary port is just behind it. And yes it is a fresh build and I am aware of the dreaded startup cam destruction so I asked the guy that built the engine to do the startup, we added break-in additive and it did start right away

[firefighter3931]

Hey Scott, welcome to the Charger board ! 

Regarding the distributor issue ; try disconnecting the vac advance line and put your vac guage on the nipple to see if it's pulling any vacuum at idle. If it is, then you're using the wrong nipple.  The other possibility could be an internal issue with the center carb. 

You could try backing the idle speed down to 850 and see what happens.

Fwiw, i never use the vacum advance because it usually causes tuning issues with any performance cam.

Maybe you could outline the engine combination....


Ron

[ottawamerc]

Ok maybe I got it, I dropped the idle to 700 rpm and the vacuum dropped to 5"HG and not enough to pull in the advance I'm still surprised that I need to get the idle that low.

[firefighter3931]

The stock vac cannisters start advancing at 15hg.....that's why i suggested lowering the idle speed. 

I'm still curious as to why that port/nipple on the center carb is showing a vac signal at idle ? 


Ron

[Sublime/Sixpack]

 

Fwiw, i never use the vacum advance because it usually causes tuning issues with any performance cam.

Ron
[/quote]

Ron, just for my own reference at what specs. (approximately) do you consider a cam to be a performance cam?
Thanks

[firefighter3931]

Fwiw, i never use the vacum advance because it usually causes tuning issues with any performance cam.

Ron

Ron, just for my own reference at what specs. (approximately) do you consider a cam to be a performance cam?
Thanks

[/quote]

Any cam that produces less than 14in vac at idle. That's usually the case with cams ground on a tighter lsa (108-110) with ~230@.050 (or more) intake duration. The higher the overlap, the less idle vacuum it will have.


Ron

[Sublime/Sixpack]