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Old 03-16-2004, 15:31   #1 (permalink)
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Lumpy cam and Vac Advance, From the manifold?

Hi Guys
I have a 302C with a Lumpy cam, Holley 600 Vac Sec and headers. As you'd guess she has that lopy idle. The vac advance is connected to the std vac advance port on the holley but she feels like it wants a more timing at idle so I was wondering if I should run the vac from the manifold this way she'd be running extra timing at idle.... Stupid idea?????
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Old 03-16-2004, 17:59   #2 (permalink)
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Re: Lumpy cam and Vac Advance, From the manifold?

Check the timing and see if it needs more timing.
Vacuum advance is to advance the timing when your beast is revving
in the high zone.The more revs, the more advanced it needs to be.
Vacuum advance does not effect idle what so ever.
I had an XB with 220kw,290hp at the wheels.
You will not need to move the advance hose.
Put the timing at around 10-12 degrees, and adjust your carb idle screw to get the idle right. She will fly.

Last edited by TICK4D; 03-16-2004 at 18:03.
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Old 03-16-2004, 18:18   #3 (permalink)
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Re: Lumpy cam and Vac Advance, From the manifold?

Quote:
Originally Posted by TICK4D
Check the timing and see if it needs more timing.
Vacuum advance is to advance the timing when your beast is revving
in the high zone.The more revs, the more advanced it needs to be.
Vacuum advance does not effect idle what so ever.
I had an XB with 220kw,290hp at the wheels.
You will not need to move the advance hose.
Put the timing at around 10-12 degrees, and adjust your carb idle screw to get the idle right. She will fly.
Thanks for that, I know how the vac adv works and that there is no vac at idle. I have the timing set to 18 and have adjusted the idle mix on both throats and it's idleing ok it's just that it idles a lot better with more advance, that's why I was wondering about connecting the vac adv to the manifold. This way I'd get extra advance at idle which would smooth it out with out advaning the total timeing.
Cheers!
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Old 03-17-2004, 00:59   #4 (permalink)
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Re: Lumpy cam and Vac Advance, From the manifold?

Quote:
Originally Posted by TICK4D
Check the timing and see if it needs more timing.
Vacuum advance is to advance the timing when your beast is revving
in the high zone.The more revs, the more advanced it needs to be.
Vacuum advance does not effect idle what so ever.
I had an XB with 220kw,290hp at the wheels.
You will not need to move the advance hose.
Put the timing at around 10-12 degrees, and adjust your carb idle screw to get the idle right. She will fly.
Thats wrong.

Also I would never recomend connecting a "camed" engine to manifold vacum with an auto. When you put it into gear it can stall due to the now reduced vaccum and advance. If its manual give it a try but with 18 intial that is a lot already, I 'm amazed your car still cranks over. Also if it works check your manifold vaccum reading the PV may need changing.

IMO generally more cam needs more initial timing but about the same total advance. To do this I generally weld a tab to the vac can arm to limit movement and minimise the mech advance.

Last edited by not ford; 03-17-2004 at 01:01.
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Old 03-17-2004, 13:58   #5 (permalink)
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Re: Lumpy cam and Vac Advance, From the manifold?

Quote:
Originally Posted by not ford
Thats wrong.

Also I would never recomend connecting a "camed" engine to manifold vacum with an auto. When you put it into gear it can stall due to the now reduced vaccum and advance.
That makes sence.


Quote:
If its manual give it a try but with 18 intial that is a lot already, I 'm amazed your car still cranks over. Also if it works check your manifold vaccum reading the PV may need changing.
So far I've found 2 vac ports unblocked all together.... It's happy as at 18, I've been trying to find the factory setting. That said no detonation.


Quote:
IMO generally more cam needs more initial timing but about the same total advance.
That's exactly why I was thinking of hooking it to the manifold vac, the total would stay the same but it would have full vac advance at idle.


Quote:
To do this I generally weld a tab to the vac can arm to limit movement and minimise the mech advance.
That sounds like a better idea!
Thanks
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