Forgive me for the stupid question, but it's been a looong time since I've owned a vehicle with vacuum advance. Which port does the vacuum line hook to? Is it metered vacuum at the metering block on a Holley, or is it manifold vacuum?

Thanks!

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Sean Thomas
TC #907 ACES #4468
Chevelle & ElCamino Club of Oregon #35
1970 Chevelle SS 396 (http://home.attbi.com/~70supersport/)
E/T 13.38 @ 104.15
2002 Camaro SS LS1 (http://home.attbi.com/~70supersport/pageseven.html)
E/T 13.25 @ 105.2

Your vac adavance always go's on the metered port on the carb which is the metering block on your holley.

Scott

ss there are two schools of thought on this question. One option is at the metered port, the other option is to manifold vac. There has been alot of heated debate over this. I suggest you try and see what is best for your application. you can do a search and gain more insight on the merits of each.

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67 BB Prostreet Camaro COMBAT RAT
71 BB Chevelle (SS clone)
80 Camaro Z28 355 SBC
2002 35th anniv. SS Z28

Very well said Milan! Sean for street performance once the throttle is cracked they act very much the same. Put a vacuum guage on each port and bring the throttle up from idle to about 2000rpm you should see the manifold source pulling at idle then dipping and coming right back. The ported source should not pull at idle but will be at the same place as the manifold as you rev it up. Wing it WOT on either and you'll see the vacuum drop right off.

I believe the factory used the metered source on cars that came equipped with Holleys. Don't limit your tuning to what the factory did though. If you have a big cam and it pulls against the converter (kind of a serging feeling when in gear) you might be able to smooth out the serge by using the manifold source to increase idle advance. Also if you have a dist with lots of mechanical advance built in and need to limit the initial to keep the total in check you may find using manifold helpful in giving you the added advance the mill needs to run cool at idle.

Ultimatly it's what works best for your combo and tuning style. the vacuum advance helps get your car rolling at low rpms and part throttle and goes away under load or at WOT to keep your engine from detonating yet allowing maximum advance.

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...Dennis
The '69 (http://chevelles.com/showroom/ww.jpg), the '96 (http://www.camaroslimited.com/graphics/memcars/96ss.jpg) and The El Camino (http://chevelles.com/showroom/DjD/dsc00016.jpg)
Team Camaro (http://www.camaros.net)
Camaros Limited (http://www.camaroslimited.com)

We've been all through this subject not long ago. I don't want to re-open the controversy, but just want to say this: To get an idea of what your vacuum advance is going to do when connected both ways, temporarily hook up a vacuum guage you can see while driving via a long tube. Try it both ways. Only then can you see what the vacuum does when connected either way under sustained load.

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von '69 300 Dlx SS TC #15 ACES #1575 HSCA #5
My '69 SS (http://mywebpage.netscape.com/jerryacheson/vons69.html)