hey, well after scaning this awsome site for info ( big up everyone!! ) ive managed to set my small blocks timing about right, it tops 40 deg as the engine revs out but the auto box will long have changed before that with about 35deg at 3000rpm. its idling at about 16deg

my question is what should the vac advance be up too???? when connected, i want to check it whilst i still have the timing light avaliable.

chevelletransamchevelletransamchevelletransam doh! just get both!!!!

if you have something resembling a street engine with 35 total, try about 15 vacuum, if that's too much and it pings try a 10*.

hey, well after scaning this awsome site for info ( big up everyone!! ) ive managed to set my small blocks timing about right, it tops 40 deg as the engine revs out but the auto box will long have changed before that with about 35deg at 3000rpm. its idling at about 16deg

my question is what should the vac advance be up too???? when connected, i want to check it whilst i still have the timing light avaliable.

chevelletransamchevelletransamchevelletransam doh! just get both!!!!

I think you may be able to run as much as 50-52° during cruise.

50-52 wow that sounds like alot!!! thought the vacuum was only meant to work under acceleration to advance when you need it, although when i connected mine back up it made a change straight away. when you say 15 or 10 is that a peak under acceleration or an idle/cruise increase????
and i guess there not adjustable you just get another off the shelf???
cheers guys

50-52 wow that sounds like alot!!! thought the vacuum was only meant to work under acceleration to advance when you need it, although when i connected mine back up it made a change straight away. when you say 15 or 10 is that a peak under acceleration or an idle/cruise increase????
and i guess there not adjustable you just get another off the shelf???
cheers guys

http://www.allmystuff.org/distributors.htm

From the article:

At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).

hey good one matt thanks ;-)

no vac advance at acceleration, no vacuum when the throttle is wide open.

optimally, as stated in the article above, the steady-state cruise mix is lean, keeps the plugs and chambers clean and the mileage up. that's when you need the vac advance, that lean mix burns slow. 50* is routine. but if your carb is rich at cruise it won't like all that advance. I always put effort into tuning for a lean cruise with lots of advance.

no vac advance at acceleration, no vacuum when the throttle is wide open.

optimally, as stated in the article above, the steady-state cruise mix is lean, keeps the plugs and chambers clean and the mileage up. that's when you need the vac advance, that lean mix burns slow. 50* is routine. but if your carb is rich at cruise it won't like all that advance. I always put effort into tuning for a lean cruise with lots of advance.

I set mine up this way and is much better. I visit the pumps less also.

cool needs sorting as its just cost me about 27 quid for 100 mile trip!!!! mind you stupid uk prices - you lucky buggers!!!! were on 98pence a litre whats that about 50 cent ??

27 pounds??man thats terrable,,what does that work out to in mpg>

50 cent what am i on? i meant 2 dollars !!! urr mpg didnt want to work that out hehe about 16.2 i think ish ..............

Its about $2.20 a litre US or 8.53 a gallon ARGHHHH! Now I dont feel bad about paying $1 per litre. Thank You.

Quid, pence, pounds, per litre?:confused:

J/K, it's just funny to see that for us U.S. folk, even though it's what the rest of the world uses.

I had the advance in my 68 Chevelle capped off. I took it in to be inspected today (Missouri) and they didn't pass it because of the advance not being connected. I stopped ny the local automotive store, bought a piece of hose, connected it and they passed it. Have any of you ever heard of this? Most of the time when I have had inspections done, they never raise the hood!!

Will

Maybe its considered emissions equipment?

That article sounds really reasonable, Matt. Where did u get it? It's not just Summit and Jegs that recommend ported vac adv. Barry Grant tech line, and many other sources do, also. Does this guy think none of these people know what their talking about? Nonetheless, I'm having trouble getting a good idle and off idle response, so I guess I'll try out his theory (vac adv connected to manifold). I know a lot of people prefer this way, also.