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post #19 of (permalink) Old 06-23-2005, 10:44 AM
RRich
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Re: vacuum advance question

Always with the advance light - hold the RPM to where you want, take the reading by turning the knob till the marks say 0, read the advance on the knob (or meter.) The actual timing is what the marks say PLUS what the knob says. Easy way is to make the marks say 0 and read the knob.
--- 1/2 a broken wooden clothespin makes a good ramp to use as a stop in the linkage for RPM adjustment.


Sounds like "Too much too soon" on the mechanical.

"Performance? Distributor?" Most of those are set up for drag strip use. They "pop" the advance way up almost immediatly - expecting you are going to "launch" at 6000 R's anyway. They expect you are going to rev it up unloaded to 6k, then dump the clutch. The fast advance helps you get it up to 6k fast - but not under load. At 6k the advance is all the way in anyway. At 6k the advance can be far greater than 35 too. Engine life and ping are not a problem on race engines that will only last 4 or 6 miles anyway.

They are not realistic for the street -- or especially off road. The mechanical advance uses super light springs with weights ground to advance it waaay too fast.
You have to change those so called "performance" things to make them work properly. Toss the weights and springs, use stock ones - not even the ones from a kit - get OEM STOCK. You end up with a colorful or shiney "stock" distributor - and a lighter wallet. Just shows advertising works.

Most don't even have an adjustable vacuum advance diaphram either. Save your money, use bone stock for the best performance for our purposes.
If you don't believe it - try it!

The so called "performance modules" are scam too. They simply pot the stock one inside some colored plastic.
Think about it -- do you really think they have Motorola or some other chip maker to redesign and build them a different chip for multi-millions of dollars so they can sell a limited number of them for slightly over the price of a stock module produced by the millions?
Not real. Again, save your money.


Now for what you need:
Ideally -

No vac:
Idle = 8-10
1000-1200 = advance barely starts to move
1800 = 18
2600 = 22 (Just about all in at this speed)
3000 = 25

With vac:
idle - 8-10
1000-1200 advance barely starts to move
1800 = 24
2600 = 32
3000 = 35

If you get it near that, it should perform well, start nice, and get good mileage - without excessive engine wear or ping.

Notice the mechanical moved it - or should - about 12-15 deg.
The vacuum moved it another 12-15.
The entire total - initial + mechanical + vacuum should end up around 35 degrees at about 3000. The advance systems should be "all the way in" at 3000. More than that will give driveability problems, less than that will give less gas mileage. If both the vac and mechanical are slightly too much, just drop the initial down a little, but not below 0.
Make sure the tiny pin in the slot under the weight plate has the bushing on it - stock it's rubber, aftermarket they are brass. That limits the mechanical travel.

For the techies - above 3000 the engine is straining more, ported vacuum starts to roll off, so advance actually starts lowering slightly - until it drops down totally to the power curve - set by the mechanical. That occurs about 4500-5000. Above that max power can be had by dialing even more advance, but most engines can't go much more than that. At 8000-9000 R's, it often needs in the range of 50-60 degrees!

The actual numbers are not real critical and cannot be predicted for your particular engine. But as long as the curves are smooth and they peak at about those points this should be very close.

These are generic numbers, the only way to get the exact "best curve" is with a chassis dyno under load with an exhaust analyzer, taking several measurements and experiments. Each engine - and all the related "stuff" - exhaust, intake etc - even charging system voltages and loads, are different slightly. That's why "generic."



My opinion of Accel and Bosch, and lots of other "pink" "performance" stuff - the best performance is obtained the instant you buy it - they got your money - it performed well for them, didn't it?

"Pink" -- if you want to sell something that doesn't do what you say, call it "performance," color it bright pink, bright yellow, flourescent green etc - make it colorful, kids will buy it!

Hard to tell real stuff from trash.
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