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PatAllen

Distributor advance/retard and temperature relays

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I was looking at the DAGSITES emission diagrams and i realised something, which i thought was the total oposite...

it mentions that the ADVANCE is disabled once the engine is hot...

i am sure a read somewhere that vacuum advance is an apprediated feature on light throtle for better engine response. At least, in my SDS EFI system i can tune some advance at given vaccum setting, and it does what it says.

I thought that when the engine was cold, vacuum advance was not allowed. Once engine gets to operating temp, then advance is allowed.

Or is it only for emissions purposes in this case ?

If you look at the CS diagrams next to the 02 ones, the last one works that way.

what am i missing ? i am dead sure that vacuum advance on light throtle "helps" on engine response/performance.

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Well, on the older cars, the timing doesn't have any temperature correlation...

but a stone- cold carbed engine will want a bit more advance, since the mixture's

slower- burning due to poor atomization and heat loss to the cold head.

Probably less than 10 degrees, but some helps. That's one reason an injected

car runs better- it can be easily ignition and fuel mapped for cold temps...

But yes, I agree with you that throttle position/load makes a BIG difference

in timing, and that you can advance the SNOT out of a lightly- loaded carbed car as long as that timing retards when you start to load it up.

I think BMW just didn't have enough tools for timing management, and did

the best they could with the technology they had.

t

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It's some sort of an emissions trick to help the motor run leaner at hot idle and burn more efficiently when cold. It is probably detrimental to the performance making it rev slower like with most emissions stuff. I dont think you are missing anything here.

On 80s cars a termo switch switches between ported and manifold vacuum for that reason.

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well, my automatic has a retard type, connected to the carb on the lower port so i guess it only has vacuum when the car idles, thus retarding the timing...for better idle quality ?...its a 74' so there is no solenoid on the vacuum line to the dizzy.

i have tons of dizzy, one recent one came in my hands and its a later "Automatic" one with advance vacuum and the 22deg. of mechanical advance that only automatic 02 has. I guess i will try it, connected to the intake vaccum source and see if i can fell any "improvements"

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