distributor mechanical advance

[Robin7TFour]

GREETINGS, when changing the advance springs in the distributor, what rpm should full advance be set at?
what is better for a lightweight car like the corvette?


ROBIN

 

[Eric R.]

There is no true answer for this question. Motor condition, fuel quality and many other factors go into this. As a general small block rule, I start with 1 medium and 1 light spring. This should get you a total mechanical advance somewhere around 2500 RPM. As with any performance tuning, listen for ping/knock and retard your timing as needed. If you cannot get the ping to go away then you will need to move up to both medium springs. DO NOT use the weights in the kit, just the springs. Good luck!

 

[Robin7TFour]

ERIC, thanks for the info. where did you buy your dist spring kit from?


robin


be like a duck.smooth on the surface, paddle like crazy underneath

 

[Bob Chadwick]

Lars sells a complete kit with vacuum advance canister, springs, etc. Mail him, he'll get back to you. Very knowledgable about carbs and distributors.

 

[Eric R.]

""This must not vary to about 600 rpm (dist.) at which point it shouuld kick up fast to full advance of 9 degrees (dist.) by 1500 rpm (dist.)""


Please do tell where you find these springs...

You have 20 initial at the crank until 1200 RPM,
then a fast 18 at the crank by 3000 RPM for a total of 38 degrees.


Not only does this not match any spring spec sheet I can find but it also suggests that above 3000 RPM your total advance would climb past 38 crank degrees. Is there something I am missing here?


I like your theory and would like to try it if you could explain further. Currently I do have a slight idle stability issue that I would like to correct.

 

[Robin7TFour]

GREETING , yesterday i tried out my new dial-back timing light. i ran the engine to 2800, then dialed in 34 deg. of timing(back to 0). i can see now i have to rev it slightly higher to get the setting exact.
i will let you know what happens. btw who is LARS and how do i mail him?

robin

just remember; " it suppose to be fun owning an old car"

 

[Bob Chadwick]

Lars is a member here, though he is much more active on the CF. Do a member search and email him.

He has several posts there on the subject and I have his paper on my technical assistance web page.

 

[Eric R.]

The second curve you mention would use both of the light springs from kit two. That is where my idle troubles are comming from. With the stall converter I never really see anything below 2500 RPM so I could afford a stiffer spring as long as I get my 37 degrees by 3000 RPM. At least 37 degrees was the sweet spot on the dyno. It just seems odd that out of both these kits, neither really has the springs I seem to need.

Kit one,
At 24 degrees total mechanical advance
color start rpm total rpm
gold 400 1600
silver 600 2800
black 600 4000


Kit two,
color start rpm rpm advance
black 900 4000 19 degrees (crank)
silver 1800 4000 10 degrees (crank)
gold 2500 4000 6 degrees (crank)

Someone has to make a better spring kit than these.

 

[Robin7TFour]

GREETING FROM WARM ORLANDO, here's the update. with 34 deg of total advance (using dial-back light). the car starts almost instantly when cold, great considering the choke isn't working.
bottom end performance is really good. the idle is still a bit on the irratic side. at 650-700 rpm it shakes the car .
however, there is definately more pep on the bottom end and revs to 4000 seem quite good.
i still want to get into the springs . i think it will help add a little more.

thank you EVERYONE for all the wondeful advice

you're all on my xmas list...wink


ROBIN