Adding lighter springs from a curve kit and using stock weights should give me more mechanical advance,correct? My 68 Olds post coupe currently has 20* base,and about 10* mechanical..hoping to get about 16-18* mechanical..

No, I believe it will not change the amount of mechanical advance, just a quicker curve

I think to change the amount of advance you'll need to disassemble the distributor and file the slot that limits the advance, or if the pin has a bushing remove it. The factory has alot of different cams and weights to pick from, It ususally takes alot of trial and error to get the right combination unless you have a distributor machine. My last motor I spent a whole saturday figuring out what curve the engine liked.

It's a game of trial and error. You'll notice that the tips of those weights, where they ride on the cam, are limited by little pockets in the cam. I ground the tips back slightly to get more mechanical advance. The slots on mine allowed much more advance than the weights & cam did. The weights & cam were the definite limiting factor, be they aftermarket or factory.

The springs only control the rate of advance.

As Chad said.

I tried many different combinations of weights and ended up doing some grinding myself. You can also try flipping over the center steel plate too.

The cam and weights were the limitting factor on my distributor, not the pins.

Be careful when modifying things that your srings are strong enough to get things back to the original base point at idle, or you may not be gaining advance that you think you are gaining.

With the distributor on a bench, a simple protractor works well to see what is going on with the mods.

bill

UPDATE:

Today I changed out the stock,very stiff springs in my HEI and added in some black aftermarket springs from a recurve kit..I ended up with 15* mechanical vs. 10* mech. w/the stock heavy springs...20* base at idle,then 35* total @ about 3200,I'm right where I'm wanted to be..and all I did was change the springs and got 5* more mechanical.Now a stock Olds 350 4 bbl with headers and 3.73's with a firm shifting TH400 feels great graemlins/thumbsup.gif

with the stock springs, where was the maximum rpm that you checked the total timing? if you didn't go up to above 4500rpms then it wasn't done advancing yet, so all you really did was change the rate to a quicker one where it peaked at a lower rpm. if the stock springs were working properly then there should've been no difference in total timing just at what point the timing reached it's peak. it may have been well above 4500rpms with those stock springs.

Originally posted by m71:
with the stock springs, where was the maximum rpm that you checked the total timing? if you didn't go up to above 4500rpms then it wasn't done advancing yet, so all you really did was change the rate to a quicker one where it peaked at a lower rpm. if the stock springs were working properly then there should've been no difference in total timing just at what point the timing reached it's peak. it may have been well above 4500rpms with those stock springs. ..it doesn't matter where I revved it to..3000 or 5000 it was only 30* total after 3K up to 5K before I changed the springs..now with the light springs,it goes to 35* at 3200 and stays there no matter how I rev it...

I had a similar experience as 4 Speed did. My stock springs would not under any circumstance allow more than 10 degrees mechanical. With two silver mediums I had 26 degrees mechanical advance all in by approx 2800-3000 rpm.