Bob Onit

Hey all

A few weeks agoI bought a Moroso timing curve kit and a Crane Adjustable Vacuum advance kit.

1973 L48 with Accel electronic module on the stock manual tach dist.

Checked my timing before I installed anything...
Initial timing is set to 12 degrees BTDC

The readings are... 35 degrees @ 2,500 rpm with the vacuum advance connected and 46 degrees @ 2,500 rpm with vacuum advance disconnected and plugged.

Am I in range for max advance or do I need to install the kit?
I had a hard time understanding Lars Timing paper.
Is it possible that a curve kit has already been installed?

Thanks in advance (no pun intended
Bob

bobs77vet

sounds like you have those backwards in relation to the vacuum can connected and disconnected.....assuming its a typo i would say the timing sounds pretty good to me especailly if you started at 12*

...Roger...

46 degrees wow that sounds like an awful lot of timing

...Roger...

I thought 38 was about max.

bobs77vet

yeah but thats not under a load.....when the load increasese the vacuum drops and the timing decreases... i think the max is like 52*

Bob Onit

Well......... Its a Holley Street Avenger 670
Perhaps I have the advance hooked up to the wrong port.

I folowed the instructions and as far as I can tell, the advance is conected to a port that has NO vacuum at idle...as the engine revs it pulls .... up to 20 hg.

I think I have it connected wrong..
Does 35 degrees with no vacuum advance sound correct?

MsVetteMan

Yes......

Bob Onit

Would 35 degrees with no vacuum advance indicate a curve kit bieng installed ?
Or is this a stock reading

Bob Onit

Heres a pic of the carb



I have the vacuum advance hooked up to the "Timed Spark Vacuum Source"

Hmmm........

...Roger...

If you have inital set at 12 and a total of 35 with the vacumn pluged then you have 23 degrees in your centrifugal.If you add in say 10 with vacumn you total out at 45 ---too much!

Bob Onit

Ok... how can I correct this? I'm very confused at this point
Thanks
ps: no spark knock at all

...Roger...

with all that timing I'm surprised you dont have spark knock---I think I would have your dist. set up on a dist machine at a speed shop.

Bob Onit

I have an HEI i can toss in... ill lose my manual tach of course

or I can remove the Accel module and go back to points ????

By the way... the car runs great...

kb2fzq

I was under the impression that the vac advance was only there to up the timing only during idle and once the rpm's go up, you loose the vacuum and the centrifical advance takes over....maybe I'm "very" confused as well....

Bob Onit

Im pretty sure its quite the opposite.... hence the term "Vacuum Advance"

redwingvette

Mine is setup the same, But your numbers are backwards. I get 36 with the vacuum pluged and 51 with it hooked up. That is NOT stock. I sent mine out to Lars, he recurved it and tested it in a car on a dyno. Yours has been doctored up by the sounds of it. Stock it was setup to only allow 14 degrees movement from inital. My car runs great.

BarryK

not correct.
an initial of 12* is usually about right for a mild cam with a total timing of around 36* (with not knocking or detonation). Once you add vacuum advance you are fine as long as it doesn't exceed 52*.
45* that INCLUDES the vacuum advance is not too much at all. 45* BEFORE adding in vacuum advance would be way too much.

BarryK

that's correct, at idle the vacuum advance is adding to the timing because of high motor vacuum.
under load or at WOT the motor is producing little or no vacuum so there is no additional vacuum advance and the timing is only from the mechanical advance

...Roger...

Remember if your using ported vacumn-it is venturi vacumn and it will not diminish with WOT

lightning30

correct.