I wanted to see if anyone could provide input on a 'general' set of characteristics of the effects of advancing your distributor or retarding it for the recurve guys.

Today I installed a 'performance' curve distributor, and it's 'snappy' off the line, but I've lost some of my nice low end grunt, I'm running 'regular' gas instead of 'super' and not getting any ping at high load/ WOT anymore (either that or the 87 octane I got is actually octane and not 'oxygenated'). I also now notice my carb is running much richer, my vacuum readings at all 'modes' (idle, high idle, cruise, WOT) are still the same as before the curve change, and my temp gauge reads slightly cooler than it normally should (richer stoich can cool the valves and chamber I hear...).

Anyhow, any one have some rough input on say:

factor Advance for: Retard for:

Cylinder pressure low high
Vacuum high low
Octane high low
A/F mixture rich lean
Temperature cool high


????

-D.Idiot

If you're running 10 degrees initial as you've said in another post, then you need more initial timing. I run 15 degrees with around 14 mechanical in the distributor. Anyway, I think this is what you're looking for:

Advanced timing raises your peak cylinder pressure, increases your manifold vacuum, lowers coolant temp, raises your octane requirement and has a negligable (leaning) affect on A/F. The reverse is true for retarded timing.

Mitch

Thanks Mitch that kind of confirms things....although I'm a bit leary about running 35 degrees of total mechanical advance (the one that was in the car ran fine with 8 degrees of initial, and 22 degrees of mechanical, and 20 degrees of vacuum....but always pinged under certain conditions no matter what fuel I used).....

I might take a 9R and see if running 12-14 initial, and still running 18 mech. will make a difference... So far it starts right up and runs great, just needs a smidge of finesse...


thanks again,

-D.idiot

DI if I remember correctly, you have some cam (yeah, duh, I know, all engines have cam ) I mean, longer duration prolly hi lift cam. I think that how that cam is centerlined has a big influence here...

My engine runs like crap the first 3~5 mins with the increase of initial timing. I have to choke it for almost 3/4 of a mile before it stands going unchoked. That's for confirming that more timing needs richer mixture and more gas on low end. If I remember correctly you have posted that you had a carburetion lean out at 1500 +1800 rpm? I think that we can due that to the increase of initial timing too.

I'm running a recurved lite sprung dist and there's a point where I can't go anymore further or I get crappy idle and stalling... and the starting ain't turned "heavy" yet at that point. Of course I haven't swapped to my 2bl yet so I think that some minor bugs will smooth out when I move on to more carburetion.

I noticed that "loosing some grunt on low end" thing too... try to set your idle a li'l richer (whoa not that much ) and reving up the idle to 850 or around. That has helped me there.

good luck!

_________________
Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

My cam is not that big, and it's centerlined per the specs on my cam card 4 degrees advanced (110LSA 106 CL)...

My idle is set at 800-900 already, and since I changed my timing the A/F ratio meters are now pegged to the 'rich' side (plugs are black), instead of being 2 notches toward the ideal range, sooooo.... I'll try out Mitch's idea with a governor swap and see what happens.


Thanks,

-D.Idiot

So rather than pulling the distributor, I decide to just 'give it a tweak of advance'.... like to 16 BTDC initial....(gonna need some timing tape...)

She does ping a little at light throttle under load (like just depressing the pedal slightly, it goes away after 1/4 pedal... and only in 2nd gear), so maybe she'll be happier using 89 octane.... but...

She runs REALLLLY GOOD now, she's got lots of pep in all gears, I'll have to check the mileage when I fill up later this week. I also think I need to 'tune in' the vacuum can a bit. She's rich still in the mains, so I may 'jet back' a little to see if that does the trick there, and my temp gauge is on the 'first notch' above the 'C' mark....normally she sits at 1/3 up the gauge, but i don't think I'll worry about it too much.

Thanks again Mitch!

-D.Idiot