Mechanical Advance

[392cobra]

Nick,
I have a 383 sbc in a '68 Nova,so it is certainly heavier than our Cobras.
The total advance sounds good.Can you shorten up the cent. so you can get more initial ?
If you could get the cent. in faster,like 3000,you might be better off.
I'd lose the vacuum advance all together.

[NickRCarter]

Hi Fred, Thanks for that. I have tried increasing the initial, but it just results in difficult starting and stress on the starter and a desire to keep running when switching off. It also was no as smooth at low revs with a more davanced initial. Although with more advance I would get better vacuum, but I can live with reduced vacuum. I'm not sure about the vacuum, you read so many conflicting reports. I can decide on that during further road tests. I will experiment with slightly weaker springs, but it seems the springs get weaker the whole mechanism gets sloppy.
Oh what a voyage of discovery!!
Nick

[Big-Foot]

Originally posted by 392cobra


Nick,
I have a 383 sbc in a '68 Nova,so it is certainly heavier than our Cobras.
The total advance sounds good.Can you shorten up the cent. so you can get more initial ?
If you could get the cent. in faster,like 3000,you might be better off.
I'd lose the vacuum advance all together.

Cool a fellow Nova owner too! Mine - 1970 Pro-street 468 BBC 600hp all throttle.

I agree that with his weight of car (Cobra) that he could bring in the centrifugal advance faster, but he's off to a lot better start.

I disagree, however, on the vacuum advance. In Drag Racing, Vac advance means absolutely nothing because you spend =0= (zero) time at part throttle operation. In Roadrace and any track car, we spend a considerable amount of time nursing a car through a corner or coming off of corners well out of our desired power band and the vacuum advance helps with that considerably.

Yes, if the vacuum advance brings the timing up to 60* that's fine because as soon as you put any load on the engine, the vacuum signal drops and the timing will retard to keep you out of detonation.

[NickRCarter]

Hi Randy, Had a chance today as the roads are now dry, to take the car out for a quick test drive. It ran very smoothly, no detonation and very very responsive. So at the moment I have 10 degrees initial, 24 degrees of mechanical + 20 degrees of vacuum.
I keep seeing information on SBC's running with an initial of 16+ degrees. From my limited experience, when I have advanced mine to just 13 degrees it kicks back when starting from warm.
Is there, in your opinion, any merit in running such initial figures and if so what are they?
I understand I could advance my initial to say 14 degrees and still stay in the appropriate total advance range. I could also overcome the kick back by using the anti theft ground wire on the MSD when cranking.

Nick

[Big-Foot]

Hi Nick,

It is the total timing where you will bring in the higher Torque levels. I have found that in the vast majority of cases, there is less than 5 Ft Lbs of torque in going beyond 34 degrees total.
If she's kicking back with 13, you can imaging what she would do with more. (detonation). While the SBC is more able to deal with detonation due to it's 5 headbolts per cylinder than SBF's are with 4 - it does not help the bearings and ring lands.
I rarely take SBC's beyond 10 initial and usually they are back around 8.
I'm really glad you have things worked out now.
Stay on the conservative side with your timing and run good fuel in her and she will last a long time..