If you use the right fuel then detonation isn't an issue.

Want to trade your hectik sticker for some fully sik ones? I don't have a hectik one yet ;)

The vacuum advance thingie is there to compensate for the lack of mechanical advance at lower rpm's where there is a mostly closed throttle plate, if you mash on the gas, even at low rpm, you'll loose much of the vacuum advance too. like how the brakes don't work well if you're at WOT and trying to modulate the brakes.

When you are legally limited to pump fuel - this is what you tune your motor to use.

yeah the right fuel can only be right for so long, ie until you cant get it

the right chamber shape/design along with the right tune would be the thing to have

there is a pretty serious engine builder down the road from me that built a 202 head to handle 15:1 comp on pump fuel without detonation
so some time spent getting the head right goes a long way

I have found too much timing equals.... ping,ping,ping. The extra work you do to motor/ supports eg, compression, chamber mods/design, intercooling, water inj, fuel octane etc allows you to run extra timing therfore usually more power without pinging or in some engines that tend not to detonate easilly, were ever timings at ie the sweet spot and either way just drops power but no pinging, giving greater safety margin. I just confused myself hope that makes some sense?

Makes perfect sense. Even more so that its from someone that has themself trial and errored it.
Just like a non boosted A series, so it runs its best, you can dial in as much advance as you can until just before detination develops under load.

Well i guess i learnt allot about detonation after blowing 6 headgaskets within 6 months from detonation problems, im glad i fixed that problem (lower comp, modded chambers etc). Ive also discovered that stockas can take heaps of pinging compared to similar engine making more power. We had a mitsy colt. Pinged like crazy especially the more it was loaded up and the hotter it was. It never broke down in the 3 months it was around. My turbo 1200 when it had the problems, faint pinging only above 5k rpm only heard it ping on approx 10 diff accasions and backed off straight away, a total of no more than 10-15 seconds and a head gasket would fall out the side of the block! Frustrating. My word of advice would be that if even the faintest of pinging is heard, pull over and back out some timing. Also have a safety margin there, and a large safety margin at the expense of power if you intend to flog it through hills let it get real hot, let tyres boil with little airflow etc. Ive also found octane boosters have done nil for me, interestingly enough once i was forced to fill with 95 instead of 98 and that required a lot of timing retard...

Fully hecktic, Fully sic stickers!! Baaaaahaaaaaa I just want 1. U guys crack me up. Oops sorry 2 hi-jack the thread..On topic 2lt ford Escorts an Cortina,s used a vac advance which retarded the timing under boost an advanced it when NA. So u would lock up the weights so no mechanical advance workrg an just let the vac canister do all the work. I,m planning on adapting 1 to my 1200 {if I can} when I finally get boosted!!

the point being that the mech advance gives little advance at low rpms and more advance as rpms increase, this is basically opposite of the vacuum advance which generally decreases with rpm increase because there is less manifold vacuum, since the throttle is more open at high rpm.

some datsun dizzy's came with advance and retard vacuum mechanisms, so if you really wanted to you could do that.

Quote:

Does a vacuum advance actuator not normally retard timing as vacuum decreases?

For sure, What happens in this situation is you have 2- vac/ boost entry points on the canister, 1 behind the diaphram, 1 in front depending if yr N/A or boosted. The 1 behind the diaphram pulls under vacuum, the 1 in front pushs when boosted which does the same thing it retards the timing. Whew hope I explained it ok. Which datto,s came with this feature??