One way valves will not work. How is the vacuum/pressure removed from the diapham? Are there diaphrams that are easy to change springs? most are press sealed.

There are many ways to control detination. Controling it through ignition retard is only reducing performance to mask the actual problem.

Running simple non return valves in the tubes which feed each side of the diaphram is all that is needed to control an advance/retard set up. If you have the springs changed so that the retardation only kicks in once a high boost level is acheived would be best. The smartest way to circumvent detonation is by the implementation of water/alcohol injection. There are numerous ways of acheiving this. And some of the cheaper ones can be the most effective, when set up properly. I have a c32 laurel washer bottle which can pump 13psi. Through a .040 oriface, it can pump nearly a litre a minute.
I've read untold anectdotes of suprising gains atained from this method.

There are heaps of car models with twin actuators on the distributors. One to advance with vacuum and one that retards with postive pressure. Porsche is one of the many cars.
But what do people expect to gain buy using it?
How do people expect to dial in the boost level at which the retard actuator reduces the degree of ignition advance?

Like I said it will be interesting to see how many of these turbo A series go. But I guess its all about ####ing up so you can learn from it. Its a shame that some will be lead in the wrong direction from the start.

My advice, leave the distributor stock, or use one of the many known elec distributors regraphed to suit a NA A series.
Dont worry about bullcrap ignition retard.
If there is detination, just back of the dissy to reduce the degree of advance. Then sort out why it was detinating. 99% of the time it will be lean fuel mixture.

Early VW rabbit automatic tranny cars and turbo audis have dual port vacuum canisters on their distributors. Many people use them when boosting their VW's.

So what does it do under vacuum? advance or retard? Your description is that what ever it does with vacuum, it will do exactly the same with boost.
Whats the advantage of that?
How do you achieve in getting one to only receive vacuum and one to receive boost?
What exactly do you plan to achieve? lower emissions or performance?

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??

Quote:

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

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.

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!!

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...