Hi all,

here's a bit of curious for you. same thing with two completely different engines.

I usually had my engine timed at 14 initial (ported) and 34 max at ~3000. This should be just good and edelbrock confirmed that as well.

Now the engine is not much quicker than a good 289 stocker, and you can imagine that this drives me mad. I swapped in a demon, which for me works out great so far (more in a different thread). Now the timing

I had the car in idle and tried to floor it as quickly as possible. it's either slow coming up or just about to backfire. I thought: under load it's different, but in theory if it doesn't work under load it will never work when full load is on.
So i advanced more and more untilo the engine would rev easily and very snappy (it's nearly instant). drove it and it was _way_ quicker.
Then checked the timing and I had 24 initial. which means 44 max advance. can't be right ... under partial load i had a slight pininging, so i retarded to 19 initial, which should be 39 max and the car goes the same quick, just the pining is gone.

So what would cause this. Why do I have to advance further? is it the petrol we use (95 octane mostly) ? the weather ? being at sea level ? any other ideas?

[here comes the scary part: a friends BB chevy will not run proper unless the initial is set around 28 (like 48 all in) !!! anything below 20 will cause heavy backfire on accelleration. on both cars the TDC is verified with piston stop]

 

Thoughts:
Is the 14* and 19* initial timing being checked with the vacuum disconnected?
You say your dizzy has 20* total advance...Is that just mechanical or mechanical and vacuum together?
Increasing timing advance leans out the AFR. What is your AFR at idle with 14* initial vs. 19* initial?
How is the oil company achieving 95 ocatane?

The 20* total advance, if mechanical and vacuum together, will not be hit unless you are running high rpm (over full mechanical advance level) and have little to no throttle (high vacuum). I would be shocked if you could run more than 36-38* total advance during a WOT pull without detonation. In a WOT pull, the vacuum advance portion of the dizzy does not come in much if at all...so how much mechanical advance does your set have and how much vacuum advance does it have? Do you notice any problems getting the engine to crank and fire with the higher advance?

 

Is the 14* and 19* initial timing being checked with the vacuum disconnected?
yes. disconnected at distributor and plugged so carb cannot pull air.

You say your dizzy has 20* total advance...Is that just mechanical or mechanical and vacuum together?
that's mechanical only. with initial timing at 14 timing increase with rpm to 34 exactly. again. no vacuum. that 34 is at 3000-3500 and doesn't increase from there.

Increasing timing advance leans out the AFR. What is your AFR at idle with 14* initial vs. 19* initial?
no idea about AFR. But i set it the leanest with highest vacuum.

How is the oil company achieving 95 ocatane?
no idea. it's the cheaper one. So I guess they mix ethanol. I'll go and ask. they're neighbours, so might tell me. but then again you can't find 89 like in the states without looking for it. petrol here is0 usually at least 92.

The 20* total advance, if mechanical and vacuum together, will not be hit unless you are running high rpm (over full mechanical advance level) and have little to no throttle (high vacuum).
true. WOT should be no vacuum whatsooever. but as above. we're talking mechanical only

I would be shocked if you could run more than 36-38* total advance during a WOT pull without detonation.
i agree. it sounds scary. I had pinging with 24-44 (mech), but none anymore with 19-39.
I'll try and see if I can get G numbers with the G-tech, you should be able to see a huge difference.... with 14 initial and 19 initial

Do you notice any problems getting the engine to crank and fire with the higher advance?
not at all. starter turns the engine very quick cold and hot. I know exactly what you mean. I once saw that in a 351C that was too early, was a very slow start up until we retarded the ignition.
my engine fires at the 2nd or 3rd stroke (stroke, not turn of engine). very good and quick. no gas needed i just turn the key and it starts instantly, which is not the case when at around 14 initial. There I have to hold the throttle a bit to get it to fire

unfortuantely i can't set the max mech advance with the distributor. Otherwise I'd lock it out at 16 and see how that goes.

Kalli