I do have a slow ramp purposely to avoid detonating. I don’t want to hit it hard under load but ease into timing.
In general mopars like a shaped timing curve which Chrysler accomplished with a two stage distributor advance. Fast increase in timing advance above idle to 1400 - 1800 rpm, then slow it down. Engines that continue to get faster burn rates at higher and higher rpm need the advance to be slowed more. In general we see the 2 bbl equiped engines continue advancing at a faster rate; presumably because the higher rpm fill density is restricted by the carb as well as the cam timing.
what do you mean by “MP” Distributor?
Mopar Performance parts program. Chrysler's factory support for racers and hot rodders.
Before that it was called Direct Connection.
Here's a graph of the MP small block distributor timing vs rpm. This was meant for street and street strip and has a vacuum advance cannister on it. The advance curve is very similar to the ones on the non-emissions 273 4 bbl Hi-Performance engines.
The main issues I have is that this engine was set up for racing. High static compression around 205 psi/cylinder. A compression ratio that is probably too high guessing 11:1 (12.1 TRW pistons). Aggressive unknown solid lifter cam with iron heads and shitty 94 octane fuel with ethanol and an automatic trans.
And I gather you are using it as a dual purpose car street/strip.
I have had to work with not knowing the true compression - its frustrating not knowing but its not the end of the world.
205 is pretty decent cranking pressure especially with a radical cam. This combination is getting outside of my experience range.
I agree its possible that the WOT timing will be octane limited and worth being cautious there.
Pump gas, especially with eth, mostly slows up the early flame development. I would *think* high compression would minimize any issues from that.
The 'advantage' of an autotrans in tuning is that we can put it in gear at idle and see if the engine is or isn't making power.
So by adding such large amounts of timing BELOW idle helps prevent the engine from stalling when put in gear. It idles well at about 850-900 rpm and when put into gear does die and in fact only changes like 50 rpm. I couldn’t do this with the msd. This works real well.
That's kindof neat. A good example of how with computer controls we can do weird things.
A 50 rpm drop holding the same timing would be good on a stock engine and is great on a radical engine. Oh wait, you're saying the timing goes up as the rpm drop? Then it really wants the additional spark lead. The next question is why. Not enough enough fuel ? Reversion? I ask because with 205 psi it doesn't seem like the engine fundementally has low working compression at idle rpm.
Have you tried adding more fuel at idle?
This is a carbureted engine, right?
This is a little bit of a chicken and the egg situation. Not enough vacuum will mean less fuel gets pulled from the bowls, and what does get pulled into the intake isn't as well distributed and vaporized. Increasing the timing can help overcome that, and of course more spark lead is needed with slower burning situations.
that's probably what I'd investigate next,
