morgan wrote: Mon Apr 19, 21 5:46 pm
Yeah, that would work (the make a bushing) - its literally a thick washer with a mm diff per size or something. Trouble is I dont think I'll want to go bigger as there will be too much initial to start the car. At the moment it works as I get 17 and then it pops up to 21. 21 from the off feels ambitious...
yeah but the initial needs to be right.... getting that right dictates the rest
so if yours wants 17* that's cool the other end of things is currently an arbitrary point 35* because that's where it landed....just treat that as a maximum for mechanical advance
it doesn't have to be that it could be that 28 30 32 34.
you have a high compression motor with lifters that have the potential to alter the cam timing slightly by not pumping up at Low RPM
if they don't pump up at low RPM what do they do at High rpm. they pump up.... but the mechanism to allow the former will impact the latter also
so at high rpm you have a cam and lifter that will be providing just a bit more duration and a bit more overlap. Your Dynamic compression changes..you haven't got VVT but you have a wiff of it in your motor...
if at higher RPM your motor becomes more efficient you need less ignition advance than you would expect. the rule of thumb works on standard motors no more than 34... why have so much faith in it for you none standard motor
You need to identify the minimum it wants at 2500+ rpm any more doesn't help..
why?
if you set off the mix before it is properly tumbled and compressed it burns in small whirl pools and and some unburnt goes out the exhaust
if you hit it with a spark at the point where the piston has compressed it just enough it will go off like a war head . it burns in 1 almighty wumpfff quick effective perfect rolling front of combustion across the piston head , piston in right place valves shut ...all good.
if you are too late its still burning when the exhaust valve opens. the under bonnet temps go sky high and the opening of the valve puts out the fire in the cylinder. so you get un burnt out the exhaust think of a backdraft in a fire situation. burning house, open window air rushes in and a few second later a sheet of flame engulfs you. the massive change in pressure and new air causes the fire to shrink rapidly then expand rapidly to 10 time its size in an explosive way
in the case of a motor you don't get the oxygen/air you get unburnt fuel and exhaust gas from the last cylinder to go off i.e you belatedly quench the fire in the port and header. you create heat in the headers and exhaust valve and you set up the next cycle badly
what i'm getting at is there may be a degree 2 degrees maybe 5 ther will be some variance that helps at the top of the curve
worry about the bottom first ..
the more efficient the motor is the narrower range of ignition advance you need
i got so hung up on 15 BTDC initial and 34 Total, now my experience may be unique i can't promise that it wasn't just some Australian engine aberration... but once i let go of that... ahhhhhhh.... life got better.
and i went through this with both igntion and weber config. once i threw everything that seemed to be THE LAW out i made progress, and backed it up with the fastest leisurely drive down a flat bit of road at santa pod i've managed, until my ignition module went bad
It wants what it wants and it probably won't want what you have learned to expect
sorry i'm sounding more and more like an arrogant asshole but this caused me so much frustration
standing there for 1/2 hour at a time fuming... worse than the car... then going for another think and a cup of tea.
Dave
