Megajolt Tuning

[brainbug007]

I've finally got my megajolt all connected up and running with the basic map that came pre-loaded from trigger wheels. Not really understanding the principles used very well I'm after a guide of sorts to start learning how it works so I can make tweaks to it without breaking it or my engine. For example I'd like to know how to compare two different maps and understand them well enough to decide which is better for my setup if that makes sense? At the very least I need to know how to tweak it at IVA incase I'm over on my emmisions.

From what I understand so far you "retard" the ignition so it sparks after tdc making it more inefficent which brings down your emmissions? And to do this you increase the advance value in the given cell?

Also it's bad to have it sparking before tdc as messes up the pistons by forcing them down when they should still be traveling up the cylinder?

To bring the spark closer to tdc and increase the power, do you increase or decrease the advace?

How do you work out the advace value of tdc that you should not go above/below (see point above) which would cause it sparking btdc?

In reverse, how do you work out the maximum value you shouldn't go beyond for atdc?

Also the advance value seems to change depending on rpm/throttle, why is this?

Sorry for all the newbie questions but any help would be greatly appreciated!

[davedew]

Brian,

This is quite a complicated subject to explain, so have a look at the below link.

http://en.wikipedia.org/wiki/Ignition_timing

HTH

[brainbug007]

Thanks dave, that gives me a rough idea how it works. Actually sounds like you want it to spark before tdc due to the time it takes for the mix to ignite and the gases to start pushing down on the piston. Really for startes I'd just like to get to a point where I know how to adjust it incase I need to at IVA for emmisions.

[Talonmotorsport]

Just a thought but it might be worth having a word with a few very local MOT places and asking them to ignore the whole test and just do the emissions part for 30-45mins. Besides if your car is booked in for an MOT you can drive it there, ahem. Paying for an MOT at £45 a shot is going to be a lot less hassle than an IVA retest.

[brainbug007]

Ya I was plannin on takin the car to my local garage for a pretend mot before iva to check it over.

Is there such a thing as a formula to work out roughly what the "best" advance would be for a given rpm based on things like piston travel?

[baz-r]

haynes do quiet a good book on engine manigment writen by dave walker of emreld ecu's and ppc mag fame covers efi and ign setup.

no idea about megajolt but megasquirt and meny other aftermarket have a thing called a spark table or ve table
basicly its a graph or ref table with load and rpm on the sides and timing value in the intersection of the two values.
we ignite the mixture befoe tdc (+tdc) and ajust the amount of advance with load and rpm
the amout we want/need verys on temp air and engine,compression ratio, boost,fuel octane rating and the list go's on so two engine maps may not match unless you have exactly the same engine

no damage is done by over retarded ign but is if over advanced (adv) so we start by increasing adv to a sweet spot (best power and cleaner burn) if we advance beyond this point pinking or knock stars and if we advance some more detionation (clap of two pressure waves in cyl) this is where a hot spot melts holes in engine bits
you have possible herd pinking before when you load your car engine pulling out of a juntion with the revs to low and to little clutch or put some 2star in your tank when your car likes 4star (yester year) it sounds a little diesely or like a load of little hammers in your engine
detenition it simmular but louder and naster
so start low and advance until you get pinking then retard it a bit for each load/rpm site basicly