ign mapping

[fastdruid]

I have an ignitech programable ECU for my curvey, does anyone know what the standard ign timing map is or any suggestions as to how far I can adjust it?

Druid

Originally Posted by fastdruid

I have an ignitech programable ECU for my curvey, does anyone know what the standard ign timing map is or any suggestions as to how far I can adjust it?

Druid

Adjust it till it pinks, then back it off a few degree's

[fastdruid]

Originally Posted by ThEGr33k

Adjust it till it pinks, then back it off a few degree's

That was kind of what I was thinking, what I don't know is what pinking actually sounds/feels like! More to the point as it changes through out the rev range I'm not sure what to do. I may just take it back to dyno torque and ask them, was very reasonable to get it rejetted so a bit more dyno time to get the ign played with might be better.

Druid

[yorkie_chris]

Standard map is also dependant on throttle position, you get more advance on low throttle for better cruise efficiency.

[fastdruid]

Originally Posted by yorkie_chris

Standard map is also dependant on throttle position, you get more advance on low throttle for better cruise efficiency.

Which of course makes life trickier as the ignitech allows you to play with the map dependent on the TPS too (or just ignore it).

Druid

[yorkie_chris]

I would talk to zadar about it.

TBH you only really going to want to play with the big throttle openings id imagine? If you go for smaller too then you are going to destroy fuel ecconomy and it will run like a dog ha ha.

Pinking is preignition (incase you didnt know that...) so it kinda feels like its put the brake on for a second when you are running. hard to explain but you'll know when its happening.

Dyno people might be some of the best to talk to, or maybe some of the mini twin people as they might well play with this sort of thing?

[embee]

Originally Posted by ThEGr33k

...Pinking is preignition....

No, pinking (aka detonation, knock) is not the same as pre-ignition.

Normal combustion is a controlled progressive burn, starting with the spark at the plug and taking typically 30-50degrees of crank rotation, depending on engine speed and load and the chamber type etc. Flame speeds are of the order of a few tens of m/sec during normal combustion.

Knock is the spontaneous combustion of small pockets of mixture towards the end of the normal burn process. As the normal burn progresses, the temperature and pressure of the gas increases and under certain circumstances it can reach conditions where reactions take place and the resulting compounds will spontaneously combust before the flame front reaches them, giving a faster heat release and pressure rise, maybe one or two orders of magnitude faster than normal combustion. This then sounds like a sharp crack, or a continuous rattle if subsequent cycles also knock. The sound has a characteristic frequency, very often in the 6kHz range (and harmonics), which sounds typically metallic, rather like a ball bearing in the cylinders (the name "pinking" comes from the sound it makes). Light knock is not normally drastic, only prolonged heavy knock will cause damage (fatigue cracking of piston ring lands, fatigue pitting of the crown etc).

Pre-ignition is what it says, the burn starts before the spark, usually due to very hot deposits or overheated exhaust valves or incorrect grade plugs etc. This leads to extremely high pressure and temperatures as the heat is released during the compression stroke. This does indeed usually give sudden huge loss of power (it's fighting against the normal engine process), and invariably results in catastrophic failure within a few seconds due to the massive heat input into the pistons, which expand too much (and weaken) and usually melt/seize in the bores, a big mess.

If you're fiddling with ignition maps, I'd first recommend putting in a grade colder plug, don't advance the part load values further than they already are (usually more or less optimum anyway), and only go a degree or two at a time on full load maps. You can blend in values near full load if you do make changes, linear interpolation is usually fine. Plug temperatures increase typically 10-15degC per deg ignition, an extra 5deg ign can be enough to take the plug above the critical temp (850C or thereabouts) leading to pre-ignition and engine failure. One plug grade is something of the order of 50degC difference so gives you some safety margin.

In the absence of a proper test bed, I usually recommend doing a couple of dyno runs at standard ignition settings, then do a couple with 2deg retard (full load map only, 2deg across the whole speed range). Compare the curves (average the runs) and see where the torque has dropped significantly. If there has been significant drops anywhere, do a couple of runs with 2deg extra advance and again compare the torques. This will give you the "sensitivity" at each speed. As a rule of thumb, "maximum brake torque" (MBT) ignition minus one degree is a good value, providing it is not knock-limited, in which case "borderline knock" (BLK) minus 2deg is safer. If you have time and resource, choose ignition for MBT-1% (i.e. the ignition at which the measured torque is 1% less than the max achievable at the given engine speed).

....or leave it alone.

[yorkie_chris]

Cheers for that post embee, I just read the same thing and was about to start typing. Heh.

Originally Posted by ThEGr33k

TBH you only really going to want to play with the big throttle openings id imagine? If you go for smaller too then you are going to destroy fuel ecconomy and it will run like a dog ha ha.

You can go about 6 deg more advanced than stock throughout the map according to TSM.

However, he did not have the TPS connected, so I would presume this makes it revert to the full throttle map, so not enough advance at part throttle.

Why would playing with it destroy fuel economy and make it run like a dog? Only if you get it badly wrong.

[embee]

Originally Posted by yorkie_chris

...You can go about 6 deg more advanced than stock throughout the map according to TSM.

I know the stock tune is for 91RON so I'd expect it to be very retarded from optimum at lower speeds, but I wonder whether it really is much retarded from optimum at higher speeds, certainly by 7-8k I'd have thought it would run somewhere near best ignition.

Have you seen any sort of sensitivity numbers, i.e. how much gain per degree ignition at various speeds? Just interested really.

My concern would be that peak pressures and temperatures do rise pretty dramatically with advance at that sort of level, which is why you'd usually try to run with the least advance you can get away with before losing significant torque.