M20 WOT Ignition Maps?

[DmcL]

wondering something here..

im messing around with mapping/chipping/etc the M20 and ive got some very good maps but im noticing none deviate much from the standard WOT ignition curves. there is more advance but the curve remains nearly the same shape.

reading up on ignition timing and all that u would think the curve should basically start off low and rise as the revs rise, maybe not a straight line but something alot smoother than the standard and majority of performance maps shape wise.

im wondering is there any reason for the wierd shaped ignition maps?

here is a screenshot i took comparing standard to a good performance map and then something i reshaped to be more like what u would think the map should be like. quite a difference looking at them. any ideas why the standard and performance maps like to stay with this up/down shape of ignition map? im probably going to experiment with something similar to the curve i made below to try and figure out why its shaped like it is and not in a more traditional curve/line shape.

[Gunni]

It´s always a compromise for possible bad fuel. Even the really good chips behave that way.

[DmcL]

but surely compromising for possible bad fuel would just mean finding the max advance before knock then backing up a little, not making an ignition curve that jumps up and down like that?

i doubt id be getting knock with my late M20 anyway, shes a low comp engine so id think i should be able to advange till power drops without knock.

suppose ill just have to try out a nice rounded curve like my example and see how it goes/feels.

[tomislav]

Your best bet is to email this info to ant at ATech. He is a tuning GOD and his knowledge of ignition tuning knows no bounds. See what he says.

He can be found on this site

[DmcL]

might give him a try.. see if he knows anything about it.

ive got enough gear to test out totally custom ignition maps i just dont have a rolling road to measure small gains. if i cant feel it or if the gtechpro wont pick it up then thats about as far as i can go.

he seems to know his stuff anyway.. hes knocking out MAF conversions and all that already.. im just sorting the tune for my own home brew MAF conversion. was actually thinking about making them to order, looks like ant had the same idea

[MillRat]

Isn't it all to do with induction harmonics?

From memory there is something like 4 harmonic frequencies at play in the induction system. As such, air flow/pulses change characteristics (both up and down) as the engine progresses through the revs range. Therefore the advance required to best tune the engine also change.

EDIT: Oops, I didn't mean to revive an old thread with near on useless information.

[Ant]

good input dude

no issue with a BTT of an old thread, its whats added that counts.

there is NO way to assume maps are right/wrong

I mapped a 2.7 on TB's and had 1 deg of advance in a few sites to get MBT

[Gunni]

1deg total advance BTDC?

That makes no sense, and suggest the VR sensor is not in the right place or something is seriously wrong with the engine.

Well maybe not so crazy if you where running it at 1000rpm WOT

[Ant]

just checked Gunni 1 deg BTDC indeed !

full load @ 1100 rpms, moves to + 4 then onwards as you'd expect to mid 20s

twas a VV high ambient day and we did have some det issues, running as low as 1 was the only way to sure, EGT agreed on the day

[Gunni]

Well there you go , I guess my guesstimate was accurate and your previous post a tiny bit misleading

[GeoffBob]

but surely compromising for possible bad fuel would just mean finding the max advance before knock then backing up a little, not making an ignition curve that jumps up and down like that?

As Millrat said DmcL (with regard to induction harmonics). The short answer is it's to do with the dimensions of the inlet and exhaust system that largely define your engines volumetric efficiency (VE). Since your engines VE varies with RPM your ignition curve will fluctuate from "ideal" due to the fact that it is your engines VE that (in part) defines just how much air/fuel is getting into each combustion chamber. Your ignition timing must thus change (marginally) due to the fact that the flame velocity through the air fuel mixture is a function of the mixture density.

If your engines VE were a fixed (static) value across the range of RPM then your ideal curve (in black) that you plotted above would be correct.

Excellent question BTW. I wish I had spotted it sooner but I seldom stray this way.

[DmcL]

im still tinkering away with chips/maps so its not really reviving an oldie lol

i recently decoded a dinan chips file and had a look and the WOT ignition map is very different from the majority of others ive seen where they share the same or a similar shape to the standard ignition curve.

also running a maximum of 38 deg BTDC at the first high point and again at the end of the map, dropped back to 37 at the end yesterday tho and retarded the last point back to about 20 deg along with bumping fuelling up on the fuel WOT maps in the same place.. idea is it creates a rich condition on gearchange and should pick up that little bit quicker in the next gear when the throttle opens again.

@ ant, dont know if u would be up for it but id be up for some file swapping or whatever? always good to have loads of stuff to look at and compare.

heres a graph i edited in photoshop to show the curves of all the performance files i have atm (barring my own files). most do follow the standard shape fairly closely but there are a couple exceptions.



note that i wasnt experiencing knock even running up to 38 deg BTDC but i do have a cold air intake i made and it works well enough to keep the inlet manifold cool to touch after a hard run so might run into knock on a standard airbox or open filter above 34 or 36 deg BTDC.

[Gunni]

Here is what I used



To get

[GeoffBob]

[Gunni]

I measured my intake manifold pressure at WOT and it goes from 100-101kpa which is below 4k down to 95kpa at higher rpm´s , this has been noted to be because of the throttle body as a restriction.

So in theory, everybody should upgrade their throttle body as a starting point. This will put whatever advance is in there at the moment closer to MBT due to higher VE requiring less advance.

Also the stock engine is not det limited if everything is running fine. So there isn´t always a gain to just continue advancing timing. This is where a dyno comes in handy. As who knows one engine might like 35deg for peak torque while another 30deg and so on. Even if they are the exact same spec.

[DmcL]

@ geoffbob, ive got accel enrichment. havent messed with it yet but it looks to me like its probably for additional fuelling on fast throttle increases, probably including a gearchange. exhaust is standard bar a scorpion backbox. really need to sort some sort of system out. built a MAF conversion, have 19lb injectors, adjustable regulator and wallbro pump but need to be getting more air into it to start benefitting from the injectors, etc. im in on this latest 64mm BBTB group buy so that will be done just as soon as i get the TB back. also have the intake built up with silicone hose and flexi off the MAF and up to the filter behind the front grill. after a hard run the top of the inlet manifold is cool to touch.

@ gunni, im assuming the values on the left side are % load.. right? dont think im far off that 178bhp tbh, possibly slightly above.