ClioSport.net

Register a free account today to become a member!
Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members through your own private inbox!

Max ignition advance 182



What is the max ignition advance you can run on a 182, safely, on full load? Where in the rev range would you expect to see max.

The full load ignition map on my car is shown below. Why can the engine cope with more advance at 4400 and tails off at higher rpm. I would have thought it would take more advance at higher rpm?

ignition.jpg
 
I'd guess BenR or Stan* are the people to tell you more.
I'd expect dvance to be limited to what the engine can take regards fuel etc i think its knock which is the limiter to the amount of advance run to much advance the and the piston pressure will be putting the piston under to much straigh and you'll be loosing power.
 
  R35 GTR
Isnt this the point that most people refer to as the 5k kick?

I guess something to do with harmonics of the engine, how quickly the air is pulsing in and out of the engine, probably more efficient at this rpm?

Total guess as I have no experience with this.lol.
 
  2005 Nissan Navara
Max ign advance is theoretically at max brake torque....alla your graph, you'll notice it resembles a torque curve. This figure for timing is known as the MBT timing figure (MaxBrakeTorque). It varies with load and speed, but follows the trend of torque output due to volumetric efficiency.
 
mark, an ignition map should plateu once you have reached peak timing, which is usually midway on in the rpm range.

ignition timing is purely there to start the burn before TDC simply for the fact that it takes a period of time for the whole chamber burn wholistically and release peak cylinder pressure at a certain crank degrees ATDC, which is dependant on bore, chamber shape, fuel,VE, rod/stroke ratio, CR, AFR so on and so forth. At lower rpm the time period in terms of crank degrees revolution is less than at higher rpm, so requires less 'advance time' for the spark to start. Once you reach a certain point it becomes less beneficial to continue advancing, then detrimental as you either hurt torque because you reach peak cylinder pressures too early or rather too close to TDC, or even before it and generate negative work. Then there is the combustion problems such as pinking, knock, det and auto ignition associated with peak cylinder pressures that arrive too early. Its a downward spiral where you might only get a touch of knock, but that will overheat the piston/chamber which can lead to auto-ignition in a short period etc. Everything is linked.

Mapping ignition correctly is a true secret art, AFR any monkey can do. But to understand ignition timing and what your trying to achieve is a subject that can be as large as engine design it self. If you want to have a go you'll want to get a set of det cans minimum so you can listen to any changes in burn noise.

If you want to do it properly you'll need a dyno so you can keep an eye on BSFC, EGT & AFR on every cylinder, burn noise (det cans). And putting the relationship between them is the key to getting things spot on. I'll explain it fully when you are down next, it sorts the men from the boys ;)
 
Thanks for the replys.

So stan based on what you said the torque plot for my car does the opposite of what your saying as the max advance seems to coincide with a dip in the torque curve (which is pretty flat for an NA engine!)

graph.jpg
 
  2005 Nissan Navara
It depends who mapped it...and how badly they have done it :).....

Ben is right mind, it should level off...and It looks like that peak in ign advance at 4400rpm shouldnt really be there, and thats why there is a dip in your torque...i.e. it IS over advanced at that point, so increased negative work is being exerted on the piston (if you plotted theta.v.cyl pressure, this would be shown by the increased area to the left of the Y axis).
 
  2005 Nissan Navara
LOL, just read my previous post...i didnt mean it should actually mirror a torque curve...i meant it should peak at the same point!
 
lol, no worries stan, we knew what you meant, just continuing discussion as its more interesting than wheel bearings.

On another note mark, 28.deg is very little advance and not something to really worry about.
 
The full load fuel map looks similar to the torque curve

fuel.jpg


If an rpm site was over advanced would it cause a less efficient burn and lower AFR readings?

ie. if I reduced the timing at 4400 would the AFR value increase as the burn would have been better
 
Another question.

Too much advance causes knock which is bad. But to little advance causes the heat to go out of the exhaust valve which can damage the head?

I read quite a simplified book on mapping where it said a good gauge was to set the timing advance until knock was starting and then take 2degs off that value. Apparrently this would give a safer value ie. not borderline knock that would have very little effect on power. Book also stated that it was a rule of thumb and everything should be checked on RR! 2degs seems like quite a big margin to play in when max value is 28degs?
 
  2005 Nissan Navara
Its all relative...when you say overly advanced, advanced from what point?

Theoretically you would use MBT as the main reference for what you are saying.
If you advance from MBT, you further increase peak cyl pressure (and temp burned and unburned), and as weve said, negative work. This in itself increases BSFC...but if its mapped to give a set quantity, and u increase the demand, you are going to lower AFR...albeit marginally, and i cant say as too what extent in quantifiable terms (for one ive never tested, for two there are so many variables).

If you r****d to much, you increase EGT...this as u say could damage the valves head etc, buty more imporatantly it could cause surface-ignition.

As for the rule of thumb fo finding knock and backing of a couple of degrees..well..people do do this, yes, and i guess its a roundabout way of getting an ok ign curve together.
 
  2005 Nissan Navara
as regards the 2deg window...if u were using det cans, you would pick the onset of det a couple of degs before you would with the naked ear (if`at all)...so it really depends on your det detection set-up.

I have cyl pressure transducers which would be handy for experimenting with s**t like this, as i find it a very VERY intresting topic...combustion in general...

sadly i have no dyno yet lol
 
i think he just took a 2d slice of the full load fuel map rather than looking at the whole 3d map.

And the 2 deg r****d system is what msot people will do if they cant actually measure anything. BUT............the real issue is what the hell do they know knock sounds like. Most det cans are crap and even the good ones will not isolate the frequencies you need to hear. So like me you have to modify a bosch motorsport sensor to isolate the frequency you want to hear.
 
  2005 Nissan Navara
"that" frequency wont be constant tho...it will vary with operating parameters and conditions? do you do that on all cyls Ben?

It boils down to the operator aswell....u cant beat a "million dollar ear"...best tool in the trade.
 
Yes, its varies with block material, cylinder thickness, block design, height, density.

Which is why the sensor is set over a range, not a single.........it just stops you having to listen to valve train rattle, piston rattle, oil pumps, induction frequency etc.

'The ear' is what i was talking about.....plain old microphones are crap and just as useless as standing next to an engine trying to listen, you cant....i dont care what anybody says.

Mind you, there is probably a jap somewhere that can........probably the same guy who can hit tin cans with a spoon and tell you whats inside.
 
  2005 Nissan Navara
dunno if i agree about the ear tho...guaranteed its not as could as 'proper' electronic detection, but its good enough for most cases.

at the end of the day...u can go on forever in a spiral of "this device/method is better...blah blah"...where do u stop?? where the budget allows usually.
 
my setup only cost me about £150 and its a darn sight easier than straining in the car, whilst mapping and trying to hear something that i feel is basically impossible with bodies screaming away and exhaust noise, and mechanical engine noise.

Maybe its my ears, but with all that noise i just cant hear someone hitting a bean tin with a spoon lightly.
 


Top