Looking for general knowledge, I used the search function and there were very few posts on the actual subject matter. everything was something to the effect of " yo my car wont idle which way do i turn the "dizzy".


I am curious about what factors dictate the maximum ignition advance in an internal combustion engine?

I know basics like Fuel Octane rating which is its resistance to burn so the higher the octane (in theory) the further you can advance the timing becasue the flame front travels accross the cylinder slower. The longer the combustion process lasts the more force can be applied to the crankshaft, thus more torque and finally horsepower.

I was lookin through some of the Pre-tuned maps and the Stock honda maps for what they run as far as ignition timing, and they are all over the place even for stock maps,

Under no load (wot) and high rpm b17a1's are pulling 29-30* of ignition advance

p30 Jdm b16's are at 24-25*

jdm Gsr are at around 29-30*

Usdm Gsr's are between 28-29*



My main focus is the Gsr's, from what i have read, the usdm's are slightly lower compression, so on paper should be able to handle a bit more timing, right?

Are the discrepancies in the stock maps due to the differences in fuel country to country, the compression difference or something that I am missing.



ALso is there a product I can buy for knock detection that would interface with my Neptune RTP Ecu?

Thank you in advanced
-ben

 

unfortunately there are too many variables for there to be a correct answer. from one ecu to the next, even on the same car, the timing can/will be different. (aem, motec, hondata on the same car will generally result in different advance values)

trial and error is the only real way to figure out what your set up wants. best and fastest way to go about it is put the car on a dyno that has real time hp/torque readings like a dynapack, dyno dynamics, etc. dynojet wont do it, and mustangs dont seem to have the resolution in my experience.

for the full-throttle stuff, any dyno you can do sweep style tests will be fine. make a run, add some timing, make another run, then compare. its pretty clear whats not enough timing, and when you have added too much and the car doesnt not gain from it. shaping a timing curve is a little different, but a lot of the "big name" tuners just use flat curves from what ive seen, very few are actually shape them.

any knock monitoring devices that are worth a damn are really expensive, some of the knock boxes that go to head phones that you can listen in on work really well. ive been meaning to pick one up just to play around with it. also, most knock boxes that will send a output have very in depth set ups as well...i wouldnt trust the factory ecu to monitor knock, id want to use a external logger or a nicer ecu. more often than not, lower end computers just pick up background noise and nonsense rather than actual usable knock info.

 

Thank you, very helpful post. Wouldnt the ideal torque curve(s) go hand in hand with the ignition timing graph?

My thinking is that the most torque comes from the ideal fuel air mixture acting on the pistons for the longest possible duration, so Your torque curve is what you would need to watch while tweaking timing?


So its Basically do a run, ad a degree of timing do another one and compare,


What about part throttle? THe engine under light load should be able to handle a slightly leaner air fuel mixture (ie: cruise) Medium vacuum, light acceleration. and lean mixtures are more prone to detonation.


Thanks,
-Ben

 

Actually, you want the combustion to happen quicker (to an extent). The more you have to advance timing, the more energy is wasted as the combustion expands against the piston moving upward as well as reducing peak cylinder pressure exerted on the piston, so you lose two fold.

If you want good info in regards to combustion, this probably isn't a great place for research. Sir Harry Ricardo, considered the father of combustion research, as well as Charles F Taylor and Jim McFarland have some very good publications on the subject. I have both of Taylor's books that I got online for about $50 each.

 

what?

 

I missed it too.


I thought that when combustion started didnt matter as long as the combustion process is not self ignited (preignition), But as long as cylinder pressures were at there greatest when the piston and connecting rod are at the ideal angle to apply torque to the crankshaft throws.

 

Advancing ignition timing INCREASES cylinder pressure, the spark fires on the compression stroke as the piston is traveling up, the reason for this is because it takes time for the flame to propagate outward from the point of ignition. This is why detonation is BAD. The higher your ignition timing, the further up the piston is able to travel in the stroke before the spark plug fires, which means more compression, which means more prone to detonation.

 

compression stroke, sorry lol

 

First of all, I am speaking of design principles as in one engine combination versus another. You seems to be talking about one tune versus another for the same engine combination.

Advancing timing increase average cylinder pressure on the wrong side of TDC. The piston is already fighting the resistance of having to compress the volume already present in the cylinder after the intake valve has closed, but the sooner you light the mixture the more it pressure is built as the piston is still fighting to reach TDC. That energy is now wasted making the piston have to fight harder, which is known as a parasitic loss.

As for your last comment, you can't honestly believe that firing the plug later will cause detonation because the cylinder was compressed more, do you? That cylinder is getting compressed at the same ratio as a function of volume at TDC and BDC, not where the plug is fired. However, the sooner you fire the plug before TDC (more advance), the more pressure builds AS the cylinder volume is being compressed, which WILL and typically DOES result in reduced knock resistance.

It does matter. You do want the cylinder pressure to peak at roughly 12-15 degrees ATDC, which is where most experts will say results in the most energy being used to turn the crank. My point is that if you have an engine that requires 36 degrees of advance, it's wasting more energy than an engine that requires 22 degrees of advance. They're both dialed in to that sweet spot of 12-15 degrees ATDC, but since combustion happens quicker on the latter of the two engines, less work is wasted on the wrong side of TDC.

"If the spark is not advanced enough, the piston will already be moving down when much of the combustion takes place. In this case we loose the ability to expand this portion of the gas through the full range, decreasing performance. If the spark is too advanced, too much of the gas will burn while the piston is still rising. The work that must be done to compress this gas will decrease the net work produced."

http://rescomp.stanford.edu/~efroeh/...erformance.pdf

 

 

Stick to the topic. Judging by your embarrassing build thread, you don't have much room to insult people.

 

lol i assume you just graduated from wyotech? very clever, but your engine appears to be rotating in reverse the way you explain how your custom ignition system is working.

 

Lol @ Wyotech. Why don't you go ahead and correct me? Where do I go wrong and how does what I say compare to that article I linked by a couple guys from this little institution called Stanford University?

 

sure, let me quote your article for you

 

another quote from your article, while i do admit i may have wrote out my initial response somewhat poorly after those beers lol

 

What was that about sticking to topic?

Everyone makes mistakes, if you can honestly say you have never had a problem, you wouldnt have a user account on this support forum. **** happens, just because someone has the testicular fortitude to continue on after a problem doesnt mean you should bash them.
Easy there UTI grad here.
Alright so that links ignition timing advance and egt's which are proportional to NOX in the ehaust (combustin temp)


So its like a 3 way balancing act. Peak cylinder pressures, vs when they happen in crankshaft degrees, vs NOX and preignition.


The way Im seeing it is that you (the tuner) needs to find the happy median between A very high peak cylinder pressure at a less than ideal crank angle vs. a sligtly lower peak combustion pressure that is acting on the crank at the ideal angle.

 

my engine problems werent the result of flawed ignition timing lol dont even know why that was a question here

 

Ugh, you obviously still don't get it. That doesn't contradict anything I said.

Again, I have been speaking in terms of basic design principles and comparing different engines with different characteristics. When Engine A finds its best power at 22 degrees of advance, it will see more peak cylinder pressure than Engine B that finds its best power at 36 degrees of advance. I am not saying advancing timing on Engine A does not increase peak cylinder pressure. That's what that chart shows you; timing advance on ONE ENGINE.

 

You sunk thousands into the engine only to make what, 149whp? Some might find it ironic to be calling others dumb with those results.

 

Please tell me your Sig is a joke.

 

Aren't you the one that said less advance will cause knock?

I'm not bashing him because of his humorous attempt to build a fast car. I'm bashing him because he has the testicular fortitude to insult someone's intelligence after such poor performance.

 

Yes it is...mostly.

 

sounds like spawne said increasing timeing could increase chance of knock. EG 1834 has done nothing but sound like a douche this whole time. then he quotes your link and supports what he said. Then you bring up his build as if it gives you more credibility. F****** Tool....

 

That is, when using an engine management that has a secondary ignition correction going on in the background (or even user-definable for that matter). All of the Honda ROM editors use this, hence why a "flat" timing curve for a load column works, for the most part. If you're using Neptune, you can log "Table Ignition" (what you have set in the tables) versus "Actual Ignition" (after the corrections have been applied).

A "flat" timing curve won't really work on something like MoTec, AEM, Haltech, etc.

Your post is spot-on, Joe, just elaborating on it!

And like I said on Facebook, congrats on the DynaPack purchase. We love ours, but beware of the stigma that comes with owning one (everyone saying that is 'reads high', therefore attempting to discredit the machine's value).

 

You're not very bright are you? Read it again, pay close attention to the part in bold. If the plug fires when the piston has moved further up, that is less timing advance.