Simple Timing Question Here.

[MJTru]

First i would like to say that i have found over the years that tuners that i meet are a little reluctant to talk to teach what they know. I dont blame then as it seems a hard topic with lots of methods leading to a tuned car.

Ok so here goes. Can we agree for the simplest that the spark starts before top dead or does it start after top dead center (tdc)? about what degree do we see usually see full cylinder pressure after combustion?

Next when some say the term advance the timing whats happening. this is the part im a bit confused in my head. Is that giving it more time to burn so for exsample say the spark happens at 7 degrees atdc advancing it would strat the spark earlier to tdc mark giving it more time to burn. Or is that the other way around for exsample retarding the timing. Now if the spark is firing btdc bcause the fuel needs time to burn and reach maximum cylinder pressure by this time the piston has passed tdc and starts the power stroke. This i believe is how it works. So we are starting the fire a bit btdc and we ask to advance it, whats happening?? Does this term in this exsample (advance) starts the spark later to tdc giving it more time to burn and maximum cylinder pressure would be closer to the atdc area.

Sorry if this seems confusing. I can do my best to expalian what im trying to get across here. Just clearify a few things first.

Thanks guys. I have a strong feeling ill be ridicule for this post. I sat here thinking about it for 12 hours. Damn

[Ben C34]

The spark is always before tdc as you said the flame needs time to burn.

When people refer to advancing the timing it means even more before tdc. So more time for flame to burn.

I can't recall where it was but there's some good info in the net relating to timing.

I understand you don't have access to a Dyno, so it's harder, but you should invest in some knick detection equipment, eg kmon or similar, because without it you are flirting with danger.

[GTSBoy]

What you have written sounds correct for half of it, then you seem to confuse it all up.

Yes. Ignition occurs BTDC. Advancing the timing makes it move even more BTDC.

Yes, ignition BTDC is needed in order to give the fuel time to burn. If you do it at TDC or after TDC then it will still be burning as it comes out the exhaust port, which is wasted energy.

Some fuels are slow burning and need more timing advance.

Engines which are very efficient will burn the same fuel with less advance. More advance (for a given fuel) is an indication of a less efficient engine. "Efficient" in this case really being another word for "capable of cramming in more cylinder fill".

[MJTru]

Thanks GTSboy. You were always good at clearing things up. Your gifted mate. I know i got a little confusing at the end thats way i was nervous about being ridiculed.

One time i had lots of fire out my exhaust and it seem like it was to close to the tdc mark after i gave it more time to burn. Move the spark time more btdc it made more power and stopped the fire out the tail pipe.

Can i ask? what you would contribute to having the exhaust pop on gear shift or just busting a flame at gear shifting. ????

[MJTru]

The spark is always before tdc as you said the flame needs time to burn.

When people refer to advancing the timing it means even more before tdc. So more time for flame to burn.

I can't recall where it was but there's some good info in the net relating to timing.

I understand you don't have access to a Dyno, so it's harder, but you should invest in some knick detection equipment, eg kmon or similar, because without it you are flirting with danger.

Yes mate danger is so close i can feel it. Lol. Im actually thinking of buy a dyno for my shop. I just need to know that i would be able to use it maximize my results as dumb as that comment may sound. I have been trying to learn as the years go by. Simply by trial and error. Even with a dyno i would need these knock devices. So an early investment would be good. What would you recommend as a good knock detection tool.???

All the guys i race are in the same situation and i can say that they all run 2zj motor. Im actually building one now and can say im against a tuff challange the motors are strong and from what i see all the 2jz flaws are on the head. Yes our rbs only have the oil return only on one side but i see lots of other flaws in the jz heads. But there easily fixed. Back to the point here. These jz guys run aem ecu's and they all copy tunes from one guy to the other. It seems to me that they understand that an ecu is a buffer between the fuel injectors and load values including the volumetric efficiency (displacement) so what some guys do is just tell them what injectors to use and upload the tune by selling it to them . Then they do a road tune and clean it up a bit.looking at the knock levels. They make good money doing this. I dont understand why the same on this site cant be done using maths. Lol. I always liked that reply. But i feel using all.the same conditions. Like lets say a freshly built rb26 stock internals. On 98 ron. Giving an injector that suppied by the tuner. And afms or map sensors. Why cant tunes be sold. The rest can be easily fixed up. Im sorry if i went off topic here just thought i would mension it.

Edited July 11, 2015 by MJTru

[GTSBoy]

Gear change pops and flames come from lots of fuel and retarded timing.

You can "sell/swap" tunes, but you do so with terrible risk because every engine responds differently, even when stock. What you can get away with on one you may not be able to on another. Factor in all the other random factors, like different fuel pumps, regulators, dumps, wastegate size/type/location, intercooler efficiency, etc etc, and there are just too many reasons for things to not work.

[KiwiRS4T]

Because every car is different. Yes a similar car with the same turbo etc may have a map that you can use as a starting point but the point of a good tune is to tailor it to your own setup. A dyno is a great tool but not absolutely necessary, I have had a tuner do a great job with a wide band,knock detector, exhaust gas temp meter and an ecu with logging capability on a road tune. The dangers are two fold - you need someone to drive while you tune and you will find yourself going at illegal speeds on a public road. You won't know the KW you are making at the wheels but for yourself that is not so important - there are plenty of ways to measure performance - but if you are going to do it for paying customers they may want to see charts at some point.