V2Rocket

For those of you who are well-versed in the DME, what is the stock, 0* advance, 0* retard, ignition timing BTDC?

I want to know so that in combination with the FQS I can see how much timing I can pull total for my SC project.

Thanks!

Andy1212

Um i think you need to study more about ignition timing. Retarding ignition means ignition happens Xdegrees BEFORE TDC, not after. With the FQS, the only amount you can adjust ignition is by -2.77degrees (ignition occurs 2.77 degrees sooner).

jpk

Spencer - If you havn't seen it yet, you should look at frwilk.com He's got probably the best description of how the Bosch Motronic system works. If you dig enough, he probably has the ignition maps there somewhere.

Rogue_Ant

Spencer- PM sent.


-Rogue

V2Rocket

is that true? that seems backwards to me, as if ignition happens before TDC that means that the flame will be trying to expand while the piston is still compressing it. i thought that the idea was to wait for the piston to reach tdc and ignite so that the mixture was compressed fully and that the expansion of gases would push the piston down again.


*edit* did a quick read on wikipedia and youre right, very interesting. i guess that the time that passes between say 12* BTDC and TDC is so negligible that it is used for the spark to be able to ignite the fuel mixture. cool stuff.

blown 944

Actually..... the ignition is occurring ~2.77 later using the FQS retard but it still happens BTDC.

say stock is 12 deg BTDC, with the retarded FQS it is now firing @ 9.23 BTDC. It does this throughout the whole map.

It doesn't make too much difference at idle other than lower rpm's, but in boost at higher rpms_ 3 degrees_ can mean the difference between melted pistons and a completely fine engine.

Rogue_Ant

That is because the FQS timing adjustment setting doesn't take effect until a certain rpm is achieved...


-Rogue

V2Rocket

thats the idea

blown 944

ha..I don't agree there. In my experience it is global, including idle.

Every time I have adjusted it, it will drop idle rpm and raise EGT's slightly.

V2Rocket

sid, i constantly see you talking about EGTs, why are they so important other than trying not to melt the exhaust components?

Rogue_Ant

Hmm, are you changing fueling as well or just timing?
From my understanding of the code it shouldn't have any effect at idle. Perhaps I'm missing a divide in there... Something I'll remind myself to play with.


-Rogue

Rogue_Ant

EGT gives you a peek on what is happening in the combustion chamber. Combined with monitoring knock, and AFR gives a good picture for developing a proper tune.


-Rogue

V2Rocket

so if retarded timing leads to higher egt's does that mean a premature knock will have a lower egt?

and are there any inexpensive knock-monitoring systems that dont need to plug into the computer, just for like datalogging purposes?

blown 944

melted pistons, valves, rings,plugs,etc..

I used to tune exclusively using an EGT meter, however this was with a fixed (mechanical) distributor so the only changes were due to fueling. It is what I am most familiar with, however I have become pretty familiar with AFR's since then and use them both.

blown 944

retarded timing does lead to higher EGT's, however it also helps to prevent detonation. The problem lies with a known timing curve that still gets too high of EGT's, that represents a lean condition that can damage parts.