who told u that???? cylinder 3 is proven to run the leanest

 

how would retarding the ignition raise egt's? I figured it would be the other way around.

 

From: http://www.sdsefi.com/techegt.htm

There seems to be a lot of mystery and misinformation about using exhaust gas temperatures to tune engines. Claims by many EGT gauge manufacturers about it being the best way to tune an engine must be qualified. The BEST way to tune an engine is on the dyno- PERIOD. What EGT is good for is a reference for where the engine made maximum torque at wide open throttle. Once removed from the dyno, a similar air/fuel ratio can be established a later date by dialing in the mixture to achieve the target EGT. It is really the AFR that is important, not the EGT. Most engines will make maximum power at an AFR of between 11.8 and 13 to 1 however, the EGT may vary from 1250F to 1800F and is dependent on many factors.

It should be mentioned that the target EGT is valid only on the same engine configuration as was used on the dyno. If you change the ignition timing, cams, pistons, headers etc., the optimum EGT may also change. Raising the compression ratio with no other changes will drop the EGT at the same AFR. Retarding the ignition timing will generally raise the EGT at the same AFR. One engine might make best power at 1350 degrees while a very similar engine might be happier at 1500. You can't guess at this or you are simply wasting your money on the instrumentation. Wankel engines have higher EGTs than comparable piston engines due to their lower thermal efficiencies. 1800F is not uncommon here.

Some gauge manufacturers say you should tune to achieve maximum or peak EGT for maximum performance. This is incorrect. Peak EGT generally occurs at an AFR of around 14.7- 15.0 to 1 on gasoline. This is far too lean for maximum power and is dangerous under continuous WOT conditions. Many people think that the leaner you go, the higher the EGT gets. This is also incorrect. Peak EGT occurs at stoichiometry- about 15 to 1 for our purposes. If you go richer than 15 to 1, EGT will drop and if you go leaner than 15 to 1 EGT will ALSO drop. It is VERY important to know which side of peak EGT you are on before making adjustments. It is safe to say that peak power will occur at an EGT somewhat colder than peak EGT.

You can sometimes feel a lean of peak condition as the mixture is hard to ignite and power will be down a bit as well. Once the AFR gets close to 17 to 1 at WOT, generally the engine will start to lean misfire. Most tuners always recommend to begin jetting or programming from a known very rich initial setting and carefully leaning until torque falls off slightly, then going back richer to the point of max torque. Note the EGT at this setting. Be aware that altitude, barometric pressure and ambient air temperature may affect this optimal temperature to some degree.

Are EGT gauges better than AFR meters? Conventional narrow band oxygen sensors and digital LED meters are not the best devices to measure AFR in the richer ranges but they certainly warn of a too lean condition immediately and obviously, without translation by the driver and they are affordable. Meters combined with wide band sensors are laboratory quality usually, highly accurate and useful but very expensive and sometimes bulky. EGT gauges have the limitations above and are generally priced between the other two. I would suggest that the two types are complimentary. EGT gauges have the advantage of working long term with leaded fuel which will clog oxygen sensors. EGT gauges are widely used to set mixture on engines used for steady state high power applications where operation has been carefully documented such as in aircraft. The choice would depend on the application. Both are better if you can afford them.

All this is courtesy and copyrighted by Simple Digital Systems EFI http://www.sdsefi.com

 

pressure is constant thru the fuel rail provided that your pump is working of course. but in B-series motors(not sure about D series) cylinder 3 receives the most air flow, not less fuel

Now back to EGT's. I'll try to put this into simple terms. first think about where an EGT probe is located. its in the exhaust somewhere, of course. so knowing this dont confuse cylinder temperatures and pressure to exhaust gas temperature, they are related to eachother but are different. if you pull ignition timing what is happening? your making the spark go off later, and in doing so youre also causing the burn/combustion to happen closer to around the same time the exhaust valves open and let the gas out. therefore there is less time in between the mixture being ignited and it traveling thru the exhaust ports of the cylinder head, the gas is going to have less time to cool since its being ignited later and the EGT's are going to show an increase in temperature. in extreme cases, commonly seen with two-step rev limiters and other ignition timing devices, the spark will be going off so late that the mixture can somtimes combust within the exhaust causing the EGTs to skyrocket with only partial load on the motor. this happens when u see cars blowing fire out the exhaust, (but too much fuel can give the same visual effect).
Increases ignition timing will do that opposite until severe detonation occurs and the actual cylinder temps begin increase drastically.
Obviously there is a lot more to this but im just trying to put it into simple terms. hope this helps a little

 

the pressure does not drop down the rail. and i meant to say hottest, not leanest

 

in a hydraulic app. like the fuel rail, pressure will be equal at any given point. I believe its pascuals law( not sure if I have the right name).

mtber, that's alot of info. and surprisingly, not only did it help but it made sense. I do rely soley on the wideband to tell me what to do for tuning the fuel ( at least at this point while I am still street tuning), but I also keep the egt in sight just to help confirm that what I did isn't about to make a big mess. thanks for clarifying the issue for me.