Need EGT Help

[asoap]

Hey Guys. I'm tuning a car, and still new to this. We're about to install a PLX EGT sensor. What I'm having a problem with is what am I looking for, for tuning the time map based upon EGT? Is there a certain temperature I should be looking for? Or should I be looking for a point where it doesn't get any hotter, or get any cooler? How does timing effect exhaust gas tempurature? Like what's physically going on, I'm not seeing the connection between the time of spark and temperature. Also would I see changes to timing in the EGT almost instantly, like I would with a WB o2 sensor?

I'm planning on tuning this on the street first, and then hitting up the dyno when to finish her off. We got the AF ratio working well. We're using an s300 with PLX wideband and PLX EGT sensor.

Also a side question. I keep on hearing that an AF ratio of 12.8 is going to produce the most amount of power. This boggles my mind. I know it's a safer setting to prevent detonation, but it just doesn't make sense to me. Anybody got any insight into that?

I did a search and I can't seem to find this info. So if this info is widely out there then give me a textual beating and point me in the right direction please.

Thanks and Cheers,
-Derek

[Spunkster]

http://www.google.com/search?hl=en&q=tu ... oq=&aqi=g3

http://www.hondata.com/stech.html Look at the Tuning guide.

[asoap]

Hey Guys,

Thanks for the links. I've done a bunch of research and I've created a bunch of notes to help me out. Can you guys look these over and let me know if they are correct or not. If somebody stumbles across this page from google, then please know I'm an amature and don't trust it just yet. Read the full thread.

EGT Tuning Information

EGT sensor doesn't give any direct information about power. With Air Fuel Ratio, you'll know you should be producing the most amount of power at 14.7. But with EGT there is no exact number to show a rich lean condition or a power producing condition. Your peak EGT will change from motor to motor. It's more of a tool to give insight of what is going on inside of the motor, and make you aware of an “Oh CRAP! No no no no!” situation.

Ideally you want to find your own magic numbers.

You want to keep your EGT temps below 930-950C(1740F) on 93 octance gas. Anything higher and you're risking detonation, running lean, and general motor melting havoc. In this case, back off timing and richen up the fuel.

Ideally you want to tune your car on a dyno. You don't want to tune based upon AFR or EGT tempuratures as intsruments can be off. You will know you're done when you're producing peak torque and the motor sounds right. The AFR and EGT are tools used to help you get there.

Behaviour of EGT:
You'll produce your highest EGT at Stoichometric (14.7 – 15.0 : 1 AFR). If you're richer then that EGT is cooler because of extra fuel, if you're leaner EGT will be cooler because of excess air. It behaves like a peak point. It's crucially important to know what side of the peak you're on. Keep an eye out on your torque and AFR. You should be producing the most power in a richer AFR (12.8 – 13.2 : 1)

How Does Timing Effect EGT:
I'm not exactly sure. This is an educated guess based upon the info above. You advance/retard timing so that we can have a full complete burn of the fuel. The best burn produces the most power. If timing is off you might not get an effective burn of the fuel, and still have residual fuel or air left over in the chamber which would cause a cooler tempurature.

Is my AFR or EGT really correct? Trusting your instruments
One of the largest problems is trusting your instruments. I've never been confident in knowing that AFR readout of xx.x is ACTUALLY xx.x. But, if you take your car to the dyno and start tuning for power and dial in fuel values and timing you'll find your optimum AFR and EGT numbers. If you're producing peak power and the motor sounds right, you're there. Now knowing if they're calibrated correctly isn't as important, because you'll now have your optimum target.

Dynoing:
While on the dyno, start leaning out the AFR to see where you're producing the most amount of power and keep an eye out on the tempurature at the same time. Try to prevent really hot tempuratures(950C +) by adding fuel. When you stop producing power, richen the fuel up a bit and that is set. Or if you're in a rich condition lean that baby out.

Then work on timing. Start advancing which should increase torque. If torque starts to decrease, turn the timing back a bit. This should be giving you your ideal numbers for EGT and AFR.

Probably go over the AFR one more time to make sure it's now correct. If it isn't then do timing again also. Keep on repeating until you're set.

Of course you should always be keeping an eye out for knock and listening to make sure the motor is ok. If she doesn't sound right, abort the run and thuroughly examine your data. I ran into a condition where the wide band o2 sensor was fouled and was always reading lean. We pumped enough fuel into the motor that she ran horribly and it still said lean. We aborted and figured out the problem.

Placement of EGT Sensor
Placed on the exhaust manifold as close to the head as possible. Around 1” should be fine. Ideally you would want an EGT on every runner of the exhaust manifold.

Annoyances
Barometric pressure, altitude, and ambient air tempurature will have some effect on EGT.

Just in case nobody knows
Advancing Ignition = Igniting the spark before Top Dead Center
Retarding Ignition = Just like advancing, but in the other direction.

Simple Rules
Peak EGT = At stoichiometric (14.7 – 15 : 1 AFR)
Increasing Compression Ratio = Lowering EGT
Retarding Ignition = Hotter EGT (in General)
Advancing Ignition = Cooler EGT (in General)

Cheers,
-Derek