btmboards

iTrader: (2)

I have just recently started working on the tunning in my car. The only thing that I have done is leaned out the higher loads a little becuase my car was running so rich under load that it was chocking itself out.

My question is; why is it that in the maps the target afr starts out at 14.7 then the higher load/ rpm the richer it gets. I get why for over max load or passed redline but wouldnt it work better to have all the afr in range to be set in the 14s or am I missing somthing.

TurboTim06

iTrader: (2)

Im not sure if this will answer you're exact question or if I'm reading the question wrong but from what I get out of it you are asking why AFR becomes richer with increased Load and RPM?....HEAT is one of the main factors for this...

The reason for this is because at lower loads and rpm the engine can dissipate the heat efficiently to run this lean AFR but at higher loads and rpm you create more heat which the engine can not dissipate as efficiently so therefore the engine needs to run a richer AFR to better dissipate the heat created...Fuel actually does have a major factor on the cooling effect of an engine...A good example of this is when Alcohol Injection or E85 is used in place of gasoline...Another main factor in richening the AFR is Ignition Timing Advance in relation to RPM and Load...As you increase Spark Timing you have to run a richer AFR to avoid Detonation when tuning with gasoline...The more RPM's you run the more advance you have to fire the Spark in order to create the most complete A/F burn at optimum compression for optimum power under WOT (usually around 15* ATDC)...These are not the only reasons for richening AFR's with load and rpm though...there are also emission related factors that go with it but nobody wants to hear about that crap hahahahhaha

btmboards

iTrader: (2)

Ya that actually does answer my question exactly. thanks alot. So it would be better to try to leave it a bit richer and run a little more timing instead of leaning it out. this is my DD so I want to make sure it is running safe

TurboTim06

iTrader: (2)

Yes! Running a few points richer AFR makes for a safer tune as compared to one with leaner AFR's...Less power gains will be made though...If you turn the timing up then you really need to watch the knock counts...You will be able to run more timing with a richer AFR, Less timing with a leaner AFR

btmboards

iTrader: (2)

and one more qestion, what is the difference and when are they used of the high and low octane maps.

TurboTim06

iTrader: (2)

In theory, tuning an internal combustion engine running pump gasoline will refer to an AFR of...

...Exactly 14.7=Stoichiometric (Stoich)...Meaning the exact amount of air to burn all the fuel.

...Less Than 14.7=Rich...Meaning not enough air for a complete burn.

...More Than 14.7=Lean...Meaning more than enough air for a complete burn.

***A stoich AFR of 14.7 only refers to gasoline though...Other fuels have different stoichiometric points...For example, E85's Stoich AFR is 9.7 proving the point that E85 requires about 30% more fuel to complete a complete burn....When tuning with gasoline at WOT the best power is going to be made at around 12.5-13.5 AFR's providing no knock counts occur. Tuning for power is the easy part, tuning for drivability is the hard part. Tuning for power with gasoline is basically just running a fine line between finding how far you can go with leaning AFR's and advancing spark as rpm and load climbs while watching for knock counts and combustion temps. Leading into the answer to your 2nd question..........

The high and low octane maps switch back and fourth according to knock sensor counts...There is a threshold where the ECU determines how many knock counts is acceptable to run the high octane map and once the knock sensor see's more counts than this threshold it reverts to the low octane map. So it is always better to have your low octane map tuned richer and more conservative than your high octane map. Your low octane map is essentially a fail safe map to protect the engine from detonation.

MRGEVO

It seems you have quite a bit more reading to do mate, I would put the stock tune back on there and not touch it until you are sure you know what you are doing.

How do you know it is rich? Have you actually got a wideband and measured it?

btmboards

iTrader: (2)

All the first part I know It was the second that I figured but was unsure about. Great peice of info though thanks for all the help the change that I made was very mild and I have been watching my afr pretty close.

And yes permanitly mounted a wideband into my car and have it wired up to log with evoscan

TurboTim06

iTrader: (2)

Hey no problem man...If you ever need any tuning help just shoot me a PM I'll gladly help!

btmboards

iTrader: (2)

And I just knoticed that you were in kirkland I just moved down here recently from that area (bothell)

TurboTim06

iTrader: (2)

oh ok gotcha! damn yea thats like only a couple miles from where im at...I'm in the Rose Hill area actually used to be a tech at Lee Johnson Chevrolet if you know where that is...wow small world! haha