Max ETC Area???

[Meister]

Is this fully open? What is the proper method to calibrate this value?

[swingtan]

MAX ETC Area is the maximum WOT area of the throttle body. In theory, this would be a standard calculation fo the area of a circle, but it's not quite that simple. In all the throttle bodies I've seen ( and that's not a lot ), the internal bore of the body is not circular, but elliptical. Also, you have the area taken up by the throttle blade and the the blade shaft to account for.

So basically, for a 90mm TB, you could assume the maximum area is Pi x 45mm ^2 or 6364mm^2

BUT. in my stock tune, it's actually listed as 4725mm^2, only 2/3 of what would be expected. This would make the TB internal diameter more like 82mm Dia. allowing for the throttle shaft. Given the shape of the stock TB, I'd say this is probably very close to being correct.

The "proper" method to calibrate is in many cases, as above. Work out what the actual "hole" size is and run with that. The problem is that there are some other settings based off this figure that are not as adjustable as sometimes needed. Many people have found that when using moderate to large cam shafts, you can not get enough idle air flow for a good idle. One fix has been to drill a hole in the butterfly to let more air in, another has been to deliberately make this calibration undersized, so the ECM thinks it needs to open the throttle more. As an example, I have this set at about 4100mm^2 to get the idle the way I want it. I think this also "speeds up" the airflow corrections, as they most likely use the same base settings.

Simon

[Naf]

11534i noticed my tb% never gets to a 100%, When i press the pedal to the floor the guage stops at 88-89% with either my stock tb or my modified 90mm...But on the TB it is Wide-openned with both...

Runnin an E38 on my truck and i think this is the reason why i am smokin at WOT.

How do i fix this???

[Taz]

Hello Naf,

If you are logging SAE.TP - 88% is a typical output at WOT.

Try logging:

GM.APP (pedal position)
GM.ETCTP (electronic TP)
GM.TPDES (desired TP)

These should all output 100% at WOT.


Regards,
Taz

[swingtan]

Further to this, the SAE.TP PID is more likely to be returning the TPS voltage percentage. IE. 0V=0% and 5V=100%, as the TPS never actually reaches thes levels in real life, you get the 20% - 88% limits.

As TAZ says, use GM.APP for the pedal position and GM.ETCTP for the actual throttle blade position.

It won't make any difference to how the engine runs though, it's simply the way the ECM is interpreting data.

Simon.

[Naf]

I am tryin to check this, but my scanner is not conneting with my truck now...I tried changin the USB cable but same results.

I havin tried tuning yet, but am scared it cause me problems...