I just purchased an 01 and was looking to do a few very basic bolt ons (air intake and test pipe) and tuning. I have been reading a lot of posts about tuning but I still have a few outstanding questions. I have narrowed my list of tuners to VAFC, E-Manage, Haltech Pro Plugin and, KPro. I see large changes in altitude with in a few arounds of where I live (sea level to 10,000 feet), which of these systems would be able to handle this as well as the stock ECU?

 

kpro uses stock ecu....

 

Greddy Emanage allows tuning by throttle position or MAP sensor. MAP sensor tuning will take into account altitude changes best (just like the stock ECU).

 

You'll have to rely on the stock ECU's definitions to account for any real altitude correction. Atmospheric pressure is lower at altitude and the MAP sensor alone will not be able to account for as it's only seeing intake. IE: Tuning at x pressure / y RPM at lower altitude will not 100% be the same for the same load and RPM when seen at higher altitude.

 

That's why you tune based on MAP, because WOT at a mountain pass will hit a lower load point (requiring less fuel) than WOT at sea level. Your tune takes this into account by using the MAP sensor, whereas a TPS based tune could not account for this difference.

http://en.wikipedia.org/wiki/MAP_sensor#Example

 

Having speed density alone will not compensate for altitude changes properly

 

Not quite. X load / y RPM at 900ft ASL will not yield the same results as the same x/y at 6,000ft ASL. Atmospheric pressure will have an effect on how exhaust gasses exit the exhaust which will have an effect on how the engine pumps air. With a piggyback, we do not have access to change these values for correction/compensation, so we rely on the stock tables. Unless your setup is extremely radical, they are probably fine.

 

most good ecu's have a barometric pressure sensor built in.

I know with aem ems you can easily add a correction for baro... I do it all the time.

What you need to do is find a good tuner in your area that you trust and put whatever ecu in the car they recommend.

 

Not quite. X load / y RPM at 900ft ASL will not yield the same results as the same x/y at 6,000ft ASL. Atmospheric pressure will have an effect on how exhaust gasses exit the exhaust which will have an effect on how the engine pumps air. With a piggyback, we do not have access to change these values for correction/compensation, so we rely on the stock tables. Unless your setup is extremely radical, they are probably fine.
[/quote]

Yeah, I think we can both agree you are really reaching to say that the atmospheric pressure at the exhaust exit will have a noteworthy impact on how the car runs.

The thread title asks about the best piggyback ECU, certainly a full standalone with baro compensation would take you one step further to account for such minutiae as exhaust gas pressure vs atmospheric pressure.

But you also have to keep in mind that piggybacks all work on percentages from the stock ECU, so if the stock ECU provides a correction for these little details, so will the piggyback. It will just multiply (or diminish) the effect based on the percent change in the piggyback map for that load cell. If you do this in a standalone, you need to add all the barometric compensation logic yourself (as wadzii mentioned). Again - the stock ECU does this! No need to reinvent the wheel.

 

I do not agree. Compensations such as this and temperature play a Huge roll in how a car behaves at varying atmospheric conditions. You should take a look at a Subaru map and see how many compensations they have for boost control, MAF, injectors, etc. A clean tune in the morning can lead to a dangerously lean tune in the afternoon and vice versa if you do not address the comp tables. Boost control can be wildly erratic as well. There is the Googles if you don't want to take my word for it... But, I do have experience with it.


Yep, and thats why I mentioned that you'd be relying on the stock tables to do work here.

The problem happens when you start to go beyond basic setups were the stock tables aren't quiet "solid" for a clean tune. The Greddy will not specifically apply changes based on this. It will likely be the stock table that keeps the Greddy in check.