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That Guy
13,634 Posts
Discussion Starter #1 (Edited)
This mostly applies to AP3 owners for use, but it's worth a read for SCT owners as well because datalogging as a whole will be very similar minus device setup/use and some pid's. I had initially written it specifically for the ST, but again-the general concept of maintaining consistency applies to all vehicles.

This is not meant to supersede any recommendations from your tuner, so if they tell you anything different then definitely defer to the pro's. This is an accumulation of information that I never really thought about posting until a buddy of mine asked me to look at his logs and I realized that he had no clue whatsoever of what he was doing outside of pressing the center button on the AP3 and accelerator/brake. A lot of this is over-analyzed from repeated trial and error of trying to collect the most accurate info for my car to be tuned off of, and for me to make legitimate comparisons with.

Believe it or not, datalogging your car starts well before you get in. You may not be as anal-retentive as me, but the goal here is to minimize the number of variables that will affect your pull so that you can get a clean set of logs that are consistent enough to be compared and relied on. The cleaner your logs, the better your tuner can do magic, and the better your vehicle will perform in the long run.

Note-It is a good idea to check your plug gaps before beginning or if you're currently having issues. Obviously this doesn't need to be done every time, just once before getting serious about logging. I gap mine at 0.026-0.028" due to boost levels, but that's my preference. If your tuner gives you a recommendation then I would use that.

1. Ensure your AP3 is up-to-date and the applicable tune for the mechanical setup is loaded. KAM/ECU reset if applicable.
2. Ensure your car is either loaded as you would normally drive it or empty. It's ok in either direction, but you don't want to compare one set of logs where your car was empty against another set of logs where you happened to have 200 pounds of groceries or tools in the hatch.
3. Fuel tank full. This isn't a huge deal, but gasoline weighs 6 pounds per gallon and that gives you around 72 pounds worth of difference from E to F. Log an empty tank in an empty car and compare it to having the tank full with the above-stated groceries/tools...I'm sure you see how this compounds.
4. Verify OAR is at -1. If it isn't, do not log-plain and simple. The FiST adjusts really quickly, but if you aren't at -1 then you need to get it there first. Read: You're using an inferior fuel...
5. Setup or verify (if necessary) the parameters you are going to log in the datalogging. Nothing sucks more than driving out 45 minutes, collecting logs, 45 minutes back home, just to open your newly acquired data and find out you've only logged data to make an intake comparison. Trust. Me. I'm not going to tell you what you absolutely should be logging as that may be dependent on the situation and/or pro tuner that you're using, but for general datalogging I use default plus ignition corrections on all four cylinders.
6. Set up your gauges as you see fit. In the beginning stages of tuning I only monitored AFR during a pull to verify that I didn't go lean, but after a while I began only monitoring my weakest cylinders ignition corrections. On the way to the road I monitor my six-gauge with AFR, oil temp, and all four ignition corrections. If you keep your monitors to only parameters that are being logged then it should not affect your logging capacity (a max of 25, iirc), but you'll want to try and collect a log (not necessarily a full-pull) before going to your datalogging road just to make sure that whatever gauges you're viewing don't exceed the number of values the AP3 can log in conjunction with your established parameters.

Ok, so you're pretty much ready to go. Where are we going?

Ideally, all logging would be done at the racetrack where you could reach the speeds you're going to be reaching. For this discussion we're going to assume you're not, and will discuss a few things that you should at least take into consideration. This is largely a compromise though, so you want to find the best road possible based on where you live and within your convenience. Whenever possible try to only log from one location, simply for consistency.

1. Obviously you are going to need a long enough stretch of road that you can complete a full third-gear pull from roughly 2500 rpm up to redline, along with the appropriate stopping distance. If possible, having a stretch of road that's long enough to remove any heatsoak before turning around is optimal.
2. A road that is as flat as possible. Incline/decline will have an effect on the performance and, in-turn, the data. If you don't have the most perfectly flat piece of glass to drive on, collect data in both directions. It's generally advisable to log in both directions any way simply to cancel out wind effects.
3. A road that is as smooth as possible. Road imperfections and texture will have an effect on the data if they're severe enough so, if possible, find a place that's newly paved.
4. Traffic is obviously a consideration. The fewer, the better, and in a worst-case scenario you can always opt to collect during late night/early morning.

Your car is ready and you're at your road with great conditions for some logging. Now what?

This is the easy part. If you've prepped accordingly, you should be able to roll up, collect your data, and get back to the house. Here is a step-by-step breakdown of my CDO while logging, and you can adjust it to your needs.

1. I know I said you're at your road, but on the way to the datalogging road I try to get a few mid/heavy throttle third-gear pulls en-route, simply to make the KAM aware of what's going to be occurring. Maybe it helps, maybe nah.
2. When I arrive to my road I always complete a pass in one direction to make sure that it's clear of obstacles, debris, police, bystanders, etc. One more than the others, but basically it's just a 'route-recon' for any ex-military types. Because I use one specific road I know where I'm turning around to start my run, but it will take trial and error your first couple of times to get your distance and turnaround points. I set my cruise-control to 60 mph because I'll use it later.
3. Once I have the space needed, I will make my turn-around and begin on my downwind pass. I get my car into third gear and stabilize rpm's around 2500-ish.
4. Press the center button on the AP3.
5. You don't necessarily have to, but I wait until my gauge reappears to start the pull. Floor the accelerator until redline.
6. Remove foot from accelerator.
7. Press the center button again to stop the log, upshift as you see fit. I engine-brake in third down to my cruising speed before upshifting, but that's just my preference.
8. Return to 'normal' speed (the cruise-control that I set) and drive normally for a few minutes to shed heatsoak, especially if you're on the OEM FMIC.

Repeat as required until you have the number of logs you wish to collect. I generally collect three simply because after the third I'm already going in the home direction.

So, that's basically it. If you're consistent and have a good road/weather, your logs should be pretty consistent. Head home and download your data, make sure it's legit before emailing it to your tuner, plug it into V-Dyno, upload it to and over-analyze it for hours...whatever floats your boat.

I hope this helps.

30 Posts
Thank you so much for taking the time to write this out and post it for everyone. This is going to be extremely useful when I get to a point I'm able to get a tune, and answered a few of the questions I would have had down the road.
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