I have actually hired a person specifically to help me with "tech talk" type posts as well as R&D of new TSM products and industry products in general. We will be doing little threads like this one hopefully on a monthly basis and then also bringing you valuable information about what works and how it works so that you can make an informed educated decision with getting "sold to"
That said along with GT-R Life we wanted to take the time to give you an general overview of what the experts look for in a properly tuned turbo charged car. The following is informational data for people who may not know, and maybe a refresher or eye opener for those who already do.
Please feel free to ask questions as much as you like and we will happily answer them with information that has been proven to be consistant.
If any of you have ideas or desires as to what you would like to see explained or tested next month please feel free to email me.
TUNING TALK #101
As most of you now, at TopSpeed Motorsports we take pride in providing our customers with tested and track proven information. This thread is an attempt to inform the community about what to look for in your datalogs, to ensure that your GT-R is operating optimally. Most of our information will be directed towards Cobb software; however the same principles can be applied across several different platforms and engine management systems.
This information is not intended to be a tuning guide, this is simply a resource to help the community understand what to look for, and how to ensure the quality of their GT-R’s tune.
First off, what to log:
Air Fuel B1 new
Air Fuel B2 new
Air Fuel B1 old
Air Fuel B2 old
Dynamic Advance (DBA )
Inj. Duty Cycle
Intake Air Temp
Int. Cam Adv B1
Int. Cam Adv B2
Knock Filter 2
Knock Filter 4
Knock Filter 6
Knock Sums (CBA)
Mass Airflow B1 (MAF CALIBRATIONS ONLY)
Mass Airflow B2 (MAF CALIBRATIONS ONLY)
Theo. Pulse Width
Throttle Pos. B1
To monitor Air/Fuel ratios, we elect to log the “Air Fuel B1/B2 (new)” since they seem to be in line with most aftermarket wideband sensors vs the (old) inputs which typically read ~.5 high. While all tuners will suggest a different ideal AFR, most will agree that mid-low 11’s is considered to be safe while in boost on a turbocharged engine such as the VR38. Anything significantly higher than this can result in engine damage due to excessive cylinder temperatures.
In lower load portions of the log, such as cruising and idle, you should see AFRs near Stoich (14.7AFR). Fueling strategy in this portion of the map should be nearly identical to most stock cars on the road today.
Short Term Fuel Trims (STFT): This value indicates any immediate fuel trims the ECU may be performing in an attempt to hit the fueling targets. If the ECU detects operations leaner than commanded, it will produce a + STFT, and – STFT if it detects an overly rich condition. The ECU is capable of commanding +/- 25% STFT, typically we consider <5% to be acceptable during WOT and slightly more under light load situations due to changes in conditions etc.
Long Term Fuel Trims (LTFT): This value indicates any permanent changes have been made to that portion of the map in an attempt to hit the desired targets. These long term fueling adjustments essentially reset the STFTs to 0, which will make the car perform more smoothly overall. These values are saved on the ECU, even after ignition cycles. The ECU is capable of +/-20%, but we typically consider 3%-10% to be acceptable for this function.
Injector Duty Cycle: This value indicates a percent usage of the injectors at any given time, it is defined as commanded pulse width divided available pulse width. It is not advised to operate injectors at anything greater than 85% IDC, and any duty cycle greater than 90% is considered to be extremely dangerous. Anything greater than 90% is considered to be static, in which the ECU no longer has the ability to control fuel delivery.
First you must know what ignition timing control strategy your GT-R utilizes, CBA is the strategy which all 2009-2011 USDM GT-Rs use, while all 2012+ USDM GT-Rs utilize DBA. CBA uses a burn time calculation, whereas the DBA uses a more traditional “degrees before top dead center” strategy.
CBA (09-11): To monitor knock levels and identify any ignition timing related issues, you have to log “knock sums”. For each knock event, this value will decrease by -307 and 1 degree of ignition timing is removed for every -256 knock sums recorded. It is not uncommon to see a -300 knock sum event, however what you do not want to see is an increasing knock sum amount. IE: -300... -600.. -900.. etc. If you do see your knock sum increasing , I highly suggest you consult your tuner.
DBA (12+): Since this ignition timing control strategy uses DBTDC as a reference, it doesn’t require translation of arbitrary values to monitor what the ECU is doing. Depending on the calibration strategy, you may see a constant dynamic advance value of 0-3 degrees here when the ECU does not detect any noise (knock), or when it does you may see a negative value. Regardless of the tuner’s strategy, or the value, you need to note if that value fluctuates while in load. If dynamic advance drops more than a -2 degrees on a regular basis, I suggest you consult your tuner. This means the ECU is pulling timing due to some unusual noise, which could be an indication of engine damaging knock.
Knock Filter: Logging this function is helpful for someone who may be concerned that their tuner has eliminated the ECU’s ability to detect/react to knock. Below is a previous post made by our tuner regarding this function.
“From the factory Nissan has some extremely sensitive knock tables. I have seen logs and tunes from various protuners that are just down right scary. Cars that are pulling up to 6 degrees (-1800 knock sums) of ignition timing due to an overly aggressive ignition timing map, lean AFR's or both. Luckily for these customers the protuners did not raise the knock sensitivity tables beyond the point of being unsafe. In essence the ecu's ability to see detonation saved these customers cars from having a total engine failure.
While its not uncommon for protuners to raise these knock sensitivity tables (decreasing sensitivity) on built motors you really don't need to touch them much on stock motor cars. Things that can cause the motor to be noisier then stock are pistons, cams, valves springs, etc . In order to properly set up this table on built motor (noisier then stock) your protuner will usually use a set of det cans or external knock monitoring device. Built motors aside on stock engine cars you really should never need to raise these tables much and anything more then about %15 would be excessive not allowing the factory ecu to pull timing accurately in the event detonation does occur.
So how do you log this?
If you use a cobb accessport then all you would need to do is log the knock filter tables and graph them vs rpm. By logging knock filtters on cylinder 2,4,6 with the cobb ap you can see how the knock sensitivity tables have been set. Bellow I have graphed the stock knock filters vs rpm. I have also included a screen shot of the untouched factory Knock Sensitivity table. Notice from the data log that the knock filter tables closely follow the factory sensitivity tables.
What you wouldn't want to see is knock filter tables that are maxed out or raised so high that even when the engine is detonating the ecu doesn't record it and pull the timing which can lead to melted pistons, broken rods, and blocks with holes through them.”
Edited by [email protected], 13 August 2013 - 10:18 AM.