Tuning Mistress
Air Fuel Ratios, Spark Advance and a variety of other parameters have to be adjusted to match up with the new air flows created by the supercharger. For years I have been using VMP in Florida as my source for mail in tunes. They work with SCT systems (more on that later).
With a stock engine everything is known in terms of fuel flow curves verses engine load and RPM. A tuner can often give you a “strategy” program that will provide enhancements to power, economy, etc.
But with a custom engine like this they need to “home in” on it with multiple iterations and testing. Even with selecting injectors and a MAF that VMP had curves for it took eight iterations of download and testing. This is a custom engine tune for this car only.
Collecting Data Without a Dyno
This is best if you have the car on a dyno and can take multiple "pulls" collecting the data. Make some tweaks, and repeat until it is right. This gets expensive because you are paying by the hour and paying for the expertise of your tune technician. My local dyno uses a different tuning system which does not support my engine. And I needed to make some physical changes to the car during the process. So out into the wild we go.
Each iteration requires a download of the tune, re-programming the car, then a test run collecting new data. Finally you mail the data file back to the tuner and wait a couple of days. Repeat as necessary...
In this case most of the test runs were on a deserted country highway. My wife or a neighbor held my old laptop to record data while I floor the car from about 15 mph to 70 mph in second gear.
The only safe way to do this is to have a partner. Think about it – You are going to briefly break the speed limit in a freshly modified car pulling with all the traction the tires can muster. The last thing you want is to juggle is a laptop sliding around on the passenger seat. What could go wrong?
Your logging partner’s job is to hold the laptop and start the logging process about 10 seconds before pulling out. Then verifying that the program is running. At this time the driver is making sure the traffic is clear both ways, the car is in the correct gear, etc. Several times we had the logger running and then had to wait for a car that suddenly appeared.
When everything is right, pull out slowly make sure the car is straight and go directly for WOT without wheel spin. During the run both of you are monitoring gauges that might not be logged (boost in my case) and RPM and traffic. No need to hit redline, just get near it. Bouncing off the redline is very hard on most engines and would provide no useful information to the tuner.
Another important thing doing non-dyno data logging is to select the right location near where you live. Smooth road, wide shoulders, minimal traffic, no crossroads. In Green Bay a nearby country highway entrance ramp served very well. Sort of a slightly inclined drag strip. Here in Michigan a nearby state highway worked well. We just had to choose the right time of day (about 8 pm in August) and we had the wide two-lane blacktop to ourselves.
Science
One of the primary things the tuner is looking for is about 14.7 Air to Fuel Ratio (AFR) at idle and 11.5 to 12.5 under WOT. This is a MASS FLOW Ratio: 14.7 pounds of air for every one pound of fuel. This is the stoichiometric mix of air and fuel for perfect combustion of gasoline. At other ratios it may still burn but at this ratio it goes BANG. Other fuels work best at other ratios.
The first couple of tunes were tested with the car in the garage at idle. AFR was 9 or 10 or so. Very rich. So rich the car was sputtering and blowing black greasy soot all over.
The tuner has to creep up on the right mixture from the rich side. Too lean and things can quickly overheat and cause detonation. That said, I think they really missed the mark. So much extra fuel went down the pipes I had to replace the other AFR probe. I was not at all pleased with this situation and overall would give VMP only a 3 star grade this time.
By the third or fourth tune we were able to take the car beyond idle and drive it. I was just reporting what the AFR gauges were reading to the tuner. No real load yet.
This is when my tuner asked me why the AFR gauges were not hooked into the data logging directly. Because I did not know you could do that is why. Turns out SCT makes a special whip with a firewire plug that fits into my old SCT tuning programmer (Oh, so that is what that extra port is for...) Two analog channels, one for each AFR gauge!
So, I took the dashboard back apart, found the analog data wires from the gauges, soldered them to the new whip and plugged it into the programmer. There is also a COM output from these gauges so I wired that up to nine pin connectors (have not used them).
A few minutes configuring the ports and I could now datalog the AFR gauges.
Once we were driving the car it became apparent that the stock MAF was not suitable for this pressurized configuration. I purchased an SCT BA-2600 MAF from Summit. Plug and Play install.
Wires, Plugs & Software – Re-Programming the Car
My tuning set up is like this: SCT Programmer plugs into the OBDII Port. From here you can upload or download a tunes between the programmer and the car. If given permission, you can also modify some of the settings directly (like tire diameter, gear ratio, etc.) More on that later...
On my set up, with older equipment, the programmer can also connect to a USB port on a windows computer. I have an old Sony Vaio laptop that serves this purpose well. A program from SCT on the Windows laptop called “Device Updater” (catchy name!) is used to transfer the encrypted files with a USB printer cable. I expect newer equipment uses Bluetooth?
If you want to data log what the car is doing hook everything up at once (laptop to programmer to OBD2) and use a Windows program from SCT called “Livewire” (better name).
The analog inputs from the AFRs plug into the programmer on the additional port. VMP (and most tuners I presume) has a list of about 40 parameters to monitor. Once you have selected them all you save that arrangement off in a “config” file for easy loading next time.
So – Eight iterations, each three or four days apart and August was over. The car was running very nicely and I have a new neighbor who thinks I am crazy just like my old neighbor Lou. The tune and config file is backed up on my Google Drive.
Lawyers, the EPA, and Limitations
My tune allows me to change some of the parameters directly from the programmer. But not as many as the last tune I received from VMP in 2017. In 2018 the EPA came down on the parent company of SCT (Derive Industries) and fined them for allowing customers to basically override the pollution controls on their cars. There were several individual small speed shops put out of business as part of this same set of lawsuits.
The upshot of this action (along with ruining some lives and businesses as collateral damage) is that VMP must tune my car as if all pollution equipment is present (it is) and cannot go beyond certain limitations. In other words, the car is NOT tuned to the gnat’s ass for performance and as far as both VMP and I are concerned should still be street legal. They even required me to send a photo of the engine bay presumably to verify there was still an EGR & PCV system etc. They do not require testing where I live. But if they did, I expect Mistress would fair pretty well for a 20-year-old car. Everything is there and still functioning including the cats and O2 sensors.
What were the manual tuning limitations? In the programming controls I can manually retard global spark a few points from where they set it. This will allow me to adjust if I am traveling and cannot get 93 octane gas. Pull a couple of points out and 91 octane will work without causing detonation (at the cost of some power). Perfectly legal and highly desired since 93 octane is hard to come by in some states.
But I cannot advance global spark from where they left it (I could before). This would push the engine a little closer to the edge of detonation and create a little more power. It would also burn hotter and presumably increase NOX production beyond what a 2002 V6 Mustang is allowed. So it is a little conservative and does not cause more pollution than it should. I am fine with that.
Next is the dyno and results…