I will be testing and documenting various GT500 induction system modifications. For the purposes of this article the "intake" can be thought of as the portion between the throttle body and air filter, consisting of some tubes, a mass air meter housing, and filter.
I have not posted my GT500 test results on this forum before, but you can find many more here:
2007 Shelby GT500 - VMP Tuning Message Board
This section will cover the C&L Intake. We'll compare it to the JLT intake on my pullied GT500 and we'll also compare it to the stock intake on an otherwise stock GT500. I will also go over some specific intake and tuning information.
GT500s are very sensitive to heat and weather conditions, so each time I do testing a new "baseline" is done.
C&L rolled out their intake late in 07, and took a different approach than everyone else on the market. It's made from one cast piece of aluminum, so its very smooth from the filter to TB. It's powdercoated flat black to match the stock blower and valve covers. It fits nicely under the stock strut tower brace with no spacers. Once you are moving and air is flowing through the engine bay, heat does not seem to be an issue.
I initially started testing this intake on my GT500 back in November, when I was still running the stock blower. I saw something odd, and wanted to confirm on another GT500 before posting results. In late December I was able to test the C&L intake on a local friends totally stock GT500.
I'll first start by going over the testing and tuning that I did on my own GT500 in Novemeber. At the time a 2.6" pulley was installed on the blower. This was one of the first times a cold front came through Florida that year, so my car was producing around 550 at the wheels.
Whenever you change the intake on an 05+ Mustang, you also end up changing the Mass Air Sensor housing. This is very important, once you put that sensor in a larger or different shaped housing it all of a sudden reads differently. This is why 05+ Mustangs require tuning when a new intake is installed.
The part of the PCM tune that needs to be adjusted is called the Mass Air Transfer Function. It's basically 2 columns, 30 rows tall. There is a voltage point on the left, and an airflow value in LB/min on the right. When the MAF sensor is outputting X number of volts, the transfer function tells the computer X amount of air is flowing into the engine.
This is a screen shot of the stock GT500 MAF transfer function (xfer for short) from the SCT software, other software may display the transfer function differently, but this is how Ford does it on any 05+ vehicle.
Based on this MAF transfer function (xfer) the computer then knows how much fuel to add through the injectors. It's also very impotant to note that the transfer function is used to calculate Load or VE, the Calculated Load greatly effects where you end up in the spark table. At lower calculated loads the engine runs more timing.
When you install an aftermarket intake with a larger MAF housing the voltage output from the MAF sensor goes down. If you do not adjust the transfer function the computer thinks less air is going into the engine. It adds less fuel and calculates a lower load value. The car will run lean, and thanks to the lower load calculation it will also have too much spark timing, a great combination, if you like windows in your block.
C&L provides a transfer function with their intake kits (more on this later).
I like to run GT500s at 11.7:1 at WOT, I feel this is a little rich to keep you on the safe side, but not rich enough to cost a lot of power. All my testing is done with a lab quality AFM1000 wideband installed directly in the exhaust, before the cat converter. Installing a wideband in the tailpipe is just not accurate enough. All of my graphs are shown with the SAE correction and usually zero smoothing. Air conditions, dates, and times are printed at the bottom so you know a true back to back test was done on the same day in similar conditions.
Run 1 is with my tune's spark values and C&L's MAF tranfer function (part that controls fuel). Notice the car is 10:1 at the very end of the pull, that is why power is so low.
Run 2 is after I've made a few adjustments to the transfer function to get A/F at WOT (wide open throttle) around 11.7. Power is now starting to come around, it made 552RWHP.
Run 7 is with the JLT intake and my tune.
I feel the C&L and JLT intakes are very comparable when it comes to power numbers on a stock blower car. There is less than .003% difference between run 5 and 7. I personally like how the C&L looks and fits.
In December I did some additional testing with the C&L intake, on my friends totally stock 08 GT500. This was to rule out the very rich A/F that I saw with the C&L supplied MAF transfer function.
Even though this was done in December, it was a very poor day for air conditions. Baro was low, humidity was high, and temp was already over 80* in the shop by 9AM, that is Florida weather for you. So the numbers are correspondingly low, at all levels of modification (tuned and with intake).
Run 2 is with my tune on the stock intake, air fuel is in the high 11s. I've spent a considerable amoutn of time coming up with a good MAF xfer for the stock intake, as the factory xfer is very rich (sometimes in high 10s).
Run 3 is with the C&L intake and the C&L supplied transfer function, the car is running under 10.0 above 5000RPM. Hmm, thats the same thing that I saw on my car back in November.
The C&L transfer function is so rich that the car did not pick up any horsepower with the C&L intake, it actually lost in some areas.
Run 6 is with the C&L Intake, VMP Tune, and a proper air fuel ratio (by adjusting the MAF xfer). Once I dialed in the A/F, the power gains were right where they should have been, actually a little bit higher than expected. I have been seeing 16RWHP from all the other aftermarket GT500 intakes, and saw 18RWHP in this case.
Conclusion, the GT500 MAF xfer provided by C&L is way too rich, as proven on both my car and this 08. Why didn't C&L catch this? I'm not totally sure, I know Lee has a top notch flow bench that he derived this transfer function on. The lower end of the transfer function is actually very good. Lee told me several tuners tested it, but I was never able to get any data from them. I do know my testing procedures are much more thorough than most. Very few tuners use a $1600 AFM1000 wideband setup (and I have two), and very few put the wideband directly into the exhaust before the cat. I can surmise that installing the wideband in the tail pipe, after the cat, resulted in a leaner and delayed reading making those other tuners think everything was okay. The very extreme richness only occurs during the last 1000RPM of the run (which is also where peak power occurs) and there can sometimes be as much as a 500-1000RPM delay when using a Dynojet "sniffer" in the tailpipe.
I also found that the C&L has roughly the same amount of MAF sensor range as all the other aftermarket GT500 intakes (KN, JLT, Steeda, FRPP). On a stock pulley car I saw roughly 4.5-4.6v peak, and on a pullied car I saw 4.6-4.65v. This further supports my argument that the C&L supplied transfer function is incorrect up top.
