Project Update for June 2, 2011: We dropped the Mustang off at
True Street Motorsports in McKinney, TX today and they fixed all manner of things + diagnosed some other quirks we've run across. I finally found a good tuner shop (just 6 miles north of our location) that can custom dyno tune the 2011 GT via the SCT tuner we have, and they already have a great reputation. The owner of the shop also owns a 2011 Mustang 5.0 GT, which they've modded and tuned already.
Their tuning guru Sean Burt (who, as luck would have it, tuned our 7.0L Alpha car's new motor when it made 488 whp, back at LG Motorsports in 2009) started out by getting a baseline dyno run in the car with the existing custom tune + the Steeda cold air installed, which was
389 whp right at 5000 miles on the odometer. This compares to the initial dead-stock dyno pull (on the same style DynoJet 224) of 367 whp at 500 miles on the odometer (uncorrected it was 378 whp - it was a
cold day) on Nov 18, 2010 (see bone stock dyno chart below).
This was the corrected bone stock dyno number at 500 miles back in Nov 2010 (uncorrected print-out is here)
I explained to Sean in painful detail what I wanted: more control, not necessarily more power. Probably one of their only customers asking for a custom tune but
not wanting more peak power. I talked about tip-in throttle, falling rate vs rising rate throttle response, and the massive power-modulation issues we were having in 1st and 2nd gear, on corner exit in autocross events. I asked him to drive the car to see if he can feel the difference, before, during and after his tweaks.
After talking to some other local 2011 Mustang GT owners I was also curious why the car
feels like it has a 200 pound flywheel. I made some calls earlier this week and according to the folks at Fidanza the
OEM flywheel is only 21.5 lbs. They were the only place I called that had an answer - because they make a lighter 2011 GT aluminum flywheel (12 lbs) and had weighed the stock unit. We cannot use an aftermarket flywheel in STX, but I just wanted to know what the stock unit weighed to see if it would explain the sluggish nature of engine revving - it didn't.
This afternoon when I went to pick up the car Sean had a lot of great information for us, as well as two new tunes loaded to our SCT unit and three color print outs of the various dyno pulls. That seems trivial but when you pay for dyno tuning you sometimes have to
ask for printouts. They even videoed the dyno pull. Great service! They are also familiar with HP Tuners and other software packages, and I noticed several LSx powered cars as well as an SRT Challenger in their shop for tuning that day.
They tinkered with our Mustang off and on for several hours, made some calls to some other SCT gurus, even to some folks at Ford. Here's what they relayed to me:
1. There is a
very weird steering feedback issue we had noticed but didn't mention to him, as we thought it was just a bad wheel bearing (we already received a new pair to install, next). He brought this up after driving the car... the explanation he had was bizarre, but it makes
perfect sense. Its possibly a
programming issue (that he cannot alter), so once we test this theory to verify his conclusions I will post up about it. Don't want to spread bad information if this isn't the cause. Its something we've been noticing for a while, but had not mentioned here yet.
2. The "heavy flywheel effect" is all in ignition timing. The OEM tune adds
66 degrees of ignition advance in "engine deceleration mode" (off throttle, falling RPMs), which slows the engine responsiveness. He changed this to a normal 12 degrees and wow, what a difference. The engine response is SO much more lively! Its easier to rev match downshifts, too. I had no idea that could be in the programming.
3. Sean says they've used 7700-7800 rpm redlines in these new Coyote 5.0 engines without issue. Yikes! The dyno pulls show that the motor is starting to lose power above 6700 rpm, so it doesn't make sense to go to these stratospheric revs unless its in an autocross situation where we're barely touching those high revs, to avoid a 2-3-2 shift on a short straight. Anything we can do to avoid a lot of shifting is a win, especially after the last autocross (where I needed 4 separate 2-3-2 shifts per run!). We'll keep an eye on the harmonic balancer (check for slipping) and oil usage, but we've gone ahead and moved the redline on our car to 7700 rpm, up from our previous 7400 number, and way up from the stock 6800 redline.
Zing! I'm already looking at aftermarket SFI rated balancers, for long term durability.
4. So last, but not least - the throttle mapping. Again, everything is all new on 2011s, as they can tune 2005-2010 throttle mapping easily. Sean tried to alter the correlation of pedal to throttle like I asked for, but there are something like 3 separate data tables/variables necessary to drive this interface, and he said if he altered all 3 the computer would "throw a wrench" error code on the dash. He says he has tried this on 2011s and it keeps "relearning around the tuning". He did try something very novel on our "track tune" and it might be effective - more than just running the car in a higher gear (our autocross testing showed Costas to be faster in 3rd gear rather than running in 2nd - which was such a kludge of a fix we'll try anything). Again, this tuning trick might be a flop so we're going to hold off on explaining about what he did until I can prove that it works. We will be testing the new tune at two autocross events this weekend. He loaded another identical tune without this throttle tricking tweak as our "street tune", which I can switch to in 90 seconds if the other doesn't work out. This "street tune" in fact makes more power... but again, we cannot use the power we're making in autocross situations, so this unusual "track tune" might indeed be faster.
Today's final 2 tunes with a peak number of 392 whp, corrected
So where are we now? 4500 miles later with
one single bolt on part (cold air) and a custom tune we're at
392 whp, up +25 whp and +28 wtq on the new "street tune" over stock. That's pretty damn good power for an STX legal car with an air filter and "some 1s and 0s". A
tiny part of the increase in
peak numbers is the rise in the redline, as the bone stock dyno pull was just barely still going up at the stock 6800 rpm fuel cut. But the shape of both the new power and torque curves look nearly identical to stock, with the numbers up across the board, and the new power peak is only at 6700 rpm. So the cold air + the tune = a win.
Talked to an exhaust supplier yesterday and I'm anxious to get their full length 1-7/8" header set-up coming. Picking that larger header primary diameter to help
kill some more low end power while giving a little more on top - unless the new tune is
magic, in which case I'll go with their 1-3/4" primaries. Until now, adding any power anywhere would just make the car slower in autocross, so if this new "track tune" allows us to modulate throttle and corner exit faster then we can finally go ahead and look at more power, which is there for the taking. Then we can focus the rest of the season on more suspension bits.
Next up! Two autocrosses this weekend, including Saturday's
National Street Tire Challenge and Sunday's
Texas Region SCCA Autocross #3, both being held at the massive Mineral Wells complex. Amy and I are driving the Mustang in 2 different classes at each event, and we might even be running on different tire packages as well. We do have
a strange, new wheel and tire package we're testing this weekend, which is funny looking and sure to draw some laughs, but it might help cure some of our power issues. If it doesn't work, I won't mention it in my next post, photoshop them out of the pics, and deny we tried it if asked.
More soon,