Dyno tuning is the only way to see how your car is really running, and we brought the newly-completed 1965 / 2003 SN65 Mustang to Finish Line Performance for a chassis dyno wring-out.
We’ve been following the progress of the SN65… a truly unique Musclecar comprised of a 1965 Mustang on top and a 2003 Mustang Cobra under the hood, inside, and on the bottom. (See our first story on the SN65 for a complete description… the link’s at the bottom of the page.)
After the Julian brothers had finished the car and won Best Engineering at the Detroit Autorama, Bob Julian contacted us about the future modifications on the car. We decided to bring the car to Finish Line Performance in Naperville, IL, for a spin on the Dyno and a Diablosport tune-up to see what the SN65 was all about.
It’s important to remember that the SN65 concept was to marry two factory-stock Mustangs together to make one killer hybrid. The 2003 Cobra drive train is completely as-factory delivered save for the custom air intake - created to package the engine in the 1965 Mustang nose – and the Magnaflow dual exhaust. So, the bets were on to see how much power this car would make, and we we’re betting on the 370 HP range, which is about what a stock Cobra churns out.
It turns out that we were wrong. After the first pull, the supercharged Cobra motor laid down a 407HP number on the rear wheels, which was beyond the stock rating. It turns out that the Magnaflows and the intake worked pretty well!
The only problem was the dyno curve had some hiccups… Dan Bills at Finish Line Performance wanted to check the spark plugs. That always seems to be the first thing he checks. The factory Platinum plugs are great for mileage, but they were burning the electrode away causing misfires on the dyno. Time for a set of NGKs.
The new plugs saw a straighter curve, but less power. Out of curiosity, Dan elected to check the spark plugs again. Dan had originally gapped the NGKs to about .048”, and he found that after the first run, the gaps had closed on 6 of the 8 plugs by about .015”. Hmm.
Once re-gapped, the car seemed to be back up on power, but the curve was breaking up again. Dan broke out the Diablosport Predator to see what was going on.
The Diablosport Predator is a hand-held device that provides several functions in one unit. First off, it’s a programmer that comes from Diablo with several performance tunes installed. You can upload a performance tune into your car simply by connecting the Predator to the car’s OBDII port and following some simple instructions. You can make minor modifications to the tune parameters manually, or connect the Predator to a computer that has the Chipmaster Revolution software on board to completely create a custom tune for your car.
The next function of the Predator is a real-time data logger. Dan Bills used the Predator to log the SN65’s dyno runs so he could play them back and analyze the results, or export them to a PC to graph or save them for later analysis. Finally, the Predator is a troubleshooting tool that displays trouble codes to let you know if your engine is running properly. Dan ran the diagnostic mode on the Predator and discovered a fuel injector trouble code stored in the system.
After inspecting the engine, Dan discovered an injector retaining clip that was not 100% fastened to the injector. This was causing the erratic dyno curve and throwing the trouble code. It’s a good thing he found the loose wire… this could have caused an injector misfire and leaned out the engine and burned a piston.
Once the car was running properly, Dan used the Chipmaster Revolution software and the Diablosport Predator to tweak the tune in the car. The SN65 had already logged several dyno runs, and the blower was getting hot. One downside to supercharged cars that have roots-type blowers is that there’s a lot of metal in that system which likes to hold heat. Heat reduces performance. The dyno numbers were beginning to show a loss due to heat, and the blower belt was starting to slip at high RPMs.
Dan noted that the air / fuel ratio was on the lean side around 4000 rpm, so he Tuned the car to smooth out the curve. He eventually brought the curve from around 13.5:1 down to around 11:1 under wide open throttle conditions. This is good for making power, and also good for the longevity of the engine. You don’t want a lean condition with the pedal to the floor. Dan didn’t change the part-throttle ratios so the car should maintain it’s factory tune under daily driving situations.
The results? While the car made it’s best run right out of the box (407hp / 393 ft. lbs.), the curve didn’t look too good. Seven runs, 8 plugs, and a tune-up later, the car made 402.4 hp and 374.7 ft. lbs. of torque. Keep in mind that the final dyno curve was much smoother and the air / fuel ratio was much safer. In addition, that was after 7 runs heat-soaked the blower. Odds are, this car will make more power than the first run if allowed to cool. But we had to split, so those were the numbers we ended up with.
The SN65 is a real car that runs and drives as good or better than the 2003 Cobra it was homologated with, and it’s not over yet. Future plans call for a blower upgrade and a few more speed parts to make it more potent on the road coarse tracks. We’ll be there for the ride.
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