S197 V6 Mustang Bolt-On Test

Stuck in Third

Before getting into the dyno testing, we have to disclose that we ranall the tests in third gear. We started with Fourth gear pulls butimmediately ran into the V-6 Mustang's 111-mph (4,750 rpm) speed limiterdictated by the tire's speed rating. We had a DiabloSport Predator flashtuner on hand, and it claimed to be able to switch off, or clip, thespeed limiter. However, it repeatedly put the engine into limp-home modeinstead. Curiously, we found out after installing the cold-air kit thatyou could clip the speed limiter when the Diablo was running its ownsport tune, but not when running in stock Ford tune. It's just a glitchthat has probably been eradicated by the time you read this; it was anissue for our testing.

Faced with either running in the next closest gear, Third, or stickingwith Fourth and having the runs end before the power peak, we chooseThird gear. Because the V-6 Mustang's Third gear ratio is 1.41:1, thereis not that big of a factor to worry about, at least for horsepower. Weran some calibration runs to see what the dyno thought of the differencebetween Third and Fourth gears, and in the upper rpm range, it was onlyabout three horsepower in favor of Third gear. Torque was up 10 lb-ft ormore at the peak.

Ultimately, we decided not to monkey with the data, and are presentingit here just as it came off the dyno. You'll have to subtract just a fewhorsepower, or more-so torque, if you're trying to horseback acomparison with a Fourth gear test.

Fun With Octane

Our testing regimen had us bouncing back and forth between 87- and91-octane pump fuel. We found no power in the higher-octane gasolineunless the engine was tuned with advanced ignition timing.

Our first official test was to baseline the car in showroom conditionusing 87-octane gasoline. Ricardo reports his customers almost alwaysrun 89 octane due to their preference. This car is rated for 87-octanefuel, and we were interested in spotting even a small power increaseattributable to octane; we went with regular gas to start.

With 186 rwhp, we were impressed with the 4.0-liter's baseline output.Believe it or not, this is what a stock 5.0 Mustang's 5.0 HO V-8 putsout (assuming it's in sound mechanical condition). Of course, the V-8puts out substantially more torque and the old 5.0s weigh much less thanthe newest Mustangs. The little 4.0-liter has some snort.

To see what 91 octane would do, we pumped out the remaining 87 octaneand added a splash of 91 octane. The result was about a 3 hp loss, whichwe're attributing mainly to normal variables such as water and oiltemperature, the dyno, and so on. True, higher octane fuel burns moreslowly than low octane, and in race engines theoretically you'll see apower loss with excessively high octane fuel (for what the engineneeds), but the 4.0-liter in showroom condition isn't that highly tuned.

More practically, we determined that Ford doesn't really have apremium-fuel strategy lurking in their engine management software, sothere is no use in running high-octane fuel in these cars when stock.That's the opposite of the Three-Valve V-8's response, which is to gain5 rwhp when stepping up from 87 to 91 octane.