Dyno Test: '65 Six-Cylinder
Owner: Lucio Telles
200ci Six, C4 automatic
Lucio's '65 Mustang convertible ran very well when he drove it into Jon's shop. The six-cylinder droptop has long-tube headers and dual exhausts, which gives the 200ci six some advantage. It did have a rough idle, typical for most inline Ford sixes. Jon's objective was to make more power and clean up the idle. We did four dyno pulls. We use the term pull loosely because not all of them were wide-open throttle.
Pull 1: Baseline
Peak horsepower: 73.66 at 3,150 rpm
Peak torque: 124.07 lb-ft at 3,100 rpm
Air/fuel ratio: 13.4:1 at 70-mph cruise; wide-open throttle at 11.0:1: too rich
Autolite 1100 1V with 70 main metering jet for sea level operation
Pull 2
Peak horsepower: 55.88 at 3,100 rpm
Peak torque: 104.98 lb-ft at 2,750 rpm
Air/fuel ratio: 12.5:1 at wide-open throttle: some improvement
Same Autolite 1100 1V with smaller 69 jet to lean the mixture. A check of ignition timing was spot-on at 6 degrees BTDC at idle. With a jet swap, it's always a gamble which way power will go. We lost power with this jet swap, and Jon wasn't pleased with the result.
Pull 3
Peak horsepower: 58.21 at 3,400 rpm
Peak torque: 88.83 lb-ft at 3,400 rpm
Air/fuel ratio: 14.0:1 at 70-mph cruise: improvement
Smaller 68 jetting resulted in some horsepower improvement but with a significant loss in torque. Jon is as baffled by the numbers as we are. It's still quite rich at wide-open throttle (10.02:1).
Pull 4
Peak horsepower: 77.38 at 3,250 rpm
Peak torque: 124.86 lb-ft at 3,250 rpm
Air/fuel ratio: 14.3:1 at 70-mph cruise
Same Autolite 1100 1V with smaller 67 jetting. Jon took extra time double-checking everything this time around, coupled with concise communication with Lucio about how to manage the throttle.
Jon concluded the Autolite 1100 runs progressively richer at wide-open throttle and high rpm despite efforts to get it leaner. Regardless of the jet changes, our 200 six still runs fat, 10.43:1, with the throttle wide open. Jon was able to increase 4 hp by downsizing the jet to 67 from the original 70. This worked well in Las Cruces, New Mexico, which is at 4,000 feet. Sea level conditions or a higher elevation would have mandated different jet sizing in either direction.
We gained 4 hp with a simple jet swap but didn't gain torque. Torque is normally gained through a richer mixture, increasing jet size instead of downsizing. This proves there are no free lunches in the power game. Lean the mixture and gain horsepower along with cleaner emissions. Enrich the mixture, lose horsepower, gain torque, and pollute the atmosphere. In this case, Jon took the best approach: a leaner mixture, more horsepower, and cleaner emissions.