COTD: Gaspard de Prony edition

Illustration for article titled COTD: Gaspard de Prony edition

Back at the turn of the 20th century, when farmers needed some way to measure the power output from the newish-fangled internal combustion engines, they'd hold contests at county fairs featuring the Prony brake — a device invented by Gaspard de Prony to measure the torque from a machine. As Jstas showed in our story on the Ford Mustang's dyno runs, figuring out how much power comes from an engine is still a burning question:

I had my 2001 Lightning dyno'ed in 2002-2003 timeframe. At the time, Jim D'Amore from JDM Engineering told me that most Lightnings were laying down between 340 and 370 horsepower to the ground. Do the math concerning the "rated power" in the brochure being 360-380 spanning 1999-2003 at the time and you can tell Ford was lying about power figures. Even if you take a rather conservative and generous powertrain loss figure of 10%, you're still making about 40-50 horses over rated power. But 1/4 mile times were hinting at something north of 100 horses over stock.

We had 6 Lightning on deck for that dyno day. Granted, the consitions were beautiful. Cool, sunny, fall morning, about 55-60 degrees, sun was shining not a cloud in the sky! Relative humidity around 45%. Pretty frickin' close to what DynoJet calls "ideal conditions" when they calibrate a dyno. Of the Lightnings, 2 were modified, 4 were stock. Mine was one of the stock ones. All the trucks put down the expected power. We each paid for 3 runs and Jim even showed us the calibration documents that DynoJet did for him about 2 weeks before we were there. The dyno was accurate.

Jim's son strapped my truck down to the rollers and they went about what we thought was another mundane dyno run. First run, truck laid down 372 horsepower to the wheels. The high watermark for a stock Lightning that day. Second run 375. Third run, 376. Keep in mind, stock BHP is rated at 380. I paid for 3 runs, Jim pulled 7 because he wanted to see how far it climbed. We'd have gone more if the truck wasn't starting to overheat. The 6th run, the truck put down 383.68 horsepower and 466.46 pound feet of torque. Stock ratings were 380 horsepower, 450 pound feet of torque. Jim looked at me like I just kicked his dog and said "What'd you do to it?" I was astonished at the accusation that I wasn't being forthright and said "Honest to God, not a damn thing! The only changes are a K&N air filter, I pulled the intake boot off of the intake box and I'm running synthetics in the crankcase, radiator and intercooler. Nothing else." Jim said that that probably helps out a bit but it doesn't account for a 22 horsepower difference over the average. If you were to measure the power on an engine dyno, it'd be even greater. Probably closer to a 45 horse difference. The intake boot probably makes the most difference and everybody who has a Lightning has pulled it off. It's meant to quiet down the blower whine but it's also like making a fat kid run down the street while breathing through a bendy straw.

My truck was bought new, from Miller Ford in Mt. Holly, NJ with 8 miles on the odometer. It was sitting in the back of the lot because nobody wanted black ones. I did and I had my choice from 7 of them. I chose this one and ended up with what Jim called "a factory freak". We determined that with the massive 4R100 automatic transmission, 9.75 inch 3rd member and the Eaton Supercharger, we guesstimated power loss to be between 15 and 20 percent. Ford engineers themselves said it was probably a bit higher than that. At a 20% drivetrain loss though, the '01-'03 Lightning had a BHP/BTQ closer to 450 horsepower and 600+ pound-feet of torque.

On average, the Lightnings were making between 15% and 22% more power than rated. That's between 50 and 85 horsepower. That's a pretty wide spread and attributable to the level of power being made.

Brand new GT's make 412 horsepower or something like that. A 2% difference in power levels at those high levels is 8-10 horsepower up or down. That's in ideal conditions too. Change humidity on the days of the dyno runs by 5% and you'll lose/gain as much as 10 horsepower. More on a boosted engine.

Ford isn't juicing anything. They are just working with such large numbers that even small changes that are typically covered by a standard margin of error are still quite large. Look at it this way, your brand new Ferrari is rated at 500 horsepower at the wheels. You take it to the dyno on a cloudy day with 98% humidity and 82 degrees and you lose 10% of your power due to weather conditions alone. 10% of 500 is 50 horses. On that piss poor dyno day, your 500 horsepower Ferrari is only making 450 horses. It would show at the racetrack too if the conditions were equally as poor. Probably to the tune or 3 to 5 tenths of a second when you get through the big end. Everybody in the world would make every excuse related to weather, environment, dyno accuracy and whatnot in favor of the Ferrari but because this is a Ford, we immediately damn the company for being a bunch of shysters and forget that physics even exists? Get real.

How about instead of that, we look at the Mustang as a marvel of modern engineering. In certain trims it makes as much and in some cases more power than that same Ferrari in the example I just gave, does it reliably, all day, every day, gets better gas mileage has fewer emissions and is actually affordable! Unlike the Ferrari, it also has a tendency to NOT burst in to flames for no apparent reason.


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Congratulations, Mr. Jstas! I applaud you! It is my pleasure to award you with a yellow Mustang that you can dyno upon its arrival. This lovely lady will bring it to you very soon. When she gets there, you should proceed with caution.