Thursday, October 10, 2019

Net Gains

Found an interesting article explaining the differences between SAE Gross and SAE Net horsepower ratings, and also highlighting some of the shenanigans that went down with manufacturer's advertised horsepower ratings during the performance wars of the '60s, when "BHP" might as well have stood for "HorsePower as measured at the Brochure".

What brought this to mind recently was driving the '94 Mustang GT. The 302cid motor in that car is the tail end development of the pushrod small-block Ford V8; in another two model years it would be replaced with the overhead-cam 4.6L. It's rated in the ad copy as developing 215bhp and, while not completely overwhelming the driving experience like the 327 in my Chevy Monza did, it's always there with power on tap if you want to break the rear end loose and get up to shenanigans.

Thing is, it's a completely docile and tractable engine. It starts easily, idles calmly with hardly any "lope" from the cam, delivers reasonable MPG for what it is, and features good throttle response all across its rev range.

What makes that interesting is that it would have had, in Sixties advertising "Gross BHP" terms, close to one horsepower per cubic inch. I've driven and/or owned several of the really high-output small-blocks from the Glory Years of the Muscle Car, and those things are an experience. Hard starting in cold weather, tepid throttle response at low revs, lumpy cams that have them idling like a paint mixer (seriously, the radio antenna on my 327 Monza, which was purely camouflage and not connected to a radio, would whip violently side-to-side at traffic lights), and 10.5- or 11.5- or 12-to-1 compression ratios that demanded premium gas...if not a drive to whatever local station offered Sunoco 104.

It's interesting that the '94 Mustang GT has performance numbers that more or less perfectly overlap a '70 Boss 302, when you allow for differences in tire technology, and the 94 will do it with a/c, cruise control, and power windows. The EPA took a lot away in the early 'Seventies, but by the mid-Eighties, computer-controlled ignition and fuel delivery, as well as computer-aided design of intake & exhaust components as well as combustion chambers had given it all back and then some.