Question about horsepower

If memory is correct, HP ratings in 71 were determined without any accessories on the engine including the water pump. Starting in 72, what you see under the hood is how it was measured.

HP rating prior to 72 were SAE Gross ratings. This generally translated into about 25% higher numbers than today's Net ratings although in some cases it may be more than 25%. This would put your Grande around 220 hp by today's standards (or about 176 RWHP which is usually 15% to 20% lower than Net ratings). If you have an automatic trans the numbers may be even lower.

HP rating of 176 doesn't sound like much considering how fast this car is. Maybe HP rating is like a telescope's advertised max power. A 600X telescope works on paper but never in the real world. This car also has after market enhancements like Edelbrock manifold, Carter AFB and no points.

if you know the 1/4 (or 1/8) mile time, and the weight, you can calculate the real HP easy. google for it.

For many years through the 60s and 70s, advertised horsepower could make or break some racing classes. In some cases, it wasn't rare to see a manufacturer low-ball or high ball an engines capacity in terms of output....

Now... it woul;d be pretty bold to state how an old technology motor will compare with a new engine.... It is one thing to say that "my motor is RATED at XXX HP".... Whether that motor is actually producing that kind of power is a whole 'nother story....

Tried to get the car dyno'd but they could not work on it if it did have computer chips. Had a '78 Caddy weighing 5500 pounds and rated at 180 HP. That car had plenty of pick up.

mike

Let me give you a little history of my '71. The motor was all original and it would barely break loose one tire. After a mild rebuild (331 stroker) the car is totally different. I am still using stock heads, so I doubt my stock motor was anywhere near 200 hp, after the rebuild I am thinking it is in the upper 200 hp. Can't really campare it to the '98 Cobra I had, gearing all different. But I think it is close to 300.

This engine has been B*B'd with Edelbrock Performer and Carter AFB plus MSD coil and no points. Sounds like it has a cam but don't know what else was done to it. Do know after two months and 1300 miles of mixed driving, the oil is still the color of honey. Tells me a lot about the engine.

mike

Sorry, but that sounds more like a sled. That was back when a car was a Car. Best driven with worn out shocks. Had a 1960 Chevy Biscayne, with the fins, rusted out floorboards, no shocks, but what a smooth ride, could do 60. Only paid $100 for it, and sold it for $50. Wonder what the HP of that inline 6 was ? It had a xmas lights behind the grill.

HP ratings have changed over the years, The 69 boss 302 was rated at 290 Hp for various reasons but actually was closer to 400 HP inusage. I believe it was around 72-73-74 era that a lot of the ratings changed. Local cops ( I worked at the Sunoco station so I saw them all) had Pontiacs the 73's were

350 cid 350 hp the next year 74 had the same motor but were rated at 350 cid and 185 HP both ran the same. so it was just a number game. As far as breaking the tires loose, a lot of cars are set up between trans and rear gears so that it is hard to break the tires loose on dry level pavement, something to do with safety and cafe standards I think.

To answer your original question, no, the factory hp ratings from '71 are not interchangeable with the present ratings. Nor are the numbers you see in all the hot rod mags interchangeable with the present factory ratings. The biggest difference was the chaneover from gross to net in the early '70's. The gross numbers used prior to '71-'72 were based on dyno pulls with no aircleaners, no mufflers, sometimes using tube headers, no alternators, no smog pumps.

They also often involved quite a bit of fiction, in both directions. Check those 290 hp numbers for the Boss 302 and the 302 ci Z/28's. They're stated at approx 5000 rpm, yet the motors could pull 6800 or more. Because hp = rpm x torque/5252, you can see that the numbers from 5000-6000 are going to be higher than the number at 500. The 428 Cobra Jet's 335 is also widely doubted. At the same time, the 271 claimed for the K code 289, or the 365 claimed for the solid lifter Chevy 327, are pipe dreams.

The gross numbers appeared side-by-side with the net numbers in '71. But by '72 and '73, the gross numbers had stopped being used altogether.

During those same years the other big difference kicked in, and that was the drop in compression ratio to accomodate the new unleaded gas. The unleaded gas was to accomodate the catalytic converters, slated to come on line in '73. CR's dropped from the 10's and 11's for the hipo engines to the 9's and even the 8's. This knocked a good 30 hp off the big blocks. By the late '70's you had 455's making 150 fwhp. Ick.

About your car, your mention of a 300 hp factory rating indicates you're talking about a 4-bbl Cleveland. If it's a factory '71, it's still got the closed chamber heads, which means a full dose of the old school CR. The 4v heads are the best factory small block castings from the day, and with some skillful porting can sustain 8500 rpm. Your few bolt ons and a cam might very well have you at 300 hot rod dyno hp, which would translate to about a 260-280 modern factory number. Don't choose off against a WRX, but you might give an '07 Mustang GT a run.

180 Out

The old school CR is 10.7:1 and today's gas seems to work fine.

Did do something stupid today when someone in a Mercedes V8 Kompressor cut me off :) Don't know what HP rating those cars have but I know they pump it up. After lane playing for a while, we ended up nose to nose at a stop light. Perfect. Just as I was ready to shift to third, the race was over. By the time he pulled up at the next stop light, the driver would not even look at me.

I do miss those Sunoco 'dial your own octane' stations. What was the highest rating, 260-280? Do they still exist. Not out here on the West coast.

Horsepower is a misnomer. Torque is the real measure of an engine's capabilities.