phess11

I heard somewhere that published horsepower in the early years was measured differently than it was in the 70s and later. Does anyone know if there is any truth to this, and if so what the conversion might be for later cars?

thanks,
phil

phess11

It was different. After posting I came across this on the internet. Very interesting.

http://neptune.spacebears.com/opine/horsepwr.html

http://home.earthlink.net/~bubbaf250/specs/specs02.html


Any other thoughts?

Ian_F

yeah, they used to rate the HP at the flywheel, then in 75 I think, the started measuring it at the wheels.

Black363IROCZ

no... SAE net is actual HP measure on a dyno with accesories running off the motor. SAE gross is more or less rated HP without any accesories running off the motor or any load put on it. if an L98 was making 240 HP at the wheels it'd be a high 13 second car lol.

RB83L69

There is no "conversion". The numbers in the 60s and early 70s were sort of somebody's hallucination of what the engine might do in a perfect workd, and have little or nothing to do with how much power the engines actually put out. They're alot like the "525 HP TPI" engines you see on web sites these days; sure the long block might be capable of 525 HP with long-tube headers, no exhaust, a Super Victor intake, no water pump or alternator, race gas and optimized timing, cooling by city water, etc. etc.; not what the engine will do with TPI on it, and installed in a car, with an exhaust system and so forth.

Starting in 72 I believe it was, the "SAE net HP" rating system was adopted. It rates HP and torque at the crank; but with the engine exactly as it will be installed in the chassis. i.e. all emissions devices installed and operating, all non-optional accessories driven by the motor installed and operating (alternator, water pump, etc.), the exhaust system and intake ducting assembled and installed, and measured under certain ambient conditions.

The easiest way to "convert" 60s HP numbers is to forget the factory pie-in-the-sky numbers entirely, and look at modern duplicates of those motors using the same parts, and measure them under the modern ratings system. For instance, the "375 HP 327" heads don't come anywhere close to flowing 375 HP worth of flow, the cam is grossly inferior to modern cams, etc.; that motor, under ideal conditions, will just barely crack 300 HP. When it's actually in a chassis, you'd be real lucky to get 275 HP out of it. Which is still not too bad, it would outrun your typical L98 in a car of the same weight and traction.

okfoz

Not too long ago I was watching TV and they mentioned that ewrly in the 70's, like 1971 or 1972 they changed over from Gross HP to NET HP or something like that, where before they used to rate the Engine at the flywheel and now they rate it at the rear wheels (like stated above)...

I think "Advertised" HP ratings have been Waaaaay wrong for years, take for example the TTA and the GN/GNX etc, they were rated at 240~260 HP when in fact in the REAL world the actual numbers were closer to 300 ~ 350, when you consider that a 89TTA at 250HP is still faster than a 2001 WS6 rated at 325HP.

I think on the 3rd gen firebirds & Camaros inparticular our HP rating is just an advertising gimmic, its probably close, but no two cars will be identical. In 1987 the 350 was rated at 210, and in 88 it was at 225 or so, but there does not seem to be a HUGE 10% performance difference between the two cars.

I think we should rate cars at a 1/4 mile times, my car does 14.5's compared to 13.2's on a newer WS6 is a better compairison to me than 225HP vs 325HP, The PEAK HP is ambuguous...

Another explanation I have heard is HP was rated at PEAK in 1970 and prior, and now it is an average over a range.

I might be wrong on all of this, its just my opinion, and my thoughts...

John

paulo57509

'68 302ci @ 290HP.

RB83L69

They don't "rate" it at the wheels, it's still "rated" at the flywheel.

The difference was that before, the long block was "rated" in pretty much blue-sky mode: let's tweak it out under totally optimum conditions and see what it will do. On a motor stand, the engine doesn't have to drive a water pump or alternator or fan; it can be supplied with cool clean air through a carefully selected stack instead of an air cleaner; the exhaust can be made very nearly ideal; you can play with carburetor jetting and timing curves and whatnot to improve power output, but the motor can't really be run that way in a production car that has to work anywhere from -30° to 110°; there were no emissions devices whatsoever in those days; etc. etc. etc. The modern system "rates" the motor exactly as installed in the chassis: with the air intake as installed, the complete exhasut system as installed, all emissions devices installed and operating, all non-optional accessories (WP, alt, & cooling fan) installed and operating, spark and fuel curves as installed in the production-line vehicle, etc. In other words, it's "blue-sky" vs. "real world".

Some of us don't have to watch TV to know how things are done. And some of use were there when the changeover occurred; we don't have to depend on what we've "heard".

You're right about the numbers being fudged on alot of cars though; especially in recent years, the "ratings" have often been lower than what cars will actually do. "Ratings" are an advertising thing: people who care about it will always go for the higher numbers. But, insurance companies (the ones that insure corporations against liability, for causing wrongful deaths or whatever, not the consumer-level ones) will charge the mfr outrageous premiums on every car with a "rating" higher than some arbitrary HP/lb or whatever; so there's 2 competing concerns that the mfrs have when creating the "ratings". Plus of course, nowadays if a car doesn't produce its "rating" like certain Brand F cars are known not to, massive public furor can ensue.

The 302 is a good example of a car that was underrated for insurance reasons. It probably put out closer to 325 HP in showroom stock condition, before the addition of headers; with headers they were good for about 360 HP without even pulling a valve cover. In years before that, before liability really became an issue, alot of the "ratings" were totally blue-sky, like the 375 HP 327 (about the most egregious example I can think of).

As far as I can tell, on these cars most of the "ratings" are reasonably factual with a few exceptions, notably the L69 cars, which are somehat lower than their performance indicates. The TTA "rating" was probably not too far off of what they did as they came off the production line; of course, as we all know, it takes about 5 minutes to add 50 HP to those, so what you see and hear from people at the track or whatever, or what those cars typically run nowadays, isn't the same as they did when they were showroom stock.

The TPI cars did in fact produce incrementally more power over the years, except for the 305 auto cars; chip programming improved, the dual-cat cars came out, etc.

As far as I can tell the LS1 cars are fairly accurately "rated" too; 365 HP or thereabouts at the flywheel, real-world, should result in 300-310 HP at the wheels after the usual 20% discount, and that's pretty much exactly what they do.

Black363IROCZ

actually, an LS1 puts down about 285 HP at the rear wheels, and around 310-320 is at the fly, my friend's 99 Z dyno'd just that when he was getting a baseline for it.

Guest

I dont know where this rating at the rear wheels garbage came from, and why its still propogated. It's not done that way. Not then, not now.

87WS6

iTrader: (1)

It's my understanding that different manufacturers do it a bit different.

Guest

Maybe other manufacturers use a different standard (though I never heard anyone claim it was RWHP, and why would they), but SAE net is SAE net, its at the flywheel. The test is a process, and its dictated by standards set by the SAE (Society of Automotive Engineers). The test number is probably the J1349 listed on one of the links above.

RB83L69

The last several Dyno Day events I've been at, the LS1 cars were all doing 300-315 RWHP. Right about what one would expect, based on their factory "rating". Of course the ones with lids, exhaust, etc. tended to do a little more than the others; but it was a pretty general trend from all I could see. And AFAIK, in teh factory's literature, that motor has been "rated" at anywhere from 345 to 375 HP over the years, depending on the details; the LS6 is 405 HP. All at the crank.

Why is there some kind of issue about how this is done? like madmax says, there's a procedure and a written standard, and all the mfrs have to follow it, just like all the mfrs of amplifiers have to rate their output power the same way, and all the people who sell gasoline have to measure their gallon the same way, etc. What's so difficult about understanding that? How can there be any argument?

And the same thing goes for the 60s HP "Ratings", which are wildly inaccurate; how can anybody in one post tell us all about how old heads, the one thing above all others that produces HP, are such garbage, and then in their very next post start talking about 375 HP 327s??? That's got to be the poster child for the whole 60s HP hallucination syndrome. (must have been alot of really good acid around Detroit back then) The 375 HP 350 was a whole lot closer to being an accurate representation of the facts, even though it's still known to be over-rated, and yet it's obviously a whole lot more motor. It has the same basic heads as the "375 HP 327" except with some improvements that allowed more timing; a 265° @ .050" solid cam vs. a 221° @ .050" hydraulic; 8% more CID; etc. etc. etc. But if you build one of those motors, or find one, I dare you to get anywhere near as much power out of it as its "rating", as long as it's in showroom stock condition. And it will miss it by even more, if it's in a chassis.

Like I said at first, the only way to "convert" the earlier numbers to ones that actually mean something, is with a dyno.

89cmrodriver

ok my friend has a 68 mustang, its a 289 and he says it came stock with 345 hp? any truth behind that or does it fall in with the "blue sky" numbers?

Air_Adam

Yes, '71-72 was the changeover year.... I know that the 'gross HP' numbers were, well.... alot higher than they really are, like RB said.

My dad had a '73 Z28, and it had the hi-performance motor in it (L82 i beleive) which was factory rated at 250hp. BUT if you look at a '71 Chevy LT-1 motor, the motor is EXACTLY the same, but was rated at 330hp. It was the same heads, cam, carb, exhaut, etc etc....

That shows how fanciful the gross HP numbers were, huh?

Air_Adam

Nope, either someone fed him a line or he's BSing you...

The most any Mustang 289 (except maybe Shelbys) had was 270hp (gross BTW)

SilentBob

Actually a car making 285hp rwhp should be making almost 350 at the crank. Otherwise your loss through the driveline is only about 10%.

SB

Jekyll & Hyde

Not to bring an old post back up...

The reason that a 250hp TTA is able to take the new LS1 engines, is because from the factory the lied. The real numbers were somewhat closer to 300hp, some a little bit more. The factory has to charge more for the more power that is put out. Gas guzzler tax also has a slight factor.

LS1 engines have been under-rated for some time now, however, the f and y bodies only lose about 13%-15% for manual cars. The mustang is about the same, but Ford's auto only loses 18%. Chevy still needs to work at the automatic that they have.

GM didn't need to tell the truth about the higher output that the new LS1 cars had, they were already able to be the mustang; chevy was just trying to keep the prices down for competition.

daniel

1BADDAM

Very true, but the real reason a TTA can run with LS1's stock for stock is the TTA makes way more torque. I had a copy of a fax from PAS, the co. that assembled/tested all 89' TTA's for Pontiac, stating at the wheels 280 hp / 380 tq. 0-60 in 4.6 1/4 13.2 Yet the Pontiac #'s were 250/340. Why the lie ? Can't be more than that years Vette.

FAST RS

Can this be why cars of the 60's pushed allot more HP and then in 72 the HP dropped??? Im [utting a 455 in my 68 firebird and for 72 with everything exactly the same valve size cc it puts out roughtly 220 for the 72 enigne and for the exact same ringe in 71 it puts out 300 which is a big difference. Obviousely my 455 wount be puttin out 220 HP but im just curious if this is the reason why ive been trying to figure this out for months now. Could this be the reason why?

DJP87Z28

Another BIG reason for the drop of HORSEPOWER after 1972 was
EMISSIONS.

Jekyll & Hyde

Exactlly!!! There is a guy across the street that talks up the big blocks and how they were so fast from the factory. He talks hp numbers, but fails to remember what you just noticed.

All engine testing was done with out anything bolted on it. The L98 could have probably been a 300+hp engine if it was still tested in the old way (gross). The SAE net hp is measured with all acc, emmissions, pump gas, and all the parts have to be factory.

When someone tells you that the 427 Vette was badd-*** and the new LS1s aren't, look at the time slips. The new LS1 engines are built correctly.

FAST RS

Now it all makes sence when i found out that my 455 only put out 220 HP from the factory i was shocked then i looked at 71 and it was 100 more HP. I cant wait to get that engine in my car and drive So when im looking at jegs and see a 502 with 585 ft lbs tq and 502 HP that engine was measured the old way at the flywheel??? so in reality it would be around 400 HP with accorserys on?

Air_Adam

Depending on when your 455 was built (and with what parts), it will still be a different engine. 100hp is still a little bit too much difference to be the same engine, but they will be similar.

And yea, thats sorta true about the 502 i guess, since it would have been tested with a different exhaust, headers, no accesories, etc.

FAST RS

Im not too concerned about my 455 it is a fresh rebuild with forged pistons iske cams and springs with 10:1 comp and a built th400 extra clutches trans go compition shiftkit almunium driveshaft just need gears and a paint job and the car will be cherry its a 68 firebird btw.