The truth about horsepower

Chuck

Supporter
In the sixties the Mark I GTs with the 302 typically ran 350 to 375 HP. The Mark II GTs with the 427 typically ran 450 HP. Both could hit 200 mph.

Today 375 HP is considered modest and many reproduction SBF GTs are running 400, 500 or more HP.

So I am wondering, is HP measured the same today as it was in 1965? Is a modern dyno tested engine with that nice torque / horsepower graph showing 400 HP comparable to 400 HP as it was defined 45 years ago?

Something tells me we may be comparing apples and oranges.
 
And is there a difference between USA bhp and UK bhp?

Yes, hence why the Veyron was billed as 1000+hp in NA, but wasn't in Europe. Metric horsepower, as a rule, is defined as 0.73549875 kW, or roughly 98.6% of mechanical horsepower. This was a minor issue in the days when measurement systems varied widely and engines produced less power, but has become a major sticking point today. Exotic cars from Europe like the McLaren F1 and Bugatti Veyron are often quoted using the wrong definition, and their power output is sometimes even converted twice because of confusion over whether the original horsepower number was metric or mechanical.
 

JimmyMac

Lifetime Supporter
Yes, hence why the Veyron was billed as 1000+hp in NA, but wasn't in Europe. Metric horsepower, as a rule, is defined as 0.73549875 kW, or roughly 98.6% of mechanical horsepower. This was a minor issue in the days when measurement systems varied widely and engines produced less power, but has become a major sticking point today. Exotic cars from Europe like the McLaren F1 and Bugatti Veyron are often quoted using the wrong definition, and their power output is sometimes even converted twice because of confusion over whether the original horsepower number was metric or mechanical.

:shrug::snore:

Then perhaps regardless of it's origin, you have illustrated which end of the horse that this power came from ?

I believe that Chuck's point was about gaining 200+mph from the original cars with much lower HP and possibly this thread would get a better outcome in our transmission section.
 
Sorry for responding to Malcolm's question, maybe I was being too quick in reading and missed something (like maybe some sarcasm that I didn't spot).

Now onto another point, and apologies for the thread drift. What exactly caused that response from you? What have I done to offend you at some point? I would normally PM this, but its not the first time you've done this to me (i.e. responded with such short shrift and, in my opinion, quite rudely), so really I would appreciate knowing.
 

JimmyMac

Lifetime Supporter
Brett,

No malice was intended and my response was a reaction to your deviation.
Below is I feel a more apt explanation to your thread drift and Malcolm's question.

BRITISH HORSEPOWER
The acronym bhp may also be used for British horsepower, which has the same definition as the American SAE gross brake horsepower: 33,000 lb·ft/minute. More information on American SAE horsepower measurements is below.
<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com
P><P><B><FONT face=
SAE HORSEPOWER </B>

SAE gross horsepower<o:p></o:p>

Prior to the 1972 model year, American automakers rated and advertised their engines in brake horsepower (bhp), frequently referred to as SAE gross horsepower, because it was measured in accord with the protocols defined in SAE standards J245 and J1995. As with other brake horsepower test protocols, SAE gross hp was measured using a stock test engine, generally running with few belt-driven accessories and sometimes fitted with long tube (test headers) in lieu of the OEM exhaust manifolds. The atmospheric correction standards for barometric pressure, humidity and temperature for testing were relatively idealistic.
<o:p></o:p>
SAE net horsepower<o:p></o:p>

In the U<?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com
><st1:place alt=
</st1:place>nited States, the term bhp fell into disuse in 1971-72, as automakers began to quote power in terms of SAE net horsepower in accord with SAE standard J1349. Like SAE gross and other brake horsepower protocols, SAE Net hp is measured at the engine's crankshaft, and so does not account for transmission losses. However, the SAE net hp testing protocol calls for standard production-type belt-driven accessories, air cleaner, emission controls, exhaust system, and other power-consuming accessories. This produces ratings in closer alignment with the power produced by the engine as it is actually configured and sold. The change to net hp effectively deflated power ratings to assuage the auto insurance industry and environmental and safety lobbies.
<o:p></o:p>
SAE certified horsepower<o:p></o:p>

In 2005, the SAE introduced a new test protocol for engine horsepower and torque. The new protocol eliminates some of the flexibility in power measurement, and requires an independent observer present when engines are measured. The test is voluntary, but engines completing it can be advertised as SAE-certified.<o:p></o:p>
A few manufacturers such as Honda and Toyota switched to the new ratings immediately, with multi-directional results; the rated output of Cadillac'ssuperchargedNorthstar V8 jumped from 440 horsepower (330 kW) to 469 horsepower (350 kW) under the new tests, while the rating for Toyota'sCamry 3.0 L 1MZ-FE V6 fell from 210 horsepower (160 kW) to 190 horsepower (140 kW). Much of the drop can be attributed to <st1:place w:st="on"><st1:City w:st="on">Toyota</st1:City></st1:place> now rating engines on 87 octane, compared to Lexus which uses 91 octane. This is why the same 3.3 L 3MZ-FE V6 engine in the Lexus ES330 and Camry SE V6 did not show equal declines. The ES330 and Camry SE V6 were previously rated at 225 hp but the ES330 dropped to 218 hp while the Camry declined to 210 hp. The first engine certified under the new program was the 7.0 L LS7 used in the 2006 Chevrolet Corvette Z06. Certified power rose slightly from 500 horsepower (370 kW) to 505 horsepower (377 kW).

Ref : Wiki
............................

Now can we get back to the original point ??<o:p></o:p>
<o:p></o:p>
 
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I think there are a lot of factors that you are leaving out.

Firstly, the MkIs that broke the 200 MPH barrier were more likely
breaking the 400HP mark. The Wyer/Gulf GT40s were running
closer to 425HP IIRC.

Secondly, you need to take gearing into consideration. Perhaps with
the correct ratios, we could see more 200 MPH replicas on the right
tracks with the right drivers.

Thirdly, weight. The originals were very light compared to the replicas
we have now. Some replicas have lightweight options, so again,
perhaps the right ones could hit the 200 MPH mark.

Finally, yes, to some degree, HP measured in the 60's and 70's seems
to be somewhat different than as measured now. It seems that the
numbers from the 60's and 70's should be increased somewhat.

Just checked. The Wyer/Gulf GT40s were rated from 425 - 465 HP, and
the 427s found in the MkIIs and MkIVs were rated anywhere from
475 - 550 HP according to the books I have.

Ian
 
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Ron Earp

Admin
Finally, yes, to some degree, HP measured in the 60's and 70's seems
to be somewhat different than as measured now. It seems that the
numbers from the 60's and 70's should be increased somewhat.

Absolutely it was different, as stated in JimmyMac's post just below. Increased? No. The gross ratings from the 60s and early 70 (to 72) were quite grossly over estimated due to the testing procedures.
 
Absolutely it was different, as stated in JimmyMac's post just below. Increased? No. The gross ratings from the 60s and early 70 (to 72) were quite grossly over estimated due to the testing procedures.

Yes, my bad. I meant lowered. Although, it is notable that some 60's era engines were
"misrepresented" as having lower outputs than they really had - like some of the
big block vette 427s.

I just dug up some good info - according to info I found, the ZF in the Wyer/Gulf
cars had the following ratios:

2.23 1st
1.53 2nd
1.21 3rd
1.00 4th
0.81 5th
final drive 3.20:1

I think most of the ZFs and similar gearboxes used these days are running 3.77 and
shorter ratios, which leads to lower top speeds. And, one other important factor,
engine speed. Racing engines will usually turn higher revs than street motors.
The Ford 302 in race trim can easily crack 8000 RPM.

Ian
 
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With respect to gearing:

Note that the actual gear ratios in the Gulf car listed above are very, very short. Fourth gear is 1:1 and fifth is only .81 overdrive.

In a 'normal' ZF, third gear is 1.04, fourth is .846 and fifth is .705.

Multiplying the gear ratio times the final drive ratio gives you the effective final drive. For the top gear comparison, you get this:

3.20 x .81 = 2.592
3.77 x .705 = 2.657

So the difference isn't as profound as it initially appears.

Here's a link to a page that has a great downloadable Excel file. It's a gear calculator that allows you to change the values in green (shift point, individual gear ratios, rear end ratio, and tire diameter).

It's set up with the stock gearing on a typical Pantera ZF gearbox, plus an overdrive 6th gear. But you can put whatever gearing/rpm/tire size you like in, and it will spit out the numbers.

Pantera ZF Gearing
 
Gulf/Jwa had 4th gears with ratios of; 1/1 or 0.96/1 and 5th gears of 0.78/1, 0.81/1, 0.85/1, 0.92/1. 3.2/1 R&P or CWP were used with the 0.81/1 (5th) gearing to break 200mph ( 205 ) on a 302 with GW heads.

Same as using a 2.592/1 Diff ratio with a 1/1 top gear in a normal car.

When you consider Nascar stuff is turning between 8000/9000 on a 355ci to reach similar speeds they were not doing to bad:)
 
No matter what you may read, the correct horsepower rating for any individual
is "enough" to satisfy that individual...

Some more than others.
 
Just a note on the older engines. I was told that, for a time,some of the companies,notably GM,throughout it's divisions,with the exception of the Corvette, had a 'policy' of matching the horsepower ratings relative to car weight, the 10:1 rule. This was done to keep insurance companies and government off their back. For instance, the Chevelle and GTO weighed in around 3600lbs. the horsepower for each,top rated motor was 360. I believe the same engine as the Chevelle, in the Impala,was 385hp. Ford didn't advertise performance,non street motor hp.The high riser,sodium cooled valve Ford 427 was reputed to be around 500hp,the iron head dual quad street model, shown at 425. No back up for these facts,just what was circulated at the time they were popular. So ratings were like TV ads,what ever you wanted to call it.
 
With respect to gearing:

Note that the actual gear ratios in the Gulf car listed above are very, very short. Fourth gear is 1:1 and fifth is only .81 overdrive.

In a 'normal' ZF, third gear is 1.04, fourth is .846 and fifth is .705.

Multiplying the gear ratio times the final drive ratio gives you the effective final drive. For the top gear comparison, you get this:

3.20 x .81 = 2.592
3.77 x .705 = 2.657

So the difference isn't as profound as it initially appears.

Here's a link to a page that has a great downloadable Excel file. It's a gear calculator that allows you to change the values in green (shift point, individual gear ratios, rear end ratio, and tire diameter).

It's set up with the stock gearing on a typical Pantera ZF gearbox, plus an overdrive 6th gear. But you can put whatever gearing/rpm/tire size you like in, and it will spit out the numbers.

Pantera ZF Gearing

While I am not disputing the gist of what you are saying, there are two key points
to remember:

1) Most GT40 replicas are using Renault UN1 boxes, typically R21s or R25s, with 5th/FD
ratios of .82/3.44 or .76/3.78, or they are running Audi 016/01E boxes with 5th/FD
ratios of .73/4.11 or .76/4.11 There are also some running the 016 3U box with
.64/3.89.

2) As far as I recall, the Pantera ZF ratios you list are not the standard ones that
shipped with the majority of Panteras nor ZFs in general. Most of those ZFs, based
upon what I have read, ran .705/4.22 5th/final diffs. Many owners have since changed
to 3.77 diffs.

Multiplying the 5th and FD ratios, and using 7000 RPM and a 27 inch tire height (about
average for the various 15 inch tires), you get the following terminal speeds:

R21 - 199 mph
R25 - 196 mph
3N - 187 mph
3U - 226 mph
01E - 180 mph
original ZF - 189 mph
Gulf ZF - 217 mph
close ratio ZF - 211 mph

So, you can see how much those differences make. And, considering that many
are only pushing 6500 RPM redlines, drop everything down some.

Ian
 
I have read that 1 horsepower is the ability to lift 550 lbs, 1 foot in 1 sec. I believe James Watt wanted to tell farmers how many horses his new steam engine could replace.
 
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