Delightfull! Sorry about the metrics, people. Just some goround rules.
1 hp is 0.7456 kW(kilo Watt).
1 lb-ft is 1.356 Nm (Newton Meters).
1 pound is 0.454 kg (kilograms).
A tank of gas weighes in at the metric liters times about 0.75, so a US 17 gallon tank is 62.9 liters, and weighes about 47 kg, or around 100 pounds, I think.
Gross is power of engine striped of fan and accesories, rated at a high air pressure, and low temperature.
SAE net or DIN net is rated with all engine bits, and a more strict air pressure and underhood temperatur correction.
For a manual car producing a facory 222 hp. there is 175 hp at the rear wheels (divide by 1.27), and with an auto running warm, no more than 167 hp.
I'd if you say the SAE net flywheel figure looses 1.29 off the peak power level, you'd be close. Tires change rear wheel hp too!
I studied this at from my younger years in 1983, and came up with these conclusions:-
Rule 1:
In the USA, pre 1972, all cars were rated at SAE Gross HP, which was often 16.6% more than SAE Net on a apples verses apples basis, if the car didn't run a pwer steering pump, lower compression, extra emissions gear (like an air pump and/or EGR valve, or an A/C fan clutch or cool air scoop). Since all US 1972 cars were more emissionised than 1971 US cars, the actual SAE net figure was often 20 to 28% less than the previous years SAE Gross figures.
Rule 2:
In Australia, SAE Gross was used until 1977 for Fords, and 1979 for Holdens. These figures were converted to DIN net after that time. SAE Net and DIN Net were different by 3%, with SAE Net under estimating power figures by 3 to 5%. Back to back comparsions couldn't be drawn because there was never an "apples vs apples" engine to compare. A non emission 192 290 hp (216 kW) 351 Cleveland could be rated at an emissionised 216 SAE net hp (162kw) in 1977 with dual exhasts, and or 200 hp DIN net (149 kW) with single exhast. Remember too, that from 1973, Aussie engines had to meet ADR 27, a US 1972 exhast regulation, and the ADR 27A in 1976, which was US 1973, and then ADR 37, which was US 1975. Then just to confuse things furter, the NSW smog Nazi's had more stringent emssion standards than the rest of Australia form 1982 to 1986. And utility vehicles were less emissionised than the passenger cars too! :roll: So six cylinder Falcons lost an unspecified amount of peak power. Man, it gets complex!!!!. The same thing happened in the US, were California has more stringent emission regulations than the rest of the 'States.
Rule 3:
Generaly, US engines like 351Cleveland HO 4V's, 351 Windsor HP 4V's, Chrysler/Mopar 340's, and some302 Chev/Ford combos like the 290 hp Z/28/Boss 302'S were fudged readings were the power figure was taken at a lower rpm rate than where actual maximum power levels were reached. Respectivley, the engines were rated at 330(US Boss 351, but only 300hp Gross in the hotter spec'dsame Aussie Phase 3 GTHO 351!), 290 hp,275 hp, and 290 hp for the Trans Am pny cars. But SAE Gross figures, variously from 1983 Cam Bentys CarCraft(?) magazine, were 380 net, 330 net, 330 net, and about 330 hp net for the early 302 Z/28 and Boss 302's.
This was brought about by the US insurance companies setting 10 pounds per hp as the high insurance premium kick in rate. Hence a 290 hp Z/28 coulsn't weigh in below 2900 pouns, or it would cop a premium slug! So Detroit just took the power figures at 500 rpm of so less than the actual maximum power level, and all of a sudden a base Camaro SS 396 could rate at 325 hp if it weighed in at more than 3250 pounds, and not incur a premium hike. They weren't lying, they were just telling half the truth....
:roll:. (A bit like Bill C!
).
When SAE net figures kicked in, strong engine combos like Super Duty or HO 455 Pontiacs and 351 HO engines lost bulk avertised HP for 1972, but were only about 20 hp SAE net down on there 1971 counter parts, and this was emissions related to compression drop, and the EGR and cool -air induction restrictions which stopped engines running as cool as the 1971 versions.
Go figure this:- The stock hydraulic cammed, Autolite carbed 351C used in the 1971 DeTomaso Panteras had 326 hp DIN net, while the stock 1971 351GT Falcon was rated at 300 hp Gross. The engines were basically the same!
Regarding just looking at torque figures...as
Mustang66stated...they are influenced,as power is just torque in LB-FT times rpm, all divided by 5252. Torque figures between emission and non-emssion vehicles were significant, and it was nothing for a 155 hp, 200 lb-ft 3.5 liter Rover V8 to loose 18 hp (13%) and 27 lb-ft (15%) over the non-emissioned engine. This was just a US 1973 /AD 27A emission compliant vehicle. Compression ratio was lower, carbs were Strombergs, not SU's, and a silly air pump was needed.
99% of all HP lies go away when you rate the two -up, full tank of gas Standing 1320 ft/(1/4 Mile, or Standing 402 m) times with the DIN or SAE net flywheel figure.
Take the power at the flywheel, and plug in the kerb(curb) weight and add two people and a tank of gas. Then divide this by the kw figure. This gives a factor, the weight to power figure. This is multiplied by 325, which is the manual gearbox constant for a sedan with a 0.40-0.45 drag factor and a 24 sq ft or 2.25 m2. (It varies from car to car, but 325 is generally the best.) This then gets the 1/3 root taken, and, bang, the idealised quater mile time comes out. This is very accurate, and is good enough for HP calculation. You can use trap speeds or other methods, but it's just more math. It sucks, but it is the best method that you can use withoput buying a HP program. And HP programs get very theoretical, with diff ratio and wheel loadings, etc.
Tim, here's an example with working.
EG 1: For a
stock Cortina Six with a 2V 250 fitted, with two people and a tank of gas:-
170 hp SAE gross should be about 147 hp DIN net (taking off 17%),which is 109 kw. If the car weighes 1245 kg ( 2745 pounds) at the curb, it would weigh 1445 kg with two people and a tank of gas. So that should give 1445 divided by 109 kW, which is weight to power of 13.25. Multiply by 325, which gives a figure of 4308.5. Take the 1/3 root, and this gives 16.3 seconds.
Drop a 100 kg passenger, and the quater mile drops to 15.9 seconds.
EG 2:So for a 170 HP gross 2v 250 Falcon do to 16 second quaters with even just one person, it would take 153 hp net (about 114 kw) in a 2965 pound (1345 kg) . Diff ratio doesn't influence the quater mile time much.
EG 3:For an SAE gross 290 hp V8 running a 3.25:1, or a 2.75:1, shouldn't make a lot of difference to the actual quarter mile. If its a soft FMX slushbox with a 1650 rpm stall, it will be 0.5 seconds slower than a shift kitted auto or power shifted manual. So for a 1570 kg (3461 pounds) Falcon, the calulation is to drop 17% off the gross rating, convert it to kW, add 200 kg's, and do the math as above. That gives a 14.6 second qaurter mile. In practice, 16.4 seconds two up is 174 horsepower net, or 130 kW. S o a stock 351 Windsor or Cleveland only had 130 kw net, nowhere near 216 kw gross.
EG 4:And a stock 1970 351C 4v HO Mustang with a tare mass of 3461 pounds would have only needed 290 hp NET (216 kW) to do a 14.6 second quarter with two people. Simple. A Moroso/Quarter Mile Jr would say you could do this with about 260 hp net with one person. Who cares the engine may have been rated at 300 or 330 hp SAE gross at 5400 rpm, and up to 380 hp SAE gross at 5800 rpm.
