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-datsun 1600-
12-20-2003, 11:42 PM
Ok i want to know how to get the power figure of rear wheel horsepower/kilowatt into crankshaft/flywheel power

i know how to change kw into hp (x the kw by 1.34)

any help would be great guys

fpv_gtho
12-21-2003, 06:03 AM
you cant come up with a formula to compare flywheel and rear wheel power, it depends on the individual mechanics of each car, for instance, motor magazine tested the HSV GTS and FPV GT, the GT is down 10kw on power at the flywheel, yet was 3kw ahead of the GTS at the rear wheels, in the same test, motor i think got different readings for the Monaro CV8 and SS Commodore, which had the same engine

crisis
12-21-2003, 10:17 PM
An approximation can be come to by adding about 30% to the rear wheel figure. All drive lines will take up a different amount of power but that gives you something to work on. Otherwise you will need a engine dyno.

fpv_gtho
12-22-2003, 01:08 AM
30% is usually the worst it gets but, from RWD's with heavy duty drivelines and AWD/4WD drivelines, i think FWD usually gets around 15-20% drivetrain loss

Nildo
12-23-2003, 04:33 PM
People often make mistakes in this area. First, as fpv says, there is no formula for this. Second, the drivetrain makes a massive difference. FWD cars typically experience losses of about 20%, although auto transmissions lose more than manuals. RWD lose (generally) between 20-25%, although some are more. 4WD losses are huge. For example a '96 WRX I was witnessing being tuned began with a rear wheel kilowatt figure of 95 kw. That's a power loss of over 40%.

Also the wheel power figure will be hugely affected by the make of the dyno. For example a dynojet typically records higher figures than a Dyno dynamics. According to Zoom magazine the difference is about 8%, which sounds little, but if you consider a car with 300 kw, 324 kw is much more impressive.

Basically unless you test two cars on exactly the same dyno, in exactly the same conditions (ambient temp, airflow, fueling etc) then two results are not comparable.

crisis
12-23-2003, 04:56 PM
Basically unless you test two cars on exactly the same dyno, in exactly the same conditions (ambient temp, airflow, fueling etc) then two results are not comparable.
If you want to be that fussy , you can not actually get a definitive reading. Only one that relates to a certain set of testing criteria. Whats the point.

fpv_gtho
12-23-2003, 06:22 PM
well yuor never going to really get that accurate going for power at the wheels to begin with crisis, if you want absolute accuracy, rip the engine out and test on the flywheel again

-datsun 1600-
12-23-2003, 09:42 PM
ahhhhhh that explains why some cars which have been dynoed are less than the manufactuer claims

thanks for all the info guys :)

Misho
12-23-2003, 10:21 PM
i hate math

fpv_gtho
12-23-2003, 10:27 PM
yeah me too, but funny enough its my best subject

Egg Nog
12-24-2003, 03:41 AM
ahhhhhh that explains why some cars which have been dynoed are less than the manufactuer claims

thanks for all the info guys :)

Yeah, this makes sense. All cars will produce less power on a typical wheel-driven dynomometer than they will at the crankshaft. However, they will not produce "less than the manufacturer claims" because they manufacturer is only ever claiming power at the crank/flywheel.

fpv_gtho
12-24-2003, 04:10 AM
hows this one then: the april 2002 wheels magazine's feature article was a grey import nissan skyline gtr v-spec 2 n1 vs an hsv gts coupe. thats 206kw vs 300kw. both cars were put on the dyno and they turned out at 214kw vs 230kw.

wheels then went on to guess the flywheel output of the skyline to be over 300kw, as theyve tested a porsche 911 that has gotten less rear wheel power, with only 309kw at the flywheel

performance times severly went the way of the skyline, with 0-100km/h at 4.4 and 5.8 seconds and the quarter mile at 13.9 and 12.7 seconds. braking distances from 100km/h went the skylines way as well, with distances of 35.3m and 40.9 being achieved. some people will probably dispute the skylines 0-100km/h time but wheels noted the N1 had a 1000rpm higher redline than a normal R34 as well as larger garret turbo's pumping out 16 psi, oil cooler and blueprinted engine

Egg Nog
12-24-2003, 04:45 AM
hows this one then: the april 2002 wheels magazine's feature article was a grey import nissan skyline gtr v-spec 2 n1 vs an hsv gts coupe. thats 206kw vs 300kw. both cars were put on the dyno and they turned out at 214kw vs 230kw

Thanks for this... it's good of you to bring up that what I said before is only true when assuming that the manufacturer's specifications are accurate. If so, the WHP will always be less than the said factory crank HP.

fpv_gtho
12-24-2003, 04:48 AM
its still got to be substantially less to be believable though. would you believe a skyline had 206kw at the flywheel if it made 200kw at the wheels, or if it made about 150kw at the wheels

Egg Nog
12-24-2003, 05:00 AM
its still got to be substantially less to be believable though. would you believe a skyline had 206kw at the flywheel if it made 200kw at the wheels, or if it made about 150kw at the wheels

You do realise I'm agreeing with you, right? I have been the whole time... :)

I definately would not beleive that a Skyline making 200kw at the wheels would have so little as 206 crank hp, hence what I said about manufacturers claims. In the case of this Skyline, it seems that Nissan's claims would have to be much less than the truth. Heck, if you've got a national standard 280hp limit to deal with, that seems like the best way around it!

fpv_gtho
12-24-2003, 05:07 AM
yeah i know we're agreeing with each other, im just strengthening the argument as much as i can.

last i heard, japans limit was 276hp/280ps/206kw, yet theres still the EVO8 lancer sitting at 202kw and the WRX STI at 195kw

NoOne
12-24-2003, 05:30 AM
Back in the early '70's American car manufacturers were getting a bad rep from insurance companies about the HP figures for the cars, so to get around it they posted HP figures at a certain RPM, IE: Chrysler 426 cid Hemi rated at 425 HP at 4500 RPM actually made closer to 500+ at 5800 RPM, it did in fact make 425HP at that RPM... but that doesn't mean it was the "peak" HP.;)
Ford and GM also did this, I'm not sure who started the trend though. Could it be possible that Japanese manufacturers are adopting a similar "half-truth"?
:confused:

fpv_gtho
12-24-2003, 05:41 AM
well the r34 quotes power at the same revs as the R32 i think but with a higher torque figure at a higher rev

Nildo
12-26-2003, 04:26 PM
Crisis, you are right, it is near impossible to get an exact reading. Why do you think people can't just show up at Summernats HP heroes and wave a dynograph for their car. Beacuse they need to be on equal footing! That's also why there were boost restrictions, fuel rules and so on. For each individual car, the crucial aspect to performance is wheel power, but for the sake of direct comparisions engine figures must be quoted as they can be determined with a little less fuss for a manufacturer.

Also FPV the GTR produces well over 206 kw. The R32 produces a claimed 206 kw. Then the R34 is aslo claimed at the same figure. Yet peak torque had risen by 39 nm, and at 500 rpm higher! Most engine dyno's place the standard R34 at about 230-240 kw, with the N1 being, as you spotted, a greater still. And they have no problem murdering a GTS.

fpv_gtho
12-29-2003, 07:35 PM
well so far the japanese government is turning somewhat of a blind eye to it all and just paying attention to whos claiming more than 206kw but in the next coupe of years, with the R35, new RX-7, possible new supra, new NSX all set to aim for 300kw (250 for the RX-7) the japanese government is going to have a heart attack

Nildo
12-30-2003, 01:44 PM
The power cap was never actually a law though, just an agreement between the manufacturers and the government. I think that the Japanese government probably realises now that to remain competitive in the automotive industry they need to raise the stakes somewhat. 206 kw was plenty in an r32 GTR but these days you plain and simple need more.

HoldenHFV6
01-02-2004, 05:25 PM
Each car company has their own standard for measuring how much power a car has. There are 5 main standards that are used world wide. These are:

EEC: European standard. Measure at 99kPa and 25°C. Rated in kW.
SAE: American standard. Measure at 99kPa and 25°C. Rated in hp. 1kW = 1.341hp (SAE).
DIN: German standard. Measure at 101.3kPa and 20°C. Rated in hp (ps). 1kW = 1.360hp (DIN).
JIS: Japanese standard. Theoretically same as DIN, but we always find it is actually smaller.
British horsepower: same as SAE. Rated in bhp (could be confused with brake horse power).


Holden uses the EEC standard whereas Ford uses the DIN standard. You can see that ford tests are conducted under a richer (ie more dense) air flow.
In other words, you can't really take figures from a manufacture and compare them. For examples, the HSV R8 has 285Kw but that is equal to 292 Kw DIN. So does that mean that the R8 is more powerful than the 290Kw FPV? As the others have been saying, put them against each other on the same Dyno in the same conditions.

Egg Nog
01-02-2004, 06:08 PM
Each car company has their own standard for measuring how much power a car has. There are 5 main standards that are used world wide...........

Awesome post, and thanks for clearing all of this up. +1 reputation for you :)

HoldenHFV6
01-02-2004, 09:14 PM
Sorry made a mistake. It's not EEC but ECE (European Commision for Europe).
It may also be of interest that Holden uses ECE standard for local products but uses the SAE standard for American products (The GTO). The key difference lies in that ECE includes the parasitic losses from the power steering pump and alternator while SAE doesn't. Holden does not use DIN because it believes the exclusion of relative humidity of air make results unrealistic.

Nildo
01-09-2004, 02:35 AM
Motor magazine did do a dyno (same day, same conditions) test between 6 models of V8 holdens and the ford XR8, XR6 T and GT. I don't know if you saw that. It was before the advent of the 285 clubsport, but the Falcon on the day outdid the GTS, with 222 rear wheel kilowatts to the GT's 225. The GT won the day over all the Gen III's. For comparisons sake, the worst of the lot was the caprice, with (despite having 245 kw claimed at the flywheel) only 156 kw. Pretty ordinary for all that cash, huh?

fpv_gtho
01-11-2004, 02:59 AM
well in all honesty there were some flaws in that test, i think it was between the equally powerful SV8, SS and CV8 that they got 2 power readings so perhaps something affected the GTS and GT's power outputs as well

Nildo
01-12-2004, 04:17 PM
Actualy FPV I don't think so. There are anomalies in dyno testing which means that two runs in the same car, all other things been equal will always yield a minor difference in figures. Also remember that different cars do put out marginally different outputs regardless of having the same engine. Some are simply better built.
Also bear in mind that the Falcon may have a better driveline, reducing losses and increasing power at the wheels.

crisis
01-12-2004, 05:41 PM
Each car company has their own standard for measuring how much power a car has. There are 5 main standards that are used world wide.
Brilliant! A factual conclusion to a subject that has caused much conjecture. Reputation points are clearly in order.

crisis
01-12-2004, 05:43 PM
One reason mass produced cars will give varying results is because they are mass produced. I beleive a blue printed motor should almost always give a consistant result.

fpv_gtho
01-12-2004, 07:09 PM
Actualy FPV I don't think so. There are anomalies in dyno testing which means that two runs in the same car, all other things been equal will always yield a minor difference in figures. Also remember that different cars do put out marginally different outputs regardless of having the same engine. Some are simply better built.
Also bear in mind that the Falcon may have a better driveline, reducing losses and increasing power at the wheels.


well perhaps because the BOSS290 is hand built its helping its cause

crisis
01-12-2004, 11:51 PM
well perhaps because the BOSS290 is hand built its helping its cause
I dont think it is actually hand built. It may have the different components that are sourced from different places bolted together off the assmbly line but it would not be possible for any manufacturer to cost effectively hand build a motor. In any case being hand built does not mean it is blueprinted.

fpv_gtho
01-13-2004, 12:33 AM
well they (FPV) put all the different components of the BOSS V8's together by hand so thats close enoguh to hand assembled for me. FPV get the blocks and heads from overseas and everything else is put on by hand, theyve been doing it since about 2000 on the XR8's and about a year and a bit earlier than that for the TS/TE50

crisis
01-13-2004, 05:04 PM
My point is that unless a motor is built to the exact blue printed specs, it will probably give various readings. To do this every port valve seat, bore piston , crankshaft, mainshaft, flywheel etc must adhere to the exact weight, shape and size as the prototype. That is hand built.