A Horsepower question

Posted: Wed Apr 03, 2013 1:06 pm

Is there an easy way to release the 10 or so Horses that got locked into the stable on the North American version of the CB900F?
I read in the FAQ section Euro bikes had 95 Hp vs 84.. Question

SoupD

Posted: Wed Apr 03, 2013 2:09 pm

The difference is more in how the power was rated than anything else.....
As far as I know there were few, if any discernable changed between the two models.

It is not easy to get 10 horsepower out of a stock DOHC engine.
A 900 with CR carbs (direct lift) a High Quality pipe and cam degree might
eek out 95 horsepower from a bone stock unit....but obviously the Euro
bike didn't have these items.

Euro bikes I believe were rated DIN, U.S. is SAE bhp....the EURO numbers
are always higher using these standards.

Jebby

Posted: Wed Apr 03, 2013 2:13 pm

Buy a VFR. 105 HP 800CCs

Posted: Wed Apr 03, 2013 7:10 pm

Jebbysan wrote:

Euro bikes I believe were rated DIN, U.S. is SAE bhp....the EURO numbers
are always higher using these standards.

Jebby

Jebby, I think this may be the other way around. The DIN standard requires all accessories that are mounted to the engine to be included during the performance test. SAE requires only those that are necessary for the engine to run. This, for example, eliminates the alternator during SAE rating. As far as I remember, the automotive SAE hp numbers were always higher than the numbers according to DIN.
One other difference may be caused by stating "crank" vs "rear wheel" horsepower. As horsepower numbers were not given anymore by manufacturers for bikes in the U.S. since the late 70s/early 80s, most numbers were based on dyno runs by testers and were rw horsepower.

Posted: Wed Apr 03, 2013 7:25 pm

DOHCRob wrote:

Jebbysan wrote:

Euro bikes I believe were rated DIN, U.S. is SAE bhp....the EURO numbers
are always higher using these standards.

Jebby

Jebby, I think this may be the other way around. The DIN standard requires all accessories that are mounted to the engine to be included during the performance test. SAE requires only those that are necessary for the engine to run. This, for example, eliminates the alternator during SAE rating. As far as I remember, the automotive SAE hp numbers were always higher than the numbers according to DIN.
One other difference may be caused by stating "crank" vs "rear wheel" horsepower. As horsepower numbers were not given anymore by manufacturers for bikes in the U.S. since the late 70s/early 80s, most numbers were based on dyno runs by testers and were rw horsepower.

I think you are right Rob......I do have it backwards....and your anser explains exactly the missing 10 horses....

Jebby

Hawk Joined: Jun 11, 2007 Posts: 349 Location: NV

SAE Gross = Engine only, no accessories (ie: outside coolant, alternator, etc.)

SAE Net = All standard accessories as included in a stock vehicle (ie: alternator, water pump, A/C if equipped, etc.)

aa

Twinstar Joined: Jul 24, 2012 Posts: 94 Location: uk

Interesting little add-on to this thread.........
I had a misfire on my 900 when I first got it(fixed after ultrasonically cleaning the carbs) and one of the first things we did in the diagnosis was a dyno run. This gave 78hp. Wow! Where are the missing 17hp from the 95(UK) quoted? I was saved from huge expense/time/worry when I found a bike test in one of the many ebay magazine purchases I made which showed(on their dyno test) that the 'at the wheel' figure when new was......... wait for it.......81hp. All concerns dealt with just with a little extra info. Not sure whether SAE or Metric but it was the relative figures that were important.

Hawk Joined: Jun 11, 2007 Posts: 349 Location: NV

Everyone rates at the crank if at all possible...however efficient the drivetrain may be you still lose power and end up with a lower number. Likely Honda did the same thing here; advertised 95hp, while failing to mention that it's a crank figure that you will never see in a real world environment.

aa

Posted: Thu Apr 04, 2013 11:33 am

Every internal combustion engine has a deviation from "nominal" power due to tolerance in parts. That's why racers "blueprint" engines. Usually the tolerance is around 5%.
That means, a nominal 100 hp engine may have only 95 hp. If you would buy 10 brand new bikes of the same model and dyno them, the results would be all over the place.
In any case, what does a difference of 5 or 8 hp at that level (9,000 rpm) matter? Horsepower is the parameter that enables a vehicle to sustain a certain speed. Horsepower is calculated from measured torque and rpm. For a "seat-of-the-pants" feel it is irrelevant.

Posted: Sat Apr 06, 2013 12:14 am

Horsepower vs drag determines a bikes top speed and horsepower vs mass is what determines it's acceleration. Despite the internet ramblings you read, torque at the crankshaft means nothing without considering the rpm at which it is developed. If torque was all that mattered and HP didn't then a 600CC sportibike wouldn't dust a cruiser while only producing a third of the torque. Torque at the rear wheel is what accelerates the bike and that is crankshaft torque multiplied by the drive train. The higher your motor can rev, the more you can multiply the crankshaft torque.

Posted: Sat Apr 06, 2013 1:10 am

for whatever its worth, I ran my 900 (930)on a friend's
Dynojet dyno out of curiosity for what the rear wheel #s
were. my gearing is very close to stock, if that matters,
and at 9500rpm it made 96hp and peak torque came
7000rpm, 68ft/lbs. on a different dyno with a different operator I could get some variation but his numbers
are good enough for me to get an idea of where it is !

with an empty fuel tank it weighs 485 lbs. now I need to go
on a diet or all this for nothing ! Sad