Topic: Crank hp vs rear wheel hp

[PeWe]

I have often had thoughts about crank hp when I know the whp after dyno.
Just to compare with other old bikes that has crank hp specified, not whp.

Found Honda Fireblade data:
A retuned engine which now produces a claimed 189 hp (141 kW) and 153.2 hp (114.2 kW) at the rear wheel.

This gives: 189 crank hp = 153 whp.
Crank hp x 0.81 = whp
whp x1.235 = crank hp

I guess a CB 750 has not much different losses in the transmission with chain. (Primary chains might add up some?)

So if a bike happen to have 100whp,  123.5 hp crank hp
104 whp means  128 crank hp
106 ....... 130.9 crank hp

80 whp as my 836 = 98.8 crank hp 

(It ran like the Kawasaki 1000J and similar 100hp limited bikes here in first half of the 80's.
(Some torque missing due to displacement, visible with passengers)

My stock K2 with K7 pistons for higher compression and Yamiya no number 4-4.
58whp ---- 71.6 hp

67hp - 54.27 whp
63 hp - 51 whp

[Jerry Rxman Griffin aka MuthaF'er]

I had always heard that there was an approximate differential of 15% for a good rule of thumb

[PeWe]

Same here.
These numbers about the Fireblade indicate around 20% difference.

[gschuld]

While we are at it, many vintage high performance dyno numbers were from engine testing/R&D dynos.  Like what Muzzy, Yoshimura, and others used exhaustively to develop their engines.  These ran a chain off the output what to a resistance brake of some sort.

So there would be primary drive and transmission losses, but not drive chain/tire slippage losses one would find on a chassis dyno.

Any idea where that rated output would fall?

[scottly]

The rated "crank HP" of our 750's was 67 HP, but there is no way to directly couple a dyno to the crank, so we must rely on the manufacturers claim. It seems most dyno tests of stock bikes put the rear wheel HP at around 55, so figure about a 12 HP loss. I think it would be more or less the same loss even with an increase in HP, rather than a percentage of any increase, as some of the drag in the trans is spinning gears meshed together with no load on them. There is supposed to be a way to measure the "negative HP" on the Dyno-jet dyno, but I think you have to shut off the ignition while at high RPM, and I didn't want to wash all the oil off the pistons with gas, as the carbs don't know that the ignition is firing.

[johno]

Yeh its a big loss allright, most people talk 15 to 20 %.  there are so many variables nothing is absolute on any dyno measurement . The only way you can be reasonably accurate when measuring a performance increase is to use the same dyno and all relevant parameters the same and even then its not 100% accurate in measuring the change. I remember on a previous thread about the CR 750 HP claims by different folks,  the Honda factory and Yoshimura numbers were all over the shop and we couldn't even identify the different dynos used by Honda and Yoshimura apart from the Yoshy unit pops used which was a homemade chain drive from output sprocket direct to the water pump drive.  I am aware that was a common type of dyno in the late 60's and 70's in the Japanese factories and also in the USA in the good ol days when we were all young. They were easy to make, cheap and popular.  Most of the numbers tossed around from that era were from such dynos, engine sprocket driven pumps or roller driven pumps and the result of that is none of those numbers are relevant these days. Dynos were invented to compare runs and apply load for tuning purposes , save time, hang oscilloscopes and exhaust sniffers etc, very convenient without getting booked on the road tests. Although back then I bought a small oscilloscope and exhausted gas analyser , had no dyno so I rigged up a milk crate to hold all the gear in and out the road, worked well except depended on the weather.
But back to the numbers, I guess with our old jiggers it doesnt really matter unless your competing in a race against somebody in the same class and then it doesn't really matter what the numbers are, only the change in numbers when tuning.
 Its good that way as its easy to bull#$%* at the bar  .     

[Old Scrambler]

The Big White Dyno near Wendover, Utah, tells all and gives out a printed time-slip to hang on the wall

[MRieck]

I used the asphalt dyno at an international BMW meet in Connecticut about 20 years ago. 2 AM with the mighty FJ1200.

[johno]

Nice one Mike, your my kind of man 
20 years ago every day was an amazing adventure,

[johno]

speaking of dyno's and numbers I got to get something off my chest regarding the CR 750 numbers that are claimed by Honda and others.
So first Honda, With the CR kits there was a choice of 3 camshafts ( Daytona , TT etc ) and they were rated at different HP from low 90's to 97HP, the factory always made HP claims as it was a good marketing tool as do manufacturers today, nothings changed. Most blokes who who hot rod the SOHC are trying to replicate those numbers on modern electric drum dynos and Im saying the numbers prove that all the Honda and Yoshy numbers are crank numbers and you will not achieve them with a 61mm bore on a drum dyno period.  The HP number that has always interested me was Mark from M3 who claimed that he got 97 HP. ( coincidence the same number the factory claimed) and on one occasion he claimed momentarily got 100 HP (also coincidently 100hp being a holy grail number) So according to my theory that was an impossible claim if he was using a drum dyno.   There are not many tuners even in the US that use crank driven dynos because there is not much customer demand, Ive seen some nice ones though and super flow amongst others have sold some nice ones. The best crank driven set up Ive read about is the Vance and Hines facility, that would probably produce a 61mm bore SOHC 97HP. BUT not a drum dyno.
People on this forum are building engines that are as good or better than the factory CR 750 engines.

To make the point if someone could build a 97 HP 61mm bore SOHC on a drum dyno I will fly to US, observe the dyno run, confirm the bore size then buy the engine at a fair price.

[PeWe]

What about Honda's specifications and other bike's factory specifications?
They must have a specified procedure to measure the engines.

The relation I found match the numbers often written that a good stock Honda CB750 can reach on the wheel. 54-55whp, spec 67hp.
So when a bike is modified or not, dyno run done. The formula based on the Fireblade numbers can show a calculated crank power from Dyno whp.

When tuning the engine it is interesting for me to see at which level the bike has reached comparing the power with other stock bikes 
- As a magazine once wrote, "Taking it into the 80's".

Different dynos, different days and different numbers on same dyno, same day.
DIN,  SAE or STD.

I have charts from one dyno run in all these 3.
DIN and STD equal
SAE chart show almost 3% less.

My last run last year, 970cc
104.29 whp  DIN
101.26 whp SAE.
The dyno guy prefer the SAE numbers.

I understand that racing guys focus on correct AFR and needed power curves, better than same engine or bike has done before.

The final result is time, when crossing the finish line, hopefully before the other bikes, right?

[PeWe]

About other numbers.
I know one guy with a CB750 vintage racer.
 62mm JE pistons with good compression, chambers match the crowns, 34/28 5mm stemmed valves, Norris RX2 cam, CR31 carbs. Vance & Hines 4-1.
86whp on dyno that might be happier horses. A few less might be more correct, not more.

Another impressive number is Mike's 915 setup that reached 98whp.
If that was CycleX 67.5mm pistons they sell as 915cc kit and stock stroke very impressive!
67.5mm bore, 63mm stroke and 4 cyl make 901.75cc according to the volume formula.
902cc and 98whp a goal to at least come close!
Streetable and std fuel if I remember correctly.

Playing with numbers..
Increase 901.8cc and 98 whp by +10%  gives:
992cc and 107.8whp.
970cc is +7.5% --->105.4whp
1005cc +11.4% ---->109.1whp

Feels like possible goals on tap fuel

I do not want to do as a friend that bought a Honda cheap with stock engine that had 133whp for same money as my TMR carbs with filters
The hardest work he did on that was oil change and adjust drive chain.

CBR1100XX -97 (fairings removed, light "streetfighter" mods) very smooth behavior. Started like a car, throttle respons light and easy.
6 gears a good one, should be a good mod on a CB750.

Stock CV carbs probably the reason of soft convenient throttle response.
Keihin FCR must change that!

[bear]

Yeh its a big loss allright, most people talk 15 to 20 %.  there are so many variables nothing is absolute on any dyno measurement . Its good that way as its easy to bull#$%* at the bar  .     

Very true Johno,
I posted a copy of a dyno sheet here many years ago. We wanted to have a baseline for one of our early Hy-Vo engines.
So we loaded up the bike and drove the  six hour's down to Melbourne to run it on the dyno of a respected engine builder that many of the top sidecar racers use.
As I said we used those results as a baseline, came home and ran the bike on a friend's car dyno using the exact same setup on the bike.
There was a significant difference in the results but we could extrapolate a solid baseline using the Melbourne dynos figures.
So every engine we built or rebuild got tested on that car dyno and the results got recalibrated using our original baseline.
Not an exact science by anyone's yardstick but it served us well for many years.

[scottly]

DIN horses are smaller than SAE: 736 watts, vs 746 watts, IIRC. Also, the different correction factors use slightly different formulas to combine the effects of atmospheric pressure, temperature, and humidity on measured output, with atmospheric pressure having the greatest. Ideally, the same bike on the same dyno would give the same corrected HP at sea level as well as at 5000' elevation; this is what correction factors are for, to attempt to "level the playing field", so to speak.

[johno]

Cheers Scotly, can't wait to see how things pan out with Dennis, looking forward to it, kinda wish I was there to help play, its always quicker with jet changes etc , many hands make light work they say and Dennis will be like an old hobbling cripple 

[johno]

Why are you taking so long to Bite Dennis ? 

[Old Scrambler]

I'm Biting

Now in Phoenix.................One blow-out but I changed it myself.........even though I am 'crippled'

Regarding 'old'...............I won't turn 75 until late April

I expect to see Scottly on Tuesday now that I have some new tires on the RV and have parked most of our 'kit' in the garage at Carol's cousin's house.

[scottly]

Keep an eye on the weather, Dennis. Tuesday may or may not be a good time, weather-wise. Last Sunday and Monday it was 69F, and Thursday morning there was 1/2" of snow that turned out to be more like small hail. One report said "North AZ" might start having weather from this next system as soon as Monday, and another said late Tuesday. How long were you planning on hanging around PHX? Are you now a Snowbird?

[Don R]

  I had guys doubt my 684 horsepower 383 small block (hot dyno, blah blah) until I showed them the 8.0X time slips from the concrete and asphalt dyno. It did eventually run a 7 but I had to spray it with N02. A smaller slick probably would have done it too.

[PeWe]

High numbers are not unusual today.
Just buy you a Dodge SRT Demon, a little bit updated byond its powerful stock spec.
Perfect ride for shopping or getting a tasty burger somewhere, real fast food!
http://hennesseyperformance.com/vehicles/dodge/2018-dodge-challenger-srt-demon/hpe1000/

Silent battery cars..... Hell no!!

[Tracksnblades1]

The rated "crank HP" of our 750's was 67 HP, but there is no way to directly couple a dyno to the crank, so we must rely on the manufacturers claim. It seems most dyno tests of stock bikes put the rear wheel HP at around 55, so figure about a 12 HP loss. I think it would be more or less the same loss even with an increase in HP, rather than a percentage of any increase, as some of the drag in the trans is spinning gears meshed together with no load on them. There is supposed to be a way to measure the "negative HP" on the Dyno-jet dyno, but I think you have to shut off the ignition while at high RPM, and I didn't want to wash all the oil off the pistons with gas, as the carbs don't know that the ignition is firing.

Scotty,

Is 55hp a good number.

 I have a 76f, yoshimura 4/1 everything else stock, k&N pods (yeh I know “properly treated dirt”)
jetting 1970 specs. Never Dynoed.   It will literally smoke a 2001 Honda CR500 that I know lays down
53hp at the rear tire, weighing in @ 225lbs plus rider.  Sitting basically on the Cr5’s handle bars, at a rolling
10mph, the race is over in first gear as soon as the 76f climbs on the Yoshi… from there on it’s not even a race…

[scottly]

Scotty,

Is 55hp a good number.

 I have a 76f, yoshimura 4/1 everything else stock, k&N pods (yeh I know “properly treated dirt”)
jetting 1970 specs. Never Dynoed.   It will literally smoke a 2001 Honda CR500 that I know lays down
53hp at the rear tire, weighing in @ 225lbs plus rider.  Sitting basically on the Cr5’s handle bars, at a rolling
10mph, the race is over in first gear as soon as the 76f climbs on the Yoshi… from there on it’s not even a race…

You're funny! I have an '82 CR480, with a claimed 51 at the crank and a dry weight of 227 pounds, and by the time your 500 pound 750 got out of 1st, the 480 would have been in 4th going 70-80 MPH. There used to be a guy here with a CR500 drag bike nicknamed Chainsaw, but sadly he passed..

[Tracksnblades1]

Scotty,

Is 55hp a good number.

 I have a 76f, yoshimura 4/1 everything else stock, k&N pods (yeh I know “properly treated dirt”)
jetting 1970 specs. Never Dynoed.   It will literally smoke a 2001 Honda CR500 that I know lays down
53hp at the rear tire, weighing in @ 225lbs plus rider.  Sitting basically on the Cr5’s handle bars, at a rolling
10mph, the race is over in first gear as soon as the 76f climbs on the Yoshi… from there on it’s not even a race…

You're funny! I have an '82 CR480, with a claimed 51 at the crank and a dry weight of 227 pounds, and by the time your 500 pound 750 got out of 1st, the 480 would have been in 4th going 70-80 MPH. There used to be a guy here with a CR500 drag bike nicknamed Chainsaw, but sadly he passed..

Indeed,  perhaps you and your son can do the same with your 480..?
But then your 480 would probably do the same to a CR500.
76f 18T/45T  130/90/17 metzler
01Cr5 15T/48T 120//90/18 mich starcross (and it'll pull them as fast as you can shift them).

And my son's 14/cb1100 will out run the 76f as bad as f does the CR5.

[scottly]

76f 18T/45T  130/90/17 metzler

18/45 is gearing for the salt flats, not roll-on drag racing.

[dragracer]

Scotty,

Is 55hp a good number.

 I have a 76f, yoshimura 4/1 everything else stock, k&N pods (yeh I know “properly treated dirt”)
jetting 1970 specs. Never Dynoed.   It will literally smoke a 2001 Honda CR500 that I know lays down
53hp at the rear tire, weighing in @ 225lbs plus rider.  Sitting basically on the Cr5’s handle bars, at a rolling
10mph, the race is over in first gear as soon as the 76f climbs on the Yoshi… from there on it’s not even a race…

You're funny! I have an '82 CR480, with a claimed 51 at the crank and a dry weight of 227 pounds, and by the time your 500 pound 750 got out of 1st, the 480 would have been in 4th going 70-80 MPH. There used to be a guy here with a CR500 drag bike nicknamed Chainsaw, but sadly he passed..

That CR500 has been resurrected by a fella out of Tennessee.  It'll be showing up in the SDBA series and then a few of the Cup races in super eliminator.  Rest in peace Keith LeBlanc, see you on the other side my good friend.