Dyno results. Wheel HP vs Calculated Flywheel BHP

Richf · Post by **Richf** » Sun Feb 11, 2007 4:58 pm

My 2 cents worth

When i used to dyno my dragbike it was on a rolling road and that worked in the usual way of calculating resistance on the run down to provide a flywheel (or crank) figure . The problem i had was sticky tyres in my case slicks, so the first run came out pretty high (in the opertaors opinion) and subsequent runs after the tyre got warm often sent the calculations into error and aborted the run losing any data. I took 18 runs to get a decent one out of the dyno and truth be told i wasnt interested in the figures just the afr and a nos test.

Fast forward to buying my Skyline and the car came with a dyno sheet but it stated on the sheet the drag output was 75.5hp which was very high imo for a rwd car after a few mods and the car was taken to the same dyno and the drag was 72.5hp

Apart from the changes to the engine i had actually fitted better tyres going from some crappy 235 dunlops to 255 toyo proxy's so i was expecting the drag to go up if anything.

My last dyno run was on a hub driven dyno and the graph in comparison is much smoother , unfortunatly the figures are lower so you do lose on the bragging rights

, but i have to say i do prefer this type , anything which can increase repeatibility has to be a good thing , the more variable you can eliminate the better.

As a last comment i have a mate who owns a bike dyno and he did say he had had a few customers ask him to alter the parameters on the dyno to give inflated figures if they were selling the bike or simply wanted bragging rights

So as a tool to dianose faults and to establish an engines performance they are great but the figures should only be compared on the same car . Comparing different dynos figures is a waste of time IMO

frayz · Post by **frayz** » Sun Feb 11, 2007 5:06 pm

I say let the car do the talking on the road/track/strip.

Use the dyno for testing only.. and pub bragging.

Post by **Stuart** » Sun Feb 11, 2007 5:14 pm

Valid points about repeating the figures Rich. We did loads of runs with mine on Wednesday and the first 5 runs were all within 4bhp of each other. Measurement and tuning are great with a dyno, but it's not the be all and end all......on that we all agree :thumb:

sleepyhead · Post by **sleepyhead** » Sun Feb 11, 2007 6:04 pm

Brilliant replies

Thanks for everyone's input.

I'm walking away a much wiser person (and not to rise to the bait of talking dyno results/validating dyno results).

I'm just gonna go with by Butt-dyno-meter...right now it's quick enough for me! :lol:

At least this thread has assured me that the people questioning the dyno results are looking to either take the poster down a peg or two or want to seem to look as if they are all knowing and all powerful.

Bladerider · Post by **Bladerider** » Mon Feb 12, 2007 5:34 am

Its a fascinating topic,

If you can get all the testosterone out the air first !!!

Personally I follow the argument that the best kind of dyno has minimal losses between the engine and the dynamometer - so a dyno cell would be ideal. Then a hub dyno as this gets rid of any tyre slip, and then lastly a normal "rolling road" type dyno. That being said all dynos have one major achilles heel - they require a human to operate them, which means that there is then room to lay blame that the operator had another agenda, runs were not comparitive and so on. There is also the fact that so many external factors actually alter the performance of the engine in the first place, so this also rather puts the mockers on the "my cars more powerful than your car" debate that dyno results usually generate.

Frankly they are best as a "guide" and people take the readings as such and more importantly use them as a comparitive on the same vehicle during the same session to compare diferent setups to see which is best.

In my opinion their principle use is to save the lives of the tuners !!!!

Richf · Post by **Richf** » Fri Mar 09, 2007 12:14 pm

I will add the guy who used to build my dragbike engines is a long time drag racers and bike builder, his opinion was that dynos were largely a waste of time, he says "I dont care what horsepower it has on a piece of paper but only how fast it goes"

He has a point though , if the only information you get from the dyno is a horsepower figure the whole proceedure is pretty pointless.

Using one to check a map, draw a boost graph, calculate afr's or simply play with settings does save an awful lot of time though

Bladerider · Post by **Bladerider** » Fri Mar 09, 2007 5:24 pm

Sorry to sound very abrupt,

But that is a very "old school" and frankly outdated view, usually cooked up by people who dont have true knowledge in the sense of the word but probably tons of experience. Thats not to say they dont know their onions, but if you asked them to calculate rod specs to allow a certain maximum piston velocity for a given application would probably just saunter off down the pub saying they could "build it in their sleep".

Whilst I agree that "the black dyno never lies" it is also true that a dyno operated by someone who knows how to use it is a devastatingly useful tool. Im sure the man who doesnt care what the horsepower is certainly cares when another competitor passes him when he drops off boost changing gear. The only piece of information from a dyno NOT worth printing is the Ma HP figure, all the rest is worth its weight in gold.

J.

Richf · Post by **Richf** » Fri Mar 09, 2007 5:56 pm

I think you are missing the point , you couldnt be more wrong

You might say its old school but the guy has more skill than most of the tuners of the jap stuff that are around , he makes his own copies of the Suzuki engine cases for example and sells them to the US. What he doesnt know about enginnering isnt worth knowing , my experience of car tuners is that they have little idea about building an engine from scratch they simply fit what everyone else uses.

He builds cranks for 99% of all the Suzuki EFE and Kawasaki z1000 riders of all disciplines not just drag racing.

He built this bike from scratch http://www.thefang.co.uk/branch.htm 99% of which is home built including the fuel injection system.

The standard motor produced around 80hp , judging from his times on the strip 7.23 it must be around 400hp now, the bike lauches very hard 1.0 60fts !!

I'm not saying dyno's are worthless and neither is he but you need to take the comment from someone who has over 40 years of experience of DRAG RACING .

Dyno figures mean nothing in comparison to performance and big numbers on a piece of paper do NOT mean good performance in the 1/4 mile .

His point is that dynos dont tell you the whole story you only look at one part of the whole package, the only way to test the whole package is on the strip

Bladerider · Post by **Bladerider** » Fri Mar 09, 2007 6:27 pm

I am quite happy to be wrong in your eyes.

If I wanted to live my life on the advice of a 40year experienced bike engine builder then I would be devastated, but I believe in the evolution of things, and therefore am ready to accept the notion that perhaps a dyno isnt just about giving you a single parameter - which is like to keep saying. Perhaps I believe the other things a dyno can help generate are not just useful time savers but very important information that is helpful when not just winding the throttle fully open for 7.23 seconds of single vectored performance.

I didnt know that a discussion about dyno's was decided by a man who knows a man who fabrictates metal to an incredibly high standard !!! :P

Shame - as I was in pretty much total agreement with your first posts which seem at odds with your latest two !!

Oh and I dont for one second believe that the new trend of modern "tuners" who in the main get others to do their work for them and then stick their sticker on it to help maintain their existance know much of anything worth hearing either. Hence why people like Abbey and GBH get my business rather than the latest front room trader who simply get Abbeys or similar to do it for them !!!

Just so you know - life doesnt revolve around the drag strip !!!

J.

Richf · Post by **Richf** » Sat Mar 10, 2007 2:31 pm

Just so you know - life doesnt revolve around the drag strip !!!

It does for this guy and as far as drag racing goes its prefectly valid and accurate

His business is engine and chassis building for drag bikes in the main

He has been involved in drag racing for 40 years so he should know whats he is talking about

My comment was from a conversation with him ABOUT drag bikes and in so being is totaly relavant and again accurate, it ISNT accurate for jap cars or modern efi motorcycles and thats not what he said or i said for that matter .

One thing a dyno WONT tell you is how fast something will cover 1/4 mile and if thats the discipline you compete in that time is more important than the figure on the dyno which is his point

You may well not agree but unless you speak from a position of authority or experience WRT motorcycle drag racing your opinion isnt valid in my eyes

FWIW There is a lot more than holding the throttle open to run low sevens in 1/4 mile.