Christian and Beccy

iTrader: (14)

Believe me Chip, of all the things that Gary is good at, his maths ability isn't one of his strong points!

However, he is an expert at coming to work each morning and dropping a godforsakingly smelly shit down the bog. Of that there is no doubt.

Garage19

I propose a new PF standard.

All power figures to be quoted at the wheels unless taken on an engine dyno.

For me the fact that DD rollers use a GUESSED correction factor is confirmation that quoting flywheel figures from them is pointless.

Karlos G

iTrader: (4)

I agree!

Really interesting thread

Chip

iTrader: (3)

Doug, I think describing it as an "observed typical value" rather than a "GUESS" would be far more fair.

Personally I would sooner do it that way then any of the run down nonsense which IMHO is simply not accurate as it doesnt change with power anyway, so a 50bhp engine and a 500bhp engine on the same box will get the same rundown losses, but cogs under more pressure exert more resistance so the losses will in fact be greater on the 500bhp instance.

So I think of the two options the DD one is the better one personally!



I do agree that wheels figures are what counts though!

JonnyBravo

http://www.tracknroad.com/

I'd like to see some similar testing on theirs now

GaryEvo

i agree too chip

with a car ran on a dyno with 500bhp @fly and coast down lose of 100bhp giving 400@wheels does that mean that a 100bhp engine wouldnt turn the wheels???

dd might have a best guess but thats exactly how the manual on dyno suggests and wheel bhp is king

another graph thats always interesting is our dyno graph is same shape curve with wheel bhp and fly figure have a look at a dyno that uses coast down does......

Garage19

Everybody seems to agree ATW is king so are people only supplying/using/asking for fly figures because they like to see the bigger numbers?

Chip

iTrader: (3)

In the UK its common practice to quote flywheel, I would imagine most customers wouldnt identify with ATW figures.

After all, Ive seen LOTS of posts on here "how do I get 400bhp from my cossie engine"

But Ive seen none asking "how do i get 340 RWHP from my cossie engine"

which is the same question.


Everyone wants a 400bhp cossie engien, no one wants a 340ATW cossie engine

Chip

iTrader: (3)

Ps

Going by engines sheady has put on a dyno and then on a DD rollers, their "GUESS" as you put it at transmission losses, is within a couple of BHP of perfect in those instances!

ECU Monitor Enthusiast

iTrader: (1)

Any device designed to measure something that uses any kind of "guess" factor in my mind is no use as a reference to anything but itself...LOL

I dont aim that specifically at the DD RR.

Christian and Beccy

iTrader: (14)

I dont entirely agree with that. An 'estimated' flywheel figure, which by all accounts has been proven to be pretty close, is actually quite a good guideline. It's not black/white in terms of useful/toilet if you ask me.

OK, so PAW is a better figure to rely on.

Chip

iTrader: (3)

The problem is that mankind hasnt yet invented a way to measure transmission losses accurately.

What DD have done, is rather than use the horrific "rundown" method, they have accepted that it CANT be measured (and it really cant, they are right!) and instead just used a realistic estimate, rather than an inaccurate psedo measurement.

Karlos G

iTrader: (4)

Another reason people want @Fly BHP is to compare with manufacturers figures which I find are mostly quoted @Fly.

For example, stock RS Turbo is 132bhp@fly (or whatever it actualy is), you do your mods and your tuner says well done mate you've got 155BHP @wheels and your face drops as you were expecting 180-190bhp and then he tells you your @Fly 183BHP and things seem are a whole lot better!

But I agree 100% that ATW BHP is what counts!

Steven_RW

What have u all concluded after this? That the car registers more BHP in a lower gear? That is what I read from all the posts, anyone come up with a reason why yet?

Chip u are right that the software "should be able to account for it". It clearly doesn't.

The rr should just measure the effort it takes to stabilise the engine (or in DD shoot out mode 44, what effort it takes to stabilise the engine to 10 kmh per second accel).

The answer (as far as I can see) to christian is that a map made on a quick accel run (10 kmh per second) could be overly risky, especially if you stick 5 people in your car, point it up a steep hill in 5th on a hot summers day and nail it.

Simulating the worst scenario would ensure you have a map that is safe for all conditions and I personally (not being at the cutting edge of motorsport) would always prefer a reasonable safety margin. Especially as I don't drive in a "point and squirt" fashion, instead spend large amounts of time at WOT, generating higher temps.

Interesting topic but I am not sure we are really getting to the bottom of WHY the rr in this case is measuring less bhp in the lower gear.

If 125mph is the limit of the rr speed, can you measure a 600bhp at the rear wheels car? I ask as I guess it might try and wheelspin on the rollers in lower gears and that might mean u need to run a higher gear at a speed beyond 125mph?

I would also be interested to understand what the rr measures? I guess it can only measure the effort put in by the retarder to control the revs of the car under load and apply a calculation to that figure to come back to a useful BHP figure that people would recognise?

I don't personally think you can compare figures from rr to rr. Not wheels figures or flywheels figures, only chance might be if the rrs were both of the same manufacture to try and remove different figures generated by different build styles.

Still interested as to the theory as to WHY a rr registers a lower figure in a higher gear. Anyone got any thoughts?

RW

Karlos G

iTrader: (4)

I might be missing something here as this seems a bit too obvious but BHP comes from this equation:

Horsepower = Torque x rpm / 5252.

So surely 3rd gear will transfer more torque to the rollers than 4th gear (certainly does on the real road, and is why most average cars wheelspin in 1st, 2nd, but not 3rd, 4th, or 5th the lowers gears put down more torque), and that is why a lower gear will make more BHP (assuming the engine reaches peek output before the rev limit)?

mechanic28

iTrader: (5)

so is this thread saying r/r power runs are a worth while thing or not?

Karlos G

iTrader: (4)

My conclusion is that Chasis Dyno's are great for setting up your car to run it's best, but for a accurate Fly Wheel figure you can only really use an Engine Dyno.

foreigneRS

very easy to do with strain gauges (or other optical ways) on the gearbox input shaft - just not particularly practical before a rolling road session

GARETH T

im impressed that gary and christian has gone out there way to do these experiments! well done guys!

AlexF

still sure this thread isnt great Chip

Chip

iTrader: (3)

FPMSL!

Most retarded reply ever


Think about it!

You just said yourself what BHP equals.

So if measuing it at the wheels, whats it going to be?

Torque @ Wheels * RPM @ Wheels


So as your torque at the wheels is magically going up by being in a lower gear, tell me please sir, what is happening to your RPM at the wheels because of the same lower gear

Chip

iTrader: (3)

I love how certain you are of that conlcusion as to what happens with a sample size of 1 run on 1 rollers.

Not saying you are wrong, just saying that 1 isnt an ideal sample size generally when looking for trends

GARETH T

im confused by your statment

Chip

iTrader: (3)

Gareth.

Take a sample point, say 4000rpm

Take measurement in 4th gear at wheels for BHP
Which will consist of 2 elements, wheel rpm, and wheel torque

Now take a measure at the same RPM in 3rd gear
He is saying the BHP will go up because the torque is increased by the lower gearing.
But what of the rpm, what happens to that?

And by what ratio? EXACTLY the same decrease in rpm % wise as the increase in torque % wise

Net effect : Zero

RickyLee53

I've noticed the shapes don't change.

Of cause a 100bhp engine would still turn the wheels, but as you've pointed out, i wonder what the power would be like at the wheels at 110mph in a 4wd cossy.

As for the differences between gears.

I'd say the biggest difference would be down to load, boost levels/control, mapping/timing advance and wheel speed, most of the car's "transmission loss" is probably from tyres and wheels (weight) and friction which of cause would be higher in the taller gear.

GARETH T

thats what i hoped you was getting at LOL i thought for a second you didnt agree that a gearbox is a torque multiplier LOL

Chip

iTrader: (3)

Lol, no mate, of course I know a fucking gearbox is a torque mutliplier, but I also knows its an RPM divider at the same time.




I wish whoever said "give me a long enough lever and I'll move the world" had added onto the end "but fuck me it wont go far"

GARETH T

see now that is funny PMSL PMSL

Steven_RW

Can I just check why you think I am using a sample size of one? Do you mean that you think I am just using the example that gary put up to make my conclusion? If so, do u honestly think that I would only have seen this effect once in all my years of being into cars? lol.

Chip - seriously... You don't hang about with the AVA guys since 1995 and rely on some data that gary has put up to know that the power at the wheels goes down as you use a higher gear.

RW

Martin-Hadland

iTrader: (2)

I said this months ago when I got my rollers, ATW figures should be quoted off rolling roads.

ECU Monitor Enthusiast

iTrader: (1)

Surely thats irrelivant to you as (and I quote from your old siggy) "Reyland Horses are stronger"

(no disrespect intended !)

GaryEvo

do it martin we found that first customer we came to after saying we would only give atw figure had toys out pram

everyone is only interested in a fly firgure for bragging and im just as guilty!!!

Martin-Hadland

iTrader: (2)

They may well be stronger but I still want them to be accurate!

I normally give 2 print outs... One ATW and one At flywheel (for pub use.)

Btw, anyone that has only had a flywheel graph can simply call and I will print off an ATW graph FOC (its all stored in the computer)

Stu @ M Developments

iTrader: (12)

Bang out of order, watch the tone of your replies Chip, the fella asked sensible question that hundreds will have been thinking.

Chip

iTrader: (3)

I did watch my tone stuart, hence the crying smiley to show I meant it in jest and then an explanation to help the fella out as I would like this thread to educational, something this board lacks lately.

Lighten up!

Martin-Hadland

iTrader: (2)

I read it in the same tone as Stu did Chip!!

Chip

iTrader: (3)

Maybe someone should repost the explanation of what all the smileys mean then to help you fella's out, as I would hate to be misinterpreted as a result of people not realising the means its something said in humour.

Chip

iTrader: (3)

Anyway, now thats cleared up, if we could get the thread back on topic it would be more interested, discussions about how to interpret smileys can be done elsewhere.

pa_sjo

I wonder what it is that makes amateurs spend considerable time on the internet going round and round in circles on subjects like this? It happens on every forum, site, club, bulletin board - and this topic is a favourite!!!

TWoods

GaryEvo can I ask a genuine question, on the 2 graphs posted why does on both in 3rd gear towards end of the graph why it makes more power but less torque? Similarly why in 4th gear it makes less power and more torque at higher revs?