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The mkiv Supra Owners Club

Are you in the 700bhp club?


Noz

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Thank you Lee, what a very good write up.

That has cleared a fair few things up in my head about dyno's, although I've never put to much faith in the figures they produce anyway. I especially liked the part about rising up on the rollers, I didn't realise that why they done it like that.

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I think one of the big problems here is we all got a little carried away with adding percentages on, a hub figure is exactly what it is and we should take it as that. Some of the hub dynos do read over but like I said its the responsibility of the operator and I could make one give out a high figure just by manipulating the intake temps. The only way to directly compare is to use the same dyno everytime.

 

We need to stop guessing the flywheel figures and just use wheel and hub figures, also we need a whip round so we can donate to SRR to buy some new rollers lol...

 

More importantly a dyno is a tuning tool and not an indication of how fast a car is. Get out there and enjoy them, how they drive is much more important than how much power they have.

 

 

Spot on.

Edited by JamieP (see edit history)
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I'm gona try and not get too involved in this but will make a few points.

 

First off a hub figure is not a wheel figure anyway so cannot be directly compared to one. It is the power figure measured at the hub not including rotational mass of the wheel and tyre. This means it will be a higher figure than a wheel figure on a rolling road.

 

this does explain a lot, something that I never had considered about the eitating mass of a wheel.

So am I correct, there is 3 measurements here,

 

Rear wheel horsepower (a roller Dyno measures)

 

Hub horsepower (a hub Dyno measures)

 

Flywheel horsepower (a engine Dyno measures).

 

Still a little unsure on a couple of things though,

Is there anyway of measuring "flywheel horsepower" without pulling an engine and bolting it to an engine Dyno? If there isn't, why is it for so many years people have been adding 15% to a wheel or hub figure when no-one knows exactly what the transmission figure is exactly.

And what's changed all of a sudden. All the clubs mega powered cars in the club (Lee, Jamie, Jamesy, Wayne, Paul Whiffin, Dude etc etc) always quoted flywheel figures with this 15% added until about 6 months ago or so.

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Its a hard subject as a lot of these cars that add the % to hub figures I class as friends, I dont want to upset anyone saying there car has nowhere near that bhp, my turbo is not even rated to 1300bhp, yet using the hub figures and adding 15% i can make that power on pump fuel at not much boost, when in reality i doubt i have any more than a 1000bhp.

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You have to put the engine on an engine dyno to get the true flywheel figure but then even the environment can effect that. The engine room it's self plus the intercooler, exhaust system used.

 

The reason we were using the 15% to start with was to try and compare to SRR flywheel figures as that is roughly the calculation it uses and it was a general rule of thumb. The problem is its just a guessing game and you may as well pick a figure out the air. Different gearboxes, oils, diffs, flywheels ect ect will all give different losses. The only constant is the wheel or hub figure, the energy created at the end.

 

The only figure the dynos are actually reading is wheel and hub anything else is made up. If we just stick to using these we will have a much better idea of what we actually have.

 

Also we cannot directly compare rolling road wheel figures to hub figures as the dynos load the cars differently and as already said the rotational mass of the wheel and tyre itself. Also dyno dynamics run the car in 4th gear while hub dynos can run the car in the correct gear which is 5th.

 

But as I said before stop worrying about and drive it :)

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baileys old car at 585 bhp with f-con and nbow on a syvecs at an extimated 640 bhp from ryan g has never had a dyno run since the new ems was fitted, ive never been to hung up on not knowing wither as andy said it was a hoot before and now its a tiny bit more aggressive a hoot! :D

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You have to put the engine on an engine dyno to get the true flywheel figure but then even the environment can effect that. The engine room it's self plus the intercooler, exhaust system used.

 

The reason we were using the 15% to start with was to try and compare to SRR flywheel figures as that is roughly the calculation it uses and it was a general rule of thumb. The problem is its just a guessing game and you may as well pick a figure out the air. Different gearboxes, oils, diffs, flywheels ect ect will all give different losses. The only constant is the wheel or hub figure, the energy created at the end.

 

The only figure the dynos are actually reading is wheel and hub anything else is made up. If we just stick to using these we will have a much better idea of what we actually have.

 

Also we cannot directly compare rolling road wheel figures to hub figures as the dynos load the cars differently and as already said the rotational mass of the wheel and tyre itself. Also dyno dynamics run the car in 4th gear while hub dynos can run the car in the correct gear which is 5th.

 

But as I said before stop worrying about and drive it :)

 

 

Thanks for that Lee, there's some informative stuff there. Things are now starting to become a little clearer.

 

Up until 6 months ago you all quoted flywheel figures, I just can't understand why after all these years you big dowgs :) decided that you were not going to use this anymore. I understand why you have and but why has it taken so long.

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Thanks for that Lee, there's some informative stuff there. Things are now starting to become a little clearer.

 

Up until 6 months ago you all quoted flywheel figures, I just can't understand why after all these years you big dowgs :) decided that you were not going to use this anymore. I understand why you have and but why has it taken so long.

 

Because the manufacturers quote engine figures (very approximate ones at that!)

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I will still quote flywheel figures if ive used a dyno such as SRR, I just wont make my own numbers up, use the figures the dyno operator has given you and state if its fly/hub/wheel bhp and there is no confusion.

 

But there isn't a roller Dyno that will take your cars power SRR certainly won't due to the worn rollers as stated above by Lee.

I was at Rising Sun car show at Lincoln last weekend and they had a Dynopack hub Dyno there, and the operator was giving out flywheel figures. Robby.A put his N/A manual on and made 176 horsepower at the hubs, but the operator gave him a figure of 207hp at the flywheel, which seemed a little low to me if I'm honest. I've drove this car many times and it's one of if not the quickest N/As I've ever driven.

I questioned him about the difference in the figures and he said 15% was added as a deficit from hub to flywheel.

 

As you said in a previous post, most of my friends have supras, skylines, evos, some with big power, and they all quote flywheel figures. TBH, most people I speak to quote flywheel, it only seems to be this forum that decided to change a few months ago now, which is the only thing I can't understand if I'm honest. I understand why, just not why now after all these years, and why are all the other clubs not following suit, and who decided "ok, this isn't acceptable anymore.

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Lee you need one of these in the workshop now. :D

 

I don't see what is loading the engine up? You can idle and rev it with that setup but not load it. What does an engine dyno look like?

 

My supe was hub dyno'd and read out 394 bhp but at bpu the figures must have had a fudge factor added to give estimated flywheel power, a few weeks later it read out 375 on a rolling road.

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I don't see what is loading the engine up? You can idle and rev it with that setup but not load it. What does an engine dyno look like?

 

My supe was hub dyno'd and read out 394 bhp but at bpu the figures must have had a fudge factor added to give estimated flywheel power, a few weeks later it read out 375 on a rolling road.

 

So you made 394 bhp at the hubs on a hub dyno and 375 at the flywheel on a rolling road? same sort of results that ive seen.

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Lee you need one of these in the workshop now. :D

 

I don't see what is loading the engine up? You can idle and rev it with that setup but not load it. What does an engine dyno look like?

 

My supe was hub dyno'd and read out 394 bhp but at bpu the figures must have had a fudge factor added to give estimated flywheel power, a few weeks later it read out 375 on a rolling road.

 

Thats just a test rig you strap the engine too, you then attach the engine to a dynamometer

via the flywheel, our old engine dyno used a water brake system but others used Eddy current systems

 

Google engine dynamometer and you'll get all the info you need on how they work etc

Edited by Dnk (see edit history)
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I'm not saying you have to use a rolling road, use any dyno you like, just don't convert the numbers yourself.

 

So your saying that if the operator gives you a flywheel figure then that's ok but you can't work it out yourself? Isn't that a little daft. A calculator is a calculator, doesn't mater who presses the buttons. Or do the likes of SRR and TDI dyno calculate the figures automatically and give you a dynoplot with flywheel horsepower or does the operator just do The calculations. As I've never been to either I don't know how it all works really mate.

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So your saying that if the operator gives you a flywheel figure then that's ok but you can't work it out yourself? Isn't that a little daft. A calculator is a calculator, doesn't mater who presses the buttons. Or do the likes of SRR and TDI dyno calculate the figures automatically and give you a dynoplot with flywheel horsepower or does the operator just do The calculations. As I've never been to either I don't know how it all works really mate.

 

 

When the dyno does the working out the results seem right, hubs figures + any sort of % the end customer adds seem miles out from what ive seen, hub dynos dont have a option to give you a flywheel output according to TDI and AME.

 

What do you work your car out to be? over 900 bhp iirc? go put it on a dyno dynamics rolling road and you will be in for a big shock imo.

Edited by JamieP (see edit history)
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When the dyno does the working out the results seem right, hubs figures + any sort of % the end customer adds seem miles out from what ive seen, hub dynos dont have a option to give you a flywheel output according to TDI and AME.

 

What do you work your car out to be? over 900 bhp iirc? go put it on a dyno dynamics rolling road and you will be in for a big shock imo.

 

Honestly Jamie, this has nothing to do with my car, if those figures are not correct then it is what it is. If my car makes 700, 900 or 1000hp is erelivent, it makes me smile Everytime it makes boost. I'm just used to it now and want more power, it's a natural progression, your the biggest example of that mate ;) I'm just wanting info so I can understand it all that's all. I didn't know some dynos make the calculation for you I thought it was just the operator who did it but that's just my lack of knowlodge. I'm just asking for information that's all.

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The best way to understand it and see the difference between dynos is do what i did mate, put your own car on them and see the difference, imo hub figures from a rototest or dynapack are about the same as a flywheel number you would get from a dyno dynamics rolling road.

 

Im going the other way now, small turbo going back on soon, i miss the super fast spool.

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The dynapack can show flywheel horsepower as well as hub HP.

I spoke with Mark and it depends on how the operator has it setup but it can be used for both.

 

Also most of the fudge figures are not in DIN mode but a corrected SAE figure.

The un corrected DIN figure is a good one to use.

 

FWIW my Brother's GTR dyno'd 510 at the hubs, which mark advised would be around 580 ATF.

He had it done a little while later at a DD dyno and it made 595bhp....

 

A dyno is just for tuning, use it for that IMO.

Figures on any dyno will just be a ballpark estimate....

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