Dyno-plot losin 40bhp between fly and wheels !!

[monVR6 0]

Hi all

 

Just been looking at Pablo VR6's dyno plots in an earlier post. I dug out my plot after my AMD remap and I appear to be losing a lot of power between the flywheel and the wheels.

 

The plot reads 213bhp at the fly - but 171 at the wheels - I'm losing 40ish here which is about 24%. Pablo's is only 12.5%.

 

Have I got a problem here or could it be related to gear used, ambient temp etc??

[pablo_vr6 0]

i think mine is big time off to be honest. myself and mikevr6 are both under std power but running mid 160s to the wheels.

 

I wouldnt worry about it

[Kevin Bacon 5]

171 at the wheels is damn good!!!!

 

Transmission loss usually amounts to around 25 - 30% but as with all Rolling roads, power is measured against a brake (hence the term Brake HP) at the wheels and the fly figure is calculated, sometimes creatively.

 

You have no problems, you should be very proud of those figures.

 

K

[monVR6 0]

You have no problems, you should be very proud of those figures.

 

Why thank you Kev!! Might not handle - but I have power!

I shall sleep soundly this night!

[dr_mat 0]

Take one dose of salt with every flywheel figure quoted from a rolling road.

Oh, and, buy a new steering rack!

[Kevin Bacon 5]

Forgot to ask, is the engine standard? If so, Asim's freak of a standard 212bhp unit may have some competition :lol:

[monVR6 0]

Oh, and, buy a new steering rack!

 

I think I'm gonna have to mate - at least I'll shut-up about it then !! Potential bonus on the way at work so fingers tightly crossed!! :?

[pablo_vr6 0]

my AMD remap

 

Id expect its not std if you need a remap :)

[potatonet 0]

uh yeah corrado tranny's are terrible for power loss, get one by kraftswerk, they bring it down to about 16 to 17 percent loss. or you could be creative and attach a set of wheels to your engine, then you have 0 percent loss, well maybe 1 or 2 for rubber and give. dont actually do that though I 'm kidding.

[Kevin Bacon 5]

LOL....isn't 4th the equivalent of a 1:1, hence using that gear for dyno runs?

 

Kraftswerk sounds too much like the 80s electronic pop band :lol:

[fj 0]

I wanted to get my (standard) VR dyno'd to see where it is against the VW 190bhp figure, but all this puts me off.

 

25 - 30% power loss? That's more than 50bhp. Where does it all go? If all that heat is going to the bearings/oil, surely the whole drivetrain would just fry itself as soon as you got above 60mph? Or is the figure including a loss between the wheels and the output shaft of the rolling road? In which case all rolling roads would give a slightly different result?

 

I suppose the only way to find out how good my car is is to get it on a dyno where some other standard VRs have been and compare. Don't think I'll match 212bhp wherever I take it :lol:

 

Cheers,

[dr_mat 0]

Exactly, fj. The only way to actually take a reading of the engine's output is to put the engine on a dyno. Most places showing vast transmission losses would admit that it's optimistic at best. A "good" VR should put between 155 and 162bhp to the wheels, so if you're in this ball park, ignore the @crank figure. But then, bhp isn't so important as torque anyway...

Your point about the power loss is something that's never been adequately explained by someone who runs a rolling road. We all know what 50bhp can do (that's about 38 kW). It'll boil a large quantity of water in no time at all....

[davidwort 0]

Exactly, fj. The only way to actually take a reading of the engine's output is to put the engine on a dyno. Most places showing vast transmission losses would admit that it's optimistic at best. A "good" VR should put between 155 and 162bhp to the wheels, so if you're in this ball park, ignore the @crank figure. But then, bhp isn't so important as torque anyway...

Your point about the power loss is something that's never been adequately explained by someone who runs a rolling road. We all know what 50bhp can do (that's about 38 kW). It'll boil a large quantity of water in no time at all....

 

That's a really good point and something I'd never really thought about, the engine itself obviously generates a lot of waste heat but then that's even before the @ crank power.

If drivetrains really wasted that much energy, our wheel bearings, cv joints and gearboxes would probably glow red!

Obviously we don't drive around at peak power everywhere, but I think this little fact of where all this supposed energy goes to just supports the idea that drivetrain losses as nearly always over estimated by far. Either that or I really need a 20 row oil cooler on my gearbox :lol:

 

David.

[dr_mat 0]

The only technical, mathematical treatment I have ever seen of any of this boils down to the simple summary: drive train losses for a normal front wheel drive car with a manual gearbox are around 10% of engine output, plus 10bhp fixed losses. So a standard C VR6 will lose 19+10bhp, or around 29bhp. Hence the at the wheels figure of 161 being "normal".

[Kevin Bacon 5]

40h loss sounds about right. Assuming the engine is healthy, it's got to spin a flywheel, turn a PAS pump and alternator etc. And then once the clutch has locked (after you've spun most of your power away moving off), there's gearing, oil drag, CVs and shafts to turn, resistance in the hub bearings, brake drag, then the wheels and then against a brake in a rolling road!

 

There are too many variables to produce a 100% accurate figure. As suggested, the only way is to drop the gearbox and connect a dyno to the flywheel....and even then you've got atmospheric conditions, petrol quality, MAF sensors etc etc all playing their part in wrecking the readings.

 

Engines are just one big heater and air pump. Petrol engines are something silly like 50 or 60% efficient, if that.

 

At the end of the day, at least we have a reasonable amount to begin with. I feel sorry for 1.0 Fiesta drivers with a whopping 50 odd hp, *before* the losses :lol:

[dinkus 10]

As people have already said, the measurement at the wheel is pretty much accurate (give or take a smidge), then they fudge the calculation to get the flywheel figure.

 

So...if you're measuring the wheel bhp and want a customer to feel like they got a little extra from their rather expensive chip you 'tweak' the road to include a little extra transmission 'loss' which bumps up the calculated fly figure...;)

[Scruffythefirst 0]

There is a way to calculate transmission losses that involves a wind tunnel, a very large car park and some stupidly expensive equipment. Alternatively ALWAYS ingore crank figures. Or put the engine on a dyno, which is a good idea if you've just built a monster and have no idea what map you need.

[fj 0]

Cool, so I'll look for 160bhp odd if I get round to getting the car on a dyno.

 

It seems that any flywheel figure needs to be treated with a 'pinch of salt' as Dr Matt says. Makes you wonder how much salt VW added to come up with 190bhp! Obviously not as much as most manufacturers given the performance it gets for the power :D

 

Seriously though, I develop engines for a living, and one thing I have to do is to ensure that if we sell an engine at xxkW, it'll pull that xxkW day in, day out. We don't make engines for cars (the stuff I work on has more litres/cylinder than a VR6 has in the whole engine 8) 8) ), so there's a whole load of differences, but I was surprised at the %loss figures on here.

 

Cheers

[dr_mat 0]

VW quoted a figure derived from an engine dyno... But of course, each engine that leaves the factory will perform differently, not much you can do about that. VW will tend to be slightly conservative, but not by much.

[monVR6 0]

Back to Kev's question about the "standardness" of my VR6. As far as I know it was standard before I did anything to it. Prior to the AMD remap it was measured at 198bhp on their rolling road. After the remap, it peaked at 213bhp with 206lb/ft of the twisty stuff - (before was 191lb/ft). I must admit though, it didn't feel like a huge performance gain - just smoother really - perhaps I was expecting too much??

 

I actually noticed a bigger difference when I added a K&N panel filter - throttle response at motorway speeds was much cleaner. Oh - and of course I run it on Optimax . .

[dr_mat 0]

Hmm, 15 bhp and 15lbft torque gained just from a remap on a 2 valve naturally aspirated engine? I want some of whatever they're smoking!

Having had my VR chipped recently I can tell you that I can REALLY feel a huge difference between the "before" 185lbft and the "after" 199lbft that it was developing!! Power dropped by 1bhp though. Not that I give a monkeys about that..

The reason I gained nearly 20lbft at 3500rpm was simple: the Schrick was causing massive pinking at those revs..

[monVR6 0]

Well - I must admit the figures do sound a bit "stretchy" - but that's what the plot shows. I have heard that figures can be fiddled to produce an optimum amount for a short space of time to make the gains appear more impressive. Rather like jumping onto some scales, when you land, the weight shown would be much heavier than you actually are! Bloody hell - just grabbed some scales and tried it - I am clearly eating far too many curries !! :(

[pablo_vr6 0]

change the atmospheric pressure reading would do the trick - bhp = whatever you want :)

[MoonlightVR 0]

Having had my VR chipped recently I can tell you that I can REALLY feel a huge difference between the "before" 185lbft and the "after" 199lbft that it was developing!! Power dropped by 1bhp though. Not that I give a monkeys about that..

The reason I gained nearly 20lbft at 3500rpm was simple: the Schrick was causing massive pinking at those revs..

 

Matt, other the higher torque and lower peak rpm with the Schrick & remap, are there any other benefits to report?

[dr_mat 0]

Erm, just no pinking: I was suffering pretty bad pinking. The car does seem quite responsive, but then it always did when it was running right. Plus I'm nearly running the fuel tank dry so it's very light at the moment...

I had no pinking for some time (and great torque) with just the Schrick and no remap, I was hoping to avoid having to get it done, but since I started getting serious pinking it's become necessary. The big problem was psychological though: knowing that there are times when it *might* pink, even if it doesn't, I was a little nervous about using the throttle, so it needed to be remapped.