Power Curves (Graphs)

[Duncan]

If it's a torque and power curve then there is a very serious fundamental error with the curves!

why?

Because on a torque and bhp curve (plotted together) the curves MUST cross at 5252 rpm. This is because bhp is based on the formula....

horsepower = rpm x torque / 5252

If they don't cross at 5252 then the rolling road figures are wrong.

Alex's graphs cross around the 3200 mark so they can't be bhp/torque plots (not without being totally inaccurate) - hence me wondering exactly what they are.

D

[Bainie]

I think the torque should peak before the Bhp, I might be wrong though ??

[Duncan]

It usually does Tommy. Here's a complete torque, bhp (fly and wheel) curve along with AFR, boost pressure and ambient air temp.

D

[Andy]

i know they have to cross, but i wasnt aware that it had to be at 5250. They didnt take the cars (diesels) past 5000 so it would be impossible to show it on a graph.

[Andy]

ok, had a look at power engineering and theres do cross at 5250 too, but others show the torque and bhp on different scales.

[Duncan]

ok, had a look at power engineering and theres do cross at 5250 too, but others show the torque and bhp on different scales.

Yes, different machines may have the torque scale on the right, or combined with the bhp scale on the left (as on your example) but it always has to cross at 5250.

So, assuming that Alex's curve is not bhp/torque - it can't be a fly/wheel bhp plot either (as they cross) - so what the devil is it? Alex?

D

[AJA]

I'm not the expert here guys. It's Tunit's printout - I'd ask them if I were you.

I assumed the Blue line was the BHP and the Red was the lbft of torque.

[Duncan]

I'm not the expert here guys. It's Tunit's printout - I'd ask them if I were you.

Okay doke. As it's not my graph I'm not fussed about it (certainly won't be ringing Tunit to ask!! LOL) - just curious as to what it was as I couldn't figure it out. It couldn't be an (accurate) torque/bhp curve or even a fly/wheels bhp curve. Did they not explain it all to you? Tell you what the car was doing etc.? It's not just the maximum figures that matter - it's how the car is running fuelling etc.

I assumed the Blue line was the BHP and the Red was the lbft of torque.

Well, if that's what it's meant to be then you may as well throw the graph/readings in the bin. I don't mean that facetiously, but if it is then it's completely wrong.

D

[Caterman]

Just found this....It explains the theory and practical implications of a diesel engines bhp and torque outputs and what it would be if it could rev as high as a petrol.
Torque should be higher than bhp up up to 5252 rpm.

http://www.bankspower.com/Banks_FridayNight_070502.cfm

Still does'nt explain Tunit printout though!

[Eric_S]

Hi, guys
Sorry I couldn't make it yesterday. I knew there was a reason when Ian PM'd me earlier in the week - turns out it was my birthday! (Thanks to Admin for the greetings.) Sounds like I missed a good day.
I hope this ex-Maths teacher can help you out with your graphs homework. The Power Engineering graphs do indeed cross as predicted because they are using the same numerical scale on the vertical axis. The Tunit graphs, however, have two completely different scales - power on the left and torque on the right. A rough replot on paper of the Tunit graphs, using just one numerical scale suggested to me that, had the revs gone above 5000, the curves could very well have crossed at the predicted figure. They certainly did not cross below 5000 and, as caterman says, torque was higher than power all the way up to that point.
If your homework doesn't improve, you're all going to be in detention!