Power, Torque and rolling roads

[Webby]

All this talk about torque, have you all just come back from Torquay?

 

[dents]

i wonder what the original post was,

are you saying vtec is best?

 

[teky]

on the rollers i call it free wheeling (dead car)and not a real test of the cars perfomance on the track it will never do what the rollers say and just might do a lot more, you forgot to mention in you maths about air motion "drag" person sitting at the wheel = weight and many other equations

 

[teky]

i said that in laymans terms so all could understand without the wafflel of concentrated maths which im sure we all know about

 

[Mark300SL]

you forgot to mention in you maths about air motion "drag" person sitting at the wheel = weight and many other equations

Where does drag on the rollers affect the specific output of an engine ?
Air resistance and drivers weight is an important part of calculations for something like 1/4 mile - but plays no relevance in power calcs.
The whole idea of a dyno day is to compare cars like for like on the same rollers on the same day - I tune my CRX @ PTS because they let me run the rollers not the other way round.

I see it as an aid to outright performance - or a bit of fun depending on the day concerned

Mark

1800 Honda CRX 317hp - @ the wheels

 

[teky]

you answered your own questions m8, ill put a force 8 wind infront of you and then tell me it has no effect on your car

my post was against the rolling road as opposed to the track, the rolling road is at a stand still the track is going

ps :- please dont keep quoting me

 

[Mark300SL]

you answered your own questions m8, ill put a force 8 wind infront of you and then tell me it has no effect on your car

- I didnt see a force 8 wind the whole time I was in the dyno cell

my post was against the rolling road as opposed to the track, the rolling road is at a stand still the track is going

The whole post was about power torque and ROLLING ROADS - otherwise it would have been titled Power torque and TRACK

ps :- please dont keep quoting me

Then stop nit-picking with completely irrelevant sentances.

I am in complete agreement with the fact that the air offered resistance once moving, that weight plays a vital role in competition - but nowhere was I talking about track or competition

For your information I run the fastest 0-60 accelerating road legal FWD car in the country as a hobby - and my participation in the FWD class of this years "10 Of The Best" is why I havnt been around here much for the last few months. Incidently, I won the FWD 1/4 mile shootout with a time of 12.70 seconds @ 111mph - not bad for a little 1800

I really do understand power, drag and weight

Mark

 

[JohnM]

OK, no laughing here is the perhaps basic and unconventional power graph I (we) got:

130KW @ the wheels
30KW transmission losses
=
160KW total engine power.


Using W x 0.00136 = BHP

176.8 BHP @ the wheels
40.8 BHP transmission losses

= 217.6 r/u 218 BHP total engine power.

Now the graph shows my peak 218BHP @ just over 180 KM/h, which is about 110mph ish. Now peak power is suppossed to be at 5300 rpm, so that would correspond with 4th gear - 5300 rpm, as I can just squeeze 120mph before the rev limiter kicks in.


From there on I need help

Looks like your actual power was a little higher as that plot has simply clipped at the top of the scale. That would fall into the idiot operator category. You can work out your torque at any rpm by reading the corresponding power figure off the graph and using Torque (Nm) = Power (kW)*9549/rpm, to get rpm from road speed you need to know the gearing - owner's manual may give mph/1000rpm figures, or failing that use the gearbox ratio for the gear used, the final drive ratio and the tyre rolling circumference.

 

[GrahamC230K]

Thanks John.

I since got some more comprehensive plots from another Dyno. Details here:

http://mbclub.co.uk/forums/showthread.php?p=21795

 

[JohnM]

Wise choice going to G-Force - I guess Chris did the dyno runs? Top blokes there, did some very nice track prep work on my 993 C4 (since sold, sadly).

 

[GrahamC230K]

Yes, Chris did the runs. Very informed and helpful guy, although Mercedes not his strong point (as he admits).

 

[vixpy1]

This is my profession guys, so if anyone has any questions. don't hesitate to ask.

Charlie.

 

[GRAV888]

This is my profession guys, so if anyone has any questions. don't hesitate to ask.

Charlie.

I can feel a GTG coming on

 

[vixpy1]

Always willing to host guys.

 

[GrahamC230K]

Always willing to host guys.

You organise them over on PistonHeads don't you? Was tempted to come to one of those, but was scared of being least powerful car there.

No more engine mods for me, so my RR days are numbered for this car!

 

[vixpy1]

Hi Graham,

Yes, I run the The PH days. Put mine on the rollers this afternoon, i will post the graph up at some point.

Cheers,

Charlie

 

[stats007]

Hi Mark,

This is fine for direct comparisons , but you fail to mention that peak torque and peak power are not the same and more often than not appear in different parts of the rev band. It seems odd that on a dyno session you measure torque but then quote BHP when you are really just measuring peak torque.

e.g.

An SL500 has ~302BHP @ 5600rpm and 339 Lbft of torque at 2700 rpm.

Using your method you would have a figure of ~174 BHP - clearly not representative of the engines power.

Other than that, good post!

Andrew

 

[Dieselman]

Hi Mark,

This is fine for direct comparisons , but you fail to mention that peak torque and peak power are not the same and more often than not appear in different parts of the rev band. It seems odd that on a dyno session you measure torque but then quote BHP when you are really just measuring peak torque.

e.g.

An SL500 has ~302BHP @ 5600rpm and 339 Lbft of torque at 2700 rpm.

Using your method you would have a figure of ~174 BHP - clearly not representative of the engines power.

Other than that, good post!

Andrew

Err..!

But thats right at peak torque revs, 2700, the engine is producing 174.2 Bhp. It's only higher up the rev band that it produces more power due to the revs of the engine.

At peak power revs, 5600rpm, the engine will be producing 283 LbFt of torque.

 

[stats007]

LOL - yes that's my point - what's the point measuring peak torque and quoting BHP? You need both values to get an idea of an engines characteristics.

 

[Dieselman]

Sorry I'm lost.
Both figures are quoted with respect to the Rpm at which they occur. That is a good indicator of the characteristics as the rest of the power curve can be estimated from that.