power figures

1. SaxoJamie Saxperience Forum Bum Joined: Jul 2007 Sussex Posts: 3891 2x 106 GTi

   #1 8th October 2009, 22:35

   Had my VTR on the rolling road yesterday it is standard or least as far as I know of. It rolled 112.3 BHP at the fly which seems pretty high for a standard VTR. At the wheels it only has 75.9BHP and drag power is 36.3 BHP. I know some of the power is lost through the trasmission but from that figure it seems a lot more.
   
   According to the rr it is losing over 30% through transmission. Is this right? Would this be down to the clutch or gearbox ratio maybe. Also the peak power came out at 6185rpm almost on the redline again high up in the powerband for the VTR.
   
   Can someone explain to me more about this please.
2. fergy7197 Infrequent Poster Joined: May 2008 lanark Posts: 128 97 vts

   #2 8th October 2009, 22:56

   sounds like a very optimistic rr to be honest, usually about 30% is what a 4wd loses through trans losses
3. user_15989 Saxperience Forum Bum Joined: May 2007 Posts: 4857

   #3 8th October 2009, 23:04

   Transmission loss is due to every part that transmits the power from the engine to the wheels that has friction. For example the wheels rolling on the ground, The wheel bearings rotating. The drag from the brakes, the CV joints moving, the gearbox output bearings, the cogs meshing in the gearbox, the gearbox oil dragging on the parts in the box and that sort of thing.
4. fergy7197 Infrequent Poster Joined: May 2008 lanark Posts: 128 97 vts

   #4 8th October 2009, 23:06

   Quote:

   Originally Posted by AXracing Transmission loss is due to every part that transmits the power from the engine to the wheels that has friction. For example the wheels rolling on the ground, The wheel bearings rotating. The drag from the brakes, the CV joints moving, the gearbox output bearings, the cogs meshing in the gearbox, the gearbox oil dragging on the parts in the box and that sort of thing.

   so a 30% percent loss of power is normal on a FWD?
5. SaxoJamie Saxperience Forum Bum Joined: Jul 2007 Sussex Posts: 3891 2x 106 GTi

   #5 8th October 2009, 23:08

   yeah it's usually 15% loss through tranmission. I worked it out and mine is losing over 30% It also says I got 112 Brake at the fly very high for a standard "R" then a massive dip in power through transmission.
6. redevo7 Infrequent Poster Joined: Nov 2007 Posts: 197

   #6 8th October 2009, 23:36

   my evo loses 24% through the transmission and id expect most fwd cars to lose 12-15% only, certainly not 30%
7. Quick Saxperience Post Whore Joined: Mar 2003 United Kingdom (England) Posts: 7064

   #7 9th October 2009, 10:18

   It would appear that the rolling road is using too high a figure for transmission loss.
   
   Fly power is an estimate, wheel is a true reading.
   
   If you use 20% as loss it gives you 91 bhp.
8. yr51ocw Frequent Poster Joined: Oct 2005 Posts: 751

   #8 9th October 2009, 10:35

   quick - your maths is wrong,
   
   94.9 hp with 20% tranmission loss give a wheel power of 75.9
9. Quick Saxperience Post Whore Joined: Mar 2003 United Kingdom (England) Posts: 7064

   #9 9th October 2009, 11:17

   Quote:

   Originally Posted by yr51ocw quick - your maths is wrong, 94.9 hp with 20% tranmission loss give a wheel power of 75.9

   
   75.9 (at wheels power) divided by 100 x 20 + 75.9 = 91.08 (at fly estimate)
10. yr51ocw Frequent Poster Joined: Oct 2005 Posts: 751

    #10 9th October 2009, 11:28

    i see what you have done there, it depends on how the rr calcualtes it, whether it adds a %'age onto the whp figure, or calculates it back from the hp figure.
    
    Most rr however calcualte transmission loss though coastdown losses and not simply a fixed percentage.
11. AlexBp West Midlands Joined: Dec 2007 West mids Posts: 23149 Supra,civic GL

    #11 9th October 2009, 11:34

    things like how the clutch is setup will effect the calculation and everything
    
    i know a guy and pedal fully depressed his clutch isnt fully disengaged it drags and this caused his breathed 106 to get a fly figure of over 170 hp as it threw the drag all over the place
12. KamRacing Saxperience Addict Joined: Nov 2006 A farm shed in Aylesbury Posts: 14916 Corolla AE86 Peugeot 205 B18C (in bits)

    #12 9th October 2009, 11:43

    flywheel figures are usually a pile of toss especially on rr's that use coastdown drag. For a start there is more drag on a rolling road than the road due to two rollers..
    
    Take the wheels figure
    FWD cars - add 10 to the wheel bhp and then divide the result by 0.9
    RWD cars - add 10 to the wheel bhp and then divide the result by 0.88
    
    That works out your flywheel power at 95 bhp which is more in the realm of reality.
    At the end of the day I pretty much only work from wheels figures. This is what your car is really putting out. Flywheel figures sound nice on adverts and willy waving at the pub
    
    Kev
13. SaxoJamie Saxperience Forum Bum Joined: Jul 2007 Sussex Posts: 3891 2x 106 GTi

    #13 9th October 2009, 18:14

    I contacted the garage today and they will give me a re-run as I said there's no way a FWD car should lose 30% of power through transmission. It also said I got 108lb ft of torque do I use the same correction formula for this as BHP?
14. user_10176 Saxperience Post Whore Joined: Jun 2006 Ramsey st marys, peterborough Posts: 8288 Saxo's, Corsa (Daily)

    #14 9th October 2009, 18:36

    look, you could have more drag though your transmission due to other things like wear of plates, dnt forget the age of it aswell, there alot of factors for transmission loss, only really want of find power of an engine is to get it on a 'real' engine dyno!!
    
    i would just walk away thinking god my vtr has 112!
    
    also dnt look too much into Dyno figures if it drives ok on the raod just be happy!!!
    
    andy