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WHP, How much Transmisson Loss..
#26367
16/01/2006 02:53
16/01/2006 02:53
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Anonymous
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Anonymous
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Can anyone reccomend a % ratio i should be looking at for what a 98R 20vt would lose on the rollers as i have found my old power graph from when the gas conversion was done and i was running low boost so was wondering what i should use to calculate what it was actually pushing at the flywheel..
IIRC sumfin like 17.5-20% is about right or is that too high??
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Re: WHP, How much Transmisson Loss..
#26368
16/01/2006 02:55
16/01/2006 02:55
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Anonymous
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Anonymous
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From memory, when mine was on the RR they reckoned 171bhp at the wheels and guessed that back to 226 at the fly so whatever % that works out at
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Re: WHP, How much Transmisson Loss..
#26370
16/01/2006 02:59
16/01/2006 02:59
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Anonymous
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Anonymous
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i think 50bhp is an average loss
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Re: WHP, How much Transmisson Loss..
#26371
16/01/2006 06:38
16/01/2006 06:38
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Anonymous
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Anonymous
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Cheers guys Works out about 180-190bhp i was pushing out at low boost as well, tlking about just under 1bar as well so not bad
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Re: WHP, How much Transmisson Loss..
#26372
16/01/2006 06:54
16/01/2006 06:54
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Anonymous
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Anonymous
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Working out the percentage loss of my RR session on Saturday, Surrey Rolling Road was giving an 18.5% drop between wheels and estimated flywheel figures. Charlie seemed to imply that this was more realistic than other rolling roads, but I have no idea whether it was professional pride or the truth . I know that James' recent figures from Powerstation were a lot different to the ones he got on Saturday . All I can say is that a lot of top tuning companies and individuals seem to go to him, so presumably he knows what he is talking about Phil
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Re: WHP, How much Transmisson Loss..
#26373
16/01/2006 06:58
16/01/2006 06:58
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Anonymous
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Anonymous
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I had exactly 50bhp loss on my 16VT, it was all standard at that time.
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Re: WHP, How much Transmisson Loss..
#26374
16/01/2006 08:55
16/01/2006 08:55
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Anonymous
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Anonymous
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Cant wait to see what she will push out with either new turbo on its own or with the PA FMIC as well when i take her for a setup again on the rollers at F1 as need to get it re-sorted again
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Re: WHP, How much Transmisson Loss..
#26375
16/01/2006 18:43
16/01/2006 18:43
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Anonymous
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Anonymous
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Quote:
Working out the percentage loss of my RR session on Saturday, Surrey Rolling Road was giving an 18.5% drop between wheels and estimated flywheel figures. Charlie seemed to imply that this was more realistic than other rolling roads, but I have no idea whether it was professional pride or the truth . I know that James' recent figures from Powerstation were a lot different to the ones he got on Saturday .
All I can say is that a lot of top tuning companies and individuals seem to go to him, so presumably he knows what he is talking about
Phil
Yes, there was a slight difference between Surrey and Powerstation
Powerstation: 207bhp wheels = 288 at flywheel = 28% Surrey: 214bhp wheels = 262 at flywheel = 18%
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Re: WHP, How much Transmisson Loss..
#26376
16/01/2006 18:59
16/01/2006 18:59
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Anonymous
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Anonymous
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Same Here @ SRR 18% 252-206BHP.
Interesting to note the BIG differences at different Dyno's.
Didn't H2ypr get 269-209 = 22% somewhere in Scotland?
It will be interesting to see what %age PTS come up with after the Unichip.
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Re: WHP, How much Transmisson Loss..
#26377
16/01/2006 19:23
16/01/2006 19:23
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Anonymous
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Anonymous
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I think a realistic figure for the coupe would be around 17-19% max. More than 20% is rediculous for a FWD car if you ask me, unless you've got very worn out parts!
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Re: WHP, How much Transmisson Loss..
#26379
20/01/2006 20:55
20/01/2006 20:55
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Anonymous
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Anonymous
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Quote:
Tyres will account for as much as half your transmission losses. I ran mine too soft at the last PowerStation RR day and lost about 30% (the dyno operator mentioned it as soon as I put the car on the rollers)
Normal losses are about 20% - 25% - anything less than this is either very good, or the result of an inaccurate RR
So is the transmission loss actually calculated, or guesstimated by the RR?
Looking at the hall of fame, there are some wild differences in % between fly & wheel figures
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Re: WHP, How much Transmisson Loss..
#26380
20/01/2006 21:30
20/01/2006 21:30
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Anonymous
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Anonymous
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It should be calculated by measuring the drag on the rollers (make dyno run, declutch and keep car rolling from high revs). The general rule for FWD cars is a transmission loss of around 15%. Because of our viscodrive systems it might be slighty higher, but definately not over 20% if you ask me.
Then again, a lot of rolling roads use twin rollers which will increase drag (more contact with tyres than normally on the road).
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Re: WHP, How much Transmisson Loss..
#26382
20/01/2006 22:12
20/01/2006 22:12
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Anonymous
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Anonymous
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Quote:
Powerstation: 207bhp wheels = 288 at flywheel = 28% Surrey: 214bhp wheels = 262 at flywheel = 18%
Guess which one the max power boys will go to
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Re: WHP, How much Transmisson Loss..
#26383
20/01/2006 22:42
20/01/2006 22:42
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Anonymous
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Anonymous
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You're right John and Jon Losses will differ depending on revs, so it makes quite a difference in which gear they test the car as well. But I still think over 20% is rediculous for a FWD car. I was just wondering, does that also mean that cars like a civic type R and Honda S2000 have quite big transmission losses as they have their max power quite high up in the revs?
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Re: WHP, How much Transmisson Loss..
#26385
20/01/2006 23:06
20/01/2006 23:06
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Anonymous
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Anonymous
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Seems to me that percentage is a valid way to express losses based on the simple principle that the efficiency of any motor , machine or whatever must satisfy the following equation: Efficiency= Work out/ Work in. This is clearly a linear relationship. Also, have a read of this written by an authority in the States on Rolling Road losses, Quote:
My BIG bugbear though is with so called transmission losses measured on the overrun. Most dyno firms here now insist on giving "flywheel" bhp printouts and often the measured wheel figure is never even shown. IMHO it is IMPOSSIBLE to measure trans losses on a rolling road dyno.
What happens is this - you run the car under load until just after peak power then the operator drops the clutch and lets the car freewheel down against the roller which supposedly measures the "negative" power absorbed and treats this as a trans loss.
Now one thing is for certain - trans loss is a percentage of power input to the system. If the car is in neutral there is no power being fed in. Also the gears are now backlashed against the wrong face of the gear teeth as the roller is driving the car not the other way round. Under these circumstances I see no way in which the trans loss shown can bear any relationship to actual losses when the car is under power.
Tweaking the electronics to generate big overrun losses or just using a touch of brake pedal while the car is winding down makes for big trans losses and a nice fat flywheel power curve to keep the punters happy. I have a number of rules of thumb about transmission losses which I have established over the years from known engines.
On most Front Wheel drive cars trans losses are between 15% and 17% of the flywheel figure. VW themselves quote 15% as being an average transmission loss for their cars. (by trans loss I mean all losses between the flywheel and the road so it includes gearbox, final drive and tyre losses). Low powered cars tend to have a higher % trans loss because tyre losses are more of a constant than a % of power input and so represent a bigger proportion of the engine power than they do for powerful cars.
Rear Wheel drive cars can have 2% or so higher losses due to turning the drive through 90 degrees before it gets to the wheels but they also often have direct drive in 4th gear which cancels this out.
Trans losses will vary with the gear in which the car is tested. This is mainly due to the higher wheel speed in a higher gear leading to greater tyre losses. Always use the same gear and same tyre pressures to make comparisons meaningful for power runs taken at different times.
ALWAYS use the measured WHEEL bhp figures and if you are desperate to know a flywheel figure then add a notional trans loss yourself. The ONLY WAY to accurately know flywheel bhp is to take out the engine and put it on an engine dyno.
Last edited by cosmograph; 20/01/2006 23:09.
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Re: WHP, How much Transmisson Loss..
#26386
20/01/2006 23:19
20/01/2006 23:19
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Anonymous
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Anonymous
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What about torque figures, are they any more reliable?
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Re: WHP, How much Transmisson Loss..
#26387
20/01/2006 23:35
20/01/2006 23:35
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Anonymous
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Anonymous
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Yes, torque is directly measured so will be reliable subject to the accuracy of the resolution of the A/D converters from analogue sensor to digital readout in the PC. More words of wisdom below from some chap who repairs US dyno's Quote:
I have a nice little side business repairing SuperFlow dynomometers, the overwhelmingly dominant dyno in the US. Every magazine article I've ever read used a SuperFlow. The standard SuperFlow is rated at 1000 HP, 10,000 rpm and 800 ft-lbs of torque. The RPM signal is converted to a voltage by a tach chip before being submitted to an A/D converter. The torque signal is derived from a strain gauge attached to the absorber. This signal is also applied to the same A/D converter through an analog mux. Horsepower before SAE correction is the simple calculation:
(torque (ft-lb) * RPM ) / 5252
This computation is done in an analog multiplier for the analog readout and by the CPU for the digital readout. So good, so far. But here's the kicker. The A/D converter is an 8 bit unit. That is, it digitizes the incoming signal into one of 256 binary values. For torque, that is 800 ft-lbs / 256 = 3.13 ft-lbs per bit. For RPM, 10,000/256 = 39 rpm per bit. At a constant 6000 RPM, the best HP resolution is 3.5 hp. At a constant 500 ft-lbs of torque, the best HP resolution is 3.7 HP. This lack of precision results in the best theoretical HP measurement at 6000 RPM being +- 3.5 hp. Worst case is 3.5 + 3.7 = 7.2 hp. The root-sum-square (much more representative of the real world) is 5.0 hp. The precision varies, of course, with RPM. The important point is any horsepower variation less than about 5 hp is meaningless and is more likely attributable to quantitizing error in the electronics. Understand that this does NOT include other systematic error terms such as the errors associated with the analog electronics or the torque sensor calibration. I personally attribute no credibility to differences less than 10 hp.
The other thing to keep in mind when viewing published figures is that the most frequently published numbers are corrected to SAE Net. This correction for ambient temperature, humidity and barometric pressure is only approximate and is really suitable for generating numbers for ad copy where they are legally required. We have conclusively proved that the correction is only approximate using a client's dyno cell that is equipped to control temperature, humidity and baro pressure.
To illustrate the problems involved, I've spent considerable time with a client because his dyno isn't "producing the numbers he wants". His engines, which he sells to racers who make buying decisions largely on dyno sheets, are considerably down on power compared to what his competition claims. His dyno is spot-on calibrated. He has carried an engine around to two other shops, one of which is Bill Elliot's shop in Dawsonville, GA. The span of readings on this engine among the three dynos is over 80 HP on a 500 hp engine! I have personally checked two of the dynos and know them to be properly calibrated. The difference is in the buildup of error terms in this inherently inprecise measurement system and in the SAE net compensation between Florida at sea level and here in Atlanta at about 1000 ft elevation.
Last edited by cosmograph; 20/01/2006 23:38.
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Re: WHP, How much Transmisson Loss..
#26388
21/01/2006 00:42
21/01/2006 00:42
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Anonymous
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Anonymous
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Err thanks Cosmo. I'll pretend I understand all that and take your word for it
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Re: WHP, How much Transmisson Loss..
#26389
21/01/2006 02:49
21/01/2006 02:49
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Anonymous
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Anonymous
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Just to back up the above really, I emailed SRR to ask how they extrapolate flywheel figs and this is Charlie's reply... Quote:
As regards the Flywheel figs, we do not use the 'coast down' method, since its so unrelaliable. The Dyno takes into acount the drivetrain type, the tractive effort and other factors to formulate the estimates from the wheel figs it measures. The system was built by taking cars and running the engines on Engine dynos and then in the cars. Your typical front wheel drive car looses 17% to 20% of the flywheel power available through the transmission, It is extremely rare for FWD cars to loose more than this. I have seen 40% losses 'measured' apparently from other rollers and its simply not possible that the car looses this much power through the tyres and transmission! Hope this helps, if you have any questions, please don't hesitate to contact me. You will be pleased to know we have a kettle and coffee now!
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