Thanks.
Any thoughts on the theoretical figures some dynos give by allowing the rollers to slow down against the engine?
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| Gearbox power loss https://www.ausmini.com/forums/viewtopic.php?f=5&t=53242 |
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| Author: | drivinglights [ Fri May 15, 2009 9:03 am ] |
| Post subject: | Gearbox power loss |
Anyone got any idea how much power loss there is through a (standard: 4-synchro, 3.44 open diff) mini transmission? I've heard figures anywhere between 30 and 50%. Going to get my car chassis dynoed at some point so curious what the hypothetical flywheel figure would be. Thanks. |
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| Author: | sports850 [ Fri May 15, 2009 9:29 am ] |
| Post subject: | |
The 30-50% is often used as each gearbox varies a little bit just like each dyno varies . Probably just average it and say 40% loss and work the figure out from that , the estimated flywheel figure isn't going to be all that accurate anyway so a few % either way won't change much unless you have a super high performance engine . |
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| Author: | drivinglights [ Fri May 15, 2009 9:55 am ] |
| Post subject: | |
Thanks. Any thoughts on the theoretical figures some dynos give by allowing the rollers to slow down against the engine?
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| Author: | Lillee [ Fri May 15, 2009 9:56 am ] |
| Post subject: | |
Too many variables. Gearbox driveshaft output makes a difference, pot joints being better than hardies or ruber unis. Wheel sizes and tyre sizes will also play a role in power transfer. I heard diff types also having a role (quaife lsd versus std) In general people are seeing about 30% loss at the minimum |
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| Author: | awdmoke [ Fri May 15, 2009 10:04 am ] |
| Post subject: | |
What type of dyno? The reason why the Dyno Dynamics is so popular is simply because the correction factors & standardisation (i.e. all tests done in fourth gear, tyres all pumped to 32? PSI, etc) of the test means you can compare one dyno run to another on a different machine / day. |
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| Author: | drivinglights [ Fri May 15, 2009 10:23 am ] |
| Post subject: | |
Not sure yet! Got a specialist lined up, but don't know what he's got. The car is still up on blocks with a few crucial bits missing, anyway! |
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| Author: | Lillee [ Fri May 15, 2009 10:54 am ] |
| Post subject: | |
awdmoke wrote: What type of dyno?
The reason why the Dyno Dynamics is so popular is simply because the correction factors & standardisation (i.e. all tests done in fourth gear, tyres all pumped to 32? PSI, etc) of the test means you can compare one dyno run to another on a different machine / day. That's what they lead you to believe. I bet a case of beer that you'll get 2 different figures for your car on 2 different days because the operator put his foot down differently on one day versus the other. I'm not joking... Engine dyno is the only true repeatable measurement of hp |
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| Author: | awdmoke [ Fri May 15, 2009 11:14 am ] |
| Post subject: | |
True enough, but short of pulling the engine out it's the best way of getting a power figure. Power ATW will be affected by other uncontollable factors too, e.g. wider/stickier tyres will rob measured power. |
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| Author: | Lillee [ Fri May 15, 2009 1:47 pm ] |
| Post subject: | |
It's a good tuning tool, that's about it. Good measurement of comparison HP if run on the same day by same operator. Other than that it's academic. I refer to HP figures published from UK Mini managine's dyno shoot outs. I am sorry but no 1310 with twin 1 1/4 SUs with only a cam and exhaust mods can do 90hp atw. Sorry but no... If you walk away with X hp on your rolling road dyno sheet, and another guy has X hp on his dyno sheet from 1 year ago, it means absolutely nothing. Yes if one says 100hp and the other says 28hp arguably the 100hp one is propably a faster car but by how much can be measured in only in aspragus 
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| Author: | Morris 1100 [ Fri May 15, 2009 5:39 pm ] |
| Post subject: | |
The more power you put through a gearbox the more power you lose as the internal friction will increase with load. It is not just a matter of turning a gearbox and measuring the force taken to turn it. A wheel dyno is a tuning tool and not a measuring stick. 
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| Author: | TheMiniMan [ Fri May 15, 2009 6:05 pm ] |
| Post subject: | |
wide sticky tyres vs skinny crossplys low pressure tyres vs high pressure wheel alignment with excessive toe out/in vs set straight ahead-ish worn gearbox/drop gear assys vs new-ish bearings/gears/shafts & well thrusted box & how much or how tight/hard they pull/strap the car down on the rollers all these things play """Significant""" roles in rolling road dynos but my "Guestimation on the average mini would be ---> """around 25%-ish-approx-maybe-ish""" Big Grunt minis push gears & shafts harder into themselves & thrusts etc so they tend to loose a bit more, but then most sensible "Big-Grunt" car owners would fit C/R S/C gear kits to save loosing that little bit |
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| Author: | drivinglights [ Sat May 16, 2009 3:40 pm ] |
| Post subject: | |
Thanks to all for the info RE the chassis dyno issue! FYI, the dyno is to be used for tuning purposes only (not barstool drag-racing) but I was curious if there was a uniform way to translate that into flywheel power...obviously not! 
Not too concerned. After all, I tend to drive the whole car...not just the engine
BTW: Glad someone else is suspicious about those UK dyno-day figures. I'd almost believe them as flywheel figures, but ATW...no way! 
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| Author: | TheMiniMan [ Sat May 16, 2009 5:19 pm ] |
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It`s all just a guestimation, no matter what dyno & no matter where it is he """REAL""" test is a "Car-To-Car" race
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