davey_83 Posted April 9, 2016 Share Posted April 9, 2016 I have a habit of trash talking any and all dyno threads, so for my latest I thought I'd start a fresh. Different dyno shouldn't affect transmission losses? Also transmission losses isn't a percentage its an actual HP figure. For example a stock car with 200bhp has losses of 30hp (170whp). If its then boosted and tuned to 400bhp, the whp would be 370 not 340whp (same brakes, wheels, tyres and pressures) No not really , transmission losses are a percentage , the resistance goes up with the horsepower you are moving the same mass yes but quicker and so take more effort I personally don't think you can just use a set percentage figure to calculate the bhp figure. While hosting a rolling road meet, a stock 350z DE puts down 240whp. The next is a fresh JDM fairlady z, so jdm it still has single pot calipers. Anyways owner goes its got exhaust, larger tb, decats, tomei cams, tomei headers and manmanagement. Once warmed up the idle is a tad lumpy tbf. Does its run and makes 250whp, well bolt on UK DE's make that with a remap? You add your percentage and hand the owner a print out for 290bhp. Later its found that one of the rear calipers was partial siezed , maybe sat at the docks to long. So the brakes are now sorted and the car again comes back for a run and makes 265whp. Well all along the engine was 300bhp+ so was it right to simply use a % or should the losses have been calucalated through run down? Quote Link to comment Share on other sites More sharing options...
Richf Posted April 9, 2016 Share Posted April 9, 2016 You said transmission losses stay the same irrespective of how much horsepower the engine makes, its not a true percentage but more a sliding scale but they are certainly not fixed Quote Link to comment Share on other sites More sharing options...
davey_83 Posted April 9, 2016 Author Share Posted April 9, 2016 (edited) But not a set percentage figure, that's why the run down is done I guess. Why does more power mean bigger losses? Edited April 9, 2016 by davey_83 Quote Link to comment Share on other sites More sharing options...
Richf Posted April 9, 2016 Share Posted April 9, 2016 But not a set percentage figure, that's why the run down is done I guess. Why does more power mean bigger losses? Because drivetrains are not 100% efficient . For example if your gearbox is 95% efficient then its loses 5% of the power going through it , thats 5% of 100hp or 1000hp Quote Link to comment Share on other sites More sharing options...
davey_83 Posted April 9, 2016 Author Share Posted April 9, 2016 Agreed but for every example you can't just add a set percentage figure to calculate bhp ie the op with the seized caliper. What is the efficiency of the 350z drive train? typically Appreciate your time Rich David Quote Link to comment Share on other sites More sharing options...
Richf Posted April 10, 2016 Share Posted April 10, 2016 Agreed but for every example you can't just add a set percentage figure to calculate bhp ie the op with the seized caliper. What is the efficiency of the 350z drive train? typically Appreciate your time Rich David That's what most chassis dyno's do for two reasons 1) The market is customer driven, there is no need for a flywheel figure at all but people want the biggest number 2) They have to use something and a percentage works well as an average across a variety of makes and models No idea , the only company I know with both an engine and chassis dyno is Norris Designs they might be able to tell you There is literally tons to read on this subject some good stuff written in the US but take their figures with a grain of salt as their dynos typically read much higher than ours http://www.hotrod.com/how-to/transmission-drivetrain/ccrp-0311-drivetrain-power-loss/ Quote Link to comment Share on other sites More sharing options...
davey_83 Posted April 10, 2016 Author Share Posted April 10, 2016 NM figures for all lol That indicates to me that at a big rolling road meet, every car (same make and model) with the same whp would also have the same bhp? Irrespective of size of wheels, tyres, wheel alignment, brake and clutch condition and even completely different tyre pressures 25psi verses 45psi for example. That simply doesn't make sense to use a board % losses figure to obtain a bhp? What percentage figure typically would you use when calculating bhp? David Quote Link to comment Share on other sites More sharing options...
Richf Posted April 10, 2016 Share Posted April 10, 2016 NM figures for all lol That indicates to me that at a big rolling road meet, every car (same make and model) with the same whp would also have the same bhp? Irrespective of size of wheels, tyres, wheel alignment, brake and clutch condition and even completely different tyre pressures 25psi verses 45psi for example. That simply doesn't make sense to use a board % losses figure to obtain a bhp? What percentage figure typically would you use when calculating bhp? David There are an incredible amount of variables that influence how much power a car can put on the rollers yes, and most of the things you mention there would influence the amount of power to the wheels and therefore the calculated flywheel figure would vary also, even the way the car is strapped down can impact figures. To all intents and purposes a calculation of 18-20% is pretty accurate, but the bottom line is that if you want an accurate flywheel figure you need an engine dyno As I said before customers want the big number sheet, how many people post their whp dyno sheets ? Not many, nobody wants to say that their 370z with bolts on and a map makes 250hp but that fact is they do You would have to ask Jez what the Dyno Dynamics uses as a calculation I would guess its close to 20% These big rolling road meets should be treated as what they are , a bit of fun for like minded people who have an interest in cars to meet up and have a crack not as a means to get accurate data from your car , chances are the car wont be strapped correctly or be set up properly before the run is done , this all takes too much time if you did it all correctly you would get 4 cars done in the day and you would only provide the measured wheel or hub data 1 Quote Link to comment Share on other sites More sharing options...
davey_83 Posted April 10, 2016 Author Share Posted April 10, 2016 True whp and wtq means so much more towards how a car performs more so than bhp. But the industry is geared to prompt bhp and lb-ft figures, well in the UK anyways. Quote Link to comment Share on other sites More sharing options...
Mark@Abbey m/s Posted April 10, 2016 Share Posted April 10, 2016 okay so if a car had recorded 100bhp at the wheels @ 18% losses it would have 118bhp at the flywheel if the same car had 1000bhp at the wheels @ 18% it would have 1180bhp at the flywheel. same car so same run down losses ........162bhp difference.... @ Abbey we use 40bhp added to the hub figure to get an estimated flywheel bhp. 2 Quote Link to comment Share on other sites More sharing options...
Guest marcw79 Posted April 23, 2016 Share Posted April 23, 2016 Sounds like we, the consumer, are to blame ... We should just take whp figures and be happy to have a figure that means something within the context of the occasion on which it was taken ... I guess it wouldn't be a problem if everyone had a grasp of the complexities around the measurement of ... well ... anything really ... Let alone something as multi factorial as this ... If everyone kept their metaphorical todgers in their pants and just used figures as a rough, highly contextual measure of change on their own vehicle then this would be far less of a seemingly contentious topic ... but guys will be guys and we do love some number porn ... Sent from my Nexus 6 using Tapatalk Quote Link to comment Share on other sites More sharing options...
Richf Posted April 23, 2016 Share Posted April 23, 2016 http://mkiv.supras.org.nz/dyno.htm Just to muddy the waters further I found this calculator that offers a comparison between different makes of dyno Quote Link to comment Share on other sites More sharing options...
Mark@Abbey m/s Posted April 23, 2016 Share Posted April 23, 2016 Rich, so if the Dynapack over reads so much as per your linky so why does my dyno which is a dynapack show around 240 hub bhp for a stock Nissan 350Z DE? 1 Quote Link to comment Share on other sites More sharing options...
Richf Posted April 23, 2016 Share Posted April 23, 2016 Rich, so if the Dynapack over reads so much as per your linky so why does my dyno which is a dynapack show around 240 hub bhp for a stock Nissan 350Z DE? Not my figures Mark , just something I found Quote Link to comment Share on other sites More sharing options...
Irn Bru Posted April 23, 2016 Share Posted April 23, 2016 I've just attended a rolling road dyno day with my son and his Focus RS OC club mates up at Wallace Performance in Aberdeen. The whp dyno reading was 1 bhp different from when I had my Zed at Dynatune for the uprev remap and Dynapack hub dyno. 252 whp and 290bhp at the fly. Which ties in with my original guess of 290bhp at the fly on the Dyno test thread. Still miffed at not seeing the magic 300bhp, but happy that both dyno runs returned near identical bhp figures. So as far as I can make out the man maths is +15% of the whp to get the fly bhp. Quote Link to comment Share on other sites More sharing options...
davey_83 Posted April 23, 2016 Author Share Posted April 23, 2016 Pop along to a dynojet and you'll see 300bhp+ Only messing, those are strong numbers either way. I'd rather have 250whp and 290bhp, than 240whp and 300bhp *similar curves david 1 Quote Link to comment Share on other sites More sharing options...
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