Thorin Posted June 7, 2004 Share Posted June 7, 2004 I remember the thread a while ago about hub vs. crank power. I seem to remember that, for manuals at least, the losses were worked out to be ~11%. So for a hub output of 350bhp this would mean a crank output of 390 odd. Which sounds bang on the money to me, in my experience anyway. Quote Link to comment Share on other sites More sharing options...
Thorin Posted June 7, 2004 Share Posted June 7, 2004 In fact I believe this was the thread... http://www.mkivsupra.net/vbb/showthread.php?s=&threadid=14480&perpage=15&pagenumber=1 Quote Link to comment Share on other sites More sharing options...
dandan Posted June 7, 2004 Share Posted June 7, 2004 I say stick to comparing hub figures, don't try to compare from one set of rollers to another, and if you're being really really picky only comparisons done on the same day/morning hold true meaning. If I had to be conservative when someone asked me, I'd add 10 maybe 11% to the figure from the Thor Dyno...at most. This is in a manual, auto maybe slightly more. Just make sure you stick with the same dyno after carrying out different mods and then at leat you've got a relative idea what you've achieved with all the £££ ploughed into the car. Quote Link to comment Share on other sites More sharing options...
eyefi Posted June 8, 2004 Share Posted June 8, 2004 why would transmission losses b a percentage? 2 cars, same drivetrain, different engine. car A has 100 hp, car B has 800 hp. assuming a 20% loss car A looses 20hp and car B looses 160 through the tranny. why would this b? the friction and rotating mass of the tranny, diff, drive shafts, axles would b the same, so should the losses. also with a hub dyno u dont get the losses of a pair of wheels and tyres having to b spun. Quote Link to comment Share on other sites More sharing options...
Jake Posted June 8, 2004 Author Share Posted June 8, 2004 Originally posted by eyefi why would transmission losses b a percentage? This has been gone over before and I think we all realise that trans loses aren't a fixed percentage. Quote Link to comment Share on other sites More sharing options...
Ian C Posted June 8, 2004 Share Posted June 8, 2004 Originally posted by Jake This has been gone over before and I think we all realise that trans loses aren't a fixed percentage. Well volunteered for an addition to the technical FAQ Jake -Ian Quote Link to comment Share on other sites More sharing options...
eyefi Posted June 8, 2004 Share Posted June 8, 2004 Originally posted by Jake This has been gone over before and I think we all realise that trans loses aren't a fixed percentage. u've lost me there, it doesnt look like it from this thread. Quote Link to comment Share on other sites More sharing options...
Jake Posted June 8, 2004 Author Share Posted June 8, 2004 Originally posted by eyefi u've lost me there, it doesnt look like it from this thread. True but it's common sense isn't it? If for example a 320hp Supra loses say 20% through the drivetrain thats 64hp lost. So it takes 64hp to transmit the power But if the same car has a major powerboost to say 800hp but the drivetrain stayed the same it would still only take around 64hp to drive the mechanical parts between the engine and the hubs. OK, it'd be a bit more than 64hp lost because of some other factors like heat or whatever but not all that much, relatively speaking. So a 800hp Supra would be losing a much lower PERCENTAGE of it's power through the drivetrain. If the percentage loss stayed the same that would mean that our imaginary 800hp car was losing 160hp through same drivetrain that only sapped 64hp before. Quote Link to comment Share on other sites More sharing options...
Thorin Posted June 8, 2004 Share Posted June 8, 2004 eyefi stop causing trouble *hiijack* How's your car doing? */hiijack* Quote Link to comment Share on other sites More sharing options...
eyefi Posted June 8, 2004 Share Posted June 8, 2004 Originally posted by Jake True but it's common sense isn't it? maybe it is, but all ive ever seen banded around is a fixed percentage to convert hub or wheel to crank. i posed my original statement as a question because i had not seen this "common sense" idea discussed before, and though it seems logical to me i thought i may b missing something. ive now noticed that tbourner and dandan brought up this notion in the other thread listed by thorin (gaylord) and id agree that the dandan equation would b alot better conversion method. Quote Link to comment Share on other sites More sharing options...
eyefi Posted June 8, 2004 Share Posted June 8, 2004 Originally posted by Thorin eyefi stop causing trouble *hiijack* How's your car doing? */hiijack* its very sort of in lots of bits, im really missing it now. Quote Link to comment Share on other sites More sharing options...
MONKEYmark Posted June 8, 2004 Share Posted June 8, 2004 Originally posted by eyefi its very sort of in lots of bits, im really missing it now. i know how you feel lad. i have been real bored cant do anything. been messing on astra have doe a ice install (fitted ariel in correct place outside of car) fixed my parcel shelf topped it up with oil. it runs like a dream now and you can hardly hear engine. was thinking of becoming a DYNO queen like all the people in here what next DYNO QUEENS + TRAILER QUEENS there is so much confusion on dynos and some places dont know how to dyno the auto`s. use them to get your car tuned for running right. mcanny has been on quite a few dynos with different results. i like to see how well cars do in the 1/4 to get an idea of power. not ideal but the black dyno dont lie i would be well happy running car in ttc mode as its mad. you always have in back of your mind whens it going to let go, so getting fueling checked is good to find any problems. if you dont get the numbers you want you come away dissapointed. when you were happy before with the performance of your car. Quote Link to comment Share on other sites More sharing options...
Tannhauser Posted June 8, 2004 Share Posted June 8, 2004 Originally posted by Jake True but it's common sense isn't it? If for example a 320hp Supra loses say 20% through the drivetrain thats 64hp lost. So it takes 64hp to transmit the power But if the same car has a major powerboost to say 800hp but the drivetrain stayed the same it would still only take around 64hp to drive the mechanical parts between the engine and the hubs. OK, it'd be a bit more than 64hp lost because of some other factors like heat or whatever but not all that much, relatively speaking. So a 800hp Supra would be losing a much lower PERCENTAGE of it's power through the drivetrain. If the percentage loss stayed the same that would mean that our imaginary 800hp car was losing 160hp through same drivetrain that only sapped 64hp before. OK, strictly amateur time now, but here goes.... Let's take one example of a transmission loss. Some of the horsepower is used to spin the flywheel, the function of which is (if I understand) only to keep the crankshaft spinning evenly to give a smooth idle. It takes a certain amount of energy to accelerate the wheels from 0 to, say, 18 rps ( I reckon that's about 60mph - prepares to duck!). The 320bhp supe engine can supply this energy in, say, 5.3 seconds. It takes 238kJ of energy per second to accelerate the rear wheels this fast. To accelerate the wheels any faster needs more enrgy per second - more bhp. In the 800bhp supra, it's supplying energy at the rate of 596kj per second. This is sufficient to accelerate the wheels to the same 18rps in, say, 3.5s. BUT...just as it takes more energy to accelerate the back wheels faster, it also takes more energy to rotate the flywheel faster. In fact, because they are both just masses that need to be moved, the amount of energy, or power 'wasted' will rise at exactly the same rate. Frictional forces within the system will also rise in proportion to the acceleration, which is a function of power.. There may be certain losses that don't depend on power, but I don't know what they might be. But intuitively it seems to me that some of the power loss must rise proportionately. Where's Darren Blake when he's needed? Cliff Quote Link to comment Share on other sites More sharing options...
dude Posted June 8, 2004 Share Posted June 8, 2004 Cliff someones fu**d with yer sig dude its all in Spanish !!!! Dude:flame Dev may wee rodney may wee !!! Quote Link to comment Share on other sites More sharing options...
Tannhauser Posted June 8, 2004 Share Posted June 8, 2004 A little googling turned up this from an engineering site: http://www.engineersedge.com/wwwboard/posts/1847.html Interesting. Edited to say: to cut to the chase, look at the final paragraph on 'iskit4iam's post. Dude, I also speak fluent West Bromwich/Black Country. Quote Link to comment Share on other sites More sharing options...
eyefi Posted June 8, 2004 Share Posted June 8, 2004 Originally posted by Tannhauser OK, strictly amateur time now, but here goes.... same boat mate. no expert but up for the novice debate. the flywheel is there to store energy (among other balance issues). apply power to spin it then remove the power source and the energy stored in the flywheel will keep it spinning. without a flywheel the engine would just drop to idle when u let off the throttle, making the car impossible at best to drive. so the fly would b parasitic when being made to spin faster but enhance torque when at a steady state. the rest of the drivetrain is ultimately rotating mass to b moved and friction to overcome. so what we r interested in here is whether it takes the same amount of torque to overcome the resistance of turning this lot with a 100ft/lbs force as it does with 800ft/lb's. acceleration is a measure from one state to another and i dont think it has an impact on this losses debate, just like the weight of the car doesnt. it does have a real world effect but not on a dyno measuring the twisting force of the engine. does any of that make any sense? Quote Link to comment Share on other sites More sharing options...
eyefi Posted June 8, 2004 Share Posted June 8, 2004 Originally posted by Tannhauser A little googling turned up this from an engineering site: http://www.engineersedge.com/wwwboard/posts/1847.html Interesting. Edited to say: to cut to the chase, look at the final paragraph on 'iskit4iam's post. Dude, I also speak fluent West Bromwich/Black Country. hmmmm, interesting. Quote Link to comment Share on other sites More sharing options...
eyefi Posted June 8, 2004 Share Posted June 8, 2004 just for ref. here is the post from tannhauser's link The answer is neither of your answers may be correct._ You_ have to look at what is causing the energy loss._ Part of the loss is due to moving the lubrication fluids around._ The energy to move the fluid is not a function of power through the system._ Part of the loss is due to frictional forces._ Frictional forces are proportional to the transmitted force, which is proportional to the transmitted power._ So friction forces will be a percentage of transmitted power and fluid movement forces will be fixed._ And there are lots of other factors making up your losses._ So, the 285HP motor may not lose 18% but is will certainly lose more than 38HP._ For the exact same drivetrain at the same rpm._ (experience tells me fixed losses are small compared to proportional losses so the practical answer is you lose 18%) Quote Link to comment Share on other sites More sharing options...
Tannhauser Posted June 8, 2004 Share Posted June 8, 2004 OK, I know how to convert between hp and torque, but TBH I get a lttle lost in the relationship between the two and that doesn't help in trying to get my head round this.. However, IMO, I think that acceleration is very relevant here. The drive train has a certain rotational mass, as you say. This is fixed and doesn't vary with the power of the car. But, force (torque) = mass x acceleration. Therefore, the faster the engine accelerates the drive train, the more torque it requires to do so. Therefore more torque is wasted, in absolute terms, the faster the drivetrain is accelerated. A more powerful engine can accelerate the drivetrain faster than a less powerful one. Therefore loss in torque or loss in power both increase in proportion to maximum power output of the engine. What do you reckon? Quote Link to comment Share on other sites More sharing options...
Justin Posted June 8, 2004 Share Posted June 8, 2004 So to conclude the only way to find out what bhp your car is - is to measure it at the flywheel which is pretty unworkable. F*ck knows what actual bhp j-specs come out of Japan are. 280 is obviously not accurate. My Thor dyno was 357 at the hubs. If I was to upgrade something (Hybrids or intercooler whatever) on the same day with the same ambient temps etc and it came out 420 then this would equal a good power enhancement. Pete always says that his measurements are at the hubs. Finding the true bhp seems to be a bit impossible. His machine is consistent so you can see, by using his kit, what difference a mod has made to your individual car. The best thing is for a few totally stock cars to be measured and see what they average out at. Then we could calculate the transmission losses a bit more accuratley. Having said that a totally stock J-Spec could be anything between 280 - 320 bhp so there is already a 40bhp discrepancy there!!!!!!! The mystery continues PS: at the pub I say my car is around 400 bhp or just over 357 rhhp + 15% = 410bhp Quote Link to comment Share on other sites More sharing options...
eyefi Posted June 8, 2004 Share Posted June 8, 2004 Originally posted by Tannhauser What do you reckon? im off to bed, see ya tomorrow Quote Link to comment Share on other sites More sharing options...
Thorin Posted June 9, 2004 Share Posted June 9, 2004 Originally posted by Justin The best thing is for a few totally stock cars to be measured and see what they average out at. Then we could calculate the transmission losses a bit more accuratley. Which is what we tried to do in the other thread that I linked and hence came up with the 11% figure. Quote Link to comment Share on other sites More sharing options...
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