Guest bastaad525 Posted December 19, 2003 Share Posted December 19, 2003 I know I've read a lot of conflicting data on this... when you dyno your car on a chassis dyno and get your hp and torque at the wheels, you then want to add x% to that number to get your numbers at the flywheel, which is what most manufacturers usually rate their cars with... good for comparing your car to factory car specs. However, when it comes to the % number to use to get your flywheel #'s, I've read that you need to add anywhere from 15% to 25%... that is a REALLY big difference in #'s!! I find that when I read magazines that do dyno testing on stock cars (like Sport Compact Car) that most cars will usually put down from 15% to 17% less power and torque at the wheels as what they are rated for at the fly (unless you're driving a Dodge SRT-4 which actually puts more to the wheels than dodge rates it at!!!). However, I've heard many people say that this is because they are relatively new cars, and that older cars will ALWAYS suffer more driveline loss than a new car would, due to who-knows-how-much wear on various parts like U-joints, tranny and diff, as well as possibly just their design not being as 'advanced'. So... my question is, on an old first gen Z, running a manual tranny, what do you guys think would be the 'right' % number to use to figure flywheel hp from rwhp? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted December 19, 2003 Share Posted December 19, 2003 Instead of pulling your trans to fix your rear main, pull the whole engine. Take it to a place with an engine dyno, and check it. Then you can tell us all the RIGHT number... within a couple % for deviation. Not too much trouble, right? Jon Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted December 19, 2003 Share Posted December 19, 2003 BAH... let it leak... I gots no $$$ to do a damn thing about it at the moment anyways. Quote Link to comment Share on other sites More sharing options...
Guest 250z Posted December 21, 2003 Share Posted December 21, 2003 don't quote me on this (these are based on what other people have said) but FWD usually loost between 10 - 20%, RWD usually loose 20 - 30% and 4WD usually loose 50 - 60+% the only thread I've seen that has mentioned a 240z's hp loss said 33% but I don't think that's right Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted December 21, 2003 Share Posted December 21, 2003 don't quote me on this (these are based on what other people have said) but FWD usually loost between 10 - 20%' date=' RWD usually loose 20 - 30% and 4WD usually loose 50 - 60+% the only thread I've seen that has mentioned a 240z's hp loss said 33% but I don't think that's right[/quote'] Believe me, I won't, because those number are ridiculous. I am willing to bet they came the new "Honda Power" magazine. Although I like the thought that with a 30% loss in my Z I have an estimated 714hp at the crank :D Quote Link to comment Share on other sites More sharing options...
fl327 Posted December 22, 2003 Share Posted December 22, 2003 33 percent, no way zcars bearly even have a driveshaft! Quote Link to comment Share on other sites More sharing options...
Guest zfan Posted December 22, 2003 Share Posted December 22, 2003 Guesstimations are 13-15 percent with a manual trans and 20 to 23 percent with an auto trans. Mike Quote Link to comment Share on other sites More sharing options...
Guest MistressMotorsports Posted December 22, 2003 Share Posted December 22, 2003 According to the guys at Superior Automotive in Anaheim, who have done a few L28 builds and have engine and chassis dynos in their shop, there is right about 18% loss in a typical Z car with a manual trans and an R180 or R200. Mike Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted December 22, 2003 Share Posted December 22, 2003 I seem to see 17-18% the most for RWD manual tranny cars now that I'm actually looking around for references, and 25% the most common for AT's... Quote Link to comment Share on other sites More sharing options...
johnc Posted December 22, 2003 Share Posted December 22, 2003 There is no number and you cannot compare nor extrapolate horsepower or torque numbers generated on a chassis dyno to numbers generated on an engine dyno. My engine/chassis combo is a perfect example. On Sunbelt's egnine dyno (which is tested and certified monthly) my engine repeatedly produced 305 hp. On a Superior Automotive's chassis dyno (which is calibrated at least monthly) my engine in my 240Z repeatedly produced 279 rwhp with Jim Thompson at the laptop. Both numbers are accurate as far as I'm concerned but they are not comparable. Either my 240Z has the most efficient drivetrain EVER installed in a car (with a 8.5% loss) or my engine gained 15 to 30 horsepower after being installed in the chassis. Quote Link to comment Share on other sites More sharing options...
baddriver Posted December 22, 2003 Share Posted December 22, 2003 I think it is a mistake to try and express the loss as a percent of horsepower, especially for a modified car. The loss should be fairly constant even when a more powerful engine is installed. Transmitting more power might increase the losses a little, but I don't think it'll be a linear relationship. I'd find the gross Hp rating for a z, and try to locate the same years net hp. The difference will probably be around 30 hp. Assume that you loose the same 30 hp if you make 140 Hp or 300. It won't be exact, but should get you in the ballpark. Quote Link to comment Share on other sites More sharing options...
Phantom Posted December 22, 2003 Share Posted December 22, 2003 Well -I think I'd claim the most efficient drivetrain. You'll have a line of the "faithful" beating a path to your doorway to be "enlightened"! All kidding aside - Since most folks can only get access to a chassis dyno - I'd go with the rwhp and call it good. If someone want to know the flywheel tell them to use the multiplier of their choice. Personally, I consider 15% to be a relatively conservative number when working from chassis dyno to flywheel so that's what I'm sticking with. It also corresponds pretty closely with the 1/4 mile to hp calculators that I've tried. Quote Link to comment Share on other sites More sharing options...
datsunlover Posted December 22, 2003 Share Posted December 22, 2003 Personaly, I think the rear wheel HP is the one to know anyway.. If someone tells me their engine has 'X' amount of Hp, they are usually braging a little bit about it. If someone says "I dynoed my car and got 'X' Hp at the wheels" they ussualy know their stuf and are probably telling the truth. The wheels are where the power goes to the road anyway.. Just my %.02 Quote Link to comment Share on other sites More sharing options...
BillZ260 Posted December 22, 2003 Share Posted December 22, 2003 Wouldn't the drag of the drivetrain take a specific amount of power to turn and anything above that be net power? 150 hp 2.6l - 20hp drivetrain loss = 130 rwhp 300 hp 5.7l - 20hp dt loss = 280 rwhp I am sure this is an over simplification, but it makes the most sense to me. Of course the two transmissions used will have equal drag for this explanation. Quote Link to comment Share on other sites More sharing options...
johnc Posted December 22, 2003 Share Posted December 22, 2003 A good chassis dyno operator should be able to determine the drivetrain loss for any vehicle they are running on the dyno. SAE published a standard in 1996: J1263 "Road Load Measurement and Dynamometer Simulation Using Coastdown Techniques" that determines drivetrain and coastdown loads. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted December 22, 2003 Share Posted December 22, 2003 I DEFINATELY dont think it's just a set number but rather a percentage... unless factory ratings get more and more innacurate as they get higher and higher? ( I know I know... that IS a possibility). Because the difference in factory rated hp and hp at the wheels always increases the higher the hp of the car is. A stock civic (not the Si) will have like 15-20hp less at the wheels than it's factory rating, while a big hp car with factory rating of like 400hp, say the supercharged Mustang SVT (390 factory hp rating I believe) 'loses' quite a bit more at the wheels. Anyways I know in the end it is hard to compare the two and they aren't really that relevant to eachother, however for me, it's nice to have an idea of how my car, with it's raised boost and other mods, compares to new cars, just by looking at their factory hp and torque ratings. Of course it's always nice to compare dyno #'s to dyno #'s, that's why I love magazines like SCC that dyno factory, bone stock cars to see how much of their claimed power is indeed getting down to the ground. But then the question arises... how accurate a comparison is that even? What about varying conditions like weather or fuel quality? I dunno... not to make such a big deal about such an imprecise 'science'... it's just nice to know what my car can, on paper at least, keep up with Quote Link to comment Share on other sites More sharing options...
johnc Posted December 22, 2003 Share Posted December 22, 2003 Dynos (engine or chassis) are tuning tools. Race tracks and drag strips are comparison tools. Horsepower and torque numbers are marketing tools. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted December 22, 2003 Share Posted December 22, 2003 I'll weigh in with my 0.02, although I'm sure it's nothing new. It makes sense to me that drivetrain losses are not constant or linear with power output, ie: not a constant 20 or 30 hp, and not a % of total power. It is probably somewhere in between, as the losses in the drivetrain will be somewhat dependent on both rpm and vehicle speed. This places variables in the transmission ratios and the rear-end ratio... Quote Link to comment Share on other sites More sharing options...
Guest daZda rally Posted December 23, 2003 Share Posted December 23, 2003 There are more variables than that even. Any helical(g/box) or hypoid(diff) gear set has sliding contact faces and and generates wasted thrust loads within its casing which the bearings must resist. Both of these produce a loss as a percentage of torque throughput of each gear set. Yes this does mean there will be minimum loss in top gear( 1 to 1 ) as two less gear train paths are used in top.(which ever gear is 1 to 1 ). There is a near linear loss assosiated with friction and oil drag that is proportional to the RPM of the parts that is added to the torque loss. There is also the inertia loss that was mentioned but this only applies if the power run is a sweep or ramp type run where the car is accelerated through a speed range, in which case the rate of accel has a huge effect on the numbers produced. If the dyno pull is at fixed RPM this effect is elliminated( harder on the both car and time(wallet) though). Perhaps the biggest variable and one no one has mentioned is the tyres. Do you all use hub dynos over there? I have not been fotunate enough to ever use one. On a roller type set up tyre size, pressure, load , temp, speed and the phase of the moon all seem to effect the power readings and are quite likely nothing like the same as it would be on a road (flat not round). So I would not ever begin to compare unless you have some experience with the particular components on the vehicle and know how much each takes. Eg - T5 takes ??%, R200 = ??%, Dunlop ??? = ??% Ps - you can tell where the power goes by what gets hot. Peter. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted December 23, 2003 Share Posted December 23, 2003 Dynos (engine or chassis) are tuning tools. Race tracks and drag strips are comparison tools. Horsepower and torque numbers are marketing tools. heheh very well said Quote Link to comment Share on other sites More sharing options...
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