The weight thing may be a recurring problem at RS from what i see. My dyno sheets list my car at #3080! holy crap, i was giving up a lot of HP. thats about #300 more than my car actually weighs. I wonder what my HP would be adjusted for that... But seriously, a WRX weighing in at 2900 is really, really difficult. The top SCCA WRX's barely make that weight and that's with nothing but a drivers seat and a ton of weight reduction parts. Stock WRX is #3200, so you'd have to get #300 off the car, which is pretty difficult to do. not saying you didnt do that, but it is difficult for some to believe as it is very uncommon. On a truck stop scale my car once weighed in a #2500. (actual weight from the most accurate scales i have had it on, not corner weighting scales is approx #2700) They're not accurate withing a +- of at least #250. If you're going to give weights of cars, its best to stick to what comes off of a corner weighting scale setup or around what the manufacturer says stock is. I know grain scales may be calibrated, but nobody really knows for sure on those things for performance cars, they just have to take your word for it. I'm not knocking the setup or skeptical about anything else, but I don't know how much the weight variable affects the HP output on the dyno. If it does, I need to have ron send me some adjusted sheets.
On a dyno, a car that produces 200 WHP at 3400 lbs should be making less when the weight is entered 300 lbs less. Put it this way, a motorbike that weighs 400 lbs and accelerates as fast as a 200 WHP 3400 lbs WRX will just dyno at ~40 WHP. Vice versa, a semi that can accelerate as fast as a 200 WHP WRX would be dynoing waaaay more WHP. You guys get what I'm saying or do I have this whole acceleration = WHP thing all messed up?
I don't understand why the weight would be so important except for 1/4 mile simulation and to help with loading during part throttle tuning. 200whp is 200whp no matter if it's from a motorcycle or semi. Of course, the 200whp motorcycle would be much faster than a 200whp semi. The dyno software should be able to figure out the HP/torque by either calculating the drum roller wieght vs how fast it gets accelerated or by direct use of a strain gauge and an eddy current retarder.
If you put the same car on the dyno twice, once at 3080 and another pull at 3440 you will see a difference in HP, how much? I have no idea.
perhaps the loaded friction of the rollers is calculated differently based on weight. just a guess...
i think jasons weight was off once. the first dyno he was light and dyno'd at 271ish, the second dyno, he was ~100lbs heavier and dyno'd 20whp less. i'm not 100% sure on those numbers, but say every 100lbs+ - equals + - 20 whp so with this example, his 300lb difference would correlate to 60whp, which is about the difference we are all arguing about here.
i thought hp was calculated by how fast the car could get the rollers moving...... i just dont see how weight could affect your hp #'s....
So if I'm seeing this right, if the weight was put in at 3083 for Parker, and that's a Low Curb Weight for the car, and they say the HP reading is rated lower when the weight is lower.. That would only mean if the weight was correct, that the HP would be higher.. Unless I read this wrong.. I would of thought that if the car was listed in lower weights the HP would read higher, and the chart showed 3083 LBs, however after talking to Parker, he said it read out to be 2990 or so, somewhere in the 2900 range... I'd also wonder why the Curb Weight would be entered into the dyno different everytime.. Wouldn't make any sense, nothing would be consistent..
If weight does play into the calculation, that is a really poor way for a dyno to operate. It makes perfect sense for 1/4 mile calculations or to help loading, but loading shouldn't change the power output much at all. If increased loading is making the pull significantly longer and the intercooler, coolant system, intake manifold, etc are starting to heat soak or cause knock and lower power, then that makes sense also.
A car with 3300lbs of weight will be offered more resistance to the initial torque of the wheels and also to the running torque of the wheels than a 2800lb car. There are multiple forces acting on a car that cannot be simulated across the board with set values on a set of rollers. Therefore the forces must be simulated and adjusted for the weight of the vehicle. The pressure exerted downward on a car on the road will obviously be greater for a 3300lb car than it will for a 2800lb car. This downward pressure also will act in a negative way on acceleration. This can be proven by taking an empty skateboard, and pushing it on a linolium floor and measuring the distance it goes...now stand on teh board and have someone push you. It takes more power to get you going and more power to keep you going. You will not be able to apply the same pressure to the board and achieve the same results. With that in mind, we are now on a set of rollers that, when not engaged, apply virtually zero resistance to motion. To simulate the resistance of the car to the road based on weight, you must apply a load that negates acceleration to the rollers. This is my theory, btw, not a definitive guide as to how dynos make calculations or anything, I'm just going on my understanding of physics and torque in general.
Also, if you were to use the explaination above in regards to the motorcycle example, it would read extremely low, why? Because if you entered the motorcycle's weight as 3300lbs, the rollers would apply the simulated force that a 3300lb car would have acting against it by it's wieght. THus the motorcycle would have to overcome that weight. It would be as if you had a 2400lb man on a 800 lb motorcycle and tried to get it moving. The rollers apply reverse force to the rear wheel to simulate wieght. The dyno does not read power based on how quickly you make the rollers move or how fast you make them accelerate to a given speed, it measures based on your vehicles ability to overcome the force applied which is based upon vehicle weight.
And if the above statements are true, then this would be a very good way for a dyno to operate since it gives a real world example of how the vehicle overcomes its own weight acting against it.
argh, i guess ron didnt notice that a GC8 WRX is a tad lighter. This does bring some of my dyno numbers into perspective. that also means on 10lbs of boost, my car makes 220-235whp/and 220-245wtq using justin's rough conversion. (on 10 lbs it did 175whp/185wtq) that doesnt sound right... but obviously the conversion factors are big guesses too, or else my car makes a sheeit ton of power when i retune for 18lbs....
Well.. From what I've viewed then.. Parker's car being rated at 3083 lbs; he was given more resistance on the roller drums than his actual weight, if the grain scale weighed him in under 3000lbs... There-fore, in reality; his HP #'s should actually be higher.. Some good info on Dyno's.. On a web-forum.. http://www.fargostreet.com/showthread.php?t=4893&page=14&pp=10&highlight=Dyno ^^^ This is when Tintmaster's was planning getting a feeler post on getting a DYNO in the ND area.. Anyways; I don't understand why people would mess with the weight to get diff. results. You'd want to try and get a consistency; so each time you dyno; you improve your HP or get a more fine tune.. at least.. Some dyno's will even configure in the difference of room temps into part so the #'s are more realistic..
A grain scale is not an accurate representation of passenger vehicle weight...get weighed on a corner weighting system.
Ya.. But as parker said; it has been tested what? Monthly to be proven to be 20-30 lbs within accuracy... Not like 200-300lbs..
Ok..... From what I understand.... We could take a, lets say a 200whp car..... And if I throw 300lbs in the trunk, and add the 300lbs to the total weight of the car, it will no longer put down 200whp?!!!?..... Somethings not adding up here.... Or is it just me?
but for the sake of argument, could be tared with a preload of an excess of 4000 lbs for all we know. Or only have a useful sampling rage within a certain range.
Well.... For the sake of argument... Its a completly electronic scale, and has proven to be accurate up to 200,000lbs, within the 20-30lb margin of error.... So... Its accurate... Theres no preload, and the usefull sampling range would be up 200,000lbs... After that, it can be up to 300lbs off....
So unless parker's car is over 200,000lbs including Parker in his car to throw off 200-300 lbs... The only thing I could say is.. Parker... GO ON A DIET! ROFL j/k buddy!
What was the low end of that scale's accuracy range. Torque wrenches can have a range of 10 - 100 ft/lbs, but if the accuracy range is from around 20 - 90 ft/lbs. You should never use a torque wrench to torque a bolt that has a torque down rating below the bottom 10% and the top 10%. I'm making assumptions here, but I would be willing to bet that a grain scale isn't usually used to measure 1.5ton vehicles. So why would they calibrate it to do so? Have you stood on that scale to see what you weigh?
Ok, everyone keep missing the little points that screw up the big picture. Readymix is 90% correct. Ok, you have a know car weight (call it X). Now we put the car on the MUSTANG dyno and enter the car's weight as X. The dyno applies a certain amount of torque and the dyno knows a certain rpm is a certain roller speed (this is the dyno calibration that is done on EVERY CAR). Now, once the pull start, it times the it takes the starting roller speed vs the ending roller speed times the time to figure part of the equation out. then it goes in and uses that number to get a CALCULATED hp. Now, if you use everything the same, EXCEPT the weight, you hp will change (heavier will equal more power). The heaver the car, the more hp it takes to excelerate the rollers for the start to the finish speed. It is alot like the drag strip where is does take time into the equation. I will post more if people still don't get it. Russ
If you weigh the car at 3000lbs i.e. and does 1/4mi. in 12sec. and a 4000lbs. car also does it in 12 sec. 1/4mi. Wouldn't you think the 4000lb car, which is 1000lbs more has to show more HP and TQ to get it in the same ETA as the 3000lbs car.
Wow...who knew this thread would get this much action! POW! Looks like Ron has alot of dyno to do this summer...=)
minus some of the bs you have to sift through, it is turning out to be somewhat informative to those of us that did not totally understand how the dyno works. Thanks eveyrone for your .02
Yes, obviously it would. But you are talking about a drag strip, we are talking about an instrument that measures the power applied to the wheels of a vehicle. Lets take your scenario...If you put a 3000lb car on a dyno and entered in the weight of the vehicle as 3000lbs, it would produce a number...this would be a horsepower figure that is based on a car that weighs 3000 lbs. Then you take a truck, that weighs 4000lbs and put him on the dyno and entered his weight as being 4000lbs he would also produce a horsepower figure based on a car that weighs 4000lbs. If you took that truck on the same dyno, and entered his weight as 3000lbs, he would pull a significantly higher horsepower number because the dyno is giving him the resistance that a 3000lb car at rest would exert. If you put the 3000lb car on the dyno and entered its weight as 4000lbs, it would read a much lower horsepower because the rollers are subjecting it to the resistance that a 4000lb car at rest would exert. The 3000lb car would have to move a 4000lb car worth of load while the 4000lb truck would have to move a 3000lb car worth of load on the dyno. Remember, the actual weight of the vehicle has nothing to do with the weight that is entered on the dyno.
oh i understood it a while back, im just saying that hopefully that statement should clear all this confusion up... smart ass
