482 RWHP dyno result AutomobileMag
- Thread starter '14 Shelby
- Start date
I just finally said enough's enough and did some searches.
-sae found % math's totally inaccurate in 2002 when they set out to find if it was viable. There are literally thousands of pages of measures results and data from that time period. They had basically set out to prove/disprove the validity of such ideas. They concluded it can't be done accurately because engine hp and hp delivered to the pavement have far too many variables at play. One rwd car may lose 70whp to the ground, it's competitor as little as 30whp, both being comparable from transmission to layout et al. They found such results. Every application will have difference losses based on the design, and optimized state of the system transferring power from the flywheel to the pavement.
Many people have had their project car eat up a little whp/tq from switching to wider, taller, larger or higher rotational mass, and rotational inertia wheels.
Many posts are all over the web with back to back tests of wheel combos on dynos varying output from insignificant noise to 20+ whp. The difference in the wheels/tires/height/rotational inertia/et al are indeed subject to the laws of physics.
Some examples:
-z06 owner lost 12whp going from 285/40/17's weighing like 39lbs with tires to 305/35/18's weighing like 51lbs with tire. 24lbs total. Didn't have pic of wheels but likely the rotational inertia was higher as well vs original combo.
Bmw m3 owners were talking at lengths about losing 20whp going from 18's to 20's. Similar weight wheels still lost power, and a member/engineer on the site brought up rotational inertia and the slightly taller overall tire height, like .8" iirc.
Evo, supra, corvette, et al forums had similar posts.
Search for yourselves, I'm content.
Some interesting things:
-a differential that splits force 90* as in a traditional f/r car loses the most power, up to 6-10% of the power being transferred depending on many variables from gear tooth type to size, etc.
-idling inertia is very minimal, but linear inertia such as acceleration is a, believe it or not, linear detriment to power delivery to the ground.
-gearing can and can't effect rwhp output readings depending on the dyno type
-clutches, converters, clutch packs, driveshafts, halfshafts and any moving component can adversely effect power delivery to the ground if improperly or not fully balanced, capable, optimized or otherwise perfect for the condition. In short, a better engineered clutch/halfshaft/et al can result in a "gain" of whp. Same with a better balanced/lighter drive shaft, etc. it's very marginal. We're talking 10th of a tq value, maybe 2wtq. It's within the noise but is also real. It's why tests are 3 pulls, etc. There can be no science of exactness when dealing with so many variables, but lots of findings show its the case. Believe it's noise of it makes you more comfortable because real world, it's impossible to feel 2wtq, but the lighter, revvier nature is noticable. It's a better mood for transient driving or max effort driving than cruising/static driving.
-the gains attainable by those last aforementioned mods is very small as the factory units do not eat up much power at all. As little a 3-4lbs of torque may be needed to spin a driveshaft on a passenger car.
-you can actually hurt the performance of a car by putting lighter wheels on it. If the weight is farther outside, and rotational inertia increases, the handling effects and wheel rate can change adversely.
-torque produced by an engine can very easily be tranfered into heat in less than optimal conditions. This alone can eat up 20+ lbs of torque in a sub par combo. Diff coolers are a great idea when really modifying a car well past factory power levels. Trans coolers too.
-heavier tires can effect power distribution to the ground, as can heavier brake rotors, but it's very insignificant.
Lots more but I'm sure anyone who cares would have already looked it up.
Quick test on a camaro ss. Back to back, just changing the wheel combo resulted in gains of 8whp and 10wtq bone stock car. The combo with ccw wheels (lightest) were the widest, at 11" and a 315 tire iirc. Keep in mind the factory tires were 275's so some friction losses mean a lighter still 9" wide ccw on 275's would likely make another hp or 2.
http://mbworld.org/forums/c63-amg-w204/432257-dyno-runs-effects-wheel-tire-weights-wheel-horsepower.html
-sae found % math's totally inaccurate in 2002 when they set out to find if it was viable. There are literally thousands of pages of measures results and data from that time period. They had basically set out to prove/disprove the validity of such ideas. They concluded it can't be done accurately because engine hp and hp delivered to the pavement have far too many variables at play. One rwd car may lose 70whp to the ground, it's competitor as little as 30whp, both being comparable from transmission to layout et al. They found such results. Every application will have difference losses based on the design, and optimized state of the system transferring power from the flywheel to the pavement.
Many people have had their project car eat up a little whp/tq from switching to wider, taller, larger or higher rotational mass, and rotational inertia wheels.
Many posts are all over the web with back to back tests of wheel combos on dynos varying output from insignificant noise to 20+ whp. The difference in the wheels/tires/height/rotational inertia/et al are indeed subject to the laws of physics.
Some examples:
-z06 owner lost 12whp going from 285/40/17's weighing like 39lbs with tires to 305/35/18's weighing like 51lbs with tire. 24lbs total. Didn't have pic of wheels but likely the rotational inertia was higher as well vs original combo.
Bmw m3 owners were talking at lengths about losing 20whp going from 18's to 20's. Similar weight wheels still lost power, and a member/engineer on the site brought up rotational inertia and the slightly taller overall tire height, like .8" iirc.
Evo, supra, corvette, et al forums had similar posts.
Search for yourselves, I'm content.
Some interesting things:
-a differential that splits force 90* as in a traditional f/r car loses the most power, up to 6-10% of the power being transferred depending on many variables from gear tooth type to size, etc.
-idling inertia is very minimal, but linear inertia such as acceleration is a, believe it or not, linear detriment to power delivery to the ground.
-gearing can and can't effect rwhp output readings depending on the dyno type
-clutches, converters, clutch packs, driveshafts, halfshafts and any moving component can adversely effect power delivery to the ground if improperly or not fully balanced, capable, optimized or otherwise perfect for the condition. In short, a better engineered clutch/halfshaft/et al can result in a "gain" of whp. Same with a better balanced/lighter drive shaft, etc. it's very marginal. We're talking 10th of a tq value, maybe 2wtq. It's within the noise but is also real. It's why tests are 3 pulls, etc. There can be no science of exactness when dealing with so many variables, but lots of findings show its the case. Believe it's noise of it makes you more comfortable because real world, it's impossible to feel 2wtq, but the lighter, revvier nature is noticable. It's a better mood for transient driving or max effort driving than cruising/static driving.
-the gains attainable by those last aforementioned mods is very small as the factory units do not eat up much power at all. As little a 3-4lbs of torque may be needed to spin a driveshaft on a passenger car.
-you can actually hurt the performance of a car by putting lighter wheels on it. If the weight is farther outside, and rotational inertia increases, the handling effects and wheel rate can change adversely.
-torque produced by an engine can very easily be tranfered into heat in less than optimal conditions. This alone can eat up 20+ lbs of torque in a sub par combo. Diff coolers are a great idea when really modifying a car well past factory power levels. Trans coolers too.
-heavier tires can effect power distribution to the ground, as can heavier brake rotors, but it's very insignificant.
Lots more but I'm sure anyone who cares would have already looked it up.
Quick test on a camaro ss. Back to back, just changing the wheel combo resulted in gains of 8whp and 10wtq bone stock car. The combo with ccw wheels (lightest) were the widest, at 11" and a 315 tire iirc. Keep in mind the factory tires were 275's so some friction losses mean a lighter still 9" wide ccw on 275's would likely make another hp or 2.
http://mbworld.org/forums/c63-amg-w204/432257-dyno-runs-effects-wheel-tire-weights-wheel-horsepower.html
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I don't think we are looking at this the same way. Some of your statements are valid but your inserting too many variables into the equation. Keven P hit the nail on the head. All we were discussion is the effect of mass on power output. Wheel size, gear boxes, dyno measurements, ect ect is making this more complicated then what was originally stated.
Simple law of physics: Energy cannot be destroyed nor created. It can only be converted into another form of energy. Take 2 engines with identical power output. One has a flywheel the other does not. Run them both up to maximum power/max rpm. Now apply an identical load to both engines and ask yourself which one is capable of producing more work? The answer is neither, the power both engines are producing is the same. The difference is the engine with the flywheel will store energy (which in the case of an automobile is something you don't want which is what you were implying and correctly so) while the engine without the flywheel does not (figuratively speaking) which is not diverting some of the power during acceleration to the flywheel which in the case of a generator or a locomotive will be an advantage making energy available during a sudden demand for power until that energy is expended.
Bottom line: under load less rotating mass with accelerate faster while more mass will decelerate slower but the work potential will be identical.
For our purposes rotating mass is the enemy but to the guy running a hammer forge it's his friend
We are definitely on the same page regarding many things. I think where you might be thinking I'm not on the same page is under the hood.
I think you are assuming I'm saying these changes make the engine produce more power. I'm saying the engine power production has never changed, just that less of its power production is being translated into heat or power to drive inertia and various loads.
^^This. Which means more power is making it to the ground. And that means a chassis dyno should read a higher output number.
Exactly.
I can tell you the 85% number is pretty close. I have a Windsor with a Tremec Magnum XL making 530 crank hp in a 2012, and a Mustang in-floor dyno is showing just a hair over 450 at the wheels. Automatics show more parasitic loss.
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