Modded 2009 ZR1 Video: 581 rwhp & 599 rw tq
#46
01-14-2009 | 07:03 AM
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I was obviously joking with my percentage statements above, as every car and every scenario is different, so it's impossible to stamp a % for every stick or auto car.
I'm no scholar by any means, but I don't understand how frictional losses won't increase with HP? I don't think it would be a fixed % as HP rises, but the HP lost would still have to rise wouldn't it? Even if the percentage of loss were dropping? With higher horsepower comes higher losses to friction and inertia.
I'm no scholar by any means, but I don't understand how frictional losses won't increase with HP? I don't think it would be a fixed % as HP rises, but the HP lost would still have to rise wouldn't it? Even if the percentage of loss were dropping? With higher horsepower comes higher losses to friction and inertia.
Shane,
My post wasn't directed towards you. That said, why would drivetrain friction increase commensurately with an increase in engine HP? It's the same tranny, same driveshaft, same differential, same lubricant etc... It robs a certain amount of power from the motor, but that amount will certainly not be equal to the gains in HP.
Now, if you increase RPM, you will see an significant increase in frictional losses, but that's a physical response to an increase in speed...not an increase in power. You'd see the same increase in friction by simply raising the rev-limit 500 rpm of an engine without making any changes in power whatsoever.
Another way of looking at it is this: Does a bicycle's friction in a certain gear increase correspondingly when you pedal with more force at the same speed? I don't think so.
Now stop arguing with your elders.
Last edited by Divexxtreme; 01-14-2009 at 07:18 AM.
#47
01-14-2009 | 07:34 AM
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Shane,
My post wasn't directed towards you. That said, why would drivetrain friction increase commensurately with an increase in engine HP? It's the same tranny, same driveshaft, same differential, same lubricant etc... It robs a certain amount of power from the motor, but that amount will certainly not be equal to the gains in HP.
Now, if you increase RPM, you will see an significant increase in frictional losses, but that's a physical response to an increase in speed...not an increase in power. You'd see the same increase in friction by simply raising the rev-limit 500 rpm of an engine without making any changes in power whatsoever.
Another way of looking at it is this: Does a bicycle's friction in a certain gear increase correspondingly when you pedal with more force at the same speed? I don't think so.
Now stop arguing with your elders.
My post wasn't directed towards you. That said, why would drivetrain friction increase commensurately with an increase in engine HP? It's the same tranny, same driveshaft, same differential, same lubricant etc... It robs a certain amount of power from the motor, but that amount will certainly not be equal to the gains in HP.
Now, if you increase RPM, you will see an significant increase in frictional losses, but that's a physical response to an increase in speed...not an increase in power. You'd see the same increase in friction by simply raising the rev-limit 500 rpm of an engine without making any changes in power whatsoever.
Another way of looking at it is this: Does a bicycle's friction in a certain gear increase correspondingly when you pedal with more force at the same speed? I don't think so.
Now stop arguing with your elders.
In your bicycle example, it would be the same if you weren't accelerating, but if you were, it would take more work to accelerate faster.
I was thinking more along the lines of if you have a brick on a concrete slab with a very weak string attached to it, it would drag the brick across the concrete if you used a a gentle tug gradually increasing speed, but would break if you tripled your strength with the tug. Not pulling any faster, but getting to the full speed of the pull much faster. Wouldn't the forces of inertia and friction be greater on the stronger pull?
Last edited by 2bscrewed; 01-14-2009 at 07:56 AM.
#48
01-14-2009 | 03:33 PM
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Scott, you left out one important detail when doing your figures; blower works off the crank and there is a slight loss to turn the blower which would also strip loss through the drive train or even at the crank. I do agree once you get to a certain level then a % can be tossed out the window.
Cheers,
Allen
Cheers,
Allen
Something everyone needs to keep in mind is that using the % method for figuring out crank HP is extremely inaccurate once you start moving away from a car’s stock HP level. Everyone continues to use the exact same percentage loss that the car had when the motor was stock, but drivetrain losses do not increase commensurately to HP increases. In other words, friction in the drivetrain does not increase correspondingly to power changes in the motor. It physically doesn’t work that way.
For example; we all agree that if a bone stock Z06 makes 440 rwhp (505 crank HP), it’s losing around approximately 12% of its power through the drivetrain, right? Now, let’s say you install a mild blower on the same car and the rwhp is increased to 600 rwhp on the same dyno. This is where most people automatically default to using the original 12% figure to determine the new crank HP. They would say that the car is now making 681 crank HP since 12% of 681 is 81. But again, friction losses in the drivetrain are not commensurate with HP increases in a motor. This way of figuring crank HP gets even more inaccurate when you start using % figures larger than 12% (i.e., 15% or 20%). The larger the % figure, the more innacurate it becomes.
A much more accurate method is to simply figure out the difference between the stock crank HP figure (using SAE ratings) and the stock rwhp number (assumning the same dyno is used before and after mods). In the case of the stock Z06 above, the difference is 65 HP (505-440=65). Thus, that same Z06 with the mild blower making 600 rwhp on the same dyno is making around 665 crank HP.
Now…if that same Z06 made 700 rwhp with more boost, you are now looking at approximately 765 crank HP, instead of 795 like the 12% formula says.
For example; we all agree that if a bone stock Z06 makes 440 rwhp (505 crank HP), it’s losing around approximately 12% of its power through the drivetrain, right? Now, let’s say you install a mild blower on the same car and the rwhp is increased to 600 rwhp on the same dyno. This is where most people automatically default to using the original 12% figure to determine the new crank HP. They would say that the car is now making 681 crank HP since 12% of 681 is 81. But again, friction losses in the drivetrain are not commensurate with HP increases in a motor. This way of figuring crank HP gets even more inaccurate when you start using % figures larger than 12% (i.e., 15% or 20%). The larger the % figure, the more innacurate it becomes.
A much more accurate method is to simply figure out the difference between the stock crank HP figure (using SAE ratings) and the stock rwhp number (assumning the same dyno is used before and after mods). In the case of the stock Z06 above, the difference is 65 HP (505-440=65). Thus, that same Z06 with the mild blower making 600 rwhp on the same dyno is making around 665 crank HP.
Now…if that same Z06 made 700 rwhp with more boost, you are now looking at approximately 765 crank HP, instead of 795 like the 12% formula says.
#49
01-14-2009 | 11:20 PM
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It absolutely does require more work, in the form of engine (or leg power)...since increasing the speed of an object requires more energy. But it's not increasing friction proportionately to the required increase in power. Thus, using a static percentage to convert rwhp into crank hp is innaccurate.
I was thinking more along the lines of if you have a brick on a concrete slab with a very weak string attached to it, it would drag the brick across the concrete if you used a a gentle tug gradually increasing speed, but would break if you tripled your strength with the tug. Not pulling any faster, but getting to the full speed of the pull much faster. Wouldn't the forces of inertia and friction be greater on the stronger pull?
Last edited by Divexxtreme; 01-14-2009 at 11:42 PM.
#50
01-14-2009 | 11:41 PM
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Scott, you left out one important detail when doing your figures; blower works off the crank and there is a slight loss to turn the blower which would also strip loss through the drive train or even at the crank. I do agree once you get to a certain level then a % can be tossed out the window.
Cheers,
Allen
Cheers,
Allen
That loss doesn't matter to this particular discussion because, remember, we're looking for the difference in power between the power at the flywheel (which is more accurate the crank, even though both terms are used interchangeably) and the actual power made at the rear wheels.
So, regardless of the power lost to the flywheel from a parasitic component (such as a blower), you still have what you have at the flywheel. Be it 600 or 700 HP. But the loss from the flywheel to the rear wheels will still be similar in HP to the loss you had when the car was stock, since the same drivetrain is being used....and can't magically increase it's friction losses proportionately to increases in flywheel HP.
Using the same blown Z06 example, if that blower was 100% non-parasitic and the engine made 700 hp instead of 665 at the flywheel, you'd see 635 rwhp instead of 600 rwhp (approximately) since the drivetrain loss still removes roughly the same 65 HP from whatever is being produced at the flywheel.
Another example would be installing a set of forged, non-titanium rods in the same motor. It has been shown that due to their weight, they will actually produce less HP than the stock titanium rods will on a LS7. So, that would be parasitic loss as well due to increased friction because of the extra weight. But again, we don’t care because all that matters for the purpose of this discussion (which is accurately converting from rwhp to flywheel HP) is the actual power lost between the flywheel and the rear wheels....not how much power was lost by the time it got to the flywheel.
Later,
Scott
Last edited by Divexxtreme; 01-14-2009 at 11:49 PM.
#51
01-15-2009 | 05:27 AM
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Allen,
That loss doesn't matter to this particular discussion because, remember, we're looking for the difference in power between the power at the flywheel (which is more accurate the crank, even though both terms are used interchangeably) and the actual power made at the rear wheels.
So, regardless of the power lost to the flywheel from a parasitic component (such as a blower), you still have what you have at the flywheel. Be it 600 or 700 HP. But the loss from the flywheel to the rear wheels will still be similar in HP to the loss you had when the car was stock, since the same drivetrain is being used....and can't magically increase it's friction losses proportionately to increases in flywheel HP.
Using the same blown Z06 example, if that blower was 100% non-parasitic and the engine made 700 hp instead of 665 at the flywheel, you'd see 635 rwhp instead of 600 rwhp (approximately) since the drivetrain loss still removes roughly the same 65 HP from whatever is being produced at the flywheel.
Another example would be installing a set of forged, non-titanium rods in the same motor. It has been shown that due to their weight, they will actually produce less HP than the stock titanium rods will on a LS7. So, that would be parasitic loss as well due to increased friction because of the extra weight. But again, we don’t care because all that matters for the purpose of this discussion (which is accurately converting from rwhp to flywheel HP) is the actual power lost between the flywheel and the rear wheels....not how much power was lost by the time it got to the flywheel.
Later,
Scott
That loss doesn't matter to this particular discussion because, remember, we're looking for the difference in power between the power at the flywheel (which is more accurate the crank, even though both terms are used interchangeably) and the actual power made at the rear wheels.
So, regardless of the power lost to the flywheel from a parasitic component (such as a blower), you still have what you have at the flywheel. Be it 600 or 700 HP. But the loss from the flywheel to the rear wheels will still be similar in HP to the loss you had when the car was stock, since the same drivetrain is being used....and can't magically increase it's friction losses proportionately to increases in flywheel HP.
Using the same blown Z06 example, if that blower was 100% non-parasitic and the engine made 700 hp instead of 665 at the flywheel, you'd see 635 rwhp instead of 600 rwhp (approximately) since the drivetrain loss still removes roughly the same 65 HP from whatever is being produced at the flywheel.
Another example would be installing a set of forged, non-titanium rods in the same motor. It has been shown that due to their weight, they will actually produce less HP than the stock titanium rods will on a LS7. So, that would be parasitic loss as well due to increased friction because of the extra weight. But again, we don’t care because all that matters for the purpose of this discussion (which is accurately converting from rwhp to flywheel HP) is the actual power lost between the flywheel and the rear wheels....not how much power was lost by the time it got to the flywheel.
Later,
Scott
I tactfully disagree in one regard... I have grown to understand a different stance and that is... the so called flywheel due to the crank's extra duty to turn a blower will create more load even on the crank therefore you will get a small percentage of loss even at the flywheel than you would an NA motor; therefore a calculation in % from an NA motor will not be the same by adding a blower and saying that percentage will stay the same since it is going through the same drive train.
Maybe look at it this way... turbo vs. a blower... no resistance on a crank from turbos being built from a free turning crank and producing gases to re-induce turbos spinning quicker thus producing more compressed intake. On a blower setup the crank is under more load hence not providing the same output, even at the flywheel. This could also be viewed the same as a larger liter NA motor taking in similar compressed content.
A simple equation in writing can be compared as such... 4 pounds of restrictive boost off turbos compared to 8 pounds of restrictive boost off a positive or even a centrifugal blower on the same engine, these two setups at different boost levels will deliver almost the same output if all variables are correct, or very similar numbers if you may. Takes a bit more to turn the blower and hence produce the same efficiency from crank load turning a blower than an unloaded crank turning creating restriction off turbos.
For the level of % at a certain HP level at a crank, I agree... hanging around a bunch that do Renegade and such, you usually hear a loss stated as an actual HP number instead of a percentage.
Cheers,
Allen
Last edited by Almo; 01-15-2009 at 05:31 AM.
#52
01-15-2009 | 05:46 AM
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That's what I'm saying. It wouldn't be a standard percentage. Say you have 15% loss on 10#'s of boost @ 500 RWHP, and you add 5 #'s of boost. Say you gain 20hp per #, I don't think you would have 15% loss on that extra power, but probably closer to 2-3%. But when you get up into the big dog hp numbers, that 2-3% is still considerable.
#53
01-15-2009 | 07:36 AM
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I tactfully disagree in one regard... I have grown to understand a different stance and that is... the so called flywheel due to the crank's extra duty to turn a blower will create more load even on the crank therefore you will get a small percentage of loss even at the flywheel than you would an NA motor; therefore a calculation in % from an NA motor will not be the same by adding a blower and saying that percentage will stay the same since it is going through the same drive train.
What I’m saying is that none of that matters, since we aren’t trying to figure the HP loss from the connecting rods to the flywheel. We are talking about power from the final output of the engine (where the flywheel meets the pressure plate) to the drive wheels. It has no bearing on the latter whatsoever.
It doesn’t matter how much power an engine is making, or how much it’s not making due to parasitic loss of a blower, an A/C compressor, an alternator, etc....
What I'm saying is…whatever the number is at the flywheel, regardless of how much it's been reduced by parasitic drag, that number will be reduced by almost the exact amount as it is on a bone stock engine (N/A, SC or TT) making half as much power, or even a TT engine making twice as much power. I’m talking about the loss AFTER the flywheel…not before (which is what it seems you are talking about).
Maybe look at it this way... turbo vs. a blower... no resistance on a crank from turbos being built from a free turning crank and producing gases to re-induce turbos spinning quicker thus producing more compressed intake. On a blower setup the crank is under more load hence not providing the same output, even at the flywheel. This could also be viewed the same as a larger liter NA motor taking in similar compressed content.
A simple equation in writing can be compared as such... 4 pounds of restrictive boost off turbos compared to 8 pounds of restrictive boost off a positive or even a centrifugal blower on the same engine, these two setups at different boost levels will deliver almost the same output if all variables are correct, or very similar numbers if you may. Takes a bit more to turn the blower and hence produce the same efficiency from crank load turning a blower than an unloaded crank turning creating restriction off turbos.
For the level of % at a certain HP level at a crank, I agree... hanging around a bunch that do Renegade and such, you usually hear a loss stated as an actual HP number instead of a percentage.
Cheers,
Allen
All sincere respect, it really seems that you and I are talking about two totally different things here. Thus, it'll probably easier for us agree to disagree.
Later,
Scott
#54
01-15-2009 | 07:42 AM
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That's what I'm saying. It wouldn't be a standard percentage. Say you have 15% loss on 10#'s of boost @ 500 RWHP, and you add 5 #'s of boost. Say you gain 20hp per #, I don't think you would have 15% loss on that extra power, but probably closer to 2-3%. But when you get up into the big dog hp numbers, that 2-3% is still considerable.
But in all seriousness, I don't believe you'll see a 2-3% increase in loss. I bet it's actually less than that.
#55
01-15-2009 | 08:26 AM
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So what you're actually saying is that you agree with me (that using a standard % based off bone stock cars in order to figure flywheel HP is not accurate)...but don't want to come right out an admit it.
But in all seriousness, I don't believe you'll see a 2-3% increase in loss. I bet it's actually less than that.
But in all seriousness, I don't believe you'll see a 2-3% increase in loss. I bet it's actually less than that.
#56
01-15-2009 | 09:06 AM
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But then in the case of a Ford, I imagine friction probably does increase with HP. That would explain why so many 700+ HP Cobras are slow.
#57
01-15-2009 | 09:45 AM
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It's nice to see you talking some ****! Hopefully I'll have some progress pics for you on Sunday. It's gonna be a moral dilemma on whether I should bust your vettes *** when you first get back, or if I should wait and let you enjoy it for a while! haha
#58
01-15-2009 | 10:09 AM
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It's nice to see you talking some ****! Hopefully I'll have some progress pics for you on Sunday. It's gonna be a moral dilemma on whether I should bust your vettes *** when you first get back, or if I should wait and let you enjoy it for a while! haha
That said; I really hope you aren't too upset when you fail to beat a 'Vette making 150+ less rwhp than you are! But if it turns out I can't beat you, Peter will be more than happy too. What are friends for?
Last edited by Divexxtreme; 01-15-2009 at 10:27 AM.
#59
01-15-2009 | 12:02 PM
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Of course fluids produce friction, which is why we use the slipperiest lubricants we can that are practical for our purposes. But they produce essentially the same friction with 1000 hp as they do with 100 hp, as long as the moving components are spinning at the same speed.
I'm glad my measly 750-800 rwhp car is already creating moral conflicts for you, bro. Please feel free to try and bust my *** as soon as I get back. That is, as long as I'm not rolling on my 20's. I'd prefer that you wait until I'm on some sticky tires for the safety of everyone concerned.
That said; I really hope you aren't too upset when you fail to beat a 'Vette making 150+ less rwhp than you are! But if it turns out I can't beat you, Peter will be more than happy too. What are friends for?
I'm glad my measly 750-800 rwhp car is already creating moral conflicts for you, bro. Please feel free to try and bust my *** as soon as I get back. That is, as long as I'm not rolling on my 20's. I'd prefer that you wait until I'm on some sticky tires for the safety of everyone concerned.
That said; I really hope you aren't too upset when you fail to beat a 'Vette making 150+ less rwhp than you are! But if it turns out I can't beat you, Peter will be more than happy too. What are friends for?
In all honesty, I just hope my car is running by the time you get back. I have been working so much OT that I haven't had time to do much of anything. Supposed to be assembling the motor Sunday, once that is done, everything else should go together relatively quickly.
When are you getting back,March or April?
