Why the LS3 isn't "under-rated"
08-15-2008, 01:29 PM
#1
Burning Brakes
Thread Starter
Why the LS3 isn't "under-rated"
I love the LS3 and just ordered an '09 'Vette. That being said, I've run across a few discussions on the board where some have suggested that the LS3 is "very under-rated" and I wanted to post a thread addressing that.
The LS3 is precisely rated because its rating is CERTIFIED HP per SAE J1349. Production engine output must consistently be within 1% of the advertised figure in order to obtain and retain the Certified rating.
http://www.caranddriver.com/features...olution_column
http://www.sae.org/certifiedpower/details.htm
Those suggesting that a fixed percentage (e.g. 17%) can be applied to somehow "convert" drive-wheel HP to flywheel HP don't understand the complexity of the subject. The link below contains one of several good articles I've seen on the subject. As pointed out in the link, high HP cars (400 + HP @ the flywheel) can lose less than 10% from the flywheel to the dyno rollers.
The NPP LS3 is rated @ 436 HP. 10% of that is 43.6 HP. 436 - 43.6 = 392.4 HP, which is at the high end of what stock LS3 NPP cars are recording.
Hence, an LS3 producing 392.4 HP at the wheels can most definitely be honestly rated (436 HP @ the crank with NPP).
http://www.sportcompactcarweb.com/pr...t_4/index.html
"Horsepower Hype--Separating Fact from Fiction
Converting rear-wheel power figures to crank numbers is anything but straight-forward. When translating wheel figures to engine claims, some experts use fixed conversion factors. That is, if a stock 218 rear-wheel hp RX-7 is rated from the factory at 255 crank hp, it must have 17-percent driveline losses. A 284 rear-wheel hp RX-7, then, must be blessed with 332 crank hp. This popular, if somewhat optimistic, correction technique assumes driveline loss is proportionate with engine output. That is, as wheel horsepower increases, driveline loss must also increase commensurably. Some would even disregard stock quotes and apply a standard 20-percent drivetrain loss figure. Using this popular correction factor, we already have a 340-hp monster! Some would vehemently disagree. These folks would tend to use a fixed number to represent driveline loss. In this case, they would believe that all RX-7s are faced with a driveline loss of 37 hp. (255 minus 218). Using this correction method, Project RX-7 produces a more conservative 321 ponies at the crank. All three techniques, (as well as other far more [Ahem.] optimistic methods) have been used at one time or another.
Our friend at Superior Dyno Service, Keith Paulsen, looks at this issue from another perspective. "The first mistake people make is assuming that factory-quoted horsepower figures are accurate," Paulsen states. "Due to marketing hype and year-to-year tuning changes, it's not always accurate to derive drivetrain loss by comparing measured wheel horsepower and factory quotes."
Paulsen also believes that drivetrain losses are neither an absolute percentage nor a fixed number. Instead, he feels the crank-to-wheel relationship is far more beguiling. From his considerable experience, Paulsen suggests that low horsepower (100-200 hp) cars may suffer from as much as 15 to 20 percent of drivetrain loss at the rear wheels. For more powerful cars (200-400 hp), the figure is around 12 to 15 percent. And for mega-powered cars (above 400 hp), the drivetrain losses can reduce to 10 percent or less. What's going on? Getting into the physics behind this complex relationship is worthy of a project in itself. (Engineering editor, Dave Coleman says he's working on it.)..."
The LS3 is precisely rated because its rating is CERTIFIED HP per SAE J1349. Production engine output must consistently be within 1% of the advertised figure in order to obtain and retain the Certified rating.
http://www.caranddriver.com/features...olution_column
http://www.sae.org/certifiedpower/details.htm
Those suggesting that a fixed percentage (e.g. 17%) can be applied to somehow "convert" drive-wheel HP to flywheel HP don't understand the complexity of the subject. The link below contains one of several good articles I've seen on the subject. As pointed out in the link, high HP cars (400 + HP @ the flywheel) can lose less than 10% from the flywheel to the dyno rollers.
The NPP LS3 is rated @ 436 HP. 10% of that is 43.6 HP. 436 - 43.6 = 392.4 HP, which is at the high end of what stock LS3 NPP cars are recording.
Hence, an LS3 producing 392.4 HP at the wheels can most definitely be honestly rated (436 HP @ the crank with NPP).
http://www.sportcompactcarweb.com/pr...t_4/index.html
"Horsepower Hype--Separating Fact from Fiction
Converting rear-wheel power figures to crank numbers is anything but straight-forward. When translating wheel figures to engine claims, some experts use fixed conversion factors. That is, if a stock 218 rear-wheel hp RX-7 is rated from the factory at 255 crank hp, it must have 17-percent driveline losses. A 284 rear-wheel hp RX-7, then, must be blessed with 332 crank hp. This popular, if somewhat optimistic, correction technique assumes driveline loss is proportionate with engine output. That is, as wheel horsepower increases, driveline loss must also increase commensurably. Some would even disregard stock quotes and apply a standard 20-percent drivetrain loss figure. Using this popular correction factor, we already have a 340-hp monster! Some would vehemently disagree. These folks would tend to use a fixed number to represent driveline loss. In this case, they would believe that all RX-7s are faced with a driveline loss of 37 hp. (255 minus 218). Using this correction method, Project RX-7 produces a more conservative 321 ponies at the crank. All three techniques, (as well as other far more [Ahem.] optimistic methods) have been used at one time or another.
Our friend at Superior Dyno Service, Keith Paulsen, looks at this issue from another perspective. "The first mistake people make is assuming that factory-quoted horsepower figures are accurate," Paulsen states. "Due to marketing hype and year-to-year tuning changes, it's not always accurate to derive drivetrain loss by comparing measured wheel horsepower and factory quotes."
Paulsen also believes that drivetrain losses are neither an absolute percentage nor a fixed number. Instead, he feels the crank-to-wheel relationship is far more beguiling. From his considerable experience, Paulsen suggests that low horsepower (100-200 hp) cars may suffer from as much as 15 to 20 percent of drivetrain loss at the rear wheels. For more powerful cars (200-400 hp), the figure is around 12 to 15 percent. And for mega-powered cars (above 400 hp), the drivetrain losses can reduce to 10 percent or less. What's going on? Getting into the physics behind this complex relationship is worthy of a project in itself. (Engineering editor, Dave Coleman says he's working on it.)..."
Last edited by harddrivin1le; 08-15-2008 at 02:21 PM. Reason: typos
08-15-2008, 01:37 PM
#3
Burning Brakes
Thread Starter
08-15-2008, 02:04 PM
#4
Team Owner
Good post. You'll find a lot of discussion as you know on this topic. I have been stating the very same information as you posted for a year now. The problem is that those that don't understand it, still won't. Those that don't want to hear it, still won't. Those that simply like to stir the pot, still will. Facts are facts. They help some, confuse others and frustrate more still.
08-15-2008, 02:05 PM
#5
CF Senior Member
Member Since: Feb 2006
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…and now the 2008 Viper owners can breathe a sigh of relief. 
As an indicator of a car's performance potential, the numbers are of interest. Blanket assumptions always have inherent risks.
Good post...thanks for sharing.
As an indicator of a car's performance potential, the numbers are of interest. Blanket assumptions always have inherent risks.
Good post...thanks for sharing.
08-15-2008, 02:41 PM
#6
This is why people use the terms wheel horsepower... as the only power that matters is those that get to the ground.
Now I will tell you I am one of those guys that say 390 rwhp is more like 440-450 to the crank, but thats because I'm using that 15% number to how people convert these things. For some reason I just don't see a 9.3% drivetrain loss as possible, but it makes little difference to me.
Its all about the power to the ground. So when I comepare car to car, I use weight and rwhp.
Now I will tell you I am one of those guys that say 390 rwhp is more like 440-450 to the crank, but thats because I'm using that 15% number to how people convert these things. For some reason I just don't see a 9.3% drivetrain loss as possible, but it makes little difference to me.
Its all about the power to the ground. So when I comepare car to car, I use weight and rwhp.
08-15-2008, 02:43 PM
#7
Burning Brakes
Thread Starter
This is why people use the terms wheel horsepower... as the only power that matters is those that get to the ground.
Now I will tell you I am one of those guys that say 390 rwhp is more like 440-450 to the crank, but thats because I'm using that 15% number to how people convert these things. For some reason I just don't see a 9.3% drivetrain loss as possible, but it makes little difference to me.
Its all about the power to the ground. So when I comepare car to car, I use weight and rwhp.
Now I will tell you I am one of those guys that say 390 rwhp is more like 440-450 to the crank, but thats because I'm using that 15% number to how people convert these things. For some reason I just don't see a 9.3% drivetrain loss as possible, but it makes little difference to me.
Its all about the power to the ground. So when I comepare car to car, I use weight and rwhp.
It is based solely on misunderstanding, urban myth and speculation.This link explains why:
http://forums.corvetteforum.com/show...22&postcount=1
ACTUAL LS3 peak flywheel HP is 430 (std. exhaust) and 436 (NPP).
We know that because the advertised peak power levels were 3rd party CERTIFIED per the governing SAE specification.
The "legendary" 1969 427 ZL1 produced 376 SAE NET HP in its "as installed" condition" (Reference: http://www.camaros.org/copo.shtml ), so 430 - 436 HP from 376 cubes and unleaded gas seems pretty darn impressive to me.
Last edited by harddrivin1le; 08-15-2008 at 02:52 PM.
08-15-2008, 02:58 PM
#9
Team Owner
Great post with a lot of good facts and info thanks for sharing.
08-15-2008, 02:58 PM
#10
Safety Car
Good post. You'll find a lot of discussion as you know on this topic. I have been stating the very same information as you posted for a year now. The problem is that those that don't understand it, still won't. Those that don't want to hear it, still won't. Those that simply like to stir the pot, still will. Facts are facts. They help some, confuse others and frustrate more still.
08-15-2008, 03:29 PM
#11
Safety Car
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St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
good article - lots of folks get their panties in a knot over this discussion and couldn't agree more on your "scientific fact" comment...the norm IMO.
08-15-2008, 03:38 PM
#12
Get Some!
Good post. You'll find a lot of discussion as you know on this topic. I have been stating the very same information as you posted for a year now. The problem is that those that don't understand it, still won't. Those that don't want to hear it, still won't. Those that simply like to stir the pot, still will. Facts are facts. They help some, confuse others and frustrate more still.
My uncle works at GM and knows for a fact that the LS3 makes like 437 HP. 
08-15-2008, 03:43 PM
#13
Melting Slicks
Member Since: Jun 2007
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The "legendary" 1969 427 ZL1 produced 376 SAE NET HP in its "as installed" condition" (Reference: http://www.camaros.org/copo.shtml ), so 430 - 436 HP from 376 cubes and unleaded gas seems pretty darn impressive to me.
I also think it's likely that aside from discovering cheap & easy tweaks that might get factory numbers higher, the new and intense pressure to improve fuel efficiency could well make the 430/436 hp we have now about as good as it's gonna get.Enjoy it while you can! It feels like the early 1970s all over again...right down to the talk about bringing back the 55 mph speed limit.
08-15-2008, 04:45 PM
#14
The 15% figure has no basis in scientific fact. It is based solely on misunderstanding, urban myth and speculation.
This link explains why:
http://forums.corvetteforum.com/show...22&postcount=1
ACTUAL LS3 peak flywheel HP is 430 (std. exhaust) and 436 (NPP).
We know that because the advertised peak power levels were 3rd party CERTIFIED per the governing SAE specification.
The "legendary" 1969 427 ZL1 produced 376 SAE NET HP in its "as installed" condition" (Reference: http://www.camaros.org/copo.shtml ), so 430 - 436 HP from 376 cubes and unleaded gas seems pretty darn impressive to me.
It is based solely on misunderstanding, urban myth and speculation.This link explains why:
http://forums.corvetteforum.com/show...22&postcount=1
ACTUAL LS3 peak flywheel HP is 430 (std. exhaust) and 436 (NPP).
We know that because the advertised peak power levels were 3rd party CERTIFIED per the governing SAE specification.
The "legendary" 1969 427 ZL1 produced 376 SAE NET HP in its "as installed" condition" (Reference: http://www.camaros.org/copo.shtml ), so 430 - 436 HP from 376 cubes and unleaded gas seems pretty darn impressive to me.
The actual SAE Certification process adheres to a strict protocol, under controlled and repeatable conditions, and with an independent SAE witness present.
I myself have gone to a lot of trouble in explaining what you are pointing out above, and agree with you entirely.
http://forums.corvetteforum.com/show....php?t=1940271
Good post. You'll find a lot of discussion as you know on this topic. I have been stating the very same information as you posted for a year now. The problem is that those that don't understand it, still won't. Those that don't want to hear it, still won't. Those that simply like to stir the pot, still will. Facts are facts. They help some, confuse others and frustrate more still.
to be true. And thats all it is. Utter
Last edited by '06 Quicksilver Z06; 08-15-2008 at 04:51 PM.
08-15-2008, 05:12 PM
#15
Melting Slicks
So if I read all this correctly, any particular drive line actually requires a fixed amount of power to overcome its total friction loses and rotate. If you ignore non-linearities (e.g., torque converters, limited slip differentials, etc.), this fixed amount of power is probably fairly constant over a fairly wide speed range. If so, why don't we see Drive Train HP ratings, where FWHP - DTHP = RWHP?
08-15-2008, 05:22 PM
#16
Burning Brakes
Thread Starter
Broadly speaking, a T56/T6060 C5/C6 drive-line will loseABOUT 50 HP on an inertia dyno- whether its coupled to an LS1, LS2, LS3, LS6 or LS7.
One of the problems with chassis dyno testing is that everybody likes big numbers. Hence, a lot of dyno shops do whatever they have to do in order to get them (e.g. set the altitude correction for 4,000 feet on cars that are tested at sea level; I personally witnessed this at a local dyno shop that I won't name).
Everybody that day was happy, though, and many returned to show their friends how much (exaggerated) power their car made.
Remember that real world, "over the road" driveline losses are much less than what's indicated on an inertia dyno, since cars in the real world don't have to turn heavy (or braked) rollers.
Last edited by harddrivin1le; 08-15-2008 at 05:32 PM.
08-15-2008, 05:47 PM
#20
Drifting
Good post. You'll find a lot of discussion as you know on this topic. I have been stating the very same information as you posted for a year now. The problem is that those that don't understand it, still won't. Those that don't want to hear it, still won't. Those that simply like to stir the pot, still will. Facts are facts. They help some, confuse others and frustrate more still.
