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Could someone please explain to me how these differences are measured and what causes the loss?

Thanks!:biggrin:
 

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sure

Flywheel HP is measured with the engine out of the car and physically attached to a Dynomometer, which connects water and fuel to the engine and captures the exhaust. The machine applies a load and the operator runs the engine and a number is then extrapolated, thus flywheel HP!

Wheel HP is calculated by strapping the entire car down on rollers and running the drivetrain against a load. It is also indicative of the effects of gearing, wheels and tires, etc.

Both numbers are subject to the standard variables and require correction to be compared. But in my experience, roller dynos are notoriously inaccurate and are only useful to compare against themselves.
 

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The loss is from the crank to the wheels via the drivetrain and is usually between 18-20%. I would imagine AWD vehicles have it harder.
 

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But in my experience, roller dynos are notoriously inaccurate and are only useful to compare against themselves.
Nice concise answer, I particularly like your ending. I think there may be a trend amongst dyno purveyors...He who can offer the customer the allusion of the greatest horsepower wins.:wink1:
 

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The loss is from the crank to the wheels via the drivetrain and is usually between 18-20%. I would imagine AWD vehicles have it harder.
This has been a pretty good rule of thumb in the past. It seems it might be getting a little out of date, particularly based on the reported dyno numbers of our members. It has been quite common for stock SRT8s the post 380-390 rwhp which would put them at a nominal 9% drivetrain loss! A possible explanation that I've heard for this has been that Chrysler underestimates is horsepower for SRT8. That would be a refreshing change if true! Another explanation is that the most popular dynamometer, Dynojet over estimates rwhp by a certain amount...maybe 6%. That would put the actual drivetrain loss at about 15% for an SRT8 which would mean that drivetrain loss would have improve in the last decade or two 3-5%, which would also make sense. I guess a pretty good compromise so that everyone is equally unhappy would be to guess that drive train loss is 12%, the Dynojet is 4% optimistic and Chrysler published horsepower for the SRT8 is 4% less that it actually is. That gets us back to our old rule of thumb and everyone get to keep a little piece of their pie.

In regards to the AWD, let's just say we're special.
 

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This has been a pretty good rule of thumb in the past. It seems it might be getting a little out of date, particularly based on the reported dyno numbers of our members. It has been quite common for stock SRT8s the post 380-390 rwhp which would put them at a nominal 9% drivetrain loss! A possible explanation that I've heard for this has been that Chrysler underestimates is horsepower for SRT8. That would be a refreshing change if true! Another explanation is that the most popular dynamometer, Dynojet over estimates rwhp by a certain amount...maybe 6%. That would put the actual drivetrain loss at about 15% for an SRT8 which would mean that drivetrain loss would have improve in the last decade or two 3-5%, which would also make sense. I guess a pretty good compromise so that everyone is equally unhappy would be to guess that drive train loss is 12%, the Dynojet is 4% optimistic and Chrysler published horsepower for the SRT8 is 4% less that it actually is. That gets us back to our old rule of thumb and everyone get to keep a little piece of their pie.

In regards to the AWD, let's just say we're special.
Most likely they understate HP. My car supposedly has 469BHP...but most E55s rate between 420-430RWHP stock which would put them between 495-505BHP stock.

SRT8s should be around 360RWHP stock if the advertised BHP is correct, but I suspect they have been understated also.
 

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Most likely they understate HP. My car supposedly has 469BHP...but most E55s rate between 420-430RWHP stock which would put them between 495-505BHP stock.

SRT8s should be around 360RWHP stock if the advertised BHP is correct, but I suspect they have been understated also.
Interesting information about your car, it casts a little more light on the industry. I would have to ask you to explain your logic though. Having one manufacture advertise a lower bhp can be somewhat explained as a refreshing anomaly. To have two different manufactures advertise a lower bhp one really needs to question the method of determining rwhp.

With your numbers there is a 9% difference between bhp and rwhp with both the E55 and the SRT8. If you look at the competitive nature of the automobile industry, especially when it comes to performance cars, what would be the strategy of advertising a lesser amount. Aren't the manufactures marketing the bhp? Don't we base our purchase of a performance car on the performance and isn't the bhp a big selling point for performance?

Based solely on the above two cars and their bhp vs. rwhp numbers I would suggest revising your drivetrain loss estimates from 18-20% down to 10-12%. This would leave a contingency for dynomometer exaggeration of 3%. Better engineered components, lighter components, and a higher standard of manufacturing all seem probably over the last couple decades and would all contribute to this reduction of drivetrain loss on modern performance cars.

Of course to have a meaningful data set we would have to look a lot more that just two cars and probably need to make a number of categories. The rule of thumb I have used in the past has been 10-15% loss for front wheel drive, 15-20% loss for rear wheel drive, and 20-25% loss for AWD. The 5% within each category leaves room for both the 3000 lb performance coup and the 4500 lb luxury sedan. But again, this rule of thumb might need to be updated to reflect modern engineering and manufacturing.

And if I may, what brings an E55 owner to these boards, are you a former 300 owner? I am interested in your impressions of your car and what made you buy one. I also would be interested in how tall you are and how much you weigh.
 

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Interesting information about your car, it casts a little more light on the industry. I would have to ask you to explain your logic though. Having one manufacture advertise a lower bhp can be somewhat explained as a refreshing anomaly. To have two different manufactures advertise a lower bhp one really needs to question the method of determining rwhp.

With your numbers there is a 9% difference between bhp and rwhp with both the E55 and the SRT8. If you look at the competitive nature of the automobile industry, especially when it comes to performance cars, what would be the strategy of advertising a lesser amount. Aren't the manufactures marketing the bhp? Don't we base our purchase of a performance car on the performance and isn't the bhp a big selling point for performance?

Based solely on the above two cars and their bhp vs. rwhp numbers I would suggest revising your drivetrain loss estimates from 18-20% down to 10-12%. This would leave a contingency for dynomometer exaggeration of 3%. Better engineered components, lighter components, and a higher standard of manufacturing all seem probably over the last couple decades and would all contribute to this reduction of drivetrain loss on modern performance cars.

Of course to have a meaningful data set we would have to look a lot more that just two cars and probably need to make a number of categories. The rule of thumb I have used in the past has been 10-15% loss for front wheel drive, 15-20% loss for rear wheel drive, and 20-25% loss for AWD. The 5% within each category leaves room for both the 3000 lb performance coup and the 4500 lb luxury sedan. But again, this rule of thumb might need to be updated to reflect modern engineering and manufacturing.

And if I may, what brings an E55 owner to these boards, are you a former 300 owner? I am interested in your impressions of your car and what made you buy one. I also would be interested in how tall you are and how much you weigh.
Don't forget that both these manufacturers were under the same umbrella when these vehicles were introduced. :)

Yes, I used to own a 2005 300C (Cool Vanilla with every option + Borla Exhaust and Mopar CAI) which is why I registered as a member here. I liked the 300C a lot. However, I am one of those people that gets bored with a car after a few years. My partner in my company had a Cadillac STS-V at the time and I needed to one up him with my next car. I looked hard at a 300C SRT8 but my wife talked me into getting a whole different kind of car (I think she hopes I might not get bored with it as quickly :) ) instead of the same car with a bigger engine.

My impressions? Well, since this is a 300C forum, I can't be too blunt without people getting upset. It is a whole level above the 300C in several areas...which is expected from a car that costs twice as much. My reason for getting the 300C was all the sales pitches about shared materials with Mercedes in the 300C vehicle...from the same E class frame being used to the same transmission...etc...etc. I can tell you that some materials may be shared, but not what salesman would have you believe. It is NOT a Mercedes E class car with a Hemi engine thrown in. Some things similar for sure, but the tranny on the E55 is butter compared to the 300C...the airmatic suspension on the E55 is much nicer than the 300C..The interior, seat comfort, and leather are all night and day. The blinkers are identical though with the same quick three blink function...Was so glad too as I love that.

300C has some things that I liked better though as well. The NAV in the 300C was TONs better. The mods for the 300C are MUCH less expensive.

Both are great cars for the price levels they compete in....period.

And I am 6'1" 205 lbs as of last weigh in at the gym. :)
 

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Timeless...Thanks for the honest feedback. I understand the desire to move on. Obviously a different price and class car. Does that have a Whipple on it. I drove a Ford GT with a Whipple a couple years ago and decided then that was the FI for me. I test drove a couple of Mercedes and a couple BMWs before buying my C and although they seemed very well built cars they were claustrophobic to me. I had been driving crew cabs before and the C and the DeVille were the two cars that felt like they had enough room. Thats why I asked your size. I'm 6'2" 190ish so we would fit about the same. How is the fit in the E55? I'm not really sure the fact that mods are more expensive matters does it? What would you really want to upgrade?
 

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Timeless...Thanks for the honest feedback. I understand the desire to move on. Obviously a different price and class car. Does that have a Whipple on it. I drove a Ford GT with a Whipple a couple years ago and decided then that was the FI for me. I test drove a couple of Mercedes and a couple BMWs before buying my C and although they seemed very well built cars they were claustrophobic to me. I had been driving crew cabs before and the C and the DeVille were the two cars that felt like they had enough room. Thats why I asked your size. I'm 6'2" 190ish so we would fit about the same. How is the fit in the E55? I'm not really sure the fact that mods are more expensive matters does it? What would you really want to upgrade?
Here is a nice article discussing the Mercedes (and others) supercharger: AutoSpeed - Supercharger Steal - Part Two

The E55 does not feel as wide as the 300C, but the trunk is actually deeper. They are very comparable with regards to interior room with comfort going to the E55 of course. :)

The E55 is very mod friendly...just can get expensive. ECUs have to be sent off (no Diablo Predator here) to be tuned ($1500.00), larger crank pulleys are available to increase supercharger PSI ($899-$2999.00), larger throttle bodies ($2000.00), headers ($3000.00), as well as other misc upgrades usually involving cooling (Tstats, IC Pumps, Cooling Wraps). For info, check out mbworld.org.

You can easily and with enough money get these to 700BHP monsters. As to why? Well, why do we mod any car? I personally like the feeling of being able to take just about everything on the road. :) The stock E55 is actually faster than an old school stock Lamborghini Diablo...something that makes me smile inside.
 

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Timeless...More teasing you about the want for upgrades after dropping $80K on a car. I was guessing it came with an internal compression type twin screw. Swapping SC pulleys is sure an easy way to make horsepower. They must not have had that model or equivalent (E550?) on hand when I was looking. If you're comfortable in it I'm sure I would have been too. Thanks for the info...let me know when you hit 700 rwhp.:)
 

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Timeless...More teasing you about the want for upgrades after dropping $80K on a car. I was guessing it came with an internal compression type twin screw. Swapping SC pulleys is sure an easy way to make horsepower. They must not have had that model or equivalent (E550?) on hand when I was looking. If you're comfortable in it I'm sure I would have been too. Thanks for the info...let me know when you hit 700 rwhp.:)
No, I was not the guy that dropped $90K on the car...I was the guy that waited two years and got it for half. ;)

No way I would buy one of these AMGs new...even if the money was meaningless.
 
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