Eforce dyno.
Safety Car
Joined: Nov 2007
Posts: 4,435
Likes: 874
From: Bay Area CA
Isn't HP loss from drivetrain a constant using the stock HP rating ?
For the C6 drivetrain, drivetrain parasitic loss is around 13% for the M6 and 15% for the A6 (with stock drivetrain parts). I guess these percents change slightly as crankshaft Net HP changes, but for all practical purposes, the 13% and 15% loss is ... "close enough for government work".
436 HP (stock) X .13 (13% manual 6 sp.) = 56.68 HP loss whether you have mods or not as long as the drivetrain is the oem ?
Sure, that would be for a stock OEM drivetrain
However, the HP loss driving a blower needs to be figured in ?
Don't need to figure out how much HP it is taking to drive the blower ... We are just concerned with the SAE corrected shaft HP (flywheel) the engine is producing. That's flywheel HP corrected to SAE J1349 standard atmospheric conditions.
BTW ... If a dyno is set up properly, the RWHP displayed will also be corrected to standard SAE J1349 conditions too.
Keeping in mind, type of blower Centri vs Roots? Pulley size and HB diameter? How is net HP accurately calculated ?
Figuring Net crankshaft HP can never be 100% accurate with data from just the dyno pull, but it's very close (as long a the actual dyno RWHP number was corrected to SAE J1349 standard) and then the 13% or 15% drivetrain HP loss is figured in ... Again, close enough.
BTW ... The SAE J1349 standard is sea level, atmospheric pressure of 29.23" Hg, 77 degrees F, and zero humidity
The SAE J1349 standard took the place of the old SAE J607 that used 60 degrees F and 29.92" Hg as the standard conditions
For the C6 drivetrain, drivetrain parasitic loss is around 13% for the M6 and 15% for the A6 (with stock drivetrain parts). I guess these percents change slightly as crankshaft Net HP changes, but for all practical purposes, the 13% and 15% loss is ... "close enough for government work".
436 HP (stock) X .13 (13% manual 6 sp.) = 56.68 HP loss whether you have mods or not as long as the drivetrain is the oem ?
Sure, that would be for a stock OEM drivetrain
However, the HP loss driving a blower needs to be figured in ?
Don't need to figure out how much HP it is taking to drive the blower ... We are just concerned with the SAE corrected shaft HP (flywheel) the engine is producing. That's flywheel HP corrected to SAE J1349 standard atmospheric conditions.
BTW ... If a dyno is set up properly, the RWHP displayed will also be corrected to standard SAE J1349 conditions too.
Keeping in mind, type of blower Centri vs Roots? Pulley size and HB diameter? How is net HP accurately calculated ?
Figuring Net crankshaft HP can never be 100% accurate with data from just the dyno pull, but it's very close (as long a the actual dyno RWHP number was corrected to SAE J1349 standard) and then the 13% or 15% drivetrain HP loss is figured in ... Again, close enough.
BTW ... The SAE J1349 standard is sea level, atmospheric pressure of 29.23" Hg, 77 degrees F, and zero humidity
The SAE J1349 standard took the place of the old SAE J607 that used 60 degrees F and 29.92" Hg as the standard conditions
Race Director
Joined: Mar 2011
Posts: 13,262
Likes: 3,151
From: SW Florida
2021 C6 of the Year Finalist - Modified
Like what others have said in this thread ... that on highly modified cars in the real high HP range, that 13% - 15% drivetrain loss don't hold true anymore .... However, in most cases in the less modified car (not making 800+ RWHP), it's a pretty good estimate of RWHP vs Net crank HP (if Net HP is important to you)
Of course in the real world, certainly RWHP and RW Torque is what propels the car down the track ... considering that the tires can put the power to the ground.
Of course in the real world, certainly RWHP and RW Torque is what propels the car down the track ... considering that the tires can put the power to the ground.
Team Owner
Joined: Nov 2007
Posts: 24,035
Likes: 2,342
From: Gilbert AZ
Same thing applies to 500-600 hp cars though. The percent goes down.
Either way it is just a ballpark, so without pulling motor and measuring, it is a guess. So stop even talking about motor HP and problem solved.
Either way it is just a ballpark, so without pulling motor and measuring, it is a guess. So stop even talking about motor HP and problem solved.
Race Director
Joined: Mar 2011
Posts: 13,262
Likes: 3,151
From: SW Florida
2021 C6 of the Year Finalist - Modified
I never said the 13% - 15% formula was 100% accurate, but for someone just wanting to get an idea what there Net crank HP is ... I can't think of anything that's really perfect other than an engine dyno. And not many folks are going to go through the trouble to pull there engine out of the car and send it off to a company that has an engine dyno in there shop.
I don't know at what point the percent goes down, but I do know that my bone stock 2011 GS / A6 which was rated at 436 Net HP, made exactly 371 SAE corrected RWHP on the dyno .... and that is exactly a 15% drivetrain loss.
Of course, another thing ... not all chassis dyno's spit out the same numbers even though they should all be showing SAE 'corrected' RWHP.
.
I don't know at what point the percent goes down, but I do know that my bone stock 2011 GS / A6 which was rated at 436 Net HP, made exactly 371 SAE corrected RWHP on the dyno .... and that is exactly a 15% drivetrain loss.
Of course, another thing ... not all chassis dyno's spit out the same numbers even though they should all be showing SAE 'corrected' RWHP.
.
Last edited by Turbo6TA; Jul 2, 2019 at 03:58 PM.
Team Owner
Joined: Nov 2007
Posts: 24,035
Likes: 2,342
From: Gilbert AZ
Exactly, not all dynos will show 376rwhp on a stock car, some will do 330, some 390. Does the drivetrain percent change? No. The only thing anyone should be claiming is what their car did on what day and what dyno. Anything else is making **** up and pointless.
Instructor
Joined: Apr 2017
Posts: 151
Likes: 60
From: Fort Worth, TX
I'd like this twice if it was an option.
