The Official C8 Corvette Thread...

Started by Gotta-Qik-C7, April 25, 2018, 07:28:09 PM

r0tor

Quote from: giant_mtb on October 17, 2019, 06:57:52 AM
What's your point?  A run-flat is going to have some sort of different construction than a non-RF, presumably affecting performance in some way.

The comments were surrounding "no ZP" and acting like it was some sort of performance advantage... When actually it's just the designation for run flat which in and of itself is a disadvantage.


There is some credible argument that GM was using an extremely softer than normal PSS compound for performance.  Mercedes actually used it in the GTR because it was much sticky (and worse in the rain) then what they or BMW/Porsche/ect was speccing from Michelin.

In the end its just down again to it being a car still in development.  They haven't gotten the snap oversteer under control so it's tuned to understeer, the new braking system still needs to be baked, and then they can focus more on smaller things like cheater compounds.  I'm sure over the next 10 years they will get there.
2011 Jeep Grand Cherokee No Speed -- 2004 Mazda RX8 6 speed -- 2018 Alfa Romeo Giulia All Speed

MrH

2023 Ford Lightning Lariat ER
2019 Acura RDX SH-AWD
2023 BRZ Limited

Previous: '02 Mazda Protege5, '08 Mazda Miata, '05 Toyota Tacoma, '09 Honda Element, '13 Subaru BRZ, '14 Hyundai Genesis R-Spec 5.0, '15 Toyota 4Runner SR5, '18 Honda Accord EX-L 2.0t, '01 Honda S2000, '20 Subaru Outback XT, '23 Chevy Bolt EUV

CaminoRacer

2020 BMW 330i, 1969 El Camino, 2017 Bolt EV

MrH

For a forum that always complains about how there's too much focus on numbers and not enough on experience, you guys sure are riled up over something very very minor :lol:

It's a better driving car, that's substantially faster off the line, looks better, and has more room to move up the performance ladder without being hampered by it's chassis layout.  And none of you are buying it anyways. Not sure why any of you are complaining. I welcome the new vette with open arms.
2023 Ford Lightning Lariat ER
2019 Acura RDX SH-AWD
2023 BRZ Limited

Previous: '02 Mazda Protege5, '08 Mazda Miata, '05 Toyota Tacoma, '09 Honda Element, '13 Subaru BRZ, '14 Hyundai Genesis R-Spec 5.0, '15 Toyota 4Runner SR5, '18 Honda Accord EX-L 2.0t, '01 Honda S2000, '20 Subaru Outback XT, '23 Chevy Bolt EUV


12,000 RPM

Quote from: MrH on October 17, 2019, 09:56:32 AM
For a forum that always complains about how there's too much focus on numbers and not enough on experience, you guys sure are riled up over something very very minor :lol:

It's a better driving car, that's substantially faster off the line, looks better, and has more room to move up the performance ladder without being hampered by it's chassis layout.  And none of you are buying it anyways. Not sure why any of you are complaining. I welcome the new vette with open arms.
r0tor is a complainer :huh:

I agree, this is meaningless, nobody here is going from a C7 to a C8 as a track car, or anything for that matter.
Protecctor of the Atmospheric Engine #TheyLiedToUs

MX793

Apparently MT put their press car on a dyno and it made well over 500 hp at the wheels.  Ringer?
Needs more Jiggawatts

2016 Ford Mustang GTPP / 2011 Toyota Rav4 Base AWD / 2014 Kawasaki Ninja 1000 ABS
1992 Nissan 240SX Fastback / 2004 Mazda Mazda3s / 2011 Ford Mustang V6 Premium / 2007 Suzuki GSF1250SA Bandit / 2006 VW Jetta 2.5

r0tor

2011 Jeep Grand Cherokee No Speed -- 2004 Mazda RX8 6 speed -- 2018 Alfa Romeo Giulia All Speed

12,000 RPM

Protecctor of the Atmospheric Engine #TheyLiedToUs

r0tor

2011 Jeep Grand Cherokee No Speed -- 2004 Mazda RX8 6 speed -- 2018 Alfa Romeo Giulia All Speed

12,000 RPM

Quote from: r0tor on October 22, 2019, 07:06:14 AM
... and if that was the car C&D tested?
My mortgage and other bills will still come next month :huh: It's of zero consequence to me.
Protecctor of the Atmospheric Engine #TheyLiedToUs

MX793

Quote from: r0tor on October 22, 2019, 07:06:14 AM
... and if that was the car C&D tested?

They had different cars (mfr plates were different, looked like different colors as well), though both recorded the same acceleration times.  C&D's car was most likely in the same state of tune.
Needs more Jiggawatts

2016 Ford Mustang GTPP / 2011 Toyota Rav4 Base AWD / 2014 Kawasaki Ninja 1000 ABS
1992 Nissan 240SX Fastback / 2004 Mazda Mazda3s / 2011 Ford Mustang V6 Premium / 2007 Suzuki GSF1250SA Bandit / 2006 VW Jetta 2.5

Rich

No comparison can be made from the dyno to the SAE number. It's not a ringer and doesn't make more power than advertised.
2003 Mazda Miata 5MT; 2005 Subaru Impreza Outback Sport 4AT

Soup DeVille

It would be foolish for Chevy to supply a ringer these days with every hot rod shop in the country owning their own dyno.
Maybe we need to start off small. I mean, they don't let you fuck the glumpers at Glumpees without a level 4 FuckPass, do they?

1975 Honda CB750, 1986 Rebel Rascal (sailing dinghy), 2015 Mini Cooper, 2020 Winnebago 31H (E450), 2021 Toyota 4Runner, 2022 Lincoln Aviator

MX793

Quote from: Rich on October 22, 2019, 09:55:28 AM
No comparison can be made from the dyno to the SAE number. It's not a ringer and doesn't make more power than advertised.

Not necessarily true.  An inertial or brake chassis dyno can accurately measure how much power is applied directly to the dynamometer from the wheels of the car.  How much, precisely, is at the crankshaft is a matter of speculation since there will be friction losses, plus the inertia of the rotating components from the flywheel to the tires (in the case of an inertial dyno) that would need to be quantified.

What is certain, however, is that the amount of power put into the chassis dyno by the wheels must be less than what is at the crankshaft.  If a chassis dyno is reporting 50 more horsepower at the wheels than the engine is rated to at the crank, then the engine is making more than 50 hp above its factory rating at the crank.
Needs more Jiggawatts

2016 Ford Mustang GTPP / 2011 Toyota Rav4 Base AWD / 2014 Kawasaki Ninja 1000 ABS
1992 Nissan 240SX Fastback / 2004 Mazda Mazda3s / 2011 Ford Mustang V6 Premium / 2007 Suzuki GSF1250SA Bandit / 2006 VW Jetta 2.5

CaminoRacer

Didn't they say the HP number advertised was the minimum number "on a bad day"?
2020 BMW 330i, 1969 El Camino, 2017 Bolt EV

MX793

#976
Quote from: CaminoRacer on October 22, 2019, 10:29:34 AM
Didn't they say the HP number advertised was the minimum number "on a bad day"?

IIRC, SAE certified ratings require you fall within a statistical range of the reported number.  I believe the reported number is a minimum value, but you also can't grossly under-report.  Unless there was something wrong with that dyno, based on the numbers reported, that car is making at least 20% more power than stated (I'm assuming only 5% driveline loss, which I'm sure is unreasonably low).  I don't recall the exact % variation SAE requires, but it's pretty small.  Like 5%.
Needs more Jiggawatts

2016 Ford Mustang GTPP / 2011 Toyota Rav4 Base AWD / 2014 Kawasaki Ninja 1000 ABS
1992 Nissan 240SX Fastback / 2004 Mazda Mazda3s / 2011 Ford Mustang V6 Premium / 2007 Suzuki GSF1250SA Bandit / 2006 VW Jetta 2.5

GoCougs

Chassis dynos are terrible for accuracy, because they don't measure power directly. The only way to do it is how they do it to get the SAE number (engine dyno, which measures power directly).

I have no doubt that each of this first batch of C8 press cars have been meticulously gone over but a ringer making 600 hp net would be unconscionable in that it would grossly skew buyer perception and would invite engine failures, which would be a PR catastrophe. Such an action would jeopardize the SAE certification as well.

afty

The MT article has some possible explanations (https://www.motortrend.com/news/2020-chevrolet-corvette-c8-power-dyno/)

QuoteA couple of days later, engineers provide us two reasons for the discrepancy of power. The first one is that when the Corvette is cold, it actually produces more horsepower than when it's hot. But that doesn't make sense—we saw similar numbers after six runs, and the car was pretty hot by the end of the second run. The other explanation is that Chevrolet certifies most of its engines through the SAE, the Society of Automotive Engineers, which follows a strict set of rules and standards to determine the horsepower and torque ratings. In other words, the SAE acts as an independent party that's present during the engine tests and is the one who determines the final output ratings. Their testing does not involve a simple pull from idle to redline, either. Rather, rpm are slowly ramped up and allowed to stabilize before accelerating further. This process results in significantly more heat generation than any single pull from our six dyno runs. For that reason, the engineers say, it's not uncommon for single chassis dyno pulls to register higher output (and it is extremely unlikely any car will ever generate less than rated output). According to Chevy engineers, this is an expensive process, given that someone from the SAE has to be present, but the automaker has done this for years, and it's a procedure that it continues to follow with most of its engines in the U.S.

Chevy engineers also say that the drivetrain loss of a dual-clutch transmission, like the one in the Corvette, is less than 15 percent—but hesitated to give us an exact number (and even if it was zero loss, we still measured more wheel-horsepower than rated crank horsepower).

MX793

Quote from: GoCougs on October 22, 2019, 01:22:04 PM
Chassis dynos are terrible for accuracy, because they don't measure power directly. The only way to do it is how they do it to get the SAE number (engine dyno, which measures power directly).

I have no doubt that each of this first batch of C8 press cars have been meticulously gone over but a ringer making 600 hp net would be unconscionable in that it would grossly skew buyer perception and would invite engine failures, which would be a PR catastrophe. Such an action would jeopardize the SAE certification as well.


Chassis dynos cannot accurately measure crank horsepower.  They can accurately measure wheel horsepower.  If your chassis dyno says you are making more at the wheels than the rating at the crank, either the engine is under-rated or the dyno is broken.
Needs more Jiggawatts

2016 Ford Mustang GTPP / 2011 Toyota Rav4 Base AWD / 2014 Kawasaki Ninja 1000 ABS
1992 Nissan 240SX Fastback / 2004 Mazda Mazda3s / 2011 Ford Mustang V6 Premium / 2007 Suzuki GSF1250SA Bandit / 2006 VW Jetta 2.5

GoCougs

Quote from: MX793 on October 22, 2019, 01:31:09 PM
Chassis dynos cannot accurately measure crank horsepower.  They can accurately measure wheel horsepower.  If your chassis dyno says you are making more at the wheels than the rating at the crank, either the engine is under-rated or the dyno is broken.

Chassis (inertial) dynos are terrible at accurately measuring wheel horsepower. Chassis dynos derive torque from acceleration, so if vehicle A has more drivetrain inertia than vehicle B, it will dyno lower than vehicle B, despite having identical wheel horsepower. As one can imagine, virtually no two vehicles have the same drivetrain inertia, and the dyno and/or operator has to account for vehicle-to-vehicle drivetrain inertia differences (and it/they don't). This is why absolute chassis dyno measurements rarely add up.

Chassis dyons are good a relative measurement however (i.e., fairly precise) for gauging changes on a particular vehicle (assessing the affect of tuning/mods).

Payman

Quote from: GoCougs on October 22, 2019, 02:04:15 PM
Chassis (inertial) dynos are terrible at accurately measuring wheel horsepower. Chassis dynos derive torque from acceleration, so if vehicle A has more drivetrain inertia than vehicle B, it will dyno lower than vehicle B, despite having identical wheel horsepower. As one can imagine, virtually no two vehicles have the same drivetrain inertia, and the dyno and/or operator has to account for vehicle-to-vehicle drivetrain inertia differences (and it/they don't). This is why absolute chassis dyno measurements rarely add up.

Chassis dyons are good a relative measurement however (i.e., fairly precise) for gauging changes on a particular vehicle (assessing the affect of tuning/mods).

I imagine that aftermarket companies that make cold air intakes, chips, turbos, etc use this to advertise that their product adds more hp than it actually does. When they dyno the car with their chip and it shows 595 hp, they can claim ZOMG IT ADDS 100 HORSEPOWER! over the SAE rated 495 hp. But if you actually dyno'd the car before you added the chip, the difference is probably more like a 20 hp increase, if any at all.

MX793

The dyno will accurately measure (or calculate, since it actually measures acceleration) the power applied to the dyno roller.

They cannot accurately account for friction losses or the inertia of the driveline (which essentially shows up as a "loss" on an inertial dyno even though it technically is not a loss).  Hence, they are rubbish for establishing crank power with any accuracy and will report that lighter driveline components or wheels result in more power.  However, the laws of physics make it very clear that the drive wheels cannot impart more power to the dyno roller than is available at the crank. 

If an inertial chassis dyno registers more power at the wheels than is supposed to be at the crank, either the engine is under-rated or the dyno is broken (either mechanically or the equations that run in the background to compute power).
Needs more Jiggawatts

2016 Ford Mustang GTPP / 2011 Toyota Rav4 Base AWD / 2014 Kawasaki Ninja 1000 ABS
1992 Nissan 240SX Fastback / 2004 Mazda Mazda3s / 2011 Ford Mustang V6 Premium / 2007 Suzuki GSF1250SA Bandit / 2006 VW Jetta 2.5

GoCougs

Quote from: MX793 on October 22, 2019, 02:17:22 PM
The dyno will accurately measure (or calculate, since it actually measures acceleration) the power applied to the dyno roller.

They cannot accurately account for friction losses or the inertia of the driveline (which essentially shows up as a "loss" on an inertial dyno even though it technically is not a loss).  Hence, they are rubbish for establishing crank power with any accuracy and will report that lighter driveline components or wheels result in more power.  However, the laws of physics make it very clear that the drive wheels cannot impart more power to the dyno roller than is available at the crank. 

If an inertial chassis dyno registers more power at the wheels than is supposed to be at the crank, either the engine is under-rated or the dyno is broken (either mechanically or the equations that run in the background to compute power).

Inertia is not a loss. If vehicle A and Vehicle B both have identical crank horsepower and identical drivetrain losses, yet vehicle A has 10% more drivetrain inertia, vehicle A and vehicle B will have identical constant speed wheel horsepower, yet vehicle A will show 10% less wheel horsepower on an inertial chassis dyno. This is why chassis dynos are generally terrible at accuracy. Some sophisticated chassis dynos can account for drivetrain inertia beyond simple estimate (they actually run in reverse to measure both drive train losses (torque to drive the drivetrain at constant speed) and drivetrain inertia (torque to accelerate the drivetrain)), but these are not widely available AFAIK, esp. for run-of-the-mill tuner shops.

MX793

#984
Quote from: GoCougs on October 22, 2019, 02:34:39 PM
Inertia is not a loss. If vehicle A and Vehicle B both have identical crank horsepower and identical drivetrain losses, yet vehicle A has 10% more drivetrain inertia, vehicle A and vehicle B will have identical constant speed wheel horsepower, yet vehicle A will show 10% less wheel horsepower on an inertial chassis dyno. This is why chassis dynos are generally terrible at accuracy. Some sophisticated chassis dynos can account for drivetrain inertia beyond simple estimate (they actually run in reverse to measure both drive train losses (torque to drive the drivetrain at constant speed) and drivetrain inertia (torque to accelerate the drivetrain)), but these are not widely available AFAIK, esp. for run-of-the-mill tuner shops.


I specifically said inertia is not a loss.  On an inertial dyno, however, increasing drivetrain inertia (e.g. heavier wheels) will register on the dyno as a reduction in power, because the acceleration of the drum slows due to there being more rotating mass for the engine to accelerate.

I think we are in violent agreement on the limitations of a chassis, and especially inertial, dyno.

That said, an inertial dyno cannot and will not report more power "at the wheels" than is available at the crankshaft.  It can't report the same power as the crank.  If you put a 300 hp (crank) car on an inertial chassis dyno and it says you spun the drum up with 350 hp, either your car makes more than 350 hp, or the dyno is broken/malfunctioning.
Needs more Jiggawatts

2016 Ford Mustang GTPP / 2011 Toyota Rav4 Base AWD / 2014 Kawasaki Ninja 1000 ABS
1992 Nissan 240SX Fastback / 2004 Mazda Mazda3s / 2011 Ford Mustang V6 Premium / 2007 Suzuki GSF1250SA Bandit / 2006 VW Jetta 2.5

Rich

2003 Mazda Miata 5MT; 2005 Subaru Impreza Outback Sport 4AT

12,000 RPM

Quote from: Rockraven on October 22, 2019, 02:13:49 PM
I imagine that aftermarket companies that make cold air intakes, chips, turbos, etc use this to advertise that their product adds more hp than it actually does. When they dyno the car with their chip and it shows 595 hp, they can claim ZOMG IT ADDS 100 HORSEPOWER! over the SAE rated 495 hp. But if you actually dyno'd the car before you added the chip, the difference is probably more like a 20 hp increase, if any at all.
Yea, it's generally best to reference independent tests. Truthfully, a lot of bolt ons are just good for noise (which is fine)
Protecctor of the Atmospheric Engine #TheyLiedToUs

CaminoRacer

Quote from: MX793 on October 22, 2019, 10:36:55 AM
IIRC, SAE certified ratings require you fall within a statistical range of the reported number.  I believe the reported number is a minimum value, but you also can't grossly under-report.  Unless there was something wrong with that dyno, based on the numbers reported, that car is making at least 20% more power than stated (I'm assuming only 5% driveline loss, which I'm sure is unreasonably low).  I don't recall the exact % variation SAE requires, but it's pretty small.  Like 5%.

Yeah there's no way it's making that much more than advertised.
2020 BMW 330i, 1969 El Camino, 2017 Bolt EV

GoCougs

Quote from: CaminoRacer on October 22, 2019, 08:25:44 PM
Yeah there's no way it's making that much more than advertised.

Dat inertia, and the flaw of "wheel" horsepower. Engine dyno or no dyno IMO (but a course of PITA if you're testing-n-tuning).

To get those accel numbers it's likely a highly violent launch control (though no mention of such a thing AFAIK).

r0tor

Yea, the magical "inertia" issue that only happens when a C8 is on it...
2011 Jeep Grand Cherokee No Speed -- 2004 Mazda RX8 6 speed -- 2018 Alfa Romeo Giulia All Speed