flywheel vs total hp
08-09-2005, 12:33 AM
#2
Guest
Posts: n/a
RE: flywheel vs total hp
drivetrain loss never really is a set number, more of a guestimate based on the vast majority of rated flywheel hp vs what people get on their base dyno runs.
If you make 260 flywheel hp you will never make 260 wheel hp until you modify your engine.
Edit: It's also hard to tell how much flywheel power you truely make. A lot of manufacturers underrate their cars (03-04 Cobras and Mach I's for example) for "insurance" purposes.
As another example, a few years ago when MM&FF tested the 02 Camaro SS and 03 Cobra on the dyno's the SS made 317 to the wheels, stock. Where as it was rated at 325 at the flywheel. The SVT made something like 378ish to the wheels where as it was rated for 390 crank horses.
So, gauging true flywheel power and the percentage of drivetrain loss is hard unless you have access to an engine puller and engine dyno. Gauging the wheel power is also hard since different runs can produce different results. engine temp, engine efficiency, Air temp, pressure, altitude, etc can all have an effect of dyno'ing different numbers. I've seen people dyno two times in a row and get numbers to the wheels that were at least 20 hp/tq apart from each other.
If you make 260 flywheel hp you will never make 260 wheel hp until you modify your engine.
Edit: It's also hard to tell how much flywheel power you truely make. A lot of manufacturers underrate their cars (03-04 Cobras and Mach I's for example) for "insurance" purposes.
As another example, a few years ago when MM&FF tested the 02 Camaro SS and 03 Cobra on the dyno's the SS made 317 to the wheels, stock. Where as it was rated at 325 at the flywheel. The SVT made something like 378ish to the wheels where as it was rated for 390 crank horses.
So, gauging true flywheel power and the percentage of drivetrain loss is hard unless you have access to an engine puller and engine dyno. Gauging the wheel power is also hard since different runs can produce different results. engine temp, engine efficiency, Air temp, pressure, altitude, etc can all have an effect of dyno'ing different numbers. I've seen people dyno two times in a row and get numbers to the wheels that were at least 20 hp/tq apart from each other.
08-09-2005, 12:47 AM
#3
RE: flywheel vs total hp
Thank you but one more thing if i cant get the total flywheel why do rear wheel cars do better that fwd cars of similar performace. and racing from a dig doesnt mean ill use or get any more horses
08-09-2005, 01:20 AM
#4
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Posts: n/a
RE: flywheel vs total hp
A lot of "doing better" has more to do with driver skill over peak power and how the car is setup to make that power. A lot of people think that peak hp being higher means that you'll instantly do better. Yet you can line a 400 hp 2600 lb Civic up against a 600 hp 3500 Cobra and, again depending on the driver, the Civic may win or the Cobra may win.
if a FWD and a RWD car make the same amount of power at the crank, the FWD vehicle will put more to the ground because it'll have less drivetrain loss.
Generally a FWD car has less drivetrain to go through.
fwd
flywheel, clutch, transmission gearing, output shaft, axles, wheel, tire, ground
rwd
flywheel, clutch, transmission gearing, output shaft, drive shaft, rear gears, TWO rear axles, wheel, tire, ground
if a FWD and a RWD car make the same amount of power at the crank, the FWD vehicle will put more to the ground because it'll have less drivetrain loss.
Generally a FWD car has less drivetrain to go through.
fwd
flywheel, clutch, transmission gearing, output shaft, axles, wheel, tire, ground
rwd
flywheel, clutch, transmission gearing, output shaft, drive shaft, rear gears, TWO rear axles, wheel, tire, ground
08-09-2005, 01:33 PM
#7
RE: flywheel vs total hp
thank you si the information was very helpful and also one last question i knew fwd handled better but if a fwd puts down more power to the wheels because of a lot less drivetrain loss why is it believed rwd is better for performance shouldnt fwd be faster
08-09-2005, 01:52 PM
#8
EXTREME Moderation
Join Date: Apr 2005
Location: BLAM-O
Posts: 7,895
RE: flywheel vs total hp
when you accelerate, the weight of the car shifts to the rear wheels (not all, but a significant amount). rwd cars get better traction on their drive wheels when they accelerate. that's why badass cars can do a wheelie.