4WD not being much better than FR

[MrFox]

Most Quattros (excluding the original and the TTs) uses a torsen center diff with 50/50 torque split, so its not biased at all.

The GT-R uses an active center diff - not really a diff at all, more an electronically controlled clutch that engages to send torque to the fronts when the computer commands it to (wheel slippage under acceleration)

The Honda Pilot/MDX has pretty much the exact same setup, except it sends torque the other way, from the front to the back.

the direction the engine is mounted has nothing to do with the "bias" of the AWD system. That is detemined by the center differential's torque splitting charistics.

:Werd

[Bubba1]

it's been around the longest hasn't it?

No, but they are probably most successful with it in competition.

[PROJECTRB240SX]

YES ENGINE DIRECTION HAS NOTHING TO DO WITH IT BUT ITS A GENERAL CLUE WHICH THE BIAS IS GOING TO PULL TO BY THE DIRECTION OF THE ENGINE. BUT NOW ALOT OF AWD SYSTEMS HAVE TORSEN SYSTEMS FOR FULL AWD.

QUATTROS DIDN'T ALWAYS HAVE THE TORSEN SYSTEM, IT USED TO BE A FRONT BIASED SYSTEM BECAUSE OF ITS RALLY ROOTS. THEY SWITCHED TO TORSEN BECAUSE OF ECONOMY AND MINIMAL DRIVETRAIN LOSSES (THIS IS BECAUSE THE TIRES WILL ROTATE AT THE SAME SPEEDS CONSTANTLY).

[RobDET]

Engine orentation has 0 effect nor can you assume anything becuase of it. An egine's orientation is due soly to the packaging constraints of an engine bay. Acura Legands had a transversley mounted v6 and was still FWD. You can make an eclipse RWD by adding the Viscous LSD eliminator and pulling the front CV's and capping them. Subaru is 50/50 and it's motor is longitudinal. So was the 323GTX (it was adjustable) with a transverse engine layout.

AWD wears out the tires slower than FWD or RWD according to C&D articles where they have hires race driver so and so and tested it several times. That's why AWD is against the rules in almost every form of racing where the cars are not derived from street legal vehicles.

[PROJECTRB240SX]

YEAH THATS BECAUSE TRANSVERSE MOUNTED ENGINES ARE FWD, SUBARU IS NOT 50/50 EXCEPT FOR SOME, THE ECLIPSE IS REAR WHEEL DRIVE FROM CONVERSIONS BUT IT WAS DESIGNED AS FWD OR FRONT BIASED AWD, THE 323 IS FRONT BIASED WITH A ADJUSTABLE CENTER DIFF THAT WAS ONLY PARTIAL ACTIVE.

I'M NOT SAYING ITS 100% BUT ITS A GOOD ASSUMPTION THAT A TRANSVERSE MOUNTED ENGINE IS FWD OR FRONT BIASED (UNLESS ADJ CENTER DIFF, OR FULL-TIME AWD IS STATED) AND A LOGITUDINAL ENGINE WILL BE RWD OR REAR BIASED (AGAIN UNLESS STATED).

[PROJECTRB240SX]

AWD DOES REDUCE TIRE WEAR BECAUSE THE POWER IS SPREAD OVER ALL FOUR TIRES AND NOT JUST TWO, THERE IS A BALANCE TO THE SYSTEM.

[RobDET]

the reason transverse motors are *usually* FWD biased is because they *usually* are derived from FWD platforms. Even the 3000GT is FWD thus a transverse layout. It is still more of a packaging issue than a drive line issue.

[PROJECTRB240SX]

YEAH, I'M NOT ARGUING WITH YOU.... I JUST MEANT IT AS A QUICK WAY TO JUDGE THE SYSTEM.

[MrFox]

Its not a bad assumption for stock vehicles. Every time power has to make a 90 degree turn there will be quite a bit of loss. So designs are biased to the wheels with the most straightforward path for the sake of fuel economy.

But the bias can be changed to anything you like, regardless of engine orientation.

[RobDET]

turns do not reduce power... paracitic loss from the gears reduces power. Having one more gear in the system will add the same amount of resistance no matter what it's orientation.

[PROJECTRB240SX]

YOU BOTH ARE RIGHT, BUT THE COMPANIES DESIGN THE DRIVETRAIN TO BE AS STRAIGHT THROUGH AS POSSIBLE. THIS IS WHY I GAVE THE ORIENTATION AS A GOOD JUDGE OF DRIVE WHEELS/BIAS.

[MrFox]

turns do not reduce power... paracitic loss from the gears reduces power. Having one more gear in the system will add the same amount of resistance no matter what it's orientation.

Normal helical gears can only transfer power in a straight line. A hypoid gearset is needed in a gear train in order to make 90deg turns. Hypoid gears consume a lot more power than helical gears - they are more heavily loaded and ride with higher contact pressures.

[RobDET]

isn't the rear end of a car helical? not the helical LSD but the ring and pintion gear?

[MrFox]

isn't the rear end of a car helical? not the helical LSD but the ring and pintion gear?

Only if its a RWD transaxle.

Here's a FR diff - Hypoid ring and pinion:

Transaxle diff - Helical ring and pinion:

These guys can explain hypoid gears better than Ihttp://auto.howstuffworks.com/gear4.htm

[RobDET]

Right i had all that in my head already... i guess i assumed all gears were created equal.