Front diff limits

[driftxsequence]

Been doing some research but havent come across anything saying the front diff is good up to ___ HP. I drive like a grandpa, never launch my cars hard so im curious if 250-300 whp is safe for the drivetrain. And since im new to the m20, what is a stock motor good up to?

[downforce22]

do some more research

http://www.stanceworks.com/forums/showthread.php?t=39694

http://r3vlimited.com/board/showthread.php?t=201774

http://www.r3vlimited.com/BOARD/showthread.php?t=336129

http://www.r3vlimited.com/BOARD/showthread.php?t=360633

[Kershaw]

If you drive like a grandpa and never launch it you could have a 1000hp m20 attached to it. It's the shock and strain of sudden launches and high rpm that kill it.

But what's the point of more horsepower if you drive like a grandpa?

[driftxsequence]

I get on it, and will drive cars hard, but that generally involves lots of revs and corners. Not hard launches and clutch dumps.

I do a lot of rolling pulls when tuning my RX7s.

My point being if i decide to make 350 whp, do i need to worry about acquiring a secondhand differential or axles etc...

[CrazyPrime]

I get on it, and will drive cars heard, but that generally involves lots of revs and corners. Not hard launches and clutch dumps.

I do a lot of rolling pulls when tuning my RX7s.

My point being if i decide to make 350whp, do i need to worry about acquiring a secondhand differential or axles etc...

has been discussed on multiple occasions. I have hard that 350whp is fine as long you don't launch at every stop light. sudden shock is what kills it ie clutch drops.

[driftxsequence]

Thanks, I'm finding that information is not nearly as consolidated here as with what I am used to.Things are scattered across multiple forums, and in multiple directories.

[flyboyx]

you can say whatever you want but if you drive your car hard, that diff won't last long at 300hp. there is no reason to spend the money and time to increase hp that much of you don't drive it hard.

[Kershaw]

I get on it, and will drive cars hard, but that generally involves lots of revs and corners.

That's not "driving it like a grandpa." You need to obey the speed limits, accelerate slowly, and drive a Cadillac Catera to do that effectively.

[nando]

It's torque, not HP, that breaks stuff (transmissions and diffs are rated for a maximum torque input - not power). HP is a function of time (RPM), which the diff doesn't necessarily care about.

Hard launching breaks stuff because torque input changes from 0 to 200-300ft/lbs in an instant. I think regardless of power - if you're beating on it, it's going to break eventually. That said, I did hundreds of hard launches with mine and never broke anything, although mine is N/A. Now the clutch slips when I dump it so I can't do it anymore, lol. Next motor will have a 240mm E34 M5 clutch, maybe it'll hold up better..

[Kershaw]

And I clutch dumped it in the rain and blew apart my diff completely stock. Really, it's just a matter of when.

[The Dark Side of Will]

It's torque, not HP, that breaks stuff (transmissions and diffs are rated for a maximum torque input - not power).

Hard launching breaks stuff because torque input changes from 0 to 200-300ft/lbs in an instant.

The *peak* torque is what breaks things. Rolling into a stock iX in first gear puts a maximum of 165 * 3.82 * 0.33 = 208 ftlbs going into the diff input. This is not enough to break the tires loose, as we know.

However, when the flywheel is turning 6200 RPM and is pulled down to 2000 RPM in a split second, the transient torque that shows up at the input shaft is *FAR* greater than the 165 ftlbs that the engine produces, and 3.82 times that going into the T-case. This *IS* enough to break the tires loose, demonstrating that it is much more torque than is produced by rolling into the throttle.

Dropping the clutch produces very high transient transient torque related to decelerating the rotating mass of the flywheel in a very short period of time.

High transient loading is not "shock" per the mechanical engineering definition of shock.

[downforce22]

The *peak* torque is what breaks things. Rolling into a stock iX in first gear puts a maximum of 165 * 3.82 * 0.33 = 208 ftlbs going into the diff input. This is not enough to break the tires loose, as we know.

However, when the flywheel is turning 6200 RPM and is pulled down to 2000 RPM in a split second, the transient torque that shows up at the input shaft is *FAR* greater than the 165 ftlbs that the engine produces, and 3.82 times that going into the T-case. This *IS* enough to break the tires loose, demonstrating that it is much more torque than is produced by rolling into the throttle.

Dropping the clutch produces very high transient transient torque related to decelerating the rotating mass of the flywheel in a very short period of time.

High transient loading is not "shock" per the mechanical engineering definition of shock.

And since the transmission is a torque multiplier, you should be able to run more power through the tcase in higher gears.

165 * 3.82 * 0.33 = 208 ftlbs at the front diff in 1st gear
vs

165 * 2.2 * 0.33 = 120 ftlbs at the front diff in 2nd gear.

With a little math, the 2nd gear equivalent of the torque given to the driveline in 1st gear is:

X * 2.2 * 0.33 = 208 ft lbs

X = 286 horsepower

What does this mean? Assuming you don't launch the car in 1st gear, but roll onto the power, the diff can see ~300 ftlbs of torque in 2nd gear or higher. That's been my basis on my turbo ix. Plus you don't usually see much boost in first gear so it isnt a scenario you would see unless you were trying to drag race or something.