[Chevy71]

Originally Posted by TrackClub

I don't like that weld on this "one piece" shaft - not in the least.
And $1000 plus install to save 3lb is pretty nuts if u ask me even if this didn't void a whole warranty.
But hey, that's just IMO. Peace

It's built and proven to handle more stress than the stock DS can. The stock one is questionable under good traction with a stock car, let alone any power adders. That's my point. I've not heard of one of their DS failing yet, on any model vehicle. They also come with a lifetime warranty. I think the welds have proven to hold up. Fireball runs a pure gForce driveline on a car they track often and is running in the 8's.

[crazydmc]

Originally Posted by RUQWIKR

Wrong. Your driveshaft speed on a rear drive (trans in front) is your engine speed divided by your trans ratio. So, in first gear, it is spinning significantly less than engine speed, in fourth (ours is 1.00 ratio), it is the same, but in 0.50 ratio 6th, it is spinning twice as fast.

That's why it is called overdrive because the trans output shaft connected to the driveshaft spins faster than the trans input shaft on the engine side.

With no clutch or torque converter slippage: Engine RPM / trans ratio = Driveshaft Speed

I understand how transmissions work.... and you do too. Discussion was about the critical speed capability (max rpm) of the drive shaft.

....assuming you reached 160mph somehow (your example) the drive shaft is turning at an rpm based on the rear diff ratio... it doesn't matter what gear you used to achieve it. Yes, in 4th gear your engine would be at higher rpm than 5th or 6th gear... but engine rpm is irrelevant here.

not wrong.

[Dynomike75]

Originally Posted by crazydmc

I understand how transmissions work.... and you do too. Discussion was about the critical speed capability (max rpm) of the drive shaft.

....assuming you reached 160mph somehow (your example) the drive shaft is turning at an rpm based on the rear diff ratio... it doesn't matter what gear you used to achieve it. Yes, in 4th gear your engine would be at higher rpm than 5th or 6th gear... but engine rpm is irrelevant here.

not wrong.

I've got to go with crazydmc here, he is absolutely correct, it has nothing to do with engine RPM. If you are at 200MPH in neutral at idle, your driveshaft will still be spinning like mad because it is hard-coupled to the rearend and thus to the wheels.

And I was thinking the same thing as others here. Why would you want to reduce your critical speed? What is the length on that from u-joint to u-joint (expansion joint) as well as the wall thickness and material? The critical speed can be calculated out, but if it is only 3.5" dia, I am guessing it is lower than 160.

[RUQWIKR]

Originally Posted by Dynomike75

I've got to go with crazydmc here, he is absolutely correct, it has nothing to do with engine RPM. If you are at 200MPH in neutral at idle, your driveshaft will still be spinning like mad because it is hard-coupled to the rearend and thus to the wheels.

And I was thinking the same thing as others here. Why would you want to reduce your critical speed? What is the length on that from u-joint to u-joint (expansion joint) as well as the wall thickness and material? The critical speed can be calculated out, but if it is only 3.5" dia, I am guessing it is lower than 160.

Not arguing the speed in neutral / clutch in. But, it is simple math with no slippage, in a gear: engine rpm / trans ratio = output shaft speed = driveshaft speed. So, for the 1LE ratios, 4000 engine rpm in 4th (1.00) = 4000 output shaft rpm = 4000 driveshaft rpm. In 6th (0.50), the output shaft and driveshaft are spinning 8000.

[mjk3888]

Originally Posted by RUQWIKR

Not arguing the speed in neutral / clutch in. But, it is simple math with no slippage, in a gear: engine rpm / trans ratio = output shaft speed = driveshaft speed. So, for the 1LE ratios, 4000 engine rpm in 4th (1.00) = 4000 output shaft rpm = 4000 driveshaft rpm. In 6th (0.50), the output shaft and driveshaft are spinning 8000.

You're not getting the point. Slow down and re read all the posts and try to understand them. We can read by the tone of your replys that all your thinking about is defending your posts instead of understanding what others are saying.

[Dynomike75]

Originally Posted by RUQWIKR

Agree - 3#'s along a small diameter long shaft does not gain you much.

Critical speed will be MUCH less than the 2-piece stock shaft. The 13/ 14 GT500 had a large 4" diameter carbon fiber shaft to get around the critical speed, and it only had 3.31 gears. Remember that with a 0.50 6th gear, the driveshaft is spinning twice engine speed. It's spinning one-to-one in 4th. They say the shaft is good to "around 160" - probably in 4th. Read up on critical speed. A driveshaft coming apart at speed won't be a good thing. Not saying it will for you, but, it's your car and your mods.

FYI - it is much more expensive for an OEM to have two piece props with center carrier bearings than old school one piece. With the two piece really being two short one piece shafts from a critical / limiting speed, that's why there are in such things as our cars, ZL1's, CTS-V's, etc.

The strange thing is that you state that they set the speed limit "probably in 4th." What we are saying is that transmission gear is irrelevant, only rear wheel speed matters (and rear end gear ratio obviously, but it is a constant), you state that what gear the person is in actually matters. If they are in neutral an pulled to 200mph by another vehicle, the driveshaft could still explode... Transmission gear does not matter in the least.

[RUQWIKR]

I was just trying to point out that overdriven trans ratios spin the driveshaft faster than engine speed. The driveshaft is still going to spin the same rpm at a given vehicle speed regardless of trans ratio. Tire size and rear gear ratio will obviously matter for the shaft rpm at a given vehicle speed. Sorry for any confusion.

[1LE caSSper]

Can't we ever just get along lol

Actually very informative points tho from you 2