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Old 04-09-2013, 10:00 AM   #1
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Fun with Math: Drive Shafts

So I just replaced my 2.73 gears with 3.73 and am thinking about that drive shaft.

I understand the factory ecm limits us to 120 mph for good reason; the factory drive shaft isn't rated for higher speeds.

But I changed out the gears to 3.73. That means the shaft is rotating at a higher rpm at the same speed than before. Does this mean I need to keep the car below about 88 mph?

Maybe I did the math wrong, too. I was thinking that going 88 mph with 3.73 gears is roughly equivalent to 120 mph on 2.73 gears.

The reason this is on my mind is because I was thinking about taking the car to the track to see what differences the new gear, CAI (and hopefully Bama's custom tunes, whenever they are done with them) make. But if that driveshaft will make that idea really dangerous, then I need to reconsider.

Thoughts? Am I way off here? Or have I got it about right?
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Old 04-09-2013, 10:07 AM   #2
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Originally Posted by DEvermore View Post
So I just replaced my 2.73 gears with 3.73 and am thinking about that drive shaft.

I understand the factory ecm limits us to 120 mph for good reason; the factory drive shaft isn't rated for higher speeds.

But I changed out the gears to 3.73. That means the shaft is rotating at a higher rpm at the same speed than before. Does this mean I need to keep the car below about 88 mph?

Maybe I did the math wrong, too. I was thinking that going 88 mph with 3.73 gears is roughly equivalent to 120 mph on 2.73 gears.

The reason this is on my mind is because I was thinking about taking the car to the track to see what differences the new gear, CAI (and hopefully Bama's custom tunes, whenever they are done with them) make. But if that driveshaft will make that idea really dangerous, then I need to reconsider.

Thoughts? Am I way off here? Or have I got it about right?
You have gotten it about right. It's actually 93mph to be excact . And yes if I were you, to play its safe you should get an aluminum one piece drive shaft
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Old 04-09-2013, 10:40 AM   #3
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Good point with the one piece drive shaft. I've always wondered why folks go through spending the money on them for the street; but changing the rear gear such as you did now makes sense, as you are turning a much higher RPM with your setup.
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Old 04-09-2013, 01:24 PM   #4
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Not a bad idea to change the driveshaft. I've always been for taking the extra safe route and building the car to handle much more than it produces. That's a good way to keep yourself out of some serious trouble, IMO!

Shane
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Old 04-09-2013, 01:45 PM   #5
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Originally Posted by AMShaneLesky View Post
Not a bad idea to change the driveshaft. I've always been for taking the extra safe route and building the car to handle much more than it produces. That's a good way to keep yourself out of some serious trouble, IMO!

Shane


I think the whole driveshaft thing may have been blown up to be more of a problem then it is but it's always better to be safe than sorry. Aftermarket shafts have failed too so I'd recommend the safety loop if anything.
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Old 04-09-2013, 01:54 PM   #6
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That raises another question for me, I wonder if the speed limiter was set to 120 for the pony package cars with 3.31's or for cars with 2.73's? Or both? If it was for the 3.31's then your be good to go a little faster.

This doesn't really do much for your question I guess but I'm just curious. Either way I would recommend a one piece DS
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Old 04-09-2013, 02:14 PM   #7
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I made a thread discussing this. Too bad no one searches these days. But I'm doing 3.31 just for the safety.

---------- Post added at 02:14 PM ---------- Previous post was at 02:12 PM ----------

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That raises another question for me, I wonder if the speed limiter was set to 120 for the pony package cars with 3.31's or for cars with 2.73's? Or both? If it was for the 3.31's then your be good to go a little faster.

This doesn't really do much for your question I guess but I'm just curious. Either way I would recommend a one piece DS
Also asked this. No one answered.

I'd assume the 2.73 since most came with it and not everyone will be buyin the performance pack.
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Old 04-09-2013, 02:39 PM   #8
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Originally Posted by GrabberBlue5.0 View Post
That raises another question for me, I wonder if the speed limiter was set to 120 for the pony package cars with 3.31's or for cars with 2.73's? Or both? If it was for the 3.31's then your be good to go a little faster.

This doesn't really do much for your question I guess but I'm just curious. Either way I would recommend a one piece DS
I believe that the limiter was set because of the speed rating of the base tires. I'm sure the weak DS kept it limited on the PP and such.
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Old 04-09-2013, 03:00 PM   #9
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Thanks for all the replies, everyone, good conversation. I'm putting the al drive shaft on my to-buy list as soon as I can manage it. I want to see how things settle out first, as I'm still waiting for a working tune from Bama for my Diablo Intune. First two have failed -- turned off speedo and car accelerates with a roar when I take my foot off the accelerator. Putting around on stock tune for now... >.< Must... be... patient... argh. But that's a different topic.
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