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Discussion Starter · #1 ·
Unless you have enough power to break the OEM shaft, spend your money on other performance parts. Copied and pasted from a tech article. I've been falling in this trap for years, but here is the truth.

Now let's think about a drive shaft. The driveshaft is a fairly thin hollow tube. Nearly all drive shaft weight is at the outside, since it is (of course) hollow. The shaft also turns at the same RPM no matter what the driveshaft diameter, because the RPM is set by the rear end ratio, tire diameter, and vehicle speed. If we make a driveshaft lighter and keep everything else the same, the vehicle acceleration change is often insignificant.

Why would it be insignificant in most cases?

In the first place, the drive shaft is small in diameter. With a small diameter, less energy is stored for a given weight. In the second place, a driveshaft is really not that heavy. A steel Mustang driveshaft weighs somewhere around 30 pounds, so we just can't take that much weight out.

Also, the driveshaft spins up gradually and smoothly over a long period of time. It accelerates fastest at slowest speeds, and that is when it needs the least energy to spin up. Because it has a long time to spin up, is a small diameter, and because it does not weigh much, the driveshaft does not remove very much horsepower at any instant of time. Despite what we are told, a change in driveshaft weight has, at best, a very small effect on acceleration. Likely any change is immeasurable in a street/strip car.

Now a lighter shaft certainly can help in a very light vehicle. It can also help in a road race car (as will a light crank and flywheel), because road racing requires instantly changing from acceleration to deceleration.

A light driveshaft won't change anything significant or measureable in a 3000-pound 11-second car, except how fast dollars leave your wallet!

Another worry is driveshaft diameter. If we go from a 30-pound 3-inch steel driveshaft to a 30-pound 3.5-inch aluminum shaft, we move the weight out 3.5/3 = 1.167 times. That increases stored energy 1.167^2 times, or 1.36 times. If we store 0.3 horsepower in the shaft, changing the diameter will increase that to 0.4 horsepower. We would have to reduce weight 14.3% to 25.7 pounds just to break even with the diameter increase.

The worst thing about a driveshaft is the diameter is so small, and the acceleration time is so long, there just isn't much horsepower being sapped from the system. A typical steel driveshaft in a typical 12 or 13 second car only stores an average of about 1/4 horsepower. If we got 100% of that back with a zero weight shaft, we would never notice it.

Good reasons to change a driveshaft are to get rid of vibration and harmonic resonances in the shaft, to make it stronger, or to simplify a two-piece driveshaft system. The silliest reason is to speed the car up. Even if we only pay $100 for a shaft, it would typically be much less than 1/4-horsepower average gain. That would be paying much more than 100/.25 = $400 per horsepower. Paying a lot more than $400 per horsepower is not a good investment.
 

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I tend to agree. Vehicles with a front engine/rear transaxle are the exception.

Good find, thanks for sharing.
 

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Well I recall AMS reporting about 8lbs weight savings for the Aluminium over the Stock shaft and 13lbs for the CF drive shaft, I think they re-use stock diameter so the decrease in rotational mass could be significant.

But Is anyone actually buying drive-shafts as a way to increase HP??? At $800-$1400 there are a lot better mods to make on this platform that do increase performance, if anything the lighter drive-shaft will help minimize drive-line loss which as you said would likely increase responsiveness rather than gain you additional power.

Not a bad post though.
 

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I tend to agree. Vehicles with a front engine/rear transaxle are the exception.

Good find, thanks for sharing.
Except for the 1961-63 Pontiac Tempest. It had a speedo cable-like rope. A somewhat thin, lightweight flexible driveshaft. Yes, I know. Not exactly a performance car with that 1/2 of a 389.
 

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Absolutely agree, the only reason for upgrading the drive shaft is if your breaking the stock one. On a "dollars best spent for performance gain" basis, the order for this platform is JB1, JB4, tires, tune, exhaust.... hmm, but maybe replacing those lousy stock tires should be first...
 
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While I agree, the article focuses more about the weight, not on the 'durability' perspective. AMS said the driveshaft is the weak link before/after they made that mid 10s run. Of course, i'd take that as half true and half marketing pitch.
 

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Agree with this OP and that the theory applies to many of the more common mods for these cars. The EcuTek delivers about 85% of all gains (+98 RWTQ) achieved with the standard bolt ons for $600.

I’m struggling to find anything else to do to the car that will actually deliver gains appropriate to the cost of parts+install.

At $150 plus $200-$300 for the install, the frozen boost heat exchanger seems like an okay trade off.

Intakes, downpipes, exhaust-none of these deliver gains that make much sense considering the cost IMO.

The fuel upgrades deliver the next big bump in power but they’re $2,500+ all in? So 4X the cost of the tune to deliver 50-70% of the gain the tune did?
 

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Outside of a tune lower downpipes and a CBE are by far the best option imo besides a tune. A Q on a safe tune alone is approximately 40hp and 50 ft/lbs less then a Q with lowers and CBE. Now the lowers and CBE are like 2k but that’s the next biggest gain outside E85 and 2k in fuel pump upgrades.

Personally I’m not a fan of the frozen boost because I’ve heard stories where they don’t actually work very well. I’ve also talked to mechanics who say they haven’t seen major benefits based on improper installation etc. Now that being said I’ve seen data to show that Visconti and AMS have very good HE. The burger one to me looks exactly like the Visconti one for less money so I would be interested in seeing those numbers.
 
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Discussion Starter · #10 ·
Outside of a tune lower downpipes and a CBE are by far the best option imo besides a tune. A Q on a safe tune alone is approximately 40hp and 50 ft/lbs less then a Q with lowers and CBE. Now the lowers and CBE are like 2k but that’s the next biggest gain outside E85 and 2k in fuel pump upgrades.

Personally I’m not a fan of the frozen boost because I’ve heard stories where they don’t actually work very well. I’ve also talked to mechanics who say they haven’t seen major benefits based on improper installation etc. Now that being said I’ve seen data to show that Visconti and AMS have very good HE. The burger one to me looks exactly like the Visconti one for less money so I would be interested in seeing those numbers.
Looks the same but apparently the Burger uses an inferior core vs the Visconti. I was advised not to go with the Burger.

Also was advised to go with a non data logged tune until I did exhaust. So the difference in adding exhaust and a retune could be closer to 60whp.
 

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Discussion Starter · #11 ·
While I agree, the article focuses more about the weight, not on the 'durability' perspective. AMS said the driveshaft is the weak link before/after they made that mid 10s run. Of course, i'd take that as half true and half marketing pitch.
Well the guys in the 500s aren’t breaking shafts yet and since 99% of people haven’t made it to 500whp yet, the durability isn’t an issue. I started the op with “unless you have enough power to break the OEM shaft”. But that’s not why people are buying them. They are buying with the assumption that it will make the car faster. In that case, the article is completely relevant.
 

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If you're breaking driveshafts before u-joints, that's a bragging point, not an issue for concern. IMO, if you have disposable income to reduce rotational mass, then sure... but, don't expect to get quantifiable gains outside of a standard deviation from run to run.

You're better off figuring out how to cloud seed to make the weather colder on track day.
 

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Haha. It would also be better to drive, or even trailer your car to a colder, lower altitude track (as the case may be).

I, for one, am going to figure out how to get a converter and trans brake in this thing. Then we can have fun trying to break stuff.
 

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If you're breaking driveshafts before u-joints, that's a bragging point, not an issue for concern. IMO, if you have disposable income to reduce rotational mass, then sure... but, don't expect to get quantifiable gains outside of a standard deviation from run to run.

You're better off figuring out how to cloud seed to make the weather colder on track day.
Distilled water injection along the intake to generate additional power IMO, no reason to be giving the other people at the drag-strip some extra power. :)
 

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Driveshafts pointless imo unless your AWD on E85 and maxed out on a track tune. That’s my opinion but AMS replaced the driveshaft because they snapped it with 512hp and 593 tq doing digs all day long. This guy thinks he needs one because he’s shaking too much at launch but personally I would use the money for a HPFP. He also thinks he needs to build the bottom end to run 26psi on race fuel, which he’s mistaken also imo. He’s running 22&24psi on 93 pump but he thinks that’s safe?


Check out the thread with 13 replies
https://youtu.be/SoWcrfKs2e4
 
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Vibration on launch can be caused by a weak center support bearing.

A one-piece propshaft would definitely fix that, if it were the cause.
 

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Well the guys in the 500s aren’t breaking shafts yet and since 99% of people haven’t made it to 500whp yet, the durability isn’t an issue. I started the op with “unless you have enough power to break the OEM shaft”. But that’s not why people are buying them. They are buying with the assumption that it will make the car faster. In that case, the article is completely relevant.

It is relevant. I'm just saying the article should have equally focused on other benefit besides weight, however small.



I haven't seen one here who expressed or wishing to buy the drive shaft because "it makes the car faster" yet...unless you refer to the folks over the q50/q60 page then I'm sure it'll hit over 1000x times lol



Then again, a lot of people buy stuff they don't really need and/or for wrong reasons, not just for car parts. Myself included ;)
 

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Carbon fiber baby!
 
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Discussion Starter · #19 ·
He also thinks he needs to build the bottom end to run 26psi on race fuel, which he’s mistaken also imo.


Check out the thread with 13 replies
https://youtu.be/SoWcrfKs2e4
Based on what? Look, I've only had this car and been on this forum for a month So I haven't had time to read everything I'd like to about these cars, However, I'm assuming they do not have forged rods or pistons. If that assumption is correct, I would think the amount of timing you could run on race gas along with 26psi Is going to generate some serious torque. If that's not over the limit it has to be right on the edge. I personally think it would be smart to build the bottom end at that point.
 

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Discussion Starter · #20 ·
I haven't seen one here who expressed or wishing to buy the drive shaft because "it makes the car faster" yet...unless you refer to the folks over the q50/q60 page then I'm sure it'll hit over 1000x times lol
What reason are you presuming people are buying it if not because they believe it will make the car faster?
 
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