aluminum driveshaft gains
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Aluminum shafts are safer if they break, much less weight swinging around at a lot of rpms
critical speed is everything in a drive shaft,they all have a max rpm regardless of what there made of. 99.9% of the time a SHAFT explosion is due to running past there max rpm potential, as far as them being safer I've seen some pretty nasty outcomes of aluminum shaft explosions!! best safety devise u can have is drive shaft loops!as many as u can put under the car and still service the shaft when necessary!LOL!
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The Mark Williams chart is very conservative. I have been down this road and talked to several of the major drivleine builders about an aluminum shaft. Mine needed to be 57" long and I got a different answer from every shop as to what was required. Good luck.
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It has to be conservative. They can't rate it at 100% or there would be no room for error. Doesn't mean its wrong.
Hutch
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I have cars seeing .07 to .10 in loss of time.
Losing pounds in the driveline is equivalent to losing hundreds being carried.
If you go from say a 24 lb shaft to a 12 lb shaft you should see a .10 since that is almost equal to losing 200+ lbs.
If you can take the motors hp and use it to better or more efficiently turn and get moving faster it will show up somewhere.
As for requirements to be figured into the shaft for it's ability to work and handle the stresses put on it, there are a few.
What type of use or racing 1.) overall weight, 2.) hp/tq, 3.) 1st gear, 4.) the most rpm you are going to see in 1 to 1 or if you are doing it in a OD gear, 5.) length
I have seen many gains in lighter driveline pieces
Losing pounds in the driveline is equivalent to losing hundreds being carried.
If you go from say a 24 lb shaft to a 12 lb shaft you should see a .10 since that is almost equal to losing 200+ lbs.
If you can take the motors hp and use it to better or more efficiently turn and get moving faster it will show up somewhere.
As for requirements to be figured into the shaft for it's ability to work and handle the stresses put on it, there are a few.
What type of use or racing 1.) overall weight, 2.) hp/tq, 3.) 1st gear, 4.) the most rpm you are going to see in 1 to 1 or if you are doing it in a OD gear, 5.) length
I have seen many gains in lighter driveline pieces
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Also, depending how a shaft breaks tells a story.
As with hutch's vibration, sounds as though the rpm was being exceeded by the length for his heavier shaft and the lighter AL shaft being able to see more rpm by loss of weight fixed his possible very dangerous breaking shaft at top end thru the lights.
When a shaft breaks upstairs it is either being exceeded in rpm, or exceeded in angle for it's use, or it wasn't balanced properly.
As speeds increase angles need to diminish.
If you are exceeding 5500 rpm you should have ZERO, 0 angle on the joints, if not you are exceeding there capability and losing hp
As with hutch's vibration, sounds as though the rpm was being exceeded by the length for his heavier shaft and the lighter AL shaft being able to see more rpm by loss of weight fixed his possible very dangerous breaking shaft at top end thru the lights.
When a shaft breaks upstairs it is either being exceeded in rpm, or exceeded in angle for it's use, or it wasn't balanced properly.
As speeds increase angles need to diminish.
If you are exceeding 5500 rpm you should have ZERO, 0 angle on the joints, if not you are exceeding there capability and losing hp
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634 Posts
this thread was recently linked and i saw some incorrect information being posted so i did a little research so others may be able to benefit from what i post.
here are a couple links that will describe these concepts better than my primitive understanding.
http://hpwizard.com/rotational-inertia.html
the above link has calculators that may be of some use.
using their calculators and assuming a 10lb difference in 5" diameter the difference when compared to static weight is only ~ 10.4lbs.
this next link takes the potential saved energy by using lighter driveshaft and converts to horsepower.
http://www.w8ji.com/rotating_mass_acceleration.htm
this following is quoted from the aforementioned link.
"The original driveshaft weighed 30 pounds and we had to spin it to 6000 RPM. If we input that, we see it consumed (and stored) 5310 joules. 480 ounces in a 3.5 inch diameter RING (hollow center) and 6000 RPM.
That is 5310/746 = 7.12 horsepower-seconds to spin the shaft to 6000. Since the time was 13 seconds, the shaft soaked up 0.548 horsepower distributed over that 13 seconds.
Now we change to the aluminum shaft. Everything is the same except the weight, it is now 15 pounds or 240 ounces. Using that flywheel calculator we find we used 2655 joules. This is 2655/746 = 3.56 horsepower-seconds. Over 13 seconds, we "stored" .274 horsepower. The net gain in available energy over 13 seconds was about 1/4 horsepower."
another link some may find useful
http://hyperphysics.phy-astr.gsu.edu/hbase/mi.html#mi
here are a couple links that will describe these concepts better than my primitive understanding.
http://hpwizard.com/rotational-inertia.html
the above link has calculators that may be of some use.
using their calculators and assuming a 10lb difference in 5" diameter the difference when compared to static weight is only ~ 10.4lbs.
this next link takes the potential saved energy by using lighter driveshaft and converts to horsepower.
http://www.w8ji.com/rotating_mass_acceleration.htm
this following is quoted from the aforementioned link.
"The original driveshaft weighed 30 pounds and we had to spin it to 6000 RPM. If we input that, we see it consumed (and stored) 5310 joules. 480 ounces in a 3.5 inch diameter RING (hollow center) and 6000 RPM.
That is 5310/746 = 7.12 horsepower-seconds to spin the shaft to 6000. Since the time was 13 seconds, the shaft soaked up 0.548 horsepower distributed over that 13 seconds.
Now we change to the aluminum shaft. Everything is the same except the weight, it is now 15 pounds or 240 ounces. Using that flywheel calculator we find we used 2655 joules. This is 2655/746 = 3.56 horsepower-seconds. Over 13 seconds, we "stored" .274 horsepower. The net gain in available energy over 13 seconds was about 1/4 horsepower."
another link some may find useful
http://hyperphysics.phy-astr.gsu.edu/hbase/mi.html#mi
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I learned my lesson, I was having my driveshaft balanced a few years ago and the guy at the shop, I asked him about the alum driveshafts. He then told me to follow him to the back of the shop and outside he had a pile of at least 100+ alum drive shafts that where tiwisted and bent from racing apps to diesel trucks.
He swears by the steel and said he would not touch the aluminum shafts period.
He swears by the steel and said he would not touch the aluminum shafts period.
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5,634 Posts
We have a Nos car down south here' thats run a best of 4.92 in the 1/8 ' standing on the bumper everytime it leaves' And yes with a C4....Running a Ford MotorSport driveshaft bought back years ago with spicer joints....Still going strong...
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If you are buying a shaft anyway, aluminum will save weight. It may give a slightly measurable improvement from its very slight improvement in inertial resistance to turning. Don't expect much if anything to show up on your time slip. It is easier to bench press a 15 lb. shaft than a 28 lb. shaft when you get old, lol. The biggest consideration by far is selecting a strong enough shaft with a critical speed well above the rpm you will take it to. The driveshaft is not something you want to fail. Watching a car get pole-vaulted is bad, being in it is worse. For me, "adequate" and "has held up so far" are phrases that do not belong in a driveshaft discussion. BTW, performance diesel trucks will give 1500+ ft-lb so their load on a driveshaft is extreme.
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From a maintenance aspect, aluminum is not good.
As long as you don't exceed the limits for a steel shaft, they have an indefinite fatigue life.
Aluminum will age, and in every application, will have a fatigue life.
Its why airplanes are only good for so many pressure cycles. Eventually they start to crack so bad you can't trust them.
As long as you don't exceed the limits for a steel shaft, they have an indefinite fatigue life.
Aluminum will age, and in every application, will have a fatigue life.
Its why airplanes are only good for so many pressure cycles. Eventually they start to crack so bad you can't trust them.
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