Straightening CV axle(s)

[DragBean]

Wondering how much if any of a fuel gain I'd get from having the CV axle(s) straight while driving?
They are currently only about 3 degrees (front to back from the car) of an angle.
I was considering moving the engine back 1" to eliminate this 3 degrees.
Or is this a waste of time?

[Gasoline Fumes]

I'd say it's a waste of time.

[DaveM]

Based on this paper, I'd agree, waste of time. I'd post a link, but do not have five posts. Google "cv joint angle efficiency NTN" It's the first hit.
They don't show joint efficiency below 3 degrees, I suspect because cv and u joints often require a bit of relative motion to distribute the grease and prevent wear in a single location.

[LittleBlackDuck]

Originally Posted by DragBean

Wondering how much if any of a fuel gain I'd get from having the CV axle(s) straight while driving?
They are currently only about 3 degrees (front to back from the car) of an angle.
I was considering moving the engine back 1" to eliminate this 3 degrees.
Or is this a waste of time?

There would be much higher gains from removing the grease and rubber boots from the joints as they contribute more to power losses.

Simon

[me and my metro]

Possible but it would cause problems with the inner ends. Just as a universal joint driveline you never want 0 degree angles. The joint will wear grooves in the cap and lock up. They need to move to live.

[DragBean]

Thanks for the input.

I'm thinking mine are probably more around 4-8 degrees...

3 degrees was kinda of a bad guess.

Anyways it seems like although moving the block an inch back would only take a half hour, it would basically be pointless.

I would say in terms of grease distribution I'd feel like the bumps in the road would be sufficient enough to distribute the grease.

[DragBean]

Wait a second, I was looking at the wrong graph

http://www.ntnglobal.com/en/products...n_064_067p.pdf

Based on Figure 9 moving the block 1 inch would probably reduce torque loss by .5 x2 (for both CVs) = 1%

Now mine are getting worn out, so I'd double that..

So now we're at 2%... almost 1 mpg...

[LittleBlackDuck]

Originally Posted by DragBean

I would say in terms of grease distribution I'd feel like the bumps in the road would be sufficient enough to distribute the grease.

Unless the roads you drive on are unbelievably rough, I would be willing to bet that centrifugal force and the action of the balls pushing grease out of their way will win out.

Seriously, I would be looking at harvesting all of the low hanging fruit before going to these lengths to get a miniscule gain that has the potential to damage parts.

Simon

[DragBean]

@littleblackduck

What about all the turns too?

[LittleBlackDuck]

Originally Posted by DragBean

@littleblackduck

What about all the turns too?

Way more drag from tyres. How often are you actually turning as a percentage of a trip? Anyhow, the total CV joint drag from turning is unlikely to be affected significantly by changing the static angles.

Another consideration is to ensure that there is sufficient plunge available so that you do not bottom out the joints during suspension travel and steering movement.

Simon