Optimal angle for half shafts? Options

[technicalninja]

Is there an optimal angle for Porsche half shafts?

I'm contemplating installing a drive package that will utilize a Boxster 6 speed and wondered what is considered "optimal".

I know 20 degrees is sort of the working limit but wondered what the minimum should be.

I believe having the half shaft perfectly level and at 90 degrees to the drive wheel will tend to wear the joints at a single point.

What should I shoot for?

[Superhawk996]

Zero angle is a non-issue. Besides rarely being achievable, the halfshaft angles are constantly changing due to:

Ride undulation

Wheel recession when encountering bumps

Weight distribution changes when accelerating / decelerating that affect ride height

Weight distribution when cornering and associated ride height change.

[Montreal914]

I believe Renegade Hybrid is regularly using the Boxster gearbox in their conversion. You might want to check a few of their videos or call them.

I know they sell the same set of HD drive shaft/CVs as Tarett, but this would be for a 901 gearbox. I actually have a set of these HD driveshaft/CV and it turns out they are Loebro bus CV and bus shafts with custom steel adaptors to bolt to the /4 901 box and stubs.

That being said, maybe they use these drive shaft/CVs with a different adaptor at the Boxster gearbox end. (IMG:style_emoticons/default/confused24.gif)

[technicalninja]

@Superhawk996 You know I know that...

What I'm asking is if you had complete freedom in mounting the transmission where would you mount it in relation to axle angle?

Chris (Tygaboy) moved his V8 as far forward as possible to reduce a severe angle.

His Ferrari has much better for/aft placement, but his differential centerline appears significantly higher with the Ferrari transmission. His recent vids show this. His axles drop enough to make boot to trailing arm clearance an issue.

He still has significant axle angle. Significant angle will work the joints harder, wear the boot out quicker but it will spread the CV wear over a much larger range and might increase joint life.


My question is for provisioning, designing the drivetrain placement.

Where would you put the diff centerline?

I'm guessing 5% off in any direction would be optimal but I wanted the opinions of others.

I DO know you understand that in steady state driving on a straight road the axle angle will not vary 15 minutes even in a full IRS vehicle.

The very first 240Z (1000 ish) had an axle angle issue where Nissan adopted a slightly modified front diff crossmember and a slightly flatter moustache bar. They moved the R160 rearward about 1/4". They didn't even need a longer driveshaft but those changed helped the car.
Those half shafts had u-joints and are comparing apples to oranges in regards to CV stuff.

[Chris914n6]

The RH SBC spacer block puts the 914 trans back 1.25" and down 3/4".

I used the blocks to move my 914 trans / Nissan VQ30 engine forward 1.25" and down 1.5". The Nissan VQ35 upgrade will require me to move the trans back to stock, to fit the Variable Cam stuff sticking out the front. Then the maybe Subaru trans swap will move the diff forward 1.25".

It doesn't matter as long as the cv angle is within limits from a 360* perspective.

[Dave_Darling]

The "optimal" at any given time is zero angle.

The angle changes throughout suspension articulation, obviously.

The CVs are under the most stress when the car is performing maximum acceleration. They are under almost zero stress when the car is not moving, and fairly little when the car is at steady-state cruise or under braking.

Under acceleration, the rear end squats.

So, to help the CVs the most you can, you would want the axles to be completely flat (and no fore or aft angle) while the back is squatted down from acceleration.

That's assuming you had absolute freedom to set the angles any way you want, and that axle angle is the only thing you care about. Neither of those assumptions are valid in most cases...

--DD

[tygaboy]

I looked into this a fair bit. Set it up so there is some angle. If you have the freedom to put things wherever you want to, you still want some angle to ensure the CV moves its lube around, etc.
The standard Renegade Boxster 6-apeed kit works fine. Tony runs that set up with a 500+ whp LS7 in his and he's only ever had a boot fail. All those Renegade kits are out there working just fine.
I moved my drive train forward because I could, not because I had to.
Here's a rich statement, especially coming from me:
"Don't overthink it."

[Superhawk996]

"Don't overthink it."

(IMG:style_emoticons/default/agree.gif)

I’ve sat through hours and hours of packaging meetings for 5 distinctly different platforms across 3 OEMs, the target is as close to zero as you can get while meeting other criteria like ride height, ground clearance, differential location, etc.

Lubrication and wear patterns will take care of themselves during normal suspension motions.

Photo below is production vehicle with IRS. 135,000+ miles on these with no signs that they are anywhere near end of life. Although angle is not zero, the angle is being dictated by ground clearance and load. If the rear end is loaded with cargo, the angle will be zero or slightly negative angle vs curb weight. As Dave alluded to, at curb weight, hard acceleration would bring it close to zero.

[technicalninja]

The "rest" angle on that looks GREAT IMO!

That is what I'm looking for...