Randy V

Ignore Imo - I'm sure you've heard the one about wrestling with a pig...

Catorce

Then why did you sound so incredulous about making cylindrical objects on a mill? have him show you an OD boring head, stare at it for an hour, then report back genius.

If you have nothing constructive to add except one line quips and barbs, find someone else to bother.

Catorce

Thanks Randy!!!

Imo000

It's unusual to make a bushing on a mill when a lathe is a lot more common machine to use for something like this. That's why I asked. Same as if I wanted to make a bushing on a gear cutter (that's what his shop does, up to 125" DIA). Sure it's possible but not common or expected.

I did have something constructive to add.....it was the unsettled suspension that you nearly bit my head off for because, you and your dyno buddy knows better.

Also, I wouldn't strap a 928 down on a fledbed by the tow hooks so it looks lkek a lowrider either. Was only trying to help at first.

Catorce

Fair enough. It is uncommon to have a 4000 pound 3 axis CNC mill in one's garage, so when i say I am going to "mill something" most people think I am working with a hobby setup. Also a good boring head setup costs 1K, and again, most people would not have that in their garage.

I am an uber enthusiast and fabricator with 6 Porsches, always buying more. So yeah, not your common wrench.

As to strapping the car down, 100% agreed. The Devore car was too wide to fit on the trailer I brought when I picked it up, so I called a flat bed. I had to leave, so I did not see it loaded. I was horrified when the flatbed pulled up and my car looked like it had been fitted with airbags in East LA

Would not have been my first choice either.

So tell you what, let's bury the hatchet and move forward. Oh, and since I was born and raised in Toronto (East York baby) I spent a bit of time in Kitchener which is near where you live. There, now we have that in common....hatchet buried!

Hoser! LOL

Charley B

Probably not an accurate assessment in Imo's case, but a classic line none the less.

I like this guy.

Imo000

Sounds good.

Catorce

So today I mounted the fuel cell and made up a little sheet metal cover plate to close the gap.

The PO decided to coat the whole inside of the car in a kind of bed liner material; I at first wasn't a fan of it, but hey, this car isn't going to be on the lawn at Pebble Beach, so I suppose the easily repaired undercoating style finish makes some sense.

I welded up the sheet metal, stitched only, then covered the seams in SEM seam sealer to keep dirt out. Hit it with 3M undercoater and called it a day.

Fuel tank is now securely mounted, yet comes out with 6 nuts; probably would take less than 5 minutes, and all from the top!

Check out the lightened rear bumper. Must've taken some time to do that. Fuel cell now sits at the same height as the old gas tank, and the same depth as well.

Next up, fuel pump and lines.

Catorce

Took a nice detour this evening, went to the Porsche Experience Center Carson with the wife. Beautiful facility, lots of amazing cars in the lobby - I was inspired.

Oh, great restaurant too.

James Bailey

Yes amazing what you can do with $60,000,000 ...... figure out how that makes sense

Catorce

LOL True, cheapest car in the display was I think a 2017 GT3RS. ~250K, walked right past it....lots of beautiful hardware there.

slate blue

G'day Catorce,

I have been reading your very interesting thread and have been around 928s for many years and remember the issue of Excellence back in the early 90s that featured these interesting cars and early developers of the 928.

I don't normally offer much advice and frankly just don't have the time, just look at my own lack of progress 🙄 And I know you know your way around a car and workshop. However regarding the suspension and how to spec the springs and the dampers I can offer some basic advice.

I employed a contract engineer who specialises is suspension and we measured the wheel motion ratio and weighed each corner. We made an adjustment for fuel. I can tell you that spring rates such as 600/400# is too proportionally stiff at the rear. Certainly 1000# all round is way off.

The front motion ratio is 0.5 and the rear is 0.78. Ignoring downforce for the time being you then need your weight at each corner as that goes into the calculation.

For a car that uses a 600# front spring and in the case of an automatic that is heavier at the rear than a manual, you would use a 250# spring and with a manual it would be more like 225#

I'm personally using Leda's which have rose joints on the bottom which is good as I didn't want a similar setup on the top as the body would have then needed serious reinforcement. The rubber factory mount cushions the blows.




Leda dampers

To get the aero balance correct this is more difficult and more expensive. For my other project car, I have Ohlins ILX 4 way adjustable with hydraulic cylinders that can raise and lower the car on the fly. Apart from getting over speed bumps easier 😀 I can lock the cylinder with a solinoid and run a pressure sensor connected to the cylinder and see and log how the aero balance is being effected and for that matter the loadings on the various corners.









That giant splitter you have will generate lots of downforce and will need to be attached very securely. That Porsche RSR has lots of neat tricks, the side skirts would be good vortex generators etc. Have you seen the 968 turbo thread where the car was transformed into a time attack car? Serious serious money. Has to be at least $500K USD in development. It has two tonnes of downforce.

Catorce

Slate Blue:

Excellent post! Some questions:

1 .What was the final poundages you wound up with per corner then?
2. Street or track car?
3. How much does your car weigh?

You had one comment in there that turned a light bulb on: "Ignoring downforce". So I am thinking, what if Devore used such ridicuoulously heavy springs because he was planning for massive downforce? Thoughts?

As to the front splitter (I am not there yet) there are lots of things wrong with it:
- It's made of aluminum and heavy
- it's attached solely with dzus fasteners

This is one of the other reasons I don't think the car ever made it to the track. i don't believe that splitter would have remained in place the way it was attached to the car.

The plan is to render that splitter in carbon and attach it much more securely than with dzus fasteners....

slate blue

Thanks Catorce,

We did this work around 3 years ago and if you want to trust my memory here goes;

0.5 x 0.5 x 600 = 150# wheel spring rate at the front.
0.78 x 0.78 x 250 = 152# wheel spring rate at the rear.

Then the important issue is the weight balance front to rear.

My wife's car had a total weight with driver and fuel (half tank)

1500 kgs the front to rear distribution was 51/49. So in theory at least that relationship is what we should have with the wheel spring rate. Or 150#/147# however the rear spring to achieve this is not available.

The Ledas at the time were in the wife's car hence the reason for the chosen spring rates. What we found was that the car rode much better with the softer rear springing. The 600/250 setup is a street setup occording to my engineer. A modern Porsche would have a wheel rate like 150# according to him.

With a 225# spring at the rear you would come out like this 150#/137#. My manual car is lighter as it has had its weight reduced but with the manual car (lighter transmission) and lightened 928s it is easier/cheaper to reduce weight at the rear. So my car had a weight of 1400 kgs and the front/rear was 53%/47% so you can see how the lighter spring better fits in terms of wheel rates to this particular car.

This is the very basics and if I can dig up other material I will happily post it. He did talk a lot about wheel frequencies and I am sorry for mixing imperial and metric but that is due to my age��. The engineer only used metric but made some allowances for an old bloke.

At the time his current role was as a Porsche cup car team engineer so he had all the date from what was then a 997 cup car. When we specced my springs for the Ohlins we can down a bit in rate from Cup car stuff (only because I am worried about the chassis) and we ended up with 1400# fronts and 550# rears. My engineer described this as a start but too soft as the 928 will be much heavier than a Cup car.

So if we ignored your aero for the time being that may be a starting for yourself also. It gives a wheel rate of 350# at the front slightly less at the rear. From memory and I do stress memory I think he was going to be around 2000# for the front if he had his way. That is a 500# wheel spring rate. He talked a lot about various race cars falling into frequencies. F1 being the highest.

His training was in world rally car and he does run a school on these areas too. His other area of expertise was in differentials and their programming. This is still an area I plan to investigate with him as he was mighty interesting to talk to.

hacker-pschorr

You are 100% correct on the procedure in the WSM for doing an alignment. I've posted it dozens of times and I've been met with opposition on the reliability of that process even though my local shop has been doing them this way for over 30 years without a problem.
What you need to realize is many shops that have attempted to do the lift / pull down alignment screw it up, so the community has fallen back on the fail safe method of finding a shop that doesn't lift the car at all (drive on alignment rig). I don't like this mentality since unless the shop is measuring and setting ride height, the suspension may still not be settled. Better safe than sorry and find a shop willing to go through the factory procedure.

The nose hanging up on the 928 has more to do with the suspension bushings being caught in a bind and being forced back to center.
This is why the WSM states to leave the lower rear bolts loose when dropping the car after installing a lower arm. This way you get the car to proper ride height then torque these bolts so they are centered at the driving position.

If this 928 has all solid front suspension bushings, this is very much a moot point......