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HIGHWAYMAN: Bringing the Devore 928 back from the dead

 
Old 11-24-2016, 11:31 AM
  #136  
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Originally Posted by Catorce View Post
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
Sounds good.
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Old 11-26-2016, 04:58 PM
  #137  
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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.
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Old 11-27-2016, 01:31 AM
  #138  
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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.
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Old 11-27-2016, 01:24 PM
  #139  
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Yes amazing what you can do with $60,000,000 ...... figure out how that makes sense
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Old 11-27-2016, 01:26 PM
  #140  
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LOL True, cheapest car in the display was I think a 2017 GT3RS. ~250K, walked right past it....lots of beautiful hardware there.
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Old 11-28-2016, 05:24 AM
  #141  
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Originally Posted by Catorce View Post
Carl,

Wound up picking up a set of double adjustable custom Konis from Darien Nunn. For whatever reason, if I am reading the part numbers right, my car currently has 1000s on all four corners!!!

The Konis that are currently on the car (besides being rusted and ugly) are all out of ride height adjustment in the front, where they are still way too tall for my liking. The ride height out front is almost stock it's so high, so they just jacked up the rear to suit. Looks like a 4x4.

So I will fiddle with the new Konis and see how it behaves and go from there. They were practically free anyways.
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.
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Old 11-28-2016, 12:12 PM
  #142  
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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....
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Old 11-28-2016, 03:37 PM
  #143  
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Originally Posted by Catorce View Post
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....
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.
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Old 11-28-2016, 04:11 PM
  #144  
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Originally Posted by Catorce View Post
Lastly, for the experts out there, read the frigging Porsche service manual on the topic. It says to perform an alignment, pull the front of the car down by 60-70mm and holding it for a minute and then bouncing the car front and rear to SET THE RIDE HEIGHT. It's in the manual for christ sakes.
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.

Originally Posted by Randy V
The 928 suspension geometry is a unique beast out in the wild.
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......
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Old 11-28-2016, 07:43 PM
  #145  
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Originally Posted by slate blue View Post
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.
Slate, very interesting data indeed. What car were you putting 1400 pound fronts on?

As an aside, I spend the morning at Joseph Fan's shop looking at his 928 race car. I am not sure many people have the kind of experience Joe and Mark Anderson have racing 928s, and he thought 1000# fronts would be excellent for my car. In fact, his car (POC Champion in class) has 1000 or 1100 pound springs right now....as fronts.
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Old 11-28-2016, 08:18 PM
  #146  
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Originally Posted by Catorce View Post
Slate, very interesting data indeed. What car were you putting 1400 pound fronts on?

As an aside, I spend the morning at Joseph Fan's shop looking at his 928 race car. I am not sure many people have the kind of experience Joe and Mark Anderson have racing 928s, and he thought 1000# fronts would be excellent for my car. In fact, his car (POC Champion in class) has 1000 or 1100 pound springs right now....as fronts.
Thanks,

I need to get back to work so just a bit more info regarding these springing rates and where you should fit into them. Please have a look at this link;

http://www.optimumg.com/docs/Springs...Tech_Tip_1.pdf

This is what the engineer was banging on about. I'm sure given your CNC experience your maths will be up to working out your frequencies. I did a bit of CNC btw and really needed to brush up in the maths area, as you know when they teach it is in the very basic nuts and bolts of programming not using the software to spit out the programming.

So you should come out in the 1.5 to 2.0 Hz range, see what you come up with regarding that and that will confirm your choice.

Also I saw a bit of discussion regarding the suspension bushes. I know you could well make your own but please check out the bushes I am using. They are made in the U.K and are used in various race series. They make a street and a race version for the 928 and while I haven't fitted mine as yet they look very nice in deed. They have nice grooving in them for lubrication and the street versions come with a life time warranty so I would say they have confidence in their product. Also the pound is at record lows against your dollar as such they are cheap. The race series is the black series.

https://rennlist.com/forums/928-foru...-bushings.html

https://www.powerflex.co.uk/road-series/why-pu

https://www.powerflex.co.uk/black-series/about-us

As to the project cars, you can read a bit about them here. There is also a 7 speed transmission thread you may be interested in.

https://rennlist.com/forums/928-foru...er-thread.html
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Old 11-28-2016, 10:16 PM
  #147  
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Originally Posted by Hacker-Pschorr View Post

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......
Yep - had that issue on the Camaro when setting that car up. Factory bushings on that car are similar to factory Porsche bushings - a metal ferrule bonded to the rubber bushing that can preload enough to bind and upset the alignment if the bushing bolts aren't totally loosened prior to the car being set down.

In my experience bushings like that are for ride comfort, and have no place on a sporting car much less a race car. Correct, solid bushes don't have that issue. Also, performance bushes like those that DON'T have a bonded ferrule don't need to be settled like that.

Good point!
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Old 11-28-2016, 11:23 PM
  #148  
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Slate,

Good info, thanks for posting.

As to the bushings, I checked those out but I don't think polyurethane will cut it on a race car. It's just on the ragged edge on my heavily autocrossed Camaro -still too much play and softness for my liking. I am thinking 90 durometer solid delrin or something along those lines.

I won't know until I take the suspension apart and see what they all look like and what the factory was thinking.
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Old 11-29-2016, 03:31 PM
  #149  
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Many of us have upgraded to the solid delrin bushings on the steering rack. Sold by a couple vendors here.
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Old 11-29-2016, 04:04 PM
  #150  
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Originally Posted by Randy V View Post
Many of us have upgraded to the solid delrin bushings on the steering rack. Sold by a couple vendors here.

For that application I'm going solid aluminum....
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