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Old 03-13-2018, 04:39 PM
csdilligaf csdilligaf is offline
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Default Porsche 917/10 & Performance Trends Suspension analyzer

I am building a Porsche 917/10 replica and using Performance Trends suspension analyzer to work out the suspension. I will be deviating from the original as getting the blueprints might be impossible and there may be better designs now days.
Project Overview
2000 lb track car
95" wheel base that is 4.5" longer than stock
Flat 6 mid engine layout. 400 hp
weight dist. 45% front 55% rear
full tube chassis, double A-Arms front and rear.
I've done builds to this extent before but this time I have purchased Performance trends suspension analyzer to see if I can do it better.
How could I post the Performance Trends file so others can look and have input?
Is there any interest in following my progress?
Here is the real deal.
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File Type: jpg porsche-917_1.jpg (125.1 KB, 0 views)
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Old 03-13-2018, 04:50 PM
csdilligaf csdilligaf is offline
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Here is the CAD version of the front left
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Old 03-13-2018, 05:35 PM
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You had me at Porsche

and yes I have subscribed
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Old 03-13-2018, 06:15 PM
csdilligaf csdilligaf is offline
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The rear was more like this picture with longer trailing links going forward but I will go with a H shaped lower and an A-arm for the upper. That will work better with a deep backspacing. The Porsche die hards will hate me but I'm building a car for me not them.
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Old 03-14-2018, 08:24 AM
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Ron Sutton posted shots like this from Performance Trends in my build thread.

He may be able to explain how it was done.
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File Type: jpg Front Geometry V5 Ride Height.jpg (117.9 KB, 0 views)
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Old 03-14-2018, 09:50 AM
csdilligaf csdilligaf is offline
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Well I have been playing with the Suspension analyzer and think I can attach the file. If you have Suspension analyzer please try to open it. I was able to click "File" "Save as" "Advanced" and pick a location outside of Suspension Analyzer and save it. Then I was able to open Suspension Analyzer click "File" "Open from floppy drive" and locate the file and open it again. I guess they just never bothered to change the language. I have not had a floppy drive for 20 years. Also I have no idea of the exported file's type but was able to put it in a zip folder to post it here.
So, please if you can open this do so and see if it works. Keep in mind that I am new to the program and this is just a rough start. There are lots of info to be corrected still but I am trying to nail down the basics of the front suspension.
I have read that for a car like this I may want to account for 1" lift and dive and 2 degrees roll for the calculations. Does this sound about right?
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Old 03-16-2018, 08:30 AM
csdilligaf csdilligaf is offline
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I've been working on the suspension in CAD and had to make changes so the upper arm does not come in contact with the wheel at full lock doing an 18 ft radius turn. I am thinking about no anti dive or squat. I figured out how to print screen into paint and post it. Still lots of spring rate, roll bar and other things to be worked on obviously but what do you think of these numbers with 1/2" dive, 2 degree roll and a tight turn? Am I getting closer?
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Old 03-20-2018, 12:34 AM
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I haven't looked at the file but none to a little anti dive in front will work. A low CG car like that with high rear weight won't have a lot of dive transfer anyway. The rear needs anti-dive anti-squat. With IRS you won't have much anti squat effect due to drive train housing torque like a stick axle car, but it needs as much anti-squat as you can get. I expected to see 60% rear weight, would like to hear your comments on what you think a good rear weight percentage is.

On your front lower A arm, I would not use rod ends on the inboard ends. I'd make them spherical bearings in a housing welded to the arm ends and jig weld them so they are identical. There is going to be a lot of front to rear loading on them from braking and side loads on rod ends will wear them out or break them in time. Do all your adjusting on the upper A arm.

To get at your suspension files, open your Perf Trends folder, look for 3D data. It should be in there. Something like C:program Files/Performance Trends/Suspension Analyzer/3-Data/ then pick Examples, or My-Tests, or make a new folder. It's not good to store files elsewhere, the program can lose track of them according to a warning they included in earlier versions I've had. You can make a new folder for your personal projects, but keep it inside the 3D-Data folder.

I just got the Brian Redman book and he stated the 917 Prototype was aerodynamically unstable. The fix was to raise the tail to increase rear downforce. Perhaps the wing used in the photo and the small lip spoiler helped enough on the car in the photo but be aware of the issue.
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Last edited by David Pozzi; 03-20-2018 at 11:11 PM.
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Old 03-20-2018, 08:56 AM
csdilligaf csdilligaf is offline
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Thanks for the input. I am still getting used to Suspension Analyzer and getting better at it. I have been working on a new KPI/Castor combo with a 5 degree kingpin and 7 degree castor. That's the great thing about using software is I don't have to make each change and try it out. I am trying to get my castor gains correct for each front tire and think I am still a little off. With 1" dive, 1 degree roll wheels at a 15 degree turn I have -1.93 degree on the outside tire and .94 degree on the inside tire. Where do you think I should be?
As for the Aero issue, yes the 917 Lemans cars in 1969 had a little wobble at 240mph on the Mulsanne straight. They changed the tail shape in 1970. The Can-am cars never got to that speed and were shaped like the first picture of a 917/10. As for the weight balance it helps to have me(200lbs) so far forward, the pedals are actually on the center line of the front wheels along with the battery, radiator and two sidepod fuel cells in the front half of the chassis.
Here is the latest changes.
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Old 03-25-2018, 11:52 PM
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I’ll take a look at your file when I get time. I recommend consulting with Ron Sutton to get some help. I did see on the previous file, the roll center moves outboard with 2” dive & 2 degrees roll. It would be better to have ithe RC stay closer to chassis centerline or move towards the inboard tire. I don’t know how to accomplish it though. Your dynamic camber looks very good. I’d read Ron Sutton’s sticky thread in this forum for what he likes.
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Last edited by David Pozzi; 03-26-2018 at 12:04 AM.
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