[WIP] 1971 Porsche 917K

Discussion in 'Vehicles' started by LeStrat, Jan 8, 2015.

  1. yoss

    yoss Registered

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    ty for the feedback !!
    impossibl to work of this free mod for the moment but we update him later , when we can , and surely add some new car around her later .
     
  2. Postipate

    Postipate Registered

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    Great mod already :)
     
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  3. Emery

    Emery Registered

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    @rocketjockeyr6 - there may very well be tire size discrepancy, but be careful in comparing to period pics rather than modern pics because modern tires are often not the same dimensions as period tires.
     
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  4. rocketjockeyr6

    rocketjockeyr6 Registered

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    [​IMG]
    Taken in 1970 during Steve McQueen's film, "Le Mans"
    Looks to be the same size as the modern pic to me.

    Agreed that this is a great mod already, dont think I was complaining. If this mod were v1.0 I wouldnt have even said anything, but as it is still v.75 and still being developed, I decided to bring it to his attention in case he decides to change it later.
    IMO, this mod is great, just bloody amazing! With an accurate 3d model it would be nothing short of perfect. :cool:
     
  5. Christopher Snow

    Christopher Snow Registered

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    Ok, I finally tried this car today. First at Kyalami 1976 for a "fun race" with Tucker Fleming and the other F3 Fanatics, and just now a few part (and one timed) lap at old Spa...so here we go:

    Before even going out, I took a look at the setup numbers and could see several things that needed changing right off to make it a 917 (and not something else). Foremost among those would be the differential, otherwise known in rFactor/rFactor2 as "power" and "coast"--the 917 was sold and raced, at least until the turbo versions were built for Can-Am using just one combination: 75 power/75 coast. According to Paul Frere, a combination of 25 power/25 coast was tried for just one single day, by test driver Peter Falk on the skidpad and after just a few runs (many of which resulted in spins as soon as he came off the throttle), the obvious decision to stick with 75/75 was taken...and that was it. So if you want to build a normally aspirated 917, stick with that. Consider going to a fully locked rear axle if you build "turbo-panzer" versions later on.

    Yes, 75/75 results in a car which has a tendency to understeer, particularly at lower speeds, and yes, that's what Porsche themselves were attempting to address with the 25/25 combo, but it just wasn't practical and they quickly gave it up and took the compromise.

    Next: The FIA mandated a minimum ground clearance of 10cm/4" the full length of the car underneath, so make that your minimum height, and;

    Reduce the camber settings to very near flat, aka 0.0 degrees*. Because of the width of the rear tires in particular, no other combination was really practical, although in theory you could angle them in very slightly (for a very few laps) before they overheat and chunks start flying off... :D ...but we're talking about a car built for long hours on dangerous tracks, and even with the single large wheelnut, tire changes were not part of the plan unless they couldn't be avoided. I seem to recall the Wyer team planning on just two changes at Le Mans, for example....

    * In WSC 1970, we maxed our camber at 1.0 degrees, and I, personally, thought that was about five times too much. Just sayin'....

    FWIW, I just finished driving the car around Spa '66 using what was basically that same Kyalami setup, and managed one timed lap (clean), at 3:24.45, essentially the same laptime the fastest Ferrari 512 managed in 1970--that car was gridded third. The slower of the Wyer cars qualified at 3:23, and Rodriguez managed a pole lap of 3:19 (!), so as it stands right now, based on laptimes this car is reasonably good, I think. There are some other odd behaviors exacerbated by the bumpiness of Spa itself (porpoising), but it isn't trying to kill me over every bump--it just wants too. ;D

    I would upload the setup, but that doesn't seem to work here--hence the long-winded explanation as to the "why" of the various changes.
     
    Last edited: Jul 30, 2017
  6. Christopher Snow

    Christopher Snow Registered

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    About tires and wheels, @yoss: If you find Frere's book it SHOULD have drawings of the suspension, and cutaways of wheels and tires, both front and rear. If your copy doesn't, email me.

    I realize people have been putting some work into the thread, noticing that the present combination appears a bit off. It's true the aspect ratio of the older tires was quite different than what you typically buy and fit today to a sports car--the tires of 1970 were definitely not "low profile," and the sidewalls were capable of some bizarre flexing even at low pressures. There is a brief sequence in the film "Le Mans" which illustrates some of that, in fact (where the Ferrari's tire is going down).

    ===

    A bit more about differentials: This info is very hard to find, which is what makes Frere's numbers from the initial 917 testing so valuable to modders. I've seen very little elsewhere, but I recall another small bit from Niki Lauda's first book (Mauro Forghieri was the source for it I think) wherein he explained a combination of about 70-75 was considered the best compromise. He was speaking in this case about F1, with his Ferrari 312's (1975-1976) being the examples he was drawing from, but even with those three-liter cars it was necessary to find a compromise that would let the car negotiate the occasional tight bend (like the Monaco hairpins) and still get the power down onto the road--wheelspin, wheelspin, wheelspin was a constant complaint, hence the need for a good amount of locking.

    As it happens, the original differentials in Papyrus's "Grand Prix Legends" were based on "ramp angles," and the sine of a 45 degree ramp is 0.71xxx. I SUSPECT, but can't prove that the ZF transmissions used in the 917 actually sport a 71/71 combination (and not 75/75), so I wouldn't complain if you set it to 70/70 either. :D Haven't tried it yet myself though.
     
    Last edited: Jul 30, 2017
  7. yoss

    yoss Registered

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  8. rocketjockeyr6

    rocketjockeyr6 Registered

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    Not sure which version this was, definitely early, but that gap between the tyre and fender looks right to my eye. Maybe this changed when the CPM was updated?
    [​IMG]
    +1 to Christopher, I usually have 10.2cm front ~11.6 rear, and -.8 front camber and between -.1 and .2 rear.
    I could be very wrong, as I cant find much material on tyre pressures, but I find it odd that the smaller front tyre has less pressure than the rear... in my experience with cars, smaller tyres need more pressure, (i.e. 60psi in a bicycle tyre, and 30psi in a 6000lb pickup truck) even "low profile" car tyres like about 40-45psi. Just my thoughts.

    Cheers
     
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  9. lordpantsington

    lordpantsington Registered

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    Just taking the sine or cosine (depending on how angle is measured) is not going to give you the locking %.
    Found some info for you:
    Differential (69-71) Disc-type limited slip. Up to 75% slip limitation.
    Source:
    ISBN 1 84155 598 3
    13 ISBN 978-1-84155-598-0

    Also found spool was available:
    https://retro-sport.com/porsche-917-titanium-spool
     
    Last edited: Jul 31, 2017
  10. jymp

    jymp Registered

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    Is the 917K still being worked on for an update ?, haven't seen much news lately.....talking about the tires, in actual 70-71' races Avon tires weren't used at all, it was Firestones & Goodyears, Avon seems to be the tire for today's 70's F1 & 917K show cars, since I suppose the Firestone's & Goodyear's are quite hard to come by for the vintage F1's and 917K's today.
     
  11. fohdeesha

    fohdeesha Registered

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    I still need to go over to my buddies garage and talk to their engineer about suspension measurements and values ( I know I promised this forever ago, but he got married and I started a business so it completely fell by the wayside).

    Once I do make it over there, it sounds like I should add diff values, tire pressures, and tire dimensions to the list of info to get? I know they run "modern" Avon's so don't know how much value the tire data would have
     
  12. Guimengo

    Guimengo Guest

    I have contact with Gunnar Porsche Racing and even more with a friend of the guy, but it's been a while since we talked. I don't know if he's still working on the 917k.

    Anyway, Yoss is the leader of all mods and he has his reasons for a break or not. I haven't touched anything for a while.
     
    Last edited by a moderator: Mar 27, 2018
  13. vegaguy5555

    vegaguy5555 Registered

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    Thanks for this great read guys!:)

    I'm sure Steve McQueen is smiling!! I had to do your recommended settings and drive his car around the Nordschleife.

    Funny how I can do more then two laps without a wreck in rF2, which I hear people complain about being too slippery. A 7:01. Not sure if that's fast or slow? But crash easier in other sims?

    Great job guys. Anyone moding or coding sim software need to drive this car in rF2.

    This is the most realistic drive. I have owned and raced V8 Vega's as in my icon and I can say the wheel in the 917K here feels a lot like I remember my Vega's feeling at 160mph. Heavy, light too 'holly hell' nothing at all over a slight rise!!:eek:

    Did Steve run the 917K on the Nordschleife?
     
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  14. Guimengo

    Guimengo Guest

    The car is a bit too fast and easy to drive - not that it's a bad thing, the real thing was easy to squirm but also fine to be handled on it - at the moment but the final push to v1.00, eventually, should be a transformative experience. The shape won't be fixed but don't get too attached to the rest as it should change closer to reality, but it doesn't mean it won't still be a blast to drive.

    ps: if you want to watch some laps, check out the videos I made of it (via signature) or the ones from Simon (posted throughout thread).
     
    Last edited by a moderator: Aug 27, 2017
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  15. rocketjockeyr6

    rocketjockeyr6 Registered

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    Hmmm, I remember reading that the original 917, before the short tail, was very scary to drive. Once the Kurzheck debuted, they said you could let go of the wheel at 200mph down Mulsanne. Also, watching Le Mans, which featured a lot of footage from the real 71 race, you can see them pitch the ass end out in the slow corners, and tuck it right back in on the shift to 2nd.
    Personally, this is one of my favourite mods ever to grace rF2.
    Avon, GoodYear, or otherwise, makes no difference to me, I just prefer the earlier version of the tyre model(3d) as I think it looks more accurate in relation to the size of the real life counterpart. Im sure that the graphical change from the current tyre to the appropriate one wouldnt be the battle, but the changes made to the CPM to reflect that sidewall profile would probably take some time.
    Too fast? Maybe for the 4.9... maybe it should be changed to represent the 5.0.
    Personally, I would be thrilled if the 1500hp twin turbo variant was made. :D

    I looked it up, and I cant find any reference of it. Although it is noted that he drove The Ring a few times, once or twice on his favourite Triumph TR6, and he did own the 917 from the movie(I believe David Piper has it now). And I do believe he said after filming Le Mans that the 917 was his favourite car he had ever driven. But dont quote me on that.;) If youre a fan, I would recommend watching the Steve McQueen documentary, "The Man and The Machine" truly a great watch.

    Cheers mates
    rocket
     
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  16. yoss

    yoss Registered

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  17. yoss

    yoss Registered

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    i m still have no time for jump on this free mod and updated him (too busy on 3d work ), but modelisation of some sister for this car still grow from 3dsmaxmodeling friend .
    for those who don't have seen the render in facebook i repost here :
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG][​IMG]
    [​IMG]
     
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  18. rocketjockeyr6

    rocketjockeyr6 Registered

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    Very nice Yoss!
    Cant wait to try her out! :)
     
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  19. vegaguy5555

    vegaguy5555 Registered

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  20. jymp

    jymp Registered

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    Question....Why are there external mirrors on top of the front fenders on the 917K ?, all pics I've seen of the car, and in the movie, there are no mirrors outside, the mirror is inside, just curious.
     

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