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Discussion Starter #1
(I'm new here - first post)
The alternative title to this thread could be: "What are your experiences Autoxing with Pin Drive width?"

I'm looking to build a 289 FIA roadster - with the 15" FIA pin drive wheels.

I am assuming, from the searching I've done, that the narrower track width is eaten up by shorter control arms?! Is this the case, or are the uprights that the control arms bolt to narrowed?

How does this affect front suspension geometry/ rear world handling?

I've spent quite a bit of time autoxing an '84 VW Rabbit GTI, so I know a thing or two about design compromises... and the creativity required to overcome them. I understand that brakes will be smaller diameter as well, but my gut feel is that it can all be made to work.

(side question --- I was going to post this in the Racing/Autox subforum, but there hasn't been a post there since 2019?! - that doesn't seem to make sense)

Any input is appreciated. Thanks!
 

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FFCobra Craftsman
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Depends on how FFR makes it narrower. I 'think' there is another set of holes for the LCA frame mount bolts so the whole LCA moves inward. I am not sure how the UCA is done. I am pretty sure there is no pin drive width for the rear IRS but there was a discussion here or the other forum last week and the thought was just use slightly narrower rear wheels/tires w/ the standard IRS. If I were you, and you want pin drive just go for it. Tire availability, or lack of, is going to hurt AX performance more than pin drive width.
 

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Discussion Starter #3
Thanks! Yes, you've pointed out the compromises/obstacles:
  • Looks like 3 Link solid axle is the way to go
  • If I really get the competitive juices going - bite the bullet & buy a 2nd set of pin drive wheels (yikes!) in 17" or 18" for more competitive rubber.
    • Initially, in my mind - learn to race the car with the 15" stock tires so I learn the limits of the car the way it's built (looks like Hoosier makes some good 15")
(See the images in the link to FFR site) Yes, LCA has inner mounting holes. The UCA - not so much. I will have to talk to FFR to see if they mod the frame for different upper mounting point? IF necessary, with a lot of cutting & welding - the upper mounts can be moved inboard. Independent Front Suspension - Factory Five Racing

QUESTION: Notice the difference in the location of the UCA mount --- both the Single Adjust Coilover & DA Coilover are shown. Why --- does the DA mounting location offer better geometry?

Thank you!
 

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Not a waxer
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Your title asks about the MK4 but then you state that you're "looking to build a 289 FIA roadster - with the 15" FIA pin drive wheels" Those are two different and unique scenarios. With the Mk4 it's not the coilover that dictates the UCA mounting position, it's the spindle. The vertical mounts (what is shown with the DA shocks in the photo's you attached) are used with the FFR proprietary spindles and the horizontal mounts (as shown with the SA shocks) are used with Mustang spindles and the FFR spindle adapter. SA or DA coilovers can be used in either configuration. Things get kind of mixed into a hybrid configuration with the FIA due to it's narrower track...the FFR spindles are used and the UCAs get installed using the upper, horizontal mounts. In either case be it a pin drive width Mk4 or FIA geometry is sacrificed in exchange for appearances.

Clear as mud now? o_O

Jeff
 

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I'm not sure the geometry change effects handling?
I know that on the Mrk4, you can't use the FFR front spindle, you would use the SN94 dogleg spindle with the upper balljoint bracket. Also the lower control arm is shorter, you still use the outer frame holes. For the rear???? , I think you'd have the narrow the rear axle.
You want great 15" tires---easy buy Avons.
 

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Discussion Starter #6
Cool. You guys are teaching me things I didn't know.

My assumption based on what I'd read previous to this Thread was that the 289 FIA & 427 Mk4 both use the same Mk4 Frame and same track width, but they just had a different body shape over them (with different size wheel arches - so different size tires & wheel backspacings)

I think what you all are saying is that the frames may be the same for both 289 & 427 Mk4, but for Pin Drive Width, the spindles & control arm mounting position is different on the UCA, and the LCA is shorter to accomodate the smaller wheel arches?!?

QUESTION: I see a lot of posts referencing the SAI geometry mod for the front suspension. It appears that the UCA with the VERTICAL mount as shown on the DA FFR images I linked --- is in the configuration that people call SAI? Is this the case, which means the SA FFR images I linked are the older non-SAI configuration - which is what you are saying comes with the 289 FIA?

Yes, rich grsc, I think rear problem is solved more easily - with a narrowed axle. I also agree, I'll look to buy the Avon's or Hoosiers, or whatever is the best oldskool 15" tire that grips - even if it costs more.
 

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I don't think the SIA mod is comparable with pin drive.
Mine is a Mrk3, but the suspension mounts didn't change
 

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I don't think the SIA mod is comparable with pin drive.
It's not. The referenced "SAI mod" predated the FFR designed spindles, was conceived and designed by David Borden and was produced and sold by Whitby as a retrofit for Mk3 and earlier roadsters. The proprietary spindles and alternate UCA mounting points that began with the Mk4 pretty much made the SAI mod kit obsolete.
I'm pretty sure Whitby quit producing it a few years ago. FFR has a weld in chassis retrofit for Pre-Mk4s that includes the vertical mount components so that their spindles can be used. I've got one along with the spindles on a shelf---all I need is time to do it (and also install those big brakes that are on the same shelf collecting dust :cry:)

Jeff
 

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FFCobra Craftsman
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In the top pic of the frame w/ SA on one side and DA on the other.
-DA shocks can not be mounted body up since they are low or no pressure gas and the oil wouldn't stay where it needs to be.
-the left side (silver shock) has an FFR spindle and the UCA is mounted on the vertical surface
-the right side (red shock) has a Fox spindle w/ the original FFR adapter and UCA is mounted on the horizontal surface
-The reason for the two different frame mounting positions is the different spindle heights. Note the height of the UCA ball joints compared to the top shock mount bolt.
-if you look at the right side, that is basically the original FFR setup using a Fox spindle. Borden realized that the SAI is terrible and wanted to fix it by moving the UCA ball joint outward. But there was no room w/ the tall spindle/adapter because the ball joint would hit the inside of the wheel even w/ the change to 17s. So he found that the SN95 spindle was shorter and used that. Now the ball joint could move outward. In fact the entire UCA was moved outward and down by welding in the new vertical mount.
-A possible option for you would be to mount the UCA to the inside surface of the vertical mount. It would take a bit of cutting and welding because there is a 3/4x3/4 tube running from the firewall past where the rear end of the UCA cross shaft is but that is not a real big deal.
FFR frame arrow by craig stuard, on Flickr
I see that the inner LCA mount holes are also a little higher. I don't know why that is but it looks like they could be filled and re-drilled.
-I would use that option if it were me. You move the entire LCA, spindle, UCA inward but keep the latest FFR overall geometry nearly unchanged.
 

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Discussion Starter #10
I see that the inner LCA mount holes are also a little higher. I don't know why that is but it looks like they could be filled and re-drilled.
-I would use that option if it were me. You move the entire LCA, spindle, UCA inward but keep the latest FFR overall geometry nearly unchanged.
In starting this thread - that was the thought in my mind. Yes, it'd take some work to move the UCA mount, but it could be done - it just depends on how how drastic you want to get with cutting & welding. I think I would need some type of suspension analysis program to determine the best place to move things for optimal geo --- cause as you say, they can all be moved with some work.

If we are on the same page --- I think an underlying premise for moving both UCA & LCA mounting points inboard (in my simplistic mind) --- is that would allow you to maintain longer UCA's and LCA's (which I assume are a geo advantage) while still achieving the narrower Pin Drive track width. Does that make sense?
 

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FFCobra Craftsman
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.....
If we are on the same page --- I think an underlying premise for moving both UCA & LCA mounting points inboard (in my simplistic mind) --- is that would allow you to maintain longer UCA's and LCA's (which I assume are a geo advantage) while still achieving the narrower Pin Drive track width. Does that make sense?
That is exactly my thought. Longer control arms are pretty much universally desired. I used to have this software.
Performance Trends
I had the Roll Center Plus version @ $149 and was very happy w/ how it worked. There is also a slightly more basic version 'Roll Center' @ $99 and then a much more advanced version 'Suspension Analyzer' starting at $299 and going up to $649. I found it very interesting to play w/ moving frame mounting points to see what would happen. One other thing to keep in mind. The original design was 100% based on the easiest, least expensive way to utilize the stock Mustang LCA and spindle. By the time FFR came out w/ their own spindle they also had an in-house engineer who did the re-design work. I feel confident in their design now so doing all you can to use the current parts as designed, but simply moving them inward as far as you need to. I don't know exactly how much additional room you need to use the pin drive parts, but I'd figure that out and then figure how much moving the UCA cross shaft gets you and go from there. Also, especially if you decide to play w/ software, realize that different wheel widths and offsets affect geometry. The center of the tire contact patch affects track width, and scrub radius.
steering axis - Bing images
It is kind of minor but still something to keep in mind.
 

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Discussion Starter #12
Thank you! That helps clarify the path I need to follow to get 'er done. One thing I will need to do is talk with FFR and see WHAT they changed on the frame & suspension to: (a) fit the 289 body; and (b) ask how they modify their front suspension to accommodate pin drive width.
 
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