Yet another 911 strut thread, Confustion about KONI inserts in KONI struts Options

[Richard Casto]

I am about to pull the trigger on a 911 front suspension. It is billed as being from a 72-74 911S (no the aluminum calipers are gone and I will be using regular A calipers instead) as it has KONI struts with the 3.5” spacing. Ultimately I am looking to install KONI Sport (aka Yellow) struts that have the adjustment knob on the top. I have read a few quality threads such as…

http://www.914world.com/bbs2/index.php?sho...c=390&st=20

This answers a lot of questions, but that thread mostly talks about Boge struts, spindle mods, etc. and doesn’t 100% clear up a question I have about KONI insert compatibility.

My confusion comes from the KONI application guide http://www.koni-na.com/pdfcatalogs/2007applguide.pdf (approx 1 MB PDF). If you don’t want to look at the PDF here is a summary of the KONI document …

65-68 911
Boge strut 86-1394 Classic
KONI strut 86-1308 Classic

69-74 911
Boge strut 8641-1039 Classic
KONI strut 86-1638 Classic

75-89 911
Boge strut 8641-1039 Special
KONI strut 86-1942 Special
(footnote) 8641-1039 Sport

914 and 914/6
All (Boge?) 8641-1077 Sport

To translate KONI types, Classic = “Black”, Special = “Red” and Sport = “Yellow”.

The implication is that "it appears" that you are really limited if you want to use the “Sport” insert as they only list the “Sport” strut for the 914 and 914/6 as well as for the 75-89 911 (but with a cryptic footnote). The 911 footnote says…

“Ext. adjust Sport alternative (both Boge and KONI) for OE KONI struts, gland nut 73.25.01.011.1 must be ordered separately”

My confusion/questions…

• Is the dimensions/structure of all Boge struts the same and all KONI struts the same (I understand that Boge and KONI struts are not the same)? If so, using Boge struts as the example, ANY Boge “compatible” insert will “fit” ANY Boge strut regardless of the year of strut and model of insert?
• That the KONI strut has a larger internal diameter and that the Boge is smaller? That the special gland nut they mention is first threaded into the KONI strut (Its external thread match the KONI struts threads) and then the Boge compatible KONI insert screws into the gland nut?
• I am making a lot of assumptions here, but if the above is true about the gland nut, does that mean that you can take ANY of those KONI inserts and using the special gland nut use it in ANY of the Boge struts?
• That the KONI application guide actually lists recommendations based upon OEM replacement and insert valving. For example if all of my above leaps of faith are correct (in that you can really mix and match) that if you do, you may just have incompatible insert valving that will affect handling dynamics. BUT it also means that you can use the proper 914 KONI "Sport" insert (that is properly valved for the 914) in any of the Boge or KONI 911 struts!?!?
• This is more of a question for someone at KONI, but they list the 8641 “series” as being externally adjustable. Basically it looks like all of 8641 inserts are “sport” types. But the above into lists the KONI insert for the 75-89 Boge strut as “Special”, but not “Sport” even though it is an 8641 series insert. Maybe this is a misprint and it really is a Sport insert?

I know someone is going to say “Just use Boge struts”. I understand that my options are greater with the Boge, but I am really trying to settle my own confusion regarding the KONI struts. And if it works as I think it might, and then I may just go with the KONI struts front end that I am looking at.

One last thing…

I have tried to document everything that I have learned on the 914 Wiki. Please feel free to look at that article and if you think you know what you are talking about, correct any mistakes.

http://www.roadglue.com/wiki/index.php/911_front_suspension

[Richard Casto]

Ok, I talked to Bob at KONI and Jason at Paragon (both were VERY helpful and answered any question I came up with). Here is what I found out.

1. It sounds like the 69-89 Boge 911 struts are dimensionally the same, so you can mix and match inserts regarding fitment. However valving may be incorrect. I think the same holds true for the KONI struts of the same time period as well. I think the 68 and earlier 911 struts may be different (we didn’t talk much about them). So while the KONI application chart does not list a sport insert for the 72-74 KONI strut, you can use the insert designed for the 75-89 KONI strut in the 72-74 KONI strut. Basically the KONI charts are going to list OEM replacements (if they provide them) as well as upgrades to something like the Sport insert, but they it must both fit AND have proper valving before they are listed on the chart. Also, there might be a model that works (both fit and valving) for the front, but they don't have a model for the rear of the same type, so they will not list the front if they don't have a matching rear. Basically they are not going to recommend a Sport for the front if they don’t offer a Sport for the rear even if one of the other front Sport models would be just fine.

2. My quest to use the 8641-1077 914 Sport insert (which is should fit into a Boge strut) in the 911 KONI strut by using the special gland nut to convert from one thread pattern to another almost works, but there is a problem in that for some reason the 914 insert necks down much lower (near the bottom) on the insert than the 911 insert. This means that as you slide the insert it, it may bottom out before it is in position. Apparently it is VERY close to working as is, and that you can machine some metal off of the necking on the insert and it will fit, but at the risk of destroying or shortening the life of the insert. Apparently this used to be an issue with some of the 911 inserts and KONI moved the necking farther up the insert. But they haven't done the same for the 914 insert. So close, but no cigar. It is not a recommended solution.

3. I asked about the difference (if any) between the "8641-1039" and the "8641-1039 sport". I found it odd that there was an 8641 series insert that was not a "Sport" insert. They are different, but only in valving. Both have the same basic construction (single adjustable via the top screw), but the non-sport has less aggressive valving.

4. While I can use the 75-89 insert in the 72-74 strut and put it all in the 914 the valving is not going to be ideal. So while I can get that insert revalved to match the 914, there is another route as well. That would be to use the body of the 86-1638 (this is the natural replacement for the 72-74 KONI strut) and have it rebuilt using "Sport" internals (and of course valved appropriately)

What am I going to do?

I am going to pull the trigger on the 73 S front end that is available to me locally. I am going to eventually be buying the 8641-1039 Sport inserts. Eric will say that I will not be happy with the valving and if he is right, I will eventually get them revalved.