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Old 06-16-2019, 02:07 AM   #1
dadsbmw
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Koni yellows- I'm sure it's been asked, but not clear

I'm sorry, I know this has been asked quite a bit, but that just seems to make the potential options more plentiful and convoluted.

Piecing together a coilover setup for my 90 325i. Planning on 375lb/in 7" front springs and 450lb/in 6" rear springs. My intent is to go lowish with a slightly firm ride, but still comfortable and easy to drive on the street. I've been doing a bit of research trying to figure out what Koni shocks to go with, and have found a few options.

The questions I end up running into are:
  • How much should I cut out of the front strut housings?
  • What front shocks? ix (8641-1144SPORT)? this other part number (8641-1210Sport)?
  • What rear shocks? ix (80-2522SPORT)? This other part number (80-2641Sport)?
  • Would there be any benefit to the GC tall rear strut mounts?

Appreciate any insight or advice you all can provide.
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2003 Z4 3.0 6-speed- Silver, 19's, daily driver
1990 Silver 325i- Lowered on H&R OE Sports, e90 drop hats, KYB shocks, color matched rocker panels, 16" Emortal RS wheels on 205/50/16 tires... Currently getting a full refresh including an S52 swap!
1997 Black Ford Probe GT- Stripped to 2220lbs, MS3X, Forged motor in midst of assembly... Dyno results and 1/4 mile times pending
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Old 06-16-2019, 05:04 PM   #2
e30davie
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8641-1210sport is 430mm body length, designed to fit in oem e30 strut. (ie no a shorter body, ie no use using if you intend on cutting). The 8641-1144sport, i cant find the dimensions on this one. but its coming up as oem IX, if the strut length is same as normal e30 then it wont be much help to you either.

I would advising figuring out exactly what height you want and wether you actually need a shorter strut. I put the 8641-1210sport in my car with lowering springs and it goes plenty low enough without needing to cut the strut. I am about ~130mm off the ground with the front cross member, and still have a reasonable amount of bump travel left in shock.

One of these days i intend on cutting the OEM spring seat off and welding on a coilover thread etc. but keeping the oem strut length. Perhaps the same would work for you.

You also might want to bump the rear spring rate up substantially. rear of an e30 has a 0.67 wheel rate, most guy seems to have ~350 in the front and closer to 700 in the rear due to this wheel rate. I currently have springs that are too soft in the rear and you dont want that, it bounces too much.
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Old 06-16-2019, 11:39 PM   #3
dadsbmw
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Thanks for the response Davie.

I only suggested the 8641-1210sport because this thread refers to them as "short".
The ix fronts are supposedly 3"-4" shorter than i's, however I'm not sure about the rear.

My original intention was to just to run stock strut housings and I'm sure I could get away with it, but as you go lower on the stock housings with stock perch location, you end up running outside of the optimal operating height of the stock. Was planning to do it more as a shock longevity thing, than a "go low" thing... but maybe I'm wrong about that. Also would rather err on the safe side and be able to go lower than I need to, rather than not be able to go low enough. I frankly have no reference for how low stock strut housings allow.

In terms of spring rates, I made the current selection based off what GC said when I called them a while ago. They suggested 375f/475r for a more street oriented setup, or 450/650 for something more aggressive. I've actually got a good number of Eibach springs sitting in my hallway right now, so maybe I'll keep a stiffer set just in case, but I think my focus is slightly more on comfort than all out handling.

Thanks again for the input
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2003 Z4 3.0 6-speed- Silver, 19's, daily driver
1990 Silver 325i- Lowered on H&R OE Sports, e90 drop hats, KYB shocks, color matched rocker panels, 16" Emortal RS wheels on 205/50/16 tires... Currently getting a full refresh including an S52 swap!
1997 Black Ford Probe GT- Stripped to 2220lbs, MS3X, Forged motor in midst of assembly... Dyno results and 1/4 mile times pending
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Old 06-19-2019, 04:54 PM   #4
e30davie
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See how you go. I have found on may cars in the past and the e30 that a softer spring does not necessarily mean comfort. The bouncing effect is alot less comfortable than a short sharp bump from a stiffer spring. I am in a bit of a pickle at the moment with my setup, koni yellows with cheap "king springs" that are a progressive spring. so soft at the start and get stiffer the more they travel. what it means is im getting an annoying bounce in the first ~1" of travel before it stiffens up. I have tried to up the damping on the konis but the adjustment is only rebound, so you end up with this over damped on rebound setup which has its on uncomfortableness. but anyway, maybe i am too picky. I should just buy a set of real springs....but options are limited in AUS and the Aus dollar is currently terrible against the USD...

If i remember on the weekend i will have a look at mine and see where it sits in the travel of the shock. Im almost certain its close to the middle at static height.

It may pay to email Koni directly and get the body length, extended length, and compressed length of all the available shocks. here are two that i have that hopefully will help, but i don't have the ones for the IX shocks.

Shock - max length/min length/body length

8641-1021sport - 614/485/432
8641-1210sport - 585/488/432

I personally went for the 8641-1210sport in the front and 80-2522sport in the rear. you can see the 1210 is almost 30mm shorter on extended length. good for keeping a short spring captive (but painful to install with non threaded sleeves, ask me how i know...)
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Old 06-21-2019, 07:31 AM   #5
Northern
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Quote:
Originally Posted by dadsbmw View Post
The ix fronts are supposedly 3"-4" shorter than i's, however I'm not sure about the rear.
iX front strut inserts are around that length because the bottom of the strut tube ends before the front axle pass-through, rears are definitely not shorter since it's almost the same as the RWD configuration.

iX front koni sport SA's work well up to around 450lb springs. Maybe you'd look into something more for a dedicated track car, but for street and weekend autox/lapping day stuff, you'd be fine. Above that, you're looking at something like Koni 8610-1437 Race, which has similar dimensions to the IX insert, but with higher valving (and cost to match). For reference, I sectioned my housings 1" and run a spacer under the insert. If you section 2" or more, you might need longer springs.

For rears, mustang shocks are the go-to (top adjustable + higher valving). My old GC kit had 8041-1026SPORT in the rear, and after a clarification email to Koni about the difference between these and the other mustang part number (8041-1186SPORT), I was told that they had identical valving, but -1186 had 5mm more length + a 50mm integrated bump stop. I don't think you can go wrong with either.

*Note* that the mustang rear konis have a 12mm thread on the top, and I think OEM RSM's only have a 10mm hole. I don't know if there's room to drill it larger or if you absolutely need to upgrade, but they're a weak point anyway and aftermarket versions with 12mm hole are pretty common and not terribly expensive.
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Last edited by Northern; 06-28-2019 at 07:00 AM. Reason: RSM Hole dia typo
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Old 06-26-2019, 02:14 PM   #6
dadsbmw
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This is perfection, thank you Northern! One last question. Is there any issue with running higher valved shocks with relatively soft springs? If running 375f/450r springs with the higher valved shocks isn't a problem, it would allow me to be prepared in case I decide I want a stiffer spring in the future.
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2003 Z4 3.0 6-speed- Silver, 19's, daily driver
1990 Silver 325i- Lowered on H&R OE Sports, e90 drop hats, KYB shocks, color matched rocker panels, 16" Emortal RS wheels on 205/50/16 tires... Currently getting a full refresh including an S52 swap!
1997 Black Ford Probe GT- Stripped to 2220lbs, MS3X, Forged motor in midst of assembly... Dyno results and 1/4 mile times pending
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Old 06-28-2019, 06:58 AM   #7
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Those rates are still higher than stock, especially up front. You shouldn't have a problem.
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