STR Z4 Coupe "build"

[John V]

I think you guys are being penny wise, pound foolish. But good luck nonetheless.

[wassup61]

At 1/3 the cost,the setup will have to do

[John V]

I guess if you can get the gear diff for $600 it might be worth a shot, yes.

[wassup61]

Not to mention the lack of an option for clutch type

[John V]

There's an OS Giken that will fit your car... it's listed on the Turner website. It's a unit that would be a good plug-and-play solution at some point. Autocrossers are having very good results with these units out of the box.

[illinipo]

Could you provide a link where you see that? Z4 3.0 manual transmission is not listed here.

http://www.turnermotorsport.com/p-13...e39-6-cyl.aspx

...But even though it is not listed I'm 99% sure it would fit anyway.

[John V]

If you have a Z4 3.0si coupe it will fit. The issue is that it will not fit if you have one of the low numeric ratios.

Going from memory here I think the Z4 roadster manual has a 3.07 so it would not work with those gears. If you have the 3.0si roadster with a 3.23 it would work. Same with the 3.0si coupe which has a 3.46.

[illinipo]

yeah lower than 3.15 has the diff shifted left or right on its axis so pretty much any e46 non-xi, non-M, >3.15 diff will fit.

[illinipo]

Wow 200 views in 3 or 4 days... put us over 2000! thanks for reading

Having troubles finding the e46 ring gear bolts... Anyone have any bright ideas? Current plan is to use the e36 factory LSD bolts which are the right size M12x1.5x24, but the head on them is a little different and I don't know if they have the teeth on the flange... If anyone has a set of 33121205561 laying around I'd appreciate some pics (edit, these bolts cross-reference all the way back to E12... but stop at 2002 when BMW started servicing differential cases as a unit from Germany)

Another option is to order some 12.9 bolts from mcmaster.... but they don't carry them as far as I can tell.

Then there is also ordering some ARP bolts but $$$$$

[99MPower]

i have a set of e36 ring bolts.. what you looking for, just pictures?

[illinipo]

Just wondering,

1. If they have teeth on the underside of the flange, and
2. Whether the head is dished or flat.


...automerge like 5 hours later below here...


'MERICA!



yep.




...Now I just need some ring gear bolts. Minor oversight while waiting for this thing to ship lol

Okay, triplepost automerge.

2 sets of 664-1001 ARP bolts will be on the way soon. It's special order unfortunately. Maybe if we call VAC....

Dab of 271 then 110Nm and they should be good to go

...

Day 2 of post 61.

664-1001 and 674-1001 are both special order with 2 week lead time. Plus there is the issue of the teeth on the flange...

I called VAC and they will sell the bolts they use for $8 per. so figure about $90 shipped.

But then I was like, well, I might as well get the 33121205561 which are $3.40 at Tischer. So I got to the verify order button when I realzed, the nickel and dime $5 handling fee and $8 shipping might not be worth it over buying locally.

So now I have one 33121205561 bolt on order at the local dealer for $4.25 plus tax. This way I can check fitment and whatnot before I order the other 9. Should be here Tuesday according to the guy. But I bet sooner because the special overnight from Germany BMW parts warehouse is like 100 miles away.

PS our truly monumental Tischer order shipped And we got enough rubber to last through September. Pretty bad when you put it like that...

[Irish1]

What's your wife think about tires cluttering up the hallway next to her cute slippers? Great thread here, fun to think how I would've solved the push in my old Z4 Coupe using your ideas.

[z3papa]

My new set of tires are sitting in my office conference room and anticipate a set of wet tires to come in the spring. Need to pull the trigger on the diff. and get to brass tax on some off season exhaust development starting this weekend.

[wassup61]

Thats my mom youre talking about... and those are just the dry/hots, Conti DW for wets are forthcoming

[illinipo]

Picked up some hardware at the local club banquet this evening... the traveling Bowling Award! 68 cones this year was enough to claim the shame.

I'll have to write a plastic parts line into the racing budget this season...

[GotCone?]

any updates?

[illinipo]

I work too hard.

The bushings came in the other day, but they are up north so I will have to wait to install them.

The bolts came in at the local dealer about 2 weeks ago. They should work fine, despite the shorter dished head. They also have a full-diameter shank on the bolt (e46+ do not) which should help load distribution to the crown gear. They do not have the teeth in the flange... but a good cleaning of the crown gear and a fresh dab of 271 should do the trick. It has done the trick on BMW's since the 1970's!

Planning to get in the garage in the next few days to bolt up the diff. Although that has been the plan for the last 3 weeks... huge project I've been trying to finish up at work is almost done.

Then I have to get together with wassup61 on a weekend and put together the new OEM shifter parts (rear bushing, front bushings, sponge, ball socket) and the rear end.

[BTM]

don't forget to have him bring your xmas gift if I can't come to hand people tools. also did you get my message about my scca number?

[illinipo]

don't forget to have him bring your xmas gift if I can't come to hand people tools. also did you get my message about my scca number?

yep yep will take care of that over the weekend prolly.


Ugh so just as this one work project is finishing up, today I got another big one to do before May... Gotta start focusing on this car on the weekends!

[Fair]

Good thread - missed it when it was started last year.

I know in the past wavetrac was looking for some people to showcase their products (might have been for their Porsche parts), you should call them directly and tell them what you're doing, might help your budget

Yea, I'm researching WaveTrac for my STX prepped Mustang. Only $995 for the Ford 8.8"... eager to see somebody thy this for autocross use. To say we have a rear traction problem would be an understatement, so I have to do something better than the OEM clutch style diff we have. The options for the Ford are pretty limited... lockers and clutch diffs, plus a handful of (problematic) Torsens.

Why not an OS Giken?

They make a damn fine diff - I love the one in our E46 330. Dan @ Diffsonline is the source. About $1700, which is painful. Not a big deal - see you chose the WaveTrac.

Wheel studs are a matter of personal preference, but the stock bolts are lighter than the stud/nut combo, and really are just dress up parts that should be replaced yearly at a significant expense.

Hmm, well honestly that's just as off base as you can get. Heheh... Look, wheel studs are not "dress up parts" at all, but rather a safer solution than wheel bolts for racing uses (you never, ever see in wheel bolts in any form of pro racing - for a reason). Wheel bolts are frowned upon by most tech inspectors at motorsports events because they cannot see the hub engagement. With long wheel studs and open lug nuts that is not a concern. Wheel bolts also have to be perfectly sized to the exact spacer width used (if any), otherwise they could have under or over engagement at the hub ("over" is also bad, as a long bolt can smash into parts behind the hubs). When a long wheel stud you can use a variety of spacer widths (or none at all) and see 100% engagement at the lug nut.

The hardware also do not need to be replaced every year, not hardly. We sell lots of wheel studs to pro race teams, and they beat the crap out of them, but yes - these teams replace wheel studs and nuts every season because its cheap - just as they would wheel bolts, if they used them (they never do). Autocrossers could keep using wheel studs and lut nuts (or wheel bolts!) for 3-4 seasons. Its also a lot easier to install a wheel over wheel studs ... with wheel bolts you have to put the wheel on the hub, hold it there, line up a hole, start a wheel bolt, then let go of the wheel. So the benefits are: added safety + convenience + ability to run various spacer widths.

Also, RTAB limiters have long since proven legal in SCCA ST & SP classes. Polyurethane rear trailing arm bushings can... bite you. I am a PowerFlex dealer and sell a lot of their fine products, but I prefer a rubber bushing and limiters in this RTAB location on the E36/46/Z4 chassis, as this point needs to both rotate and twist. Poly doesn't usually do well in dual-axis bushing locations. It can cause bind if you have too much stiffness there. Just keep that in mind if you have any weird twitchiness in the rear suspension. The other "no bind" solution for a dual axis bushing location is a spherical bearing, which isn't ST /SP legal.

PowerFlex has supposedly worked on a softer bushing for the RTAB now, so this may be a moot point. I had a car in our shop the other day with poly RTABs (unknown brand) and it most definitely was WAY stiffer than I liked there. With the subframe off the car the trailing arm could not be budged in the RTAB mount. So... I'm still not convinced. I want to test this with a proper load test fixture off the car, to measure the force required to move the trailing arm through its movement with rubber vs poly bushings. Its a pain in the butt to test properly, but its on our work schedule here.

One thing that is being underplayed on this build is maximizing tire width. I don't care what S2000 drivers say, your Z4 is bigger and fatter than them. 245mm is just a tick narrow for a car like this, in my honest opinion. If you have the heaviest car in class you pretty much have to use every inch of available wheel and every mm of tire the class allows - that being the case for the Z4.

And no excuses on fitment - if people can make 18x10's and 285s fit the E36 M3 in STU, you can make a 17x9 fit a Z4 in STR. Plus the fender liner rules are more liberal now than they were back then.

So, sorry if I disagreed on a few things here, but it happens. Please don't take offense (like in the earlier posts) - these are just my opinions based on my experiences. I've been autocrossing since the 1980s and just have differing views on some of the basics discussed on this build by the OP and his co-driver. I don't claim to be an expert, just old. The OP can of course ignore any and all advice, and keep on racing how he wants to. The Z4 is an excellent chassis for STR but it has an uphill battle with the standard parts out there, as Mark Sipe mentioned here early on. Not many people have campaigned the Z4 outside of Stock class seriously.

Good shocks are going to be key, and the spring rates offered up in the 2.5 Hz range are probably closer to what you need. AST 4150 singles or 4250 doubles are both good bang per buck options for adjustable, high end monotubes without remotes.

Good luck,

[illinipo]

I think an empty wallet is a pretty good excuse... Maybe if you gave us a huge below jobber discount on the 4150's, we could buy a set of d-force from you also below jobber price

[Fair]

I think an empty wallet is a pretty good excuse... Maybe if you gave us a huge below jobber discount on the 4150's, we could buy a set of d-force from you also below jobber price

hehehe... OK, fair enough. Budget is always a very important driving factor! I have to choose my parts wisely as well, even if I have dealer pricing on some things. I don't have Moton 4-way shocks on any of my cars, as much as I'd like to. I'm also stuck trying to pick proper 3-piece wheels (since there is no 1-piece option in the widths I want) for one of my cars - based simply on cost ($2300 vs $3200 vs $4400). I just cannot wrap my brain around $1000 apiece wheels.

I keep looking for that money tree... when I find it I'm gonna shake the CRAP out of it!

[z3papa]

I think an empty wallet is a pretty good excuse... Maybe if you gave us a huge below jobber discount on the 4150's, we could buy a set of d-force from you also below jobber price

Sounds like a prime candidate as a tester although I've never even had a response to past inquiries on that front. I can't even get a response from the guy who was the Z tester as input on settings/rates or experience despite asking a number of times.

[illinipo]

On RTABs. Out of curiosity of the binding issue, I cycled the rear end a few times with the spring out before we took the subframe down. The range of motion is free and easy through the majority of the travel. Only at extreme compression levels does the Rogue RTAB bind, well above the compression we could get with a wheel/tire rubbing the top of the fenderliner. The benefits to on-power stability when using this particular RTAB from Rogue compared to stock cannot be ignored. But, I also have not tried any of the other options. This is my first affair with a BMW.

[Toby Larsson]

Yea, I'm researching WaveTrac for my STX prepped Mustang. Only $995 for the Ford 8.8"... eager to see somebody thy this for autocross use. To say we have a rear traction problem would be an understatement, so I have to do something better than the OEM clutch style diff we have. The options for the Ford are pretty limited... lockers and clutch diffs, plus a handful of (problematic) torsens

The OS Giken lsd for the new Camaro is out and is being used successfully in both drifting and roadrace. The Ford unit has been tested for awhile and should be available very soon. The Ford unit opens up some interesting options with large number of cheap gear ratios available that can be mounted in the aluminum housing from the Cobra and equipped with cv's can be mounted in most BMW subframes as a IRS setup. Let me know if you're interested in one and I can put you in touch with the right person for more info.