Strut mods. How far off base am I

[rabrooks]

Help me beat this dead horse. I'm building a 280z track car. I want to get decent suspension without spending a fortune. I don't care for strut suspension, but I think I have to stay with it in order to curtail the spending. I know alot of people lower these cars with coil overs. but it seems to me if you set the geometry of the suspension different than intended it makes things more harsh and it doesn't work as well as if it were in its original geometry. I'm sure what I have decided to do has been thought of long before now. I want to run it by the gallery to get some feedback.

For the front,I thought I would cut the strut tube down 1.5". then add a bump steer spacer between the lower control arm and spindle. That should get the car lower while maintaining the best geometry. Its as if I put 1.5" lowering spindles on it.

The rear will be similar but I will have to weld a new pin tube to the bottom of the hub to raise that spindle (lower the rear of the car)

I'll likely run bilstein double adjustable shocks and not sure on springs. I guess Eibachs. What are your suggestions for springs

I want to run 16" wheels and tires, comment on the size tire that fits the wells the best. It will be wide body but I'm looking for diameter.

I have an LS1 with t56 for the car.

Thanks for your help

Roger

[jhm]

You're talking about sectioning the front strut tube to retain suspension travel while lowering the car and then using bump steer spacers to improve front lower control arm geometry.  That's extremely common practice with the S30 suspension.  What springs and shocks are you considering using?  The various options have been discussed liberally in the Brakes/Suspension sub-forum and the FAQs.  It seems like you're wanting to retain the stock'ish springs....but that's a very sub-optimum solution for a track car, and I doubt you'd be happy with the results.

 

If I understand your proposed rear suspension mods correctly, that is largely uncharted territory, and I can't really say that I see the benefits.  There are aftermarket adjustable rear LCAs available, or you can fabricate your own, in order to dial-in the desired rear toe geometry.  And you can achieve decent negative camber at the rear with even modest lowering.  Again, it is a common practice to section/shorten the rear strut tube to retain suspension travel when lowering; and adjustable coilovers are the preferred setup for track use.

 

Your basic premise that the factory suspension offers the best overall solution is just not correct.  In fact, the single downtube/single control arm is an outdated and limiting design; and typically requires a fair bit of modification to achieve the types of geometric camber and caster desired for track use, as well as stiffer springing and damping.  Hope this info helps, welcome to the forum and good luck with your build.  (And Happy New Year!)

[JMortensen]

The issue with lowering the car and altering the geometry in the front has mostly to do with bumpsteer. The camber curve is very consistent throughout the travel. The caster curve is affected, but that's minor. The bumpsteer curve on the Z is crappy out of the box. You can run the bumpsteer spacers to get it back to where it was (crappy) or you can make it adjustable and minimize it. You can do this with a bumpsteer spacer kit from a vendor like Apex Engineered, or you can drill out the steer knuckles and run shims to fix. Bumpsteer shims are commonly available circle track parts. FWIW I do run bumpsteer spacers to help with the front roll center and have the bumpsteer adjusted with the shims to counter both issues.
https://www.apexengineered.com/store/p11/Front_Tie_Rod_Kit.html
http://www.colemanracing.com/Bump-Steer-Bushing-Kit-P4444.aspx

As it is the roll center in the rear is quite a bit higher than the front and I can tell you from personal experience with a low race car that even very low, the rear roll center is still above ground and higher than the front roll center, which are, generally speaking, the things you want. You can weld a new pin tube under the stock one, Ben Cort did that on his autocross car, and Terry Oxandale modified the bottom of the strut housing to make it longer to raise the rear roll center higher, but it isn't the first thing that I'd be worried about. It's pretty far down the list of things to do IMO.

2 way Bilstein struts are not low dollar. They are very good, but there isn't a bolt on option for them for the Z, so you'll be fabricating to get them on your car. If you want a low dollar solution, there are weld on adjustable struts that are not as good from vendors like Tein and BC Racing. They run ~$1000 or so for the set of 4, and you get coilovers in the process. 

Be careful sectioning the rear struts on a 280. The tubes are longer and the top insulator is taller in the rear of a 280 than the front. You can just get a 240 or 280 front insulator and run that on top of your stock 280 strut and that drops it down an inch with no sectioning required. If you run camber plates front and back, that accomplishes the same thing but you'll drop the car roughly 1.5" front and 2.5" rear. If you section the rear strut tubes and change out the strut top, you'll have trouble getting the rear of the car high enough. You can literally set the frame of the car on the ground and still have several inches of suspension travel left if you screw this up. 

Edited January 1, 2019 by JMortensen

[rabrooks]

Thanks for the insight. I do pkan on running bilstiens. Ihave heard the frobts can use bilstiens for a 52i bmw without mods. I have the wrld on threaded spring perches also. I will look into the bump steer springs

I agree that factory setup isnt ideal. I dont like sruts. I was planning to develop double a arm setup. But the cost will nurt the project. So the best setup of the suspension as it is, is to keep the lower control arms close to he factory angle. I dont want a lowered car with the lower arms high outboard. So thats why i was thinking spacers up front and a new lower tube in the rear

Thanks for all the info. Its great to process it and to hear others have done tbis

 

[JMortensen]

Be sure to post what you do on the Bilsteins. I've been looking at modifying 3000GT Bilsteins. Others have done it in S14s, but it's a big PITA and I haven't done it for that reason. If there is an easier to work BMW solution, I'd love to see it and I'm sure I'm not alone.

Best of luck!

[jhm]

Also, be advised that if you do decide to replace the stock strut isolators with camber plates, you will not be able to take advantage of the camber adjustment unless you replace the stock-sized springs with smaller diameter springs and top hats as well.  The stock springs and top hats interfere with the inner portion of the strut towers and severely limit camber adjustment.  (You can achieve roughly the same amount of neg camber by simply slotting the three holes on the strut tower to allow a small inward adjustment of the strut assembly.  2.5" diameter springs are probably one of the most common ID spring used for adjustable coilovers on the S30, but there are certainly many other options to choose from.

[Leon]

1 hour ago, JMortensen said:

Be sure to post what you do on the Bilsteins. I've been looking at modifying 3000GT Bilsteins. Others have done it in S14s, but it's a big PITA and I haven't done it for that reason. If there is an easier to work BMW solution, I'd love to see it and I'm sure I'm not alone.

Best of luck!

 

3000GT Bilsteins fit fine and allow for plenty of room to section (as do the VW Rabbit ones), it's the gland nut that's the problem. I'm not sure you can get them anymore.

[jhm]

Good point on the gland nuts.  I've not been able to find original Bilstein gland nuts for either 240 or 280 strut tubes, so I've always machined my own out of stock gland nuts (or Tokicos).  I'm using the P30-0032s on all four corners.

[JMortensen]

2 hours ago, Leon said:

 

3000GT Bilsteins fit fine and allow for plenty of room to section (as do the VW Rabbit ones), it's the gland nut that's the problem. I'm not sure you can get them anymore.

Gland nut is an issue as is converting it to double adjustable, which IIRC requires remote reservoirs. I don't believe you can buy them DA from Bilstein, have to buy the reservoir, weld on the fitting and DIY. Sure would be nice to find an easier solution...

Edited January 1, 2019 by JMortensen

[rabrooks]

On the 528 BMW insert working on the 280z's, I got that info from a person that has been running  rally races for 15 years in his 280. He is sending me info on all the suspension parts he buys to make his system work, front and rear. When I get that info, I will share what is pertinent.  I know a good bit of his parts will need to be changed for stiffer springs and or different valving due to him running on dirt and me on asphalt with sticky tires.

[rabrooks]

7 hours ago, JMortensen said:

Be careful sectioning the rear struts on a 280. The tubes are longer and the top insulator is taller in the rear of a 280 than the front. You can just get a 240 or 280 front insulator and run that on top of your stock 280 strut and that drops it down an inch with no sectioning required. If you run camber plates front and back, that accomplishes the same thing but you'll drop the car roughly 1.5" front and 2.5" rear. If you section the rear strut tubes and change out the strut top, you'll have trouble getting the rear of the car high enough. You can literally set the frame of the car on the ground and still have several inches of suspension travel left if you screw this up. 

So it sounds like if I go as I plan, converting to coil overs the car will sit down 1.5" in the front and 2.5 in the rear. If that's the case, then I just need to concern myself with making an adjustment so the lca's are at original geometry. Which means the spacers up front and the pin tube dropped for the rears. Am I understanding your information correctly.

[rabrooks]

I believe my car will weigh in at 2450 or less. I'm trying for 2300. So if I hit my target of 2450, with a 52% rear and 48% front wight bias. What would you guys recommend for the spring rates and spring heights

Thanks

[jhm]

My car weighs in very similarly to your target (which is quite light for a 280, BTW).  I am running 340 lb/in springs in the rear and 300 in front.  All of my coils are 7 or 8" free length.  ST rear sway bar and Datsun 20mm front sway bar.  Tires are Hoosier A7s (275 width, 15" diameter).

 

Have you had a chance to read all the FAQs on suspension?  If not, you'll find that most of your questions have already been addressed quite adequately.

 

I would recommend trying to get closer to 50/50 front/rear weight ratio.  What's your left/right mix, and cross-weight ratio?

[rabrooks]

17 minutes ago, jhm said:

My car weighs in very similarly to your target (which is quite light for a 280, BTW).  I am running 340 lb/in springs in the rear and 300 in front.  All of my coils are 7 or 8" free length.  ST rear sway bar and Datsun 20mm front sway bar.  Tires are Hoosier A7s (275 width, 15" diameter).

 

Have you had a chance to read all the FAQs on suspension?  If not, you'll find that most of your questions have already been addressed quite adequately.

 

I would recommend trying to get closer to 50/50 front/rear weight ratio.  What's your left/right mix, and cross-weight ratio?

Thank you for this information. Based on the spring info is it safe to say your springs compress 2-2.25" 

I will shoot for 50/50 but changing so many things, what I posted is my best guess. I'll probably keep the battery in factory location. Hope to switch fuel cell moved forward by 6 inches of factory tank. If left right mix and cross weight ratio is out of wack I'll move the fuel cell over or place it in the floor of the passenger side. This is probably the best fix but it takes away a few options I'd like to have. Like passenger seat.

[JMortensen]

1 hour ago, rabrooks said:

So it sounds like if I go as I plan, converting to coil overs the car will sit down 1.5" in the front and 2.5 in the rear. If that's the case, then I just need to concern myself with making an adjustment so the lca's are at original geometry. Which means the spacers up front and the pin tube dropped for the rears. Am I understanding your information correctly.

If you do camber plates and somehow adapted them to stock springs, you'd go down 1.5 and 2.5. If you go coilovers you'll start 1.5 and 2.5 down and then can lower with the spring perches from there.

Again, IMO, I'd run the bumpsteer spacer in front to correct roll center and not worry about it in the rear. The rear doesn't have dynamic toe change and camber change is pretty linear, and the roll center will likely be higher than front and above ground, so it's a way-down-the-list thing to do after making camber, caster, and toe adjustable, reducing friction in the bushings, sway bars, better struts, chassis reinforcement, etc.

Interestingly on the corner weighting, I recently listened to one of Ross Bentley's podcasts I think it was, and they were talking about the relative advantages of diagonal corner weights vs front corner weights, and the guy he was talking to was saying that having the front corner weights even was more important that getting the diagonals even, as this means less likelihood of locking up a tire under braking. First time I had heard that, and it would imply that moving the battery to the back is probably counterproductive on a Z.

[rabrooks]

4 minutes ago, JMortensen said:

If you do camber plates and somehow adapted them to stock springs, you'd go down 1.5 and 2.5. If you go coilovers you'll start 1.5 and 2.5 down and then can lower with the spring perches from there.

Again, IMO, I'd run the bumpsteer spacer in front to correct roll center and not worry about it in the rear. The rear doesn't have dynamic toe change and camber change is pretty linear, and the roll center will likely be higher than front and above ground, so it's a way-down-the-list thing to do after making camber, caster, and toe adjustable, reducing friction in the bushings, sway bars, better struts, chassis reinforcement, etc.

Interestingly on the corner weighting, I recently listened to one of Ross Bentley's podcasts I think it was, and they were talking about the relative advantages of diagonal corner weights vs front corner weights, and the guy he was talking to was saying that having the front corner weights even was more important that getting the diagonals even, as this means less likelihood of locking up a tire under braking. First time I had heard that, and it would imply that moving the battery to the back is probably counterproductive on a Z.

I agree with all the above. Definitely using coil over style struts with camber plates. Failed to mention that earlier. My battery will stay in the factory location. Going to the ls1 and t56 changes the ratios to a level that requires more thought on my part to get back closer to the 50/50 ratio. That's why I'm moving the fuel cell forward of the original tank and not moving the battery to the rear. I may go with a fiberglass rear hatch and plexi window. I do have another option to move some weight back forward. I can go with a built T5 transmission. In a road racing arrangement I think it will hold up. No hot launches and rev matching downshifts.

[Leon]

On 1/1/2019 at 3:40 PM, JMortensen said:

Gland nut is an issue as is converting it to double adjustable, which IIRC requires remote reservoirs. I don't believe you can buy them DA from Bilstein, have to buy the reservoir, weld on the fitting and DIY. Sure would be nice to find an easier solution...

 

I bought four Bilstein gland nuts for 240Z tubes (30mm dampers) from AJUSA in 2014 but I remember them saying they were the last ones they had. Not sure if Bilstein Germany has restocked the supply chain since then. The part number I used (provided by John Coffey) was B4-B30-U232-B1

Edited January 3, 2019 by Leon

[JMortensen]

30mm gland nuts won't work on 280 housings and 280 housings are a prerequisite for 36mm pistons which is what the 3KGT and BMW run. I've got a set on my car too, but they won't do either of us any good in converting to Bimmer struts.

[jhm]

Jon, besides the larger shaft body (36mm vs 30mm), what are the differences/advantages of the larger Bilsteins?  I'm currently running the 30mm, and always interested in ways to improve the setup.  Thx.

[Kbhead]

280Z struts are longer and wider than the 240Z  struts.  Which means you can use a 240Z (30 mm) shock in a 280Z strut (if you have shortened the struts) but you can not use a 280Z (36 mm) shock in a 240Z strut (diameter is too small and no room for outside cooling fluid in the strut.   Some people put 280Z struts on their 240Z, to take advantage of the size difference which give them more shocks options.   

Advantage to the larger diameter shocks is; more fluids in the shock for pressure adjustments up and down and heat resistance.