So I got the measurements done today. A couple of pics:

https://cimg9.ibsrv.net/gimg/www.rx8...0a1e150fc.jpeg


https://cimg2.ibsrv.net/gimg/www.rx8...aa08e5479.jpeg



https://cimg4.ibsrv.net/gimg/www.rx8...6a66251cd.jpeg

so are you trying to setup the MCS with the same length and mounting?

you trying to troll me? :squint:

I submitted the dimensions and pictures to MCS earlier today.

MSC is assessing the situation. I’ll post details as they become available. Initially seems promising, but of course the devil is always in the details.

not trolling at all. was just curious what changes they are making because their website listed RX8 shocks already.

Maybe you should try reading the thread you started ... :hahano:

Ok, need to go back over to the shop to confirm a few things, but appears to be doable; 5-6 weeks and $3800 MSRP for 2WNR with the inverted tall RX8 shock tower rear setup, but final price to whatever you can negotiate with your preferred MCS supplier.


.

Nice to know that MCS is willing to play ball to do something that they haven't done before. Maybe I'll consider them for the next next autocross car...

Meant to post this awhile ago.. this was my solution to get to the rear adjuster for rebound.

https://cimg2.ibsrv.net/gimg/www.rx8...399813cfe.jpeg

Yeah, nice work there. Had I not done the inverted deal back in 2006 that may be where I’d be now. Technically wasn’t legal/clarified until quite a few years later and then I had no need. Alternatively I mentioned earlier the NC MX5 setup using the shorter NC shock tower would allow that without cutting the chassis. You would have to make & weld an aluminum cup for a spherical bearing top and also lose the top bolt-in part for tying it into the chassis/strut bar.

Still reviewing the situation though. Got to spend a little time looking at it again last night and the MCS shock has a protrusion for the gassing bolt that I’m worried might contact the the inner shock tower surface at or near full compression. On my Koni it’s much smaller and also inset into the top body cap below the OD (no protrusion). I was just looking at it with my shock and mount off the car, pulling it all the way over to the bottom opening in the mount with a flashlight . Really hard to see much.

I know mine doesn’t contact anywhere inside, but the actual clearance is hard to determine without maybe molding some clay onto the shock top in that area. I’ll have to get it mounted without spring and then jack it up to full compression to see how close it may be in reality. I know the shock doesn’t get over that far to the shock tower opening on the car. So it may not be any issue, but I’ll also ask them if there’s any alternative to having it protrude out like that.


.

maybe just have to cut a hole on the shock mounting cup where the gas bolt is for clearance? or add some more spacers at the bottom to move the shock over some?

No guarantee it will stay in any specific orientation with a spherical top bearing. Just being cautious before moving forward. Should have time this weekend to verify it fully. MCS rep is at VIR this weekend so it will be early next week before anything changes.

I had a similar thought
https://cimg9.ibsrv.net/gimg/www.rx8...c8f8861bae.jpg

haha.. I thought I was the only one. I just basically said.. we'll "because racecar" and opted to make it accessible..

Kind of still are; that’s the shorter NC MX5 shock mount

Ahh yeah I opted to keep the stock R3 mounts.. at the time I didn’t know any better to use Miata parts. Makes sense since this is just a longer Miata.

I haven’t ever seen this information before; has anyone ever checked their rear ride height at full shock compression and what dimension did you have? One of the things we did back in 2006 is perhaps make the rear shock body too short. At full shock compression my rear suspension goes into some crazy camber gain as the upper arms start going to an extreme angle. In the past this allowed me to run a really low ride height with soft spring rates; like 12” - 12.5” static from axle center to fender lip. I eventually concluded that was too low. So it looks like I can run a 1” longer body and then also longer shaft/droop length to match.

I’m also considering running tender rather than zero rate helper springs. The 1” longer body then also allows for a taller compressed spring stack height of 5” when the perch is near the shock mount and it helps to provide more clearance for compressed tender spring height. So at this longer shock length I’m measuring a ride height of 10.25” from fender lip to axle center when the shock would be fully compressed. It seems like this would be sufficient wheel travel from around a 13” static ride height, especially with stiff springs.

The other issue with the short shock body on my Koni is that the shock angle also starts getting extreme in that last 1” of shaft travel. The MCS gas bolt protrusion would definitely be an interference issue in the mount top in that case. However, at the 1” longer body length and then also running a wider spacer on the lower shock mounting post to move the bottom shock end further inboard there seems to be plenty of clearance.


So I’m thinking this is the solution, but would like to have some input from what other people might have for the vertical axle center to rear fender distance at full shock compression. This requires jacking up the rear suspension with the spring off the rear shock until it compresses fully.

TIA

.

You already found my measurements... which those were basically until hitting 'hard parts', aka something that I didn't want to hit. That was also taken with no shock in the car, so purely suspension arms and tire/wheel limiting travel, I'm not sure you can get anywhere near ride height with the droop you would want running a shock body short enough to actually compress that far.

Thing to consider: a lot of rules forbid moving the shock attachment point, this has been discussed in DSP and ruled that moving it isn't in the rules, although mine are slightly moved due to an offset spacer and I doubt anyone will protest me over it.

Edit: Not sure if I posted tire/wheel specs in the other thread either, 18x10 +38 RPF1 with 285/30/18 Hoosiers for that test.

I think maybe you’re confused by the Stock shock allowance. For SP the spacer change, or rather shock alignment because a spherical bearing is typically always narrower than the usual shock bushing width and spacers are required for filling in the gap as well as providing clearance for the spherical to rotate freely, is permitted. If you refer to the specific wording for shock allowances; suspension geometry is not changed nor is the attachment point changed on the rear upright or where the top mount attaches to the body. It simply accommodates proper fitment of the shock to not bind or have interference through the allowed range of travel as documented as such in my prior post. Try to remember that in Stock rate changes, height changes, etc are not specifically allowed like in SP.


which Stock/Street does state that an offset bushing is not allowed, but the intention of the those rules is to allow non-OE shocks, not specifically racing shocks. It also clarifies that the bushing on the shock is part of the shock, which the SP rule states that **any** shock is allowed. On a double A-arm or multi-link suspension the shock doesn’t affect geometry; camber curve, roll center, spindle/axle placement like a strut does. There are differences in the rules stated between struts and shocks for this reason. But even if it was a suspension bushing, offset suspension bushings are permitted in SP. I can’t comprehend why anyone would try to have the position it’s not allowed in SP since the only purpose is proper operation of an allowed part, not trying to get some kind of performance/handling advantage.

.

The main limitation for you in the DSP thread is due to not altering your fenders for clearance as permitted by the rules. The dimension you listed is quite a bit taller than what a OE length shock will do at full compression.

.

Lower shock spacers, as Mark stated, are legal in DSP. The stock mounting point is utilized and shocks are free.

John

I stand corrected... I could have sworn there was something in there making that illegal.

Well it’s not as obvious as the rules stating no aftermarket side skirts :rolleyes:

Anyone? Bueller???

seems like someone must have sprayed some Raid around because even the crickets are missing ...

Mark,

I measured this before I did the surgery to install spherical bearings in the rear shock hats because I needed to know how far down to position them relative to stock. Problem is, I can't find the sheet of paper I wrote all of the measurements down on :rofl:

I can measure it after I get back from Lincoln.