The Official "RX8 in DSP" Thread
#1001
On the RX8Performance motor mounts, make sure if any of you are using them that you install the thick washer under the motor mount bracket. Without it in place you are effectively lowering the engine, which is illegal for SP. There was some confusion around whether it went above or below the bracket, and after taking measurements, it should definitely be installed as pictured below.
Engine position may not be changed.
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#1002
It’s the metal bushing at the bottom of the upright that the LCA tapered ball joint stud fits into. It’s not adjustable, just the tapered hole for the ball joint stud is offset to kick the bottom of the upright outboard and induce more static camber.
The S1 bushing and stud size are different, easier to swap in the S2 parts than modify the bushings to fit the S1.
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The S1 bushing and stud size are different, easier to swap in the S2 parts than modify the bushings to fit the S1.
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#1003
I was just in the MM parts store to price out fresh arms, and saw they do have a new competition part for a S1 specific lower spindle offset bushing. Called to confirm my eyes weren't deceiving me. The S2 and NC is 30mm, and the S1 needs a 27mm. They have the parts being made, just not quite on hand (even though you can order them).
So I’m still a bit puzzled by the previous motor mount comments and picture. It looks like there’s some kind of thick spacer being used that I’ve never seen before. This is what they look like on the website and same for every set I’ve ever seen:
Compared to this picture:
#1004
So since I was messing around with the rear suspension today, I decided to bring some closure to the rear MR debacle. I’m sure that my measurements aren’t exact, but I came up with 0.84 measuring the actual shock stroke vs. axle end centerline protruding out from the hubface slightly. Which is close enough to the 0.855 rear MR that Koni determined and has been using since late 2004/early 2005 when Clyde took the Team WTF RX8 there for the prototype shock build for me to be confident in using that value.
In addition to the shock swinging through some angle arc, it’s also located well inboard of the hubface. So the shock is technically at a shorter distance from the rotation center than the hubface, and traveling a shorter vertical distance than the hubface for a given arc angle. Was pretty sure that a rear 1.00 MR wasn’t probable and proved it well enough for myself today. Would have needed to be off around 0.35” between the two measurements to have calculated a 1.00 MR. I’m not that blind yet
So for every 1” vertical rear wheel travel the rear shock/spring travel is 0.855”, or pretty close to that.
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In addition to the shock swinging through some angle arc, it’s also located well inboard of the hubface. So the shock is technically at a shorter distance from the rotation center than the hubface, and traveling a shorter vertical distance than the hubface for a given arc angle. Was pretty sure that a rear 1.00 MR wasn’t probable and proved it well enough for myself today. Would have needed to be off around 0.35” between the two measurements to have calculated a 1.00 MR. I’m not that blind yet
So for every 1” vertical rear wheel travel the rear shock/spring travel is 0.855”, or pretty close to that.
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I'm actually using 0.855, though I had the same thought that it didn't make much sense that it wouldn't be somewhere around 1. I got the number from here.
I hadn't put too much thought into it before, and just sorta accepted secondhand Koni info, but let's see if we can justify this:
Assuming that the distance from the contact patch to the shock mount on the upright is ~6" (just making up numbers that don't seem too ridiculous) and the rear wheel gains 2 degrees of camber in 4" of travel, that already works out to a MR of ~0.94 due to "lost" motion from camber gain. From there, it only takes a couple degrees of shock angle to get down to 0.885. This is probably worth measuring.
Anyway, changing it to 1 drops my numbers by about 2% because I run huge bars, but for me, the actual number doesn't matter as much as the trend that I use for myself as a tuning tool (obviously it's a better tuning tool if all the numbers are right). It would be nice if we were all on the same page though!
I hadn't put too much thought into it before, and just sorta accepted secondhand Koni info, but let's see if we can justify this:
Originally Posted by [b
TeamRX8]
RX-8 motion ratios:
front = 0.752
rear = 0.855
I'm sure that Mazda Motorsports can confirm the exact rates for the springs. I was simply curious to know how the information was obtained.
RX-8 motion ratios:
front = 0.752
rear = 0.855
I'm sure that Mazda Motorsports can confirm the exact rates for the springs. I was simply curious to know how the information was obtained.
Assuming that the distance from the contact patch to the shock mount on the upright is ~6" (just making up numbers that don't seem too ridiculous) and the rear wheel gains 2 degrees of camber in 4" of travel, that already works out to a MR of ~0.94 due to "lost" motion from camber gain. From there, it only takes a couple degrees of shock angle to get down to 0.885. This is probably worth measuring.
Anyway, changing it to 1 drops my numbers by about 2% because I run huge bars, but for me, the actual number doesn't matter as much as the trend that I use for myself as a tuning tool (obviously it's a better tuning tool if all the numbers are right). It would be nice if we were all on the same page though!
Last edited by TeamRX8; 05-19-2019 at 04:27 PM.
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AreAxeAte (08-25-2019)
#1005
I have no idea how you measured the rear MR at 0.84:1. The hub is a rigid body. How far inboard the shock is has no bearing on the MR. The video below is a good visual and you can see the wheel traces the same path as the lower shock mount, as it must... rigid body.
I measured it several months ago and got 0.98:1. If the shock were mounted to the lower control arm at the same lateral distance from the inner pivot the MR would be about 0.85. That's how I assumed everyone came up with that number.
I measured it several months ago and got 0.98:1. If the shock were mounted to the lower control arm at the same lateral distance from the inner pivot the MR would be about 0.85. That's how I assumed everyone came up with that number.
Last edited by John V; 05-19-2019 at 07:47 PM.
#1006
Sorry, just rechecked enough times to have a big headache, lol; full travel and around ride height shorter travel. Not getting anywhere near 1.0, always around mid 0.8x
My rear shock has 6” total shaft travel and from full drooped to fully compressed the vertical wheel travel was just a bit more than 7”. I did that as a double-check because the amount of measurement error isn’t likely to be as magnified like it would be for a small measurement
the hub is not traveling perfectly vertical, it’s traveling in an arc while also rotating in camber change. In camber gain the axle end is rotating up gaining some travel while the shock mount end is rotating down losing some travel is part of it. It’s hard to measure by yourself. That’s why I did it over and over again, rechecking the measurements over and over again. Using a small square with level bubble to measure down from the fender lip to the level square surface at the axle.
At 0.855 you’re only talking just a bit more than an 1/8” difference between the wheel and the shock for every 1” wheel travel. I doubt you’re eyes are that sharp watching the vid. What you do see at the bottom shock mount is the angle change in the gap between the lower shock mount and the upright. So clearly the hub is angling relative to the shock just as I described above.
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My rear shock has 6” total shaft travel and from full drooped to fully compressed the vertical wheel travel was just a bit more than 7”. I did that as a double-check because the amount of measurement error isn’t likely to be as magnified like it would be for a small measurement
the hub is not traveling perfectly vertical, it’s traveling in an arc while also rotating in camber change. In camber gain the axle end is rotating up gaining some travel while the shock mount end is rotating down losing some travel is part of it. It’s hard to measure by yourself. That’s why I did it over and over again, rechecking the measurements over and over again. Using a small square with level bubble to measure down from the fender lip to the level square surface at the axle.
At 0.855 you’re only talking just a bit more than an 1/8” difference between the wheel and the shock for every 1” wheel travel. I doubt you’re eyes are that sharp watching the vid. What you do see at the bottom shock mount is the angle change in the gap between the lower shock mount and the upright. So clearly the hub is angling relative to the shock just as I described above.
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Last edited by TeamRX8; 05-20-2019 at 12:48 AM.
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AreAxeAte (08-25-2019)
#1008
apparently I screwed up over a dozen times measuring it every which way but loose then
Too bad they didn’t give you an actual value rather than a marketing generality-speak.
Did you divide 6 by 7 yet? I can’t be off by a whole inch. Multiple times.
Too bad they didn’t give you an actual value rather than a marketing generality-speak.
Did you divide 6 by 7 yet? I can’t be off by a whole inch. Multiple times.
#1009
Not to nitpick, but they do say "approximately one"... And the MR is indeed closer to one than the rear suspension used in the NA/NB or FD RX-7 (internet says ~0.70). Seems like Engineering gave sales only enough information to only partially suffocate themselves, not completely hang themselves.
To be blunt, if you don't believe Team, you should do your own measurements and verify.
To be blunt, if you don't believe Team, you should do your own measurements and verify.
#1010
Not to nitpick, but they do say "approximately one"... And the MR is indeed closer to one than the rear suspension used in the NA/NB or FD RX-7 (internet says ~0.70). Seems like Engineering gave sales only enough information to only partially suffocate themselves, not completely hang themselves.
To be blunt, if you don't believe Team, you should do your own measurements and verify.
To be blunt, if you don't believe Team, you should do your own measurements and verify.
I wonder if the difference is that I didn't go as far into bump as he did? The rear camber gain is so extreme at the upper end of bump travel that I can see things getting really wacky there. I didn't measure up there because my setup has progressive bump rubbers limiting the rear suspension from getting that much into compression.
Last edited by John V; 05-20-2019 at 09:01 AM.
#1011
Again, maybe I screwed up over and over again for several hours just making sure only because some guy sitting at a computer questioned it. Not just me, the guy at Koni Motorsports too who did this for a living.
All your assumptions were accounted for. I intentionally didn’t measure from the ground because if the chassis moves on the jackstands it will throw the numbers off. I determined the actual shock measurement change directly on the shock. The first round of measurements didn’t use the last 1” shock travel. The shorter measurements were in the 11.5” -13.5” racing ride height range. The hub assy as a whole is travelling in an arc and the hub itself is rotating; any rods sticking off of those points are also arcing/rotating. Which you want the actual shock shaft distance change, not the vertical distance change. The axle change needs to be true vertical. That’s why I used a bubble level square to measure that axle distance change relative to the fender lip.
I’m done here. Use whatever MR you want.
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All your assumptions were accounted for. I intentionally didn’t measure from the ground because if the chassis moves on the jackstands it will throw the numbers off. I determined the actual shock measurement change directly on the shock. The first round of measurements didn’t use the last 1” shock travel. The shorter measurements were in the 11.5” -13.5” racing ride height range. The hub assy as a whole is travelling in an arc and the hub itself is rotating; any rods sticking off of those points are also arcing/rotating. Which you want the actual shock shaft distance change, not the vertical distance change. The axle change needs to be true vertical. That’s why I used a bubble level square to measure that axle distance change relative to the fender lip.
I’m done here. Use whatever MR you want.
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Last edited by TeamRX8; 05-20-2019 at 11:29 AM.
#1012
Well on a more positive note, further measurements showed that whacking the rear fender for 315 tire clearance is easily accomplished within the rule allowance.
At the front the rear pinch weld and front corner light look like potential issues. I don’t have any problem with cutting the fender, except that it might be easier to deal with the corner light by flaring/rolling it instead. Not sure how the fender cutting rule affects a corner light if the fender cut goes through the middle of the corner light? Are we allowed to just cut that part off too?
At the front the rear pinch weld and front corner light look like potential issues. I don’t have any problem with cutting the fender, except that it might be easier to deal with the corner light by flaring/rolling it instead. Not sure how the fender cutting rule affects a corner light if the fender cut goes through the middle of the corner light? Are we allowed to just cut that part off too?
#1013
Well on a more positive note, further measurements showed that whacking the rear fender for 315 tire clearance is easily accomplished within the rule allowance.
At the front the rear pinch weld and front corner light look like potential issues. I don’t have any problem with cutting the fender, except that it might be easier to deal with the corner light by flaring/rolling it instead. Not sure how the fender cutting rule affects a corner light if the fender cut goes through the middle of the corner light? Are we allowed to just cut that part off too?
At the front the rear pinch weld and front corner light look like potential issues. I don’t have any problem with cutting the fender, except that it might be easier to deal with the corner light by flaring/rolling it instead. Not sure how the fender cutting rule affects a corner light if the fender cut goes through the middle of the corner light? Are we allowed to just cut that part off too?
The fronts, I had to do some minor fender trimming and I cut the corner light's rear mounting surface off of the fender. But I didn't modify the light. I don't see any allowance in the SP rules to modify the light.
#1014
It must be positive-reinforcement day, lol ...
In addition to cutting out as much sheetmetal as permitted, I have an extra hood and trunk lid to strip down to bare aluminum too
there wasn’t anything about cutting hoods that formed part of the fender either i.e. BMW Z3, until it was clarified. What if the allowed fender cutting removed it entirely? What is the purpose of allowing fender, fender liner, etc. modification for tire clearance if 3” long section of plastic corner light is sticking out there begging to get torn off? I suppose it will need to be submitted for clarification about what the actual intent of the rule is in that regard.
Just so we’re clear, all I did is see where the vertical hub plane is at ride height to determine the permitted fender modification area, lifted the suspension until the shock was fully compressed, laid a half circle out on the body panel 1/2” larger than the tire OD relative to the fully compressed axle center, and then drew lines down to the the lower well opening to determine the permitted cutting clearance area.
That works well in the rear, the front is a bit trickier due to the additional clearance needed for the tires being steered/turned and the front hub plane being further outboard relative to the bodywork, but it’s a good starting point. Not really concerned about DOT regulations or style points ... maybe I’ll throw on some aluminum sheetmetal hoops to keep the rocks at bay.
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In addition to cutting out as much sheetmetal as permitted, I have an extra hood and trunk lid to strip down to bare aluminum too
there wasn’t anything about cutting hoods that formed part of the fender either i.e. BMW Z3, until it was clarified. What if the allowed fender cutting removed it entirely? What is the purpose of allowing fender, fender liner, etc. modification for tire clearance if 3” long section of plastic corner light is sticking out there begging to get torn off? I suppose it will need to be submitted for clarification about what the actual intent of the rule is in that regard.
Just so we’re clear, all I did is see where the vertical hub plane is at ride height to determine the permitted fender modification area, lifted the suspension until the shock was fully compressed, laid a half circle out on the body panel 1/2” larger than the tire OD relative to the fully compressed axle center, and then drew lines down to the the lower well opening to determine the permitted cutting clearance area.
That works well in the rear, the front is a bit trickier due to the additional clearance needed for the tires being steered/turned and the front hub plane being further outboard relative to the bodywork, but it’s a good starting point. Not really concerned about DOT regulations or style points ... maybe I’ll throw on some aluminum sheetmetal hoops to keep the rocks at bay.
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Last edited by TeamRX8; 05-21-2019 at 12:51 AM.
#1015
Probably best to submit a letter for clarification of the rule, regarding the front corner light.
What I did was cut the rear mount off of the fender for the corner light and left the unmodified corner light in place. To keep it from popping out and to hold the bumper corners to the fender, I used those ricer bumper O-ring things (no idea what they're called) with the rubber o-ring covering the outside of the corner light.
The bigger problem is the pinch seam behind the front tire. I think David Colletti found a way to align the car and limit steering so it's a non-issue but he doesn't post here often.
What I did was cut the rear mount off of the fender for the corner light and left the unmodified corner light in place. To keep it from popping out and to hold the bumper corners to the fender, I used those ricer bumper O-ring things (no idea what they're called) with the rubber o-ring covering the outside of the corner light.
The bigger problem is the pinch seam behind the front tire. I think David Colletti found a way to align the car and limit steering so it's a non-issue but he doesn't post here often.
Last edited by John V; 05-21-2019 at 06:02 AM.
#1016
Yes, I believe the same Mustang limiting spacers the FD3 guys use on their steering rack also work on the RX8. Thought I had posted it before, but here it is again:
https://www.rx7club.com/suspension-w...miter-1117648/
https://lmr.com/item/LRS-3504HDW/79-...Limiter-6-Pack
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https://www.rx7club.com/suspension-w...miter-1117648/
https://lmr.com/item/LRS-3504HDW/79-...Limiter-6-Pack
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Last edited by TeamRX8; 05-21-2019 at 11:35 AM.
#1018
#1020
Probably best to submit a letter for clarification of the rule, regarding the front corner light.
What I did was cut the rear mount off of the fender for the corner light and left the unmodified corner light in place. To keep it from popping out and to hold the bumper corners to the fender, I used those ricer bumper O-ring things (no idea what they're called) with the rubber o-ring covering the outside of the corner light.
The bigger problem is the pinch seam behind the front tire. I think David Colletti found a way to align the car and limit steering so it's a non-issue but he doesn't post here often.
What I did was cut the rear mount off of the fender for the corner light and left the unmodified corner light in place. To keep it from popping out and to hold the bumper corners to the fender, I used those ricer bumper O-ring things (no idea what they're called) with the rubber o-ring covering the outside of the corner light.
The bigger problem is the pinch seam behind the front tire. I think David Colletti found a way to align the car and limit steering so it's a non-issue but he doesn't post here often.
#1022
The brake stuff is looking good overall, but still need to find someone with a big enough lathe to trim the ODs and widths down to the OE dimensions allowed by the rules. Before I started this it never occurred to me/never previously noticed that the brake rotor has a different hubcentric size than the wheel; 2.83”/71.88mm. The hubcentric for the new hats is 2.80”, so also have to get those IDs turned slightly before stuff is going to bolt on.
#1025
some of us should consider running for Congress
Just saw the Mineral Wells Pro is in my backyard this weekend, but need to work on the RX8 instead.
So doing some calculations based off actual weights and measurements, but approximating density and assuming I didn’t mess up the calculations a half dozen times in a row came up with these initial estimates:
11.95” OD x 0.95” wide 2-pc front rotor - 11.6 lbs **actual
11.89” OD x 0.71” wide 2-pc rear rotor - 8.2 lbs **actual
These are full face rotors; no slots, drilling, etc. An SM build could take advantage of 11.75” front & rear “MX5” sizing to save some more, plus those are standard rotor ODs so less machining involved than OE RX8 dimension limitations of SP. For SP I have to trim the next closest sizes down both in diameter and thickness to achieve these specs.
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Last edited by TeamRX8; 08-22-2019 at 12:26 AM.