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Well I might be fudging too much on a wing and a prayer, lol. yeah, probably, but there are some savings for sure. I have to guess some because it's not really possible for me to accurately know how much weight reduction the rotor machining will achieve until weighing them afterword. I did make some general assumptions, but getting rid of the entire steel OE rear caliper and mounting bracket is a good chunk of weight in itself.
By my calcs and making some assumptions like equal force distribution until the ABS software kicks in it appears to shift some bias to the front; 64.4% front OE bias calculated vs 68.4% calculated for these revisions. The ABS should be able to handle that and considering there is likely more WT to the front using the R tires coupled with more weight reduction in the rear than the front my expectation is it will be fine. Of course I still have to get it all on, functioning, and the rest of the car done too.
Four alloy hats, rotors, and mounting bolts (solid mount, not dynamic) was about $760 shipped. Both rotors are 12.19" OD and need trimming down to the min OE dimensions. The rear rotor is 0.81" wide and will work like that, or it can be cut down to the 0.71"/18mm OE width for min weight and then have some brake pad shims to make up for the minimum recommended 0.79" rotor width of the caliper (0.08" total,range is 0.79" - 0.86' rotor width). Front rotor comes at 1.10" wide, but it's got plenty of meat to take it down all the way to the 0.95"/24mm OE min or the RB calipers can squeeze in another mm or so to call it 1" even.
The front rotor I really wanted though would have chopped off several more lbs, but the max size was only 11.75" The face was plenty thick and it's a specialty iron alloy for severe heat duty with only16 curved vanes; 11.75" OD x 0.99" wide @ 7.1 lbs. With hat and hardware that be around 9 lbs, I'd be all over that in a Miata. Or maybe an SM RX8
edit: so I had failed to notice the brake rotor hubcentric is different than the wheel. i measured 2.842” OD and the hats are 2.8” ID. So just some minor cutting to get them right.
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If you are looking for other areas of unsprung weight to remove, the MX5 front spindles are a direct replacement and a bit (maybe a pound?) lighter. They also have the advantage that you can run the Mazda motorsports offset lower bushings to increase negative camber.
The ruleset only allows us to swap parts within the the 2004-2011 RX8 model line and some things are assembly only. Like you can swap between an S1 and S2 engine, but you can’t interchange internal parts trying to make a hybrid engine. So the MX5 upright would not be an allowed modification. The bushings are allowed and I did it on my S1, but it was expensive and a pita to make work. It’s a straight deal if you swap in S2 LCA and uprights though, which both are permitted. Not cheap even buying parts through Motorsports, or you could chance buying them cheaper off a parts salvage and hope nothing is bent.
Good to know, thanks. I happen to have a 2009 parts car.
AC
Originally Posted by TeamRX8
The ruleset only allows us to swap parts within the the 2004-2011 RX8 model line and some things are assembly only. Like you can swap between an S1 and S2 engine, but you can’t interchange internal parts trying to make a hybrid engine. So the MX5 upright would not be an allowed modification. The bushings are allowed and I did it on my S1, but it was expensive and a pita to make work. It’s a straight deal if you swap in S2 LCA and uprights though, which both are permitted. Not cheap even buying parts through Motorsports, or you could chance buying them cheaper off a parts salvage and hope nothing is bent.
Some long-planned exhaust mods; parts were sitting in the corner for the last year or so.
Hoping that replacing the typical small center auger muffler (Moroso spiral flow) with a full length 4” auger insert down the the tunnel will let me swap out the packable dual rear mufflers with dual straight pipes instead, each also having a small auger insert. I also lost the ultra high flow cat that was previously on there before though. So I’m not entirely sure if it will pass sound or not. Might be wishful thinking for it to be ok based on past readings, but only one way to find out.
Also intending to remove the 3 slip-fit long tube extensions off the back end of the header and run it as a short tube instead by moving the collector up with a single 3” tube extension behind it. I still need to find that box, lol.
Haven’t weighed the whole thing out yet, but that configuration of the header and the angled piping to the center tunnel is four pounds lighter than my previous emission legal STX exhaust of race manifold header and HJS racing cat converter. Expecting it to be lighter overall with the weight more centered between the axles. Despite going for every possible ounce, it’s not my goal to be the lightest RX8 on the scales, but the best balanced for a reasonably low weight.
Looking for more information on fully compressed rear ride height (without spring, fully bottomed shock):
Originally Posted by roflcopter
From my measuring, I determined some limits as well as what I think the static numbers are going to be for suspension travel. I'd love to get some feedback on what others have seen to make sure I'm in the ballpark before ordering piles of parts.
Ok, well I have to re-order all the brake parts again. Had used Autoplicity in the past with great results, but they changed or something; went full fubar this time (never, ever go full fubar!). Supposedly everything was in stock, but the order wasn’t moving then took just as long to get it cancelled. Lost 1.5 - 2 weeks trying to save a $5
the roll centers are ever so slightly different. I can't remember which direction off the top of my head.
The S2 uprights can also use the MX-5 offset LCA bushing which gives you move camber.
I was unaware there were offset bushings for an LCA. More direct camber adjustment would also mean more caster adjustment too, correct? I know the two are not independent of one another for the 8. Or so the folks with alignment tools have said.
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.
Is the roll center altered in a way that is advantageous though? With the offset UCA bushings you can get plenty of camber and pretty much whatever caster you want with all S1 parts... -3.3 camber at -7.5 caster on my car, could go further if I wanted.
Is the roll center altered in a way that is advantageous though? With the offset UCA bushings you can get plenty of camber and pretty much whatever caster you want with all S1 parts... -3.3 camber at -7.5 caster on my car, could go further if I wanted.
Mazda press release for the S2 stated that they lowered the front roll center a little from the S1.
Originally Posted by MilesJ
Tire Rack now has 2 good flow-formed DSP wheels in stock
Flow One F2 - Gloss Gunmetal Metallic and Gloss Black
18x10.5 +50, 22.35lbs, $287.30
18x11 +52, 22.8lbs, $275.33
Both are on the website as rear only options on the newest Mustangs.
If you let them know you want to use them on an RX8 they should get you the rings and lugs that work for our cars instead of the Mustang stuff.
That's awesome. That still might be too much offset, but at least you can fix it with spacers.
+43 is about perfect for 10.5”, but I’m not sure the extra weight is worth it for the added width over similar priced, lighter 10” options. At least for DSP, but then I’m not convinced that anything over 295 is the way to go either. I’m still not keen on the added mass and momentum for anything over 275 even. I may learn otherwise, but my goal is to try and skin the cat using balance, weight, and accel/decel factors. Still thinking about squeezing 275/35-17 on my 13.8 lbs x 9” wide BC wheels. That’d be about 55 - 60 lbs less unsprung rotating mass over a set of those wheels with 315 tires.
The 315 Hoosier is a much, much better tire than the 285/30/18 or the 295/30/18 (which is one of the soggiest, laziest tires I've ever driven). After talking to the Hoosier guys about it I have some theories as to why the 315 is so much faster and easier to drive than the other 18" choices but nothing concrete. I personally wouldn't bother building the car (DSP or otherwise) around any tire other than the 315. The 275/17 wasn't competitive grip-wise on the DSP BMWs compared to BMWs running the 315, but maybe it's a different story on the lighter RX-8. Though the E36s running that 275 were about the same weight as the DSP RX-8s.
I'm at +40 on my front wheel fitment (18x11) to give clearance to the upper shock mount, and +43 in the rear, so yes you'll need spacers with what tire rack is offering. No biggie. My wheels are Mustang fitment (+53) so pretty close to Tire Rack's wheels.
Originally Posted by roflcopter
With the offset UCA bushings you can get plenty of camber and pretty much whatever caster you want with all S1 parts... -3.3 camber at -7.5 caster on my car, could go further if I wanted.
If you want to slam the front end and run the car super stiff to compensate you can get lots of front camber. If you want to run a softer setup with a little more ride height you'll end up camber limited. I haven't had my car running long enough to do any meaningful data collection but -3.3 is probably short of what you ultimately will want. The A7 responds very favorably to static camber in the -4 range in my experience (and not just on strut cars).
If you want to slam the front end and run the car super stiff to compensate you can get lots of front camber. If you want to run a softer setup with a little more ride height you'll end up camber limited. I haven't had my car running long enough to do any meaningful data collection but -3.3 is probably short of what you ultimately will want. The A7 responds very favorably to static camber in the -4 range in my experience (and not just on strut cars).
The -3.3 seems to be a good balance of wear to performance, the car isn't at the point of sacrificing lots of money for a few hundredths yet. One thing to remember is that the large amount of caster helps a lot when turning, without giving up any straight line braking ability.
The 275/17 wasn't competitive grip-wise on the DSP BMWs compared to BMWs running the 315, but maybe it's a different story on the lighter RX-8. Though the E36s running that 275 were about the same weight as the DSP RX-8s.
well the 275/35-17 is what Brian Heitkotter had on when he won DSP in a BMW, but I hear what your saying and will keep it for future consideration.
We also can’t directly address the pinch weld at the back of the front wheel well like you did for SM either. The other thing is the Renesis doesn’t kick out much more than 150 lb/ft torque to the rear wheels, less at lower rpms. I think that’s more of an issue than the total weight factor.
Ps: anybody who is serious about DSP could care less about wear to performance considerations and other rationalized baloney sammiches ... also calling Bob Smith on that overly generalized caster claim too.
The 315 Hoosier is a much, much better tire than the 285/30/18 or the 295/30/18 (which is one of the soggiest, laziest tires I've ever driven). After talking to the Hoosier guys about it I have some theories as to why the 315 is so much faster and easier to drive than the other 18" choices but nothing concrete. I personally wouldn't bother building the car (DSP or otherwise) around any tire other than the 315. The 275/17 wasn't competitive grip-wise on the DSP BMWs compared to BMWs running the 315, but maybe it's a different story on the lighter RX-8. Though the E36s running that 275 were about the same weight as the DSP RX-8s.
I'm part of the unwashed masses (haven't driven many Hoosier cars aside my own) but if the 295 is soggy, I can't imagine how the 285 or 315 must be. Maybe I'll pick up a set of 285s to try... it would be difficult to fit 315s under my car without actually trying.
Mark, Brian is Brian and he won because he's Brian , I'd argue he would have been even faster on 315s than he was on 275s. The class is a different pace now as well.
The 315 can fit under DSP rules with careful steering limiting and wheel offset and alignment. David Colletti is on this forum and he and I worked on that during the offseason and he isn't having any problems with tire fitment. edit: But yes, you need to make some fender modifications to make them fit. Tamra posted a few pictures on how they did their car, I have seen what David did with his car and it's a little less invasive but still works.
After doing some quick napkin calculations it would seem an N/A RX8 would be able to use a much smaller filter setup than you are planning to run with your setup. By my numbers it would be overkill to have two filters in the configuration you are planning, am I off on my calculations or was the plan to go way big?
Sorry, wasn’t around much when this was posted. My intake is not designed around flow capacity. It’s designed around smooth laminar (low velocity) flow entering the MAF tube. Since we can’t remove the plastic shroud the area available for a filter isn’t much larger than the MAF tube itself. A proper large radius airhorn is only possible in an enlarged filter box housing within the engine compartment. That’s essentially what I had in STX. Which I’m also running fine filtering socks over the main filters too. It’s not like there’s any real negative to having extra surface area, particularly wrt engine throttle response.
Mark, Brian is Brian and he won because he's Brian , I'd argue he would have been even faster on 315s than he was on 275s. The class is a different pace now as well.
The 315 can fit under DSP rules with careful steering limiting and wheel offset and alignment. David Colletti is on this forum and he and I worked on that during the offseason and he isn't having any problems with tire fitment. edit: But yes, you need to make some fender modifications to make them fit. Tamra posted a few pictures on how they did their car, I have seen what David did with his car and it's a little less invasive but still works.
Well I appreciate your patience with my resistance to the idea, which you’ve got me thinking about it some more. Maybe it just bums me out to have multiple sets of 10”/10.5” rims stacked up waiting for tires, lol.
Well I appreciate your patience with my resistance to the idea, which you’ve got me thinking about it some more. Maybe it just bums me out to have multiple sets of 10”/10.5” rims stacked up waiting for tires, lol.
I'm not saying you're wrong. Just saying I don't know anyone who switched to the 315 and went slower. Or anyone who hated the feel.
05-03-2019, 04:43 PM
The face was plenty thick and it's a specialty iron alloy for severe heat duty with only16 curved vanes; 11.75" OD x 0.99" wide @ 7.1 lbs. With hat and hardware that be around 9 lbs, I'd be all over that in a Miata. Or maybe an SM RX8 
