Dang, I was going to have you let me know when you have a TrueTrac to get rid of, I just grabbed a junkyard '10 Explorer diff on Thursday.

not sure whether to 😢 or 😡

.

I won't be selling mine. More than likely I'll end up keeping it and putting it in a carrier with a taller final drive for use on the track.

I ran the car at an Optima DriveAutoX this weekend (Asphalt surface / Yoko tires) and it was phenomenal. I guess I'll see how the car is in Toledo in a month or so but right now I'm not hating the helical.

Ha - who needs a Quick Change when you can just bring along an extra carrier!

Yep, it's so easy to swap diffs (takes about an hour and a half on my lift) that it's a bit of a no-brainer to have two available.

Sorry I couldn't find your wheels :(

It's all good. Maybe when winter rolls in and the brambles / grass die they'll turn up.

I'm always looking for wheels on Facebook/Craigslist anyway, so I'll see if someone happens to be inexplicably selling only two fancy wheels.

Much appreciated.

What an awesome build! Just read through the whole thread. You're 8.8 swap information was really helpful for me as I will be putting one in my car soon too.

I may have missed it, but what are the offset on your 18x11 wheels? I'm trying to fit a 315 on my car as well.

Just curious what your intention is that requires an R&P less than a 3.90 ratio?

Because maybe some people don’t recognize that’s the main (“only” imo) reason behind doing it.

@DCT8:

I was running an effective offset around +20 up front and +45 out back. I'm now on 18x12s with +20 offset front and rear. Either setup requires modification to the fenders.

My rationale for going to the 8.8 was the gearing change but also durability and parts availability. The RX-8 diff is pretty tough, but the Ford 8.8 has a lot more real world data for high power applications on sticky tires. There just aren't that many people really torturing the RX-8 rear end. That it's also lighter than the RX-8 unit is a nice benefit.

I have a 4-speed in my car so to have reasonable gear ratios for autocross I need something in the 4.11-4.56 range (I'm at a 4.30). What's nice with the 8.8 is I also put together a diff with a higher ratio (i.e. way lower numerically than 4.3) so I can do higher speed track stuff and just have to swap pumpkins.

Latest videos from the SCCA Finger Lakes Tour. Strano took top PAX both days and won SM convincingly.

That thing seems to spool QUICK. Love seeing the reactions from the other racers.

Yeah there isn't really any lag to speak of. You lead the turbo a small amount and then ride the traction control on corner exit. It's actually pretty easy to drive, but it gets from one element to the next FAST. And the aero effect is very real.

The car looks awesome! What internals are you running on the 2.5 now? I think I remember earlier on in the thread that you swapped some forged parts in.

Molnar forged rods and Super tech forged pistons. King bearings. Balanced crank. That's it.

Thanks for the info! I'm going to be using the same engine in my NC miata.

Are you using headstuds or different cams than stock. I don't think I remember reading anything suggesting you were but maybe the setup has changed.

Don't forget to key the crank!

With an engine having a lower redline (below 8000 rpm) a taller R&P may be required to achieve the necessary top speed, which is what I was referring to. So for this particular engine swap, it is more or less required for that reason. It wasn’t clear to me if some of the comments being made were considering the same 2.5L piston engine or not.

The RX8 rear differential can easily handle this power level with an aftermarket LSD such as an OS Giken (same part # as previous RX7TT). Obviously the Tochigi Fuji limited slip design is not intended for such abuse and really isn’t recommended for competition even with the NA Renesis engine imo. The RX8 differential case is stronger than the RX7TT, which was known to have some flex issues at a higher power level that a bolt on girdle assembly often resolved. It’s not necessary with the RX8 diff case.

Does the claim of it being lighter also include the weight of the welded-in steel mounting structure and axle assemblies that went along with the 8.8 swap? My understanding at the time is that it wasn’t, but maybe I’m wrong. Even if it is lighter, in a weight limited class such as SM this is likely not an issue at all given that the weight is both low and centered. In my general experience of playing the RX8 weight game to the extreme, removing weight from the rear is easy on an RX8 chassis and often works against offsetting what is 99.9% of the time the typical and expected front weight bias being greater than 50%.

The actual weak link is the Mazda axle stub that goes through the rear wheel hub/bearing. No matter how strong the rest of the axle assembly is, at a certain torque/power level it’s the axle stub that ends up shearing off between the wheel hub splines and the CV-joint end. This occurs before any of the other RX8 axle parts fail. The aftermarket axle does not replace this axle stub, it attaches to it at the CV-joint. Back in the day there was a 20B Turbo RX8 on here that started shearing the axle stubs around the 800 whp level. Down at the more typical 400-500 whp/400-450 wlb-ft likely to be used in SM this isn’t really an issue. Which the 8.8 swap still uses these same Mazda axle end stubs regardless.

So my only point of bringing it up was to make sure there was an understanding of when it may be needed and when not. There is history to support using the RX8 differential **when it’s suitable for the application**. Again, that being the key point.


https://cimg8.ibsrv.net/gimg/www.rx8...efb2e5522c.jpg
.
https://cimg9.ibsrv.net/gimg/www.rx8...b792a5f52.jpeg
.
https://cimg0.ibsrv.net/gimg/www.rx8...e9adc987e.jpeg
.

The weight includes the steel mounting structure. Still lighter than the RX-8 cast iron assembly.

No need to key the crankshaft unless you're using a dog-ring gearbox. With a synchro box the friction washers hold everything together just fine.

I'd like to be able to use the RX8 diff but it's not the best for my application. I'm going to be running a 1:1 high gear transmission and a 2.5 motor as well. I won't be revving it that high.

Glad to hear that! Looking forward to the weight savings.

What kind of traction control strategy do you use? Purely wheel speed, or is there some accelerometer or RPM delta data used?

It monitors driven wheel speed versus undriven wheel speed and targets a percent slip. It then cuts spark events based on what it sees (more slip means more spark events cut). I currently don't have any accelerometers referenced.

It works surprisingly well and doesn't affect the balance of the car. If we lean on the traction control from a standing start it will basically pull 0.72-0.76 longitudinal g's all the way through first and second.

Responding to DCT8s PM here since I like to keep all this stuff out in the open.

Camshafts are a set of Kelfords that used to be sold by Dynotronics under their "Integral 1.5" name. They are a relatively mild cam. Idle is like stock but they make a lot more power up top than stock. Valve springs are Supertech. Stock retainers, stock valves, no head porting or even port work.

I am running ARP studs. Lots of people in the MZR/Duratec/Ecoboost/DISI world think they are weaker than the factory bolts. I don't believe that to be the case, I think the issues people have with them are because they don't torque them properly. They are fussy to get torqued correctly. I like them because the factory head bolts are not re-usable once torqued, and I had the head off the engine several times during the build. If I weren't going for the power level I have, I would have just used stock bolts. Bottom end is stock other than having the crank balanced, removing the gear for the balance shafts, and keying the snout. Stock bolts holding the mains. Oil pan is a custom baffled deal.

Pistons are Supertechs, I think they're not sold anymore. They are around 10.5-10.7:1 static CR.

I rev the motor to 7600. Probably higher than I should but it gives me the MPH I want with the gearing I want.

That's how I have the Megasquirt on my M3 set up - I added a switch to turn it off and on and a pot to adjust the slip %. I've mostly played with it in the snow and found that it has trouble stopping wheelspin if I get on it too hard. On dry pavement I don't have the kind of power that would light up the tires after 1st gear, so I haven't used it much there.