So i'm in the process of installing a CD009 Transmission with Ford 8.8 Differential. I would like to rebuild the Ford 8.8 and install gears that make sense. It currently have 3.73 in the differential and I purchased 3.55 ratio. Im looking for advice and rear world driving with this set up and what everyone has run and like. From what I gathered the 3.55 will be close to stock transmission and 4.10 gear. Thank you all for your input and time in advance.

The car is a street car. 13b Half bridgeport and SXE366 turbo. Full 3.5inch turbo back. When turned on E85, whatever RWHP it makes. So lets say 600WHP+

 

Here's a comparison of the two I did. 3.55 is similar at the ends to stock, with closer (more) ratios in between), 3.73 stretches it out a bit. That 6th year will be very tall.

 

For whatever reason the image shows in preview, but isn't showing up in the post right now sorry.

 

Thank you for that, that is an awesome graph! Looks like the 3.55 is the way to go unless someone has more input on real world driving and racing between the 3.55 and 3.73 with the CD transmission.

 

Must-reads:

https://motoiq.com/project-fd-rx7-re...ssion-upgrade/

https://motoiq.com/project-fd-rx7-re...-differential/

https://motoiq.com/project-fd-rx7-re...c-lsd-and-wpc/

https://motoiq.com/project-fd-rx7-re...irs-mount-kit/

I'm very happy with the CD009 and 3.55s at 420whp (soon to be 600whp+). Even at this power level, it's pretty easy to spin the tires in 2nd gear. A 3.73 will not put the power down as well in 2-3-4th gear as the 3.55. I personally wouldn't go with anything shorter than a 3.73 and feel the 3.55 is ideal unless you want to shift more for the sake of "driving engagement" and to stay busy.

I HIGHLY recommend the Eaton TruTrac torsen LSD. It is phenomenal, silent, and makes drifting effortless if you want.

 

What is the part number on the TruTrac that works with the 8.8?

 

TT70P52670 - aka:

Eaton 913A561 Ford 8.8" 31 Spline Detroit Truetrac Differential

 

Would you not run a wavetrac so you don't single spin like the factory diff in wet weather or unloading a corner?

I went back to Detroit in my utility after having a truetrac clone as although it was smooth and ok most of the time it failed exactly when I wanted it to work.

I think a Detroit would be unpleasant in the fd although would probably help for drifting.

 

I have a Wavetrac that I'm putting in my NSX to replace my OS Giken, which is way too aggressive even after tuning the plate configuration, using custom OSG plates, custom preload springs and internal resistance springs to soften and loosen it up.

The TrueTrac is awesome. I had one in a 600whp daily driven Mustang, I competed in Mustangs on slicks that had them, and it's a much better diff than the Torsen T2 and T2R, which are both MILES better than the stock FD LSD. Ive driven my mustang in snow and frequent rain and have never had the issues that typically plague torsens or that many people assume they do in the wet or unloaded. I've never heard of a TrueTrac fail either, and I've personally seen or had a T2 and T2R fail on track, although the T2R had an update 15? Years ago and never had a problem after thet... A 350Z (Nismo?) Torsen lost all of its bias ratio and locking ability when the inside rear tire became even slightly unloaded. The TrueTrac is a game changer, is incredible, and does not suffer from any of these issues. It puts down power out of a corner or enables me to slide it in the dry or wet with a lot of control.

I'm looking forward to testing the Wavetrac, but until then, I have a lot of extremely positive experience with the TrueTrac on the street, track, and racing.

 

The higher the weight bias on the drive axle, lower relative roll stiffness on the drive axle and being IRS as opposed to beam all help the gear type diffs. I just figured if they make both where you are the wavetrac would be the choice.

The parallel cross gear designed centres are definitely more robust than the old torsen designs like the factory FD.


When I get back to my FD I'll be adding springs to the cusco for higher breakaway. Obviously the OSG is pretty aggressive and it's not required with the rear weight bias of the NSX.

 

Generally-speaking, I agree. Solid-axle Mustangs typically are the opposite, with less weight on the rear axle, often higher roll stiffness to overcome the understeer and poor weight distribution, while being a solid/stick/beam-axle. Despite this, I've raced solid-axle S197 platform Mustangs with proper clutch-type/Salisbury differentials, where we frequently adjusted the ramp angles, clutch packs, etc.. , Detroit lockers, and many Torsens (T2, T2R, TrueTrac). While clutch-type LSDs with ramps are hands down the best and offers the most adjustability; the Eaton/Detroit TrueTrac is my GO-TO LSD for 99% of Mustangs whether they're on the street, track, or race cars.

I'm very intrigued by the Wavetrac and am looking forward to replacing my OS Giken clutch-type/Salisbury with it in my NSX. However, the Wavetrac is currently $1,495 vs $749 for the TrueTrac. I highly doubt the Wavetrac is "twice the LSD" or offer double the benefit of the TrueTrac. I'm not sure how well the TrueTrac's torsen design and behavior would work on a mid-engine car, and inherently there are benefits to having some preload stability that the Salisbury and (probably) Wavetrac deliver, I would probably test it if there was one available for the NSX, but since there isn't, my only real option is to try the Wavetrac since i've experienced pretty much every clutch type LSD on the market for the NSX.

For front-engine rear-drive platforms that have TrueTracs as an option, it is my go-to recommendation. I was really intrigued on how it would behave on the lightweight 50/50 (more like 48/52 front/rear) weight distribution FD having liked its characteristics in solid axle S197 Mustangs and IRS S550 Mustangs. Having put over 1,000 miles on it now in my FD, driving on the street, canyons, rain, goofing around and drifting it, i'm EXTREMELY happy with the TrueTrac in my Explorer Ford 8.8" Diff RX-7. The handling, power-down, and break-away characteristics of the chassis are excellent and predictable. I absolutely would choose this over an OS Giken LSD in the FD for 99% of cars that are not dedicated track cars. Whether I would choose it over a Wavetrac remains to be seen.

The factory FD and Miata Torsens barely function as an LSD, even at low power levels. Add a turbo to a Miata or crank up the power of the FD, and the impressions of Torsens as a LSD can easily be ruined. Torsen T2s are barely adequate at 350-400hp in Mustangs, while the T2R is a fantastic differential. However, the Eaton/Detroit TrueTrac is less expensive than the T2R and performs MUCH better and has been proven to be reliable with 4-digit power figures.

Are you adding the RS coil springs to an MZ Cusco LSD to increase preload and breakaway torque? What are your handling goals for those changes?

 

it's a Cusco RS. I currently don't notice any more turn in resistance on a neutral throttle than the factory diff. I occasionally get some single spin in wet conditions or when driving on cold semis, although climate here is pretty mild. Have not had successful lockup a couple of times trying to do stationary flick turns too, wheel alignment is fairly aggressive to diagonal weighting is pretty significant with lock on. I think I can increase the breakaway and it will feel more settled in 95% of circumstances (throwing into a corner too) with minimal downside in terms of additional perceived push. It certainly won't feel any worse in that regard than a Detroit 😆

 

I'm not sure what this means.

So what are you doing to modify the Cusco RS? Is it currently configured as a 1-way, 1.5-way or 2-way? I used that diff on an S197 Mustang race car, a couple S2000s and an MR2 SW20 time attack car.

What model "Detroit" LSD did you use and in what car?

 

caster pretty much maxed out, so with steering lock on you unweight a diagonal even more.

I have a genuine Eaton Detroit assembly modified by Harrop Engineering who I belive have the Australian Eaton licence to suit whatever Dana variant rear 6 lug went into Thai built Ford Ranger/Mazda BT50 4WD.

I also have a Goanna Gear "lokka" spider/side gear replacement kit in an MX83 Cressida. Fitted one to my cousin's hiace van too which transformed it.

I've driven and/or owned every generation rx7 with factory open or viscous or clutch or torsen/Mazda speed sailbury/welded/ Australian "Guru" helical (similar to truetrac/quaife)/aftermarket Japanese style clutch diffs.

It's been a while since I went over the manual on cusco centre but my intention would be to reassemble the cusco with maximum clutch plate faces engaged, 2 way ramp configuration and 12 springs, I think they are delivered with 6 or 8 springs fitted.

Detroit would arguably be a good circuit training tool to teach people to enter corners fast enough to be on coast or trailing throttle to avoid push.

 

Internet issues double

 

Ah yes, increasing caster increases the jacking effect and diagonal weight transfer that unloads the inside rear tire which typically makes it difficult and causes problems for torsen differentials putting down power. This isn't a problem in Mustangs with high caster when using the Torsen T2R or Eaton/Detroit Truetrac differentials, although the regular T2 does run into problems.

"Eaton Detroit" has many differential variants from lockers to posi-trac and Truetrac. Is your LSD in the Ranger a "Truetrac"?

The "Lokka" appears to be a "locker" differential that completely locks the axle together like a spool when engaged. I raced with them for years in a Mustang and they are quite aggressive when they engage and aren't ideal on road courses.

Wow, you want that thing to be pretty aggressive and more like a spool. What do you use the car for? I'm not sure if having that aggressive of a decel lock and increasing preload by using all 12 springs would be the fastest around a road course (which would increase understeer) if that's your intended use.

 

I think there may has been some marketing spin from retailers under the "Detroit" banner, but the only genuine Eaton "Detroit" models (actual part numbers with detroit attached to the description) are assembled mechanical self locking carriers that drop in to housing or bearing/pinion carrier, as opposed to Eaton "No Spin" kits being mechanical self locking cross pin/side gear and spring replacements that drop into factory side gear/pin/spider gear carriers for trucks (propper heavy vehicles as per rest of world, not utilities), loaders and heavy industrial applications. "Posi" is pretty average design clutch types and truetrac model designation are helical LSD centre assemblies.

I currently have the legitimate Detroit mechanical self locker in my utility, I did have a TrueTrac clone in it, but it would occasionally light up the torque lift side of the axle in the wet when tryingto pull across intersections, I prefer to err on the side of predictability over smoothness. With the camber and castor I have added in the front end it actually maintains enough lateral grip to lift the inside rear wheel enough to effectively have no contact in low speed corners in dry conditions, it's much more entertaining to drive than the OEM positive half to a degree or camber and more modest castor which was no doubt intended to provide understeer at the limit. This is a bit of an edge case being both a 4wd that I do actually use offroad occasionally and having both poor FR weight distribution and the load bearing rear end creating a high relative roll stiffness. I imagine most people would prefer the helical LSD but I see it as a driving input and planning challenge to be smooth as it is. You will always get an occasional clunk with a manual transmission.

Interestingly, with auto transmission, going to higher rate rear springs and anti-roll bar in the Cressida significantly reduced how noticeable the lokka was in it, up until the point you overpower the inside wheel in a low speed turn. You do still notice the push in corners but reduced roll seems to help mechanical grip overcome it. Cressida is supposed to be a cheap and cheerful project, otherwise I would have tried to get hold of a Supra torsen which is a direct fit and seem to be more robust than the rx7 ones.

With the rx7, again with the current wheel alignment and generally running on longish wearing semi slicks it's incredibly neutral most of the time arguably a touch lose with trail braking on corner entry so I'm happy to compromise a bit on breakaway torque in the pursuit of consistent power down in low grip situations/being a hooligan. The Cusco RS seems to be generally softer/smoother in progression from slip/differential action to lockup than OSG or KAAZ or othe other Cusco design variants from what I have read.

 

Absolutely, and i'm sure it differs further by region.
Here in the States, Eaton had a shift to further promote and tie the "Detroit" name to the Truetrac in addition to the Detroit Locker and "Posi" (non salisbury, clutch-type), ELocker, and NoSPIN differential line.