When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
i talked to Ray, the owner, builder, brutalizer last night and apparently it had slipped my mind that he had engineered some additional pinion support.
this is a 3rd gen section but the FD and T2 FC use the same rear gears, other than the FC pinion is longer, so it is relevant as it shows that the OEM gears can withstand quite alot when properly supported.
BTW, i am not saying they are better than the cobra alternative, just that they may well be fine w some supporting mods.
Howard/Rob/Anyone... you guys ever get a chance to play around with your diff/subframe mounting? I will be dropping my rear subframe out here soon and am looking for some more ideas.
Zkeller has run Paul's subframe with success apart from the front diff bushings wearing a bit quickly. I will be running 300M axles, a T2 clutch-type unit in a stock FD housing with Paul's subframe (which is a work of art BTW) and I will eventually reinforce the casing with a PFS girdle. The loose ends for me at this point are the inner CVs and the ring and pinion which Carlos seems to be cleverly addressing.
I have a upgraded subframe by Paul but it has not been installed yet. Has anyone been running some serious RWHP with Paul's mod, and if so, how has it been holding up? It was a little pricey but the design and build quality seem high.
My build is planned for about 500-550 RWHP and upwards of 500 lb ft torque for road racing. I am currently looking to purchase a Kaaz and 300m axels. With that power level, does anyone think it is also worth purchasing upgraded inner CV's or is that just for something above my power level?
The inner CVs aren't even available yet, but they're being worked on (I have sent parts in to be mocked and measured, but I still waiting for my manufacturer to get the ball rolling on this). There are only a hand full of racers like Ari, Adam S. etc who can really say when they begin to break. I speculate that it is somewhere around the 6-700 HP mark for a well sorted car or and probably just under 500hp once you throw wheel hop into the mix. Again this is speculation through hearsay and inference on my part since I have never personally broken an inner CV, nor does my car even run at the moment. At any rate, upgraded inner CV's should not be necessary for an RX-7 that is setup for road racing exclusively.
Been getting some t2 diff related questions so I thought I'd give this thread a bump.
I see that this thread still needs to be updated to include information on the new Cobra IRS conversion that is now available as well as further theory regarding pinion support etc.
I want to add to this great thread, which was a big source of information for writing the MotoIQ.com articles on upgrading the rear end of the FD RX-7. I consolidated all of the information from this thread and added more (updated) information taken from other threads and talking directly to many people who broke various drivetrain components.
Project FD RX7 Restomod: Part 14 - When to Upgrade the Differential
The FD RX-7 has many drivetrain limitations that start to fail as power approaches double the factory output. Upgrading to a Ford Explorer 8.8” differential is not just for high horsepower builds, it actually makes a lot of sense, even financially, at a far lower power level than most RX-7 owners realize. It becomes the obvious solution when you:-Consider installing an expensive clutch-type LSD.
-Make more than 550whp.
-Make more than 450whp and push the car.
-Drag racing or drifting with over 350whp.
-Upgraded axles are needed.
-Changing the final drive ratio is needed.
Check out this article where we point out the parts cost of upgrading to the Explorer 8.8" (after selling the stock parts) is similar to the price of upgrading the stock diff with an aftermarket LSD and adding a brace.
Project FD RX7 Restomod: Part 15 – Building the Ford 8.8 Differential with a Detroit Truetrac LSD and WPC
We take a junkyard Ford Explorer 8.8” differential and transform it by installing one of our favorite LSDs, the Eaton Detroit Truetrac, then we hand deburr the ring and pinion gears, WPC treat the gears and bearings, and modify the aluminum housing to fit the high-power goals, handling and drivability requirements of our FD RX-7.
The aluminum Ford Explorer 8.8" diff is actually lighter than the factory cast iron housing, and the Ronin mounting kit is also lighter than the factory PPF.
Project FD RX7 Restomod: Part 16 – Installing the Ronin Ford 8.8 IRS Mount Kit using DSS axles
We busted out the TIG welder and installed the Ronin Speedworks Ford 8.8” IRS Mounting Kit. Then we shipped off the subframe to get powder coated before installing the show car quality rear end into our FD with the new DriveShaft Shop “Direct-Fit” Axles.
Installing the Ronin Speedworks Ford 8.8 IRS Mount Kit might seem intimidating, but it was actually a lot easier than I originally thought. If you have a MIG welder, angle grinder, and know how to use a level; or know someone who can TIG weld and has more grinding tools, the installation process was very straight-forward with easy-to-follow directions. This further reinforces the argument that I made in PART 14:
“As soon as you need to replace the OEM limited slip differential with an expensive aftermarket clutch-type LSD, the Ford Explorer 8.8” swap becomes the better solution”
It’d probably be less expensive to retro an RX8 diff … which didn’t start spinning off outer wheel hub shaft on an 800+ hp 20B conversion back in 2007. I’m not aware of one ever breaking the casing like on the FD3.
Otherwise the best thing you can do is dump the Torsen for an OS Giken LSD.
.
It’d probably be less expensive to retro an RX8 diff … which didn’t start spinning off outer wheel hub shaft on an 800+ hp 20B conversion back in 2007. I’m not aware of one ever breaking the casing like on the FD3.
Otherwise the best thing you can do is dump the Torsen for an OS Giken LSD.
.
The price of a braced stock diff with an OS Giken is about the same as having a Ford 8.8 with upgraded axles (after selling the OEM parts). I go into depth on this in Part-14.
except that the 8.8 needs an OS Giken too, but I know you don’t agree with that …
.
It really doesn't. Not all clutch type diffs perform the same, and not all torsens perform the same. The LSD is just one aspect of the cars handling. To make a car handle and perform the best, the rest of the cars setup needs to be adjusted for a specific clutch type. Both can be made to work quite well but the setups will not be the same.
To have a OS Giken in a Ford 8.8 with upgraded axles would be about $900 more than to have an OSG in a stock, weak diff with weak axles.
A Wavetrac would be a $600 premium over the Truetrac.
Depending on your power goals, as soon as you "need" to upgrade the stock LSD in the stock diff housing, you might as well go 8.8
well I slipped up by stating that from a competitor mindset, the Torsen is completely fine for a street vehicle. Some of those other ones you listed too.
however, they’re not all the same, but I’m choosing to not argue with you about it now, no different than the last time you stated the same thing in a different thread.
Again, I was really only intending to point out that an RX8 diff and axles has handled as much power as most 13BREW FDs are ever going to see. The FD3 axles are a direct plug in, you can even put the factory Torsen in it, and it then comes down to how easily the PPF end can be grafted together. If the PPF is deleted then it only needs a nose support. Edit: assumed the rear ears mount up or that the FD rear ear mount bolts on, bad assumption on my part, but not sure on either one.
A 3/4/X rotor, built V8, etc is a different story. I get that it doesn’t fit this particular narrative though and will leave you to it. My apology for interrupting otherwise.
.
well I slipped up by stating that from a competitor mindset, the Torsen is completely fine for a street vehicle. Some of those other ones you listed too.
however, they’re not all the same, but I’m choosing to not argue with you about it now, no different than the last time you stated the same thing in a different thread.
From a competitor mindset, the Eaton Detroit Truetrac (torsen) is an awesome diff and I've personally won races and time attack events with the Truetrac.
You can't take a car setup optimized for a Truetrac and throw a clutch type diff in there and expect it to work the same or as good, and vice versa. The characteristic of a diff is a crucial part of the car's handling and the entire setup needs to be optimized for the differences in any differential. Not all clutch type diffs perform the same, and not all torsens perform the same.
Originally Posted by TeamRX8
Again, I was really only intending to point out that an RX8 diff and axles has handled as much power as most 13BREW FDs are ever going to see. The FD3 axles are a direct plug in, you can even put the factory Torsen in it, and it then comes down to how easily the PPF end can be grafted together. If the PPF is deleted then it only needs a nose support. Edit: assumed the rear ears mount up or that the FD rear ear mount bolts on, bad assumption on my part, but not sure on either one.
A 3/4/X rotor, built V8, etc is a different story. I get that it doesn’t fit this particular narrative though and will leave you to it. My apology for interrupting otherwise.
.
What is the power/torque limitation of that diff housing? I see there is a Ford 8.8 diff conversion now out for higher powered RX8s as well.
The stock FD's inner axle stubs start to fail around 400-550whp (400lb-ft of torque) and the outer CV joints fail around 600whp. IMO if you're going to go through the trouble of upgrading the LSD, you might as well go 8.8
From a competitor mindset, the Eaton Detroit Truetrac (torsen) is an awesome diff and I've personally won races and time attack events with the Truetrac.
You can't take a car setup optimized for a Truetrac and throw a clutch type diff in there and expect it to work the same or as good, and vice versa. The characteristic of a diff is a crucial part of the car's handling and the entire setup needs to be optimized for the differences in any differential. Not all clutch type diffs perform the same, and not all torsens perform the same.
What is the power/torque limitation of that diff housing? I see there is a Ford 8.8 diff conversion now out for higher powered RX8s as well.
The stock FD's inner axle stubs start to fail around 400-550whp (400lb-ft of torque) and the outer CV joints fail around 600whp. IMO if you're going to go through the trouble of upgrading the LSD, you might as well go 8.8
First off @Billj747, the articles / Videos on MotoIQ are awesome and were a huge resource for me building my FD! Just wanted to chime in here with my experiences on the different axle set-ups for the 8.8 and my failures so far. For context, my FD is a LS3 / T56 / McLeod RXT /8.8 w/ Truetrac. Primary use over the last 4 years is drag racing and drag n' drive events. Ran the original Ronin Speedworks 8.8 swap axles for 6 years with no problems on a Mickey Thompson ET Street S/S radial. When I switched the car over to a Hoosier DR2 radial, I broke an axle on the first launch. I always assumed that the stock Mazda outer CV would break first, but the shaft actually broke at the splines of the outer CV. Ordered up a set of Ronin Grande Axles and got them in the car just before taking it on Miles of Mayhem (Canadian version of drag week). I shattered an inner CV bearing on the drivers side axle on day 3. Fixed the car in the pits and kept going to finish out the week. The Grande axles lasted a total of 19 passes and 1200 street miles. Passenger side was bent 0.150", drivers was bent 0.053". I went through the suspension and made sure every thing cycled without binding through its full range of motion to try and figure why the half-shafts bent. There was no smoking gun to be found, I guess it was just some bad heat treating post-machining or something. I got a set of the Pro-level DSS axles in the car now and have 2 drag n drive events planned for this summer. The next upgrade for the car will be a Black Magic slipper clutch as the RXT / Hoosier DR2 combo is good at shredding drivetrain parts!
Last edited by instrument_guy; 05-15-24 at 02:19 PM.
02-23-07 | 07:06 AM
