RX-7 Gearing and Final Drives

Hello all! I'm Ben, and I'm new to this forum, but have been reading GRM for a long time.

I currently race a 2001 Focus ZX3 logbooked rally car, (and it'll be for sale pretty soon for any interested). Rally is my thing, I eat, sleep, and breathe it, well, figuratively anyway. But I'm not a super great mechanic guru yet, but I'm trying to build my knowledge as best I can, and forums are a Godsend for that!

ANYWAY, getting to the point. I'm considering getting out of FWD rallying and into a RWD car, and of the good options available, the RX7 (1st Gen) is one of the only cool looking ones that I will consider getting into. (I'm also looking into BMW e36 Compact, and the Volvo 142 or 240). However, I'm having trouble getting good info on the final drive and gearing options available.

What I'd like is at least a 4.30:1 final drive. I heard rumblings of using a Miata gear set to get something better like this. But out of what year/model Miata? Anything like this that is easy and cheap, at least to obtain, would help greatly!

How about for LSD's? What's good for gravel that's available? Are there any clutch-type ones around?

I'm going to ask around on the rally forums and maybe RX7 forums later on, but thought I'd ask first here.

Thanks in advance!

Ben

Look at these pages and see if they help. mazda motorsports

SoloMiata

A friend of mine had a 1st gen Miata Torsen installed in his 84 GSL-SE axle housing. If I remember right it was a direct fit. He had 275 rwhp going through it as well if that helps.

This is all off the top of my head but the info should be correct. Read up on it before you trust me though. Just giving you things to look for.

1st gen GSL's and GSL-SE had stock clutch type LSDs. Stock the all the cars S, GS, GSL had a 3.90 ratio. The GSL-SE had 4.11 (or close) The GSL-SE's also had a different bolt pattern, vented rear discs etc.

There are aftermarket gear sets available from Mazdaspeed, Racing Beat, MazdaTrix. 4.44, 4.88. The junkyard upgrade here is to pull a front diff from a Kia Sportage and take the 4.77 ring and pinion.

There are aftermarket expensive LSD's available. I understand a Miata Torsen will fit with little or no mods but you would need to read up on that.

Thanks for the quick responses, guys!

I love junkyard upgrades, cheap is the way to be! So does the Kia ring and pinion fit in the GSL-SE or the GSL-SE, or both? A 4.77 FD would be REALLY nice!

Front diff from B2000 has a 4.44- don't recall which year, but that's the one I have in the rear of my MG with an RX7 clutch type diff (converted miata rear subframe).

The Sportage R&P goes right into a 1st gen housing, IIRC for all diffs: GS, GSL and GSL-SE. As I understand it, you can even bolt the whole Sportage 'chunk' into the RX7 housing. RX2 stuff will work as well. RX3 and 2nd gen RX7 stuff will also bolt into the axle housing, but they have the 'long nose' diff and a very limited selection of R&P's.

The Jensenator has an RX2 axle housing, GSL calipers and rotors, axles redrilled for 4x100 bolt circle (you can pick from a HUGE selection of wheels that way), 1st gen clutch type limited slip and 3:89 R&P. I plan to do the Sportage R&P sometime soon.

So, stick with the GSL housing and put a disc conversion and the Sportage R&P into it and BAM! good to go? While mentioning discs, did the GSL come with discs typically, or more often than not, drums? (Obviously, I know little about RX-7s, please bear with me.) If drums, are there any other vehicles that provide a cheap and very good bolt-on brake conversion? (Kinda like the quad piston RX7 fronts bolt straight onto the rear of the Volvo 240, or is it the front? Either way, they cross right over.)

All GSL's have rear discs and LSD's already. Base, S, and GS are all rear drum/open diffs. GSL-SE stuff is pricier but better (4x114.3 bolt pattern, rear discs, LSD).

Doesn't the standard GSL have the 4x114.3 pattern, too?

Okay, I'm gonna hijack my own thread for a moment. Are there any motors that swap easily into the RX7, (and any other that'd bolt straight onto the RX's trans?) I'm mainly wondering about the Ford 2.3L.

The only 1st Gen RX-7 to have 4x114.3 was the 13B Injected GSL-SE, period the end. All normal GSL models have the standard carburetored 12A and 4-wheel discs with a 4x110 bolt pattern that is shared with all other 79-85 RX-7's.

Why engine swap? Didn't a stock RX7 win the overall Rallycross Championships in RWD last year? If you insist, the 302/5.0 Ford will be a much better fit than the very tall 2.3L. And unless you are talking 2.3T, the 5.0 will blow it out of the water in HP/TQ. Both engines are significantly heavier than the rotary.

If you want to run a Ford 2.3, listen to John VanLandingham and get yourself an XR4ti.

Otherwise, get yourself a Volvo 240/242 and go play.

You may want to familiarize yourself with Grannys Speed Shop.

A 5.0 will bolt in as well as a SBC. If you go that way you may want to rethink a 4.77 unless you don't plan on any highway driving.

The only thing that will bolt to a rotary tranny is a rotary. Now that means any of 'em; 12A, 13B, 13BT, 13BTT, 13 REW, Renesis, 20B.... the mind boggles.

By the way, Mazdatrix sells a 5.62:1 R&P but it's a pricey devil.

I'm with P71, stick with the rotary. That way you keep the weight behind the front axle centerline which is a BIG part of the 1st gen's decent handling. If you absolutely MUST swap engines, instead of the heavy 2.3 I'd look at the Nissan VG series. Not a difficult swap, keeps weight well back, available in twin turbo... or the 3800 L67 supercharged engine from a Park Avenue Ultra...

4 x 114.3 is 4 x 4 1/2, there is a reasonable selection of wheels for that pattern (think 240SX, 240/260/280Z/ZX, 510 Datsun, MGB etc) but nowhere near what's available for 4 x 100. Remember the Miata uses 4 x 100 and EVERYBODY makes a wheel for that. Any decent machine shop can easily redrill the rear axles and front hubs for the 4x100 pattern and while they are at it install studs, which greatly simplifies wheel changes when you are in a hurry.

I'd consider a swap for a lighter and equally or more powerful engine because the rotary is a bit of a handful to keep reliable and its quite heavy, I'm told. And there's absolutely no way I'd swap in a V8.
I've talked with JVL a lot and he really pushes the 240 and Xratty, and yeah, the Volvo 240 is a GREAT way to get into RWD rally, but I can't stomach their sheer massive brickness. I don't mind boxy cars, but the 240 takes it too far. Xratty's...ugly, but painted right can look pretty cool. Not really sold on them, though. John knows A TON about rally and proper setup, and builds some darn good gravel suspenders. He would/will poo-poo my RX-7 idea, but they do make decent rally cars. Provided you strengthen the car properly, and have the right gearing and suspension. And a reliable engine and cooling system.

Or are the engines more reliable than I've been lead to believe?

Also, for the Kia Sportage diff; it's from the rear axle, not the front, axle correct?

NA rotaries are quite reliable if (like any engine) you keep it cool, keep the oil changed etc. 200K+ and still going strong is not unusual. Having said that, the supply of 12A parts is drying up, see if your class will allow the use of the later 13B motor, it's pretty much a bolt in swap and the FI greatly simplifies maintenance along with giving a horsepower bump.

Boosted cars are another story. The single turbo cars have been known to cook the rear rotor (the turbo sits right there just outside the exhaust port, thus it retains a LOT more heat than the front one) and the twin turbo cars were generally killed by a combination of lack of maintenance and tweaking to try to get even more power. In fact, that is probably the single biggest problem with rotaries: everyone tries to get big block Chevy power levels from 1.3 liters and then wonder why it goes KABOOM.

The R&P comes from the FRONT diff of the Sportage. Same with the 4:44 unit in the B series pickups. I forget which Miata had the 4:30, IIRC it was 94-96 but I could be wrong.

A 240SX would be a good chioce if you decide against an RX7. If you go 240 huntin', I'd go for a coupe; they weigh roughly the same as a hatchback but the weight is lower in the car (they aren't carrying that 75 pound hatch 2 feet off the ground). I am not real up on Nissan diff swaps but there are boneyard choices, mostly 300Z/ZX and various Infiniti models but IIRC they are all viscous units. A bud who runs a 300ZX has gone through several of the stock viscous diffs, he finally bought a ($$$$) NISMO piece.

If you want to run in Rally America events, the engine and chassis have to be from the same manufacturer. There is no place for an RX7 with a Chevy or Ford V8 to compete. If you can show that the Ford 2.3 was used in Mazda pickups you MIGHT get away with that one. Engines like the current Duratec can be used in both Ford and Mazda chassis.

Also, V8 cars compete in G5, which is restricted to experienced competitors. Novices have the option of competing in G2, Open Light, and some of the slower Production categories.

NASA and CARS do things differently.

Jensenman,

It's impossible to put studs in the front rotors of a 1st Gen. The actual bolt plate is not the same as the rotor and you'd have to drill right through the rotor to get to the backside of the bolt plate. Also, just by the way the bolt plate is designed, a 4x100 won't work (huge center bore and a large taper). 4x114.3 is the best you can get out of a re-drill, and you still have to use bolts.

Sure it's possible. Weld up the stock holes, face it off flat, then drill and tap 4 holes for 12mm x 1.25 pitch on a 4x100 bolt circle, then get a VW stud conversion from EMPI and have at it. My local machine shop already confirmed it will work, would run about $125/pair to do it. Gotta think outside the box.

Here are some studs I bookmarked a while back that I might use on my FB one day if I ever need them. Several guys on RX7Club have used these with good results.

http://www.bildon.com/catalog/DetailsList.cfm?ID=M12.DE.Stud&Nav=10&SubNav=none

$125 a pair! Might as well just buy stock GSL-SE rotors and run 4x114.3

I still don't think it's possible though. My local machine shop said the 4x100 was too small and was interfering with the radius on the backside of the bolt plate. Also, how the heck are you going to stud the thing and still meet SCCA/NHRA regs?

(Pic of RX7 front rotor):

1fastben wrote: I'd consider a swap for a lighter and equally or more powerful engine because the rotary is a bit of a handful to keep reliable and its quite heavy, I'm told. And there's absolutely no way I'd swap in a V8.

The flip side of this is my (modified with a lot of aluminum parts) 350hp 5.0 84 FB RX7 weighs within 20 lbs of what it did as a rotary, but makes 3 x times the hp and 4 x the torque. No weight penalty, a turbo would create a lot of weight, no reliability issues, fuel injected so clean and tunable power for rally use.

http://grassrootsmotorsports.com/reader-rides/220/

Just saying

Here's the type of studs:

Hard to see in this pic but the end of the stud has an Allen wrench hole for installation. They are installed with Loctite Red. Had them on my '79 RX7, worked great.

Dunno about NHRA, but the last time I looked at the GCR it said 'any type of studs or bolts can be used to mount wheels'.

P71 wrote: The *only* 1st Gen RX-7 to have 4x114.3 was the 13B Injected GSL-SE, period the end.

In North America.

Rest of world, all '84-85 models had that bolt pattern. I think. Definitely some countries.