Viper Differential Install Into '93 RX-7

[Orlando_87GN]

I thought by making this thread it would motivate me to actually get this done! As some of you know the Mazda RX-7's came with a pretty undesirable rear end gear ratio for us LC2 lovers. The absolute tallest gear possible for the RX-7 is a 3.90 ratio which came in automatic transmission cars. The rear ratio I am currently using is actually 4.10 which came in a standard transmission. Needless to say this gearing isn't optimal for the Buick engine. At the track the gearing is so short I am shifting into OD before the 1/8th mile. . While the car runs out OK (128mph) it's not optimal and it can do much better.

Time for a different solution. I purchased a Viper 3.08 pumpkin off eBay a few years ago. It's a Dana44 and will probably be indestructible for my application. The 3.08 gears will be perfect for the light car and short tires. I will modify the stub axles on it to accept CV axles and fabricate a way to mount it properly in the Mazda sub frame. The only work that I have done so far is I have removed the rear (thanks Scottie) and started measuring/planning my options. This weekend I am going to start breaking down the CV's, taking measurements to determine what axles I am going to use. I am hoping to use the CV's from a TurboII car which already have a 4 bolt flange pattern on them.

Here are a few pictures of 'the beginning'.

[Nashty]

Done yet?

I think you secretly like doing the hard jobs. Looks like you'll lose a few pounds too. Good work Mike !

[JOHNZAZA]

Can get a few rear ends if anyone needs one.

[gnx7]

Keep us updated with pics/findings.

Nice to see you are taking the plunge and moving forward on this project.

I'm curious if you will have to cut the mounting ears on the batwing like the Corvette rear pumpkin install on the FC.

[Orlando_87GN]

I'm curious if you will have to cut the mounting ears on the batwing like the Corvette rear pumpkin install on the FC.

I will. Eventhough the Viper batwing is much more narrow than the C4 rear, it's still too wide and would interfere with the a-arm mounts in this rear. Sucks but I am not going to duplicate this rear and don't care about shortening the cover.

[Orlando_87GN]

I was worried about what axles to use. It was looking like I was going to need the stock 3rd gen axles shortened and resplined. That would have been expensive and not local.

I knew the Turbo II shaft was shorter but I didn't think the 3rd gen outer hub would fit. Luckily for me it did. The picture attached is the 3rd gen outer CV (at the wheel) , Turbo II shaft and Turbo II inner CV. This gave me a shorter overall CV assembly (needed because the Viper diff is wider) and a 4 bolt flange to bolt everything up.

Too good to be true?

[turboted231-1]

u go mike, looking good. cant wait to see how the 8.8 will hold up when i get the motor in mine, get er done, ted

[Orlando_87GN]

Coming together!

[gnx7]

Great progress Mike. I assume the centerline location of the stub axles in the Viper diff are at the same location as the FD diff stub axles?

Is that the factory 3:07 gearing in the pumpkin? Did you rebuild the LSD or just going to run it as is? It has a factory TrackLok LSD right? I assume that is a clutch pack style LSD?

[Orlando_87GN]

Originally Posted by gnx7

Great progress Mike. I assume the centerline location of the stub axles in the Viper diff are at the same location as the FD diff stub axles?

Is that the factory 3:07 gearing in the pumpkin? Did you rebuild the LSD or just going to run it as is? It has a factory TrackLok LSD right? I assume that is a clutch pack style LSD?

The centerline is very close. I needed shorter axles because the Viper diff is wider overall.

The rear is the 3.07/3.08. I haven't rebuilt the unit. It looked and smelled brand new when I took the rear cover off. I bought this pumpkin years back from a Dodge guy on eGay. He said a tree jumped out in front of a very low mileage Viper causing a total loss. I don't know what style clutch it has, but I figure the Viper was a much heavier car and if the Dana 44 was good enough for it, it will be fine in the little Mazda. I think the Viper was a '99 model. I read somewhere the rear is actually called a Dana 44.5, whatever that means.

Good news is, I had installed a Dana 36 in the 2nd gen RX-7 and never had a problem with it once I had it rebuilt. The 44 is a lot beefier.

[Orlando_87GN]

New pics.. almost done...

[firebird_1252]

looks amazing!


with the 3.08's what rpms do you think you'll be going threw the traps at?

how much mph do you think you'll gain?

[Scottie-GNZ]

Awesome Mike. Looks like you just might have her ready to roll up to Reynolds next weekend.

Rob,

with basically the same engine in my 2nd-gen RX7 (couple of #s heavier than the 3rd-gen), I trapped 136.07 and gained 27.62 with a busted TH400 that amounted to 16+% slip through the traps. That was with 2.73s and a 27" ET Street!

Mike's car should trap at least the same or faster if the LU clutch will hold.

[GNVenom]

I used the Dana 44 in my project back in 95, with a C4 batwing setup right out of the Vette. Actually mounted it from the snout perch. I've torn the bolts out twice over the years...Ran 11.80 with the 3.08 so the ratio is perfect. I've since then replaced the pumpkin with a 3.45 out of a ZR1, but really didn't make much of a difference in terms of performance. Stay with the 3.08, it's perfect for the car.

[Orlando_87GN]

Yeah, the 3.08's are going to be nice. My last RX-7 had 2.59's which worked better than anyone would have thought.