91 Miata diff swap

[6PAK72]

OK, so I specify gearing in these 3 factory-supplied gear ratios: 3:90, 4:10 and 4:30.

Suggestions? Warnings?

Thanks!

[Stynger]

1.6 4:30
The Miata 1.6 doesn't have the balls for anything higher, unless you're looking for gas mileage.

[6PAK72]

I figured, but I was asked, so...

Thanks a lot.

[TroyV]

Les is pulling your leg.. The lower numbers make you go faster.

[Dave_G]

1.6 4:30
The Miata 1.6 doesn't have the balls for anything higher, unless you're looking for gas mileage.

Well, yeah, the 4.3 would be better than the 4.1. But if you're swapping in a Torsen from a 1.8 like I did, the 4.1 diffs are much, much more plentiful and easier to find. You can find a 4.3 Torsen from a '99 if you wait long enough, but it might be a long wait. I wasn't patient enough for that.

So, while I might wish I had a 4.3 diff, my wheezy little 1.6 does just fine with a 4.1. I'd much rather have a 4.1 LSD than a 4.3 open diff.

[paultg]

1.6 4:30
The Miata 1.6 doesn't have the balls for anything higher, unless you're looking for gas mileage.

Well, yeah, the 4.3 would be better than the 4.1. But if you're swapping in a Torsen from a 1.8 like I did, the 4.1 diffs are much, much more plentiful and easier to find. You can find a 4.3 Torsen from a '99 if you wait long enough, but it might be a long wait. I wasn't patient enough for that.

So, while I might wish I had a 4.3 diff, my wheezy little 1.6 does just fine with a 4.1. I'd much rather have a 4.1 LSD than a 4.3 open diff.

This is what I did as well. You can play with shorter tire diameters to compensate for the change in gearing.

[CP]

Be careful with the axle seals when pulling the axles out. If they get nicked they'll leak. There's also a circular spring in the seals that tends to get mangled during axle changes. Be wary of it. It's a good idea to apply some liquid wrench to the diff housing bolts for a few days prior to their removal (air tools highly NOT recommended for the procedure). We're constantly breaking ears off the diff housing while racing, so I've done a few swaps at the track with good results. Grey RTV was used to seal the two pieces together.

If you've got the old 1.6 style rear housing (smooth surface/no cooling fins) it might be worth your time to find one with the fins for added cooling. These diffs get HOT, so change the fluid often. You'll know if it's cooked by the smell when it comes out.

[6PAK72]

Thanks for the detail, Cy.

[6PAK72]

Troy, Les told me that the lower volume fuel injectors he just put into your engine will make you go faster, too.

[paultg]

Since we are on the subject of differentials; I'm not sure I would have swapped out for open 1.6L 4:30 diff for a 4:10 torsen for track duty only. I autox the car so I felt a noticiable difference at those events. I never tracked the car with the open diff, do folks experience traction issues with the open diff at an HPDE say at NHMS? If not, I don't know if I'd bother changing the diff.

Paul G.

[CP]

I'll bet T3 is a bitch with an open diff...probably T11/12 too.

[Stynger]

Troy, Les told me that the lower volume fuel injectors he just put into your engine will make you go faster, too.

That would be illegal.

[WillM]

4.3 because the gearing is better for any 5-speed Miata, especially the 1.6.
Torsen because a used VLSD will eventually explode, and an open diff is crap at NHMS.

"4.3 Torsen Differential, the very best there is."
"When you absolutely, positively, need to pass every car in your rungroup, accept no substitutes."

...or something like that.

[6PAK72]

T3 IS a bitch with an open diff - I slide all the way from the turn-in to the top of the hill. T11/12 is OK, I mostly am on maintenance throttle until the apex of 12. T2A is crazy, though. In Wasilko's car I can turn in and put it nearly on the curb, and accelerate into 2B. In my car if I try that...well, Will has followed me through there at least 3 times where he has had to drive around a spinning blue Miata.

Thanks again, this is great info.

Troy, I'm going to flow-meter your new engine

[eastcoastbumps]

Les is pulling your leg.. The lower numbers make you go faster.

You stay in the power band longer with the taller gears.