R-spec Tremec TR3550...?

[JoeAsheville]

This was news to me, so I hope I can get some clarification.

As we all know, lots of BS gets spread around, especially online. Somebody claims that the TR3550 has an R-spec for the 95 R, where the 5th gear is 0.87 instead of the "standard" 0.68. It's been a while since I've driven #181, and quite frankly I didn't really pay that much attention to RPM cruising in 5th, so I have no idea. At some point in the future I have another motor I'll be swapping in to preserve the original, and I'm wondering if it's worthwhile to keep the original TR3550 or put in a close-ratio TKX...so I'm fiddling around with some gear ratio calculations, hence the question regarding the 5th gear ratio.

If the R spec TR3550 indeed has a 0.87 overdrive gear, it should be just fine for my purposes the way it is (no need for the TKX) behind the 408.

 

[tomshep]

There was no R-specific TR 3550 EVER. All Rs came with a 3550 with the .68 overdrive. When they started racing the Rs they discovered on the large tracks such as Daytona the cars couldn't accelerate when in OD with the factory 3.27 rear gears. So a .8 OD was substituted to allow the cars to accelerate. (I honestly can't remember if it was .87 or a slightly different ratio.)

When the TKO came out they did offer a .8 OD variation and it is a direct swap, but that was an upgraded 3550. 3rd gear is the weak link in the 3550 in our cars. If you are putting in a stronger motor than the stock 351 I would upgrade the tranny. Unless you plan on running it in a track environment I'd keep the .6 OD for better highway rpm.

Tom

 

[tomshep]

Just reread your post and saw the 408. You will blow 3rd in the 3550. Put in a TKX or TKO. But I'd do the .6 OD. Your motor will have plenty of torque.

Tom

 

[tomshep]

To expand on this slightly. Mechanically and functionally, the R 3550 is the same as an off the shelf 3550. However, they R tranny was unique. It had to do with the vent for the tranny. A regular 3550 had a vent towards the front of the tranny. Ford discovered this vent was an issue for the assembly line when marrying the motor/tranny to the chassis. So the R has a unique vent that is on the shifter plate and the forward vent is eliminated.

The last 8 of the R VIN is also stamped on the driver's side of the tranny below the shifter.

Tom

 

[JoeAsheville]

Great information, Tom. Greatly appreciated! I didn't think it was a 0.87 stock but wasn't sure. I did spot that vent on the shifter but didn't know it was specific to the R model.