How to put a Momo T-frame seat and a racing harness in a Miata

By Dana Keen

Disclaimer: Miata.net does not endorse or recommend any modifications to your vehicle. The modifications described herein have not been tested or approved by any safety agency. Use this information at your own risk.

The Momo T-Frame seat mounts into pre 1999 Miata fairly easily using the stock seat rails bolted into the stock locations on the car .i.e. No drilling into the floor of the car.

It may work in newer Miata's but I  have no experience with 1999+ Miata's.

The Momo T-Frame has a metal tubular frame inside the fabric. In my case I made the seat more comfortable for street driving by slightly bending the rails to widen the seat base for ease of entry/exit. I did this with floor jacks and a lot of blocks and old rags.

The only metal fabrication or modifications are the drilling of new seat-to-rail bolt holes in the rails and the elongating of the rail-to-floor bolt holes in the rails.

The first 2 pix show how the rails are bolted to the seat. The attaching bolt is inside the yellow rectangle. It is important that it is centered within the rail channel so that the parts of the rail can slide back and forth over each other.

These next 2 pix show how the rail-to-floor bolt hole is elongated so that the stock floor mounts can be used. I achieved the elongated hole with a hand held power drill and a cone shaped grinding bit.

Here is the view when the seat is in the car. A proper selection of washers and bolt will allow for a secure and non fatiguing mounting. You  can get the proper pitch metric bolts and washers at the local Orchard Supply Hardware store.

OK. Now for the harness. The one used is an inexpensive RCI harness: about $60.00 when i bought it. However I recommend the better cam release harness by RCI: about $125.00 because it is so much easier to deal with at the track. I wanted to have BOTH the stock seat belt and racing harness's installed: the stock belt is much easier to deal with in around town driving.

As I recall the stock right side seat belt mounts to the seat itself; and the Momo seat has no such mounting hole. But there is a mounting hole on the floor in approximately the right location. The only challenge is increasing the length of the metal seat belt release bracket so that you can easily reach the release button. I did this by bolting the seat belt mount to a stout piece of Orchard Supply door hinge material and then bolting this to the floor. The racing harness attaches right at the floor. All this using high(er) grade bolts.

The left side mount is much more straight forward. Note how the use of bolts that are not completely threaded with an additional nut allows the belt/harness to rotate freely.

Here is the complete installation. Note that the stock seat belt is threaded though the Momo seat belt hole prior to bolting it to the floor. The over the shoulder harness's are attached to a roll bar or shock tower brace. When at the track you thread them though the holes in the seat. When not at the track they can be pulled out and tucked behind the seat and the stock seat belt used (as shown in pix).