Transmission Selection & Surgery – 2 Hours

After an 8 week break, due partly because of the excessive hot weather (7th hottest on record here in North Texas), but mainly because of work commitments in Europe, California and New York, it was with excitement that I cranked up the AC in the garage today.

There are many reasons I chose the Tremec TKO 600 (TCET 4617) over the standard T-5, and I thought I would re-visit these:

1. The primary reason was that with 275/40 R17 tires and a 3.31 differential, the engine would be laboring around 1900 RPM in 5th gear at 70 MPH, with a T-5 or TKO 500 (both have a 0.68 5th gear ratio). The TKO 600 offers a choice of a 0.82 or 0.64 final gear ratio. Choosing the 0.82 option results in a 70MPH cruising RPM of 2400, you may ask what difference does this make. (Please feel free to download the following calculator)



After driving in a number of cars recently many owners complained of having to drop into 4th gear to overtake at around 70MPH as the engine was not yet at the sweat spot, hopefully the transmission selected will overcome this.

There is a down side; the car will be a little thirstier on gas, and the top end speed will be reduced to around 150MPH, but as I don’t live near a German autobahn it’s unlikely this car will ever get a chance to prove itself.

2. Standard on all TKO transmissions is a choice of manual or electronic speed sensors, neutral safety circuit and a reverse gear sensor.

3. Although the TKO is over specified for the torque this engine will produce, the heaver drive train will be less susceptible to failure and wear with the aggressive driving the car will see.

4. Another available option is a mid-shift, although this is not planned, once I start driving the car and if I don’t like the shift location I do have the option to change.

This week I collected my transmission from Standard Transmission and Gear in Fort Worth (See web link), this is a great company and the deal they made was outstanding, strongly recommended. An issue with all TKO transmissions is that they require surgery before fitting in the Cobra.

The upper picture shows the unmodified rear of the transmission, the alternative rear transmission mounts need removing as these will interfere with the 4” round cross chassis member.


Second picture shows the modified transmission, this was achieved with a steady hand and a Sawzall, it took a couple of blades to complete the surgery both 14 and 18 tpi metal blades seem to perform the best.


Lastly transmission mount (last picture) was bolted to the transmission, remember to use the second mounting plate provided as this is actually a spacer and is not an either or option.

With luck and a fair wind I am hoping to bolt up the transmission during the week and drop the complete engine transmission and drive train in over the Labor Day weekend.