Muscle Mustangs & Fast FordsHow To Drivetrain
Off The Brake! - 4R70W Swap
We swap a 4R70W into our Three-Valve Fox with help from Performance Automatic and Summit Racing Equipment
There’s no doubt that driving a Mustang with a manual transmission on the track is fun. But what do you do when you want to increase your consistency? Use an automatic!
I like to think I’m a decent driver. I have a lot of seat time in a lot of different cars, and I’m happy with what I’ve been able to do in the cars I’ve raced. Our former Mustang, Project Shake ’N’ Bake, was a 3,700-pound Mach 1, and we got that to go 12.40s in road-race trim. Our Three-Valve Fox made less power with a five-speed, but went a best of 12.16 at 115.
While we were ecstatic about the performance, it wasn’t very repeatable. The car would normally perform in the 12.30 and 12.40 range, with occasional dips into the 0.20s and 0.10s when we did everything right. To race this car a little more competitively, we decided to swap out the five-speed for an automatic.
Our Three-Valve Fox is a mash-up of different and rather odd components. The base of the project is a Three-Valve 4.6L, the trans was a TR3650, and the rear suspension is based around a torque arm from Maximum Motorsports, so what is the right auto for it? We turned to Performance Automatic and Summit Racing Equipment for a trans with the strength to handle all the power we can throw at it on the track and street. The answer was a PA AODE/4R70W Competition Transmission (PN PA45101C-46L, $3,653.23).
We chose this trans for a few reasons. First and foremost, the 4R70W can handle a ton of power. It has overdrive, which makes street driving much more tolerable than a non-overdrive trans. And PA offers the 4R70W with a full manual valvebody and a transbrake. This means we will not need a transmission controller to handle shifting, and hard launches are as easy as letting go of a button. Plus, this keeps a good amount of the driver interaction, and driving the car isn’t boring.
|4R70W Gear Ratios|
|Fourth gear (Overdrive)||0.70:1|
When it comes to an automatic transmission, the torque converter is just as important as the trans, and we wanted a top-notch piece for this project. A call to Chris Sehorn at Circle D Specialties got the ball rolling on a custom billet converter tailored to our project from one of its 4R70W Pro Series Stage III 245mm billet converters (PN 30-13-04-5C, $1,100). The weight, torque, and horsepower, along with our plans for the car, dictated the Circle D build, and the stall is set at 4,000 rpm. Circle D designs and manufactures the billet components on its in-house CNC machine, so you get an extremely durable setup that is made in the USA.
After ordering the trans and converter, we ordered all of the supporting parts from Summit Racing Equipment. Our friendly parts supplier sent us a Hurst Quarter-Stick shifter (for a C4), a new transmission crossmember mount, a massive trans cooler, AN lines and fittings to connect it all, and the correct flexplate from PA.
Once everything was installed and working correctly, we put a few street miles on the new combo and headed to the track. Auto-Plus Raceway at Gainesville, Florida, prepped the dragstrip for us on a hot September day. Combined with the intermittent rain, the conditions weren’t favorable, and it showed in our times. Out of the gate, we laid down a couple of high 12.80 passes. With a little work, and trying a few different things when it came to launching the car and locking the converter, we whittled out e.t.’s down to the mid-12.60s.
Later that week, we took the trip to Bradenton Motorsports Park, where the cooler air, and great track conditions yielded three passes between 12.26 and 12.28, all at 110 mph. Our 60-foot times are consistently in the 1.70-second zone, with a best of 1.69.
The best part of our new combo is the consistency. We roll in, lower the tire pressure, run four or five mid-12.20 passes, air the tires up, and head home. Did we mention the car is also pulling daily driver duty? While the new low times are not as quick as our previous best, we can now crank out time close to our best run after run. That is worth its weight in gold!
A Look Inside the Converter
There are three main elements that combine to transfer the power from the engine to the transmission: the pump, the turbine and the stator.
The converter is completely filled with fluid, which comes from the transmission. The fluid starts off its flow from the inside of the pump and then it is centrifugally pumped to the outside of the pump. The pump is welded to the front cover, which is bolted to the flex plate.
The engine rotates the pump and the fluid is pushed towards the turbine where the input shaft of the transmission connects. The fluid then flows to the stator and is redirected and the combined momentum of the fluid helps to spin the pump. This is how a torque converter can multiply the output power which is known as STR or stall-to-torque ratio.
The fluid then continues this movement as the turbine speed increases. Eventually, the turbine is spinning about 90-95-percent as fast as the pump. This is called the coupling phase, and the converter is simply transferring the engine power to the input shaft.
Safety and Comfort
What is your safety worth—$599? If you race a car with five-point harnesses, there’s no reason you shouldn’t have a head and neck restraint.
The stigma has always been that they are expensive and uncomfortable, but NecksGen has put both to rest. The NecksGen head and neck restraint sells for $599 and can be used with many different seat configurations. On top of being inexpensive, it is also comfortable. It takes the pressure from the shoulder belts and distributes it more evenly, and its cushioned straps conform to fit you perfectly.
Whether you have a race seat or a stock seat, the NecksGen head and neck restrain is a necessity if you race! Visit necksgen.com for more info.