Project Professional Awesome Time Attack Evo: Part 4 – Drivetrain

Project Professional Awesome Time Attack Evo: Part 4 – Drivetrain

by Daniel O'Donnell

Today, boys and girls, we’re heading back into the technical side of the Professional Awesome Evo. For your reading and viewing pleasure, we’ll be showing all the secrets in the drivetrain of the fastest Limited Class time attack machine ever to compete at Buttonwillow Raceway.

When we had the Evo VII chassis, we started with the standard AYC (Active Yaw Control) rear differential and ACD (Active Center Differential) that came with the car originally, but after regularly having complications with various pumps and electronics, we decided to switch to the mechanical setup offered in the early years of USDM Evos. For us, this consists of the Wavetrac front differential we’ve had for some time, the standard OEM viscous center differential and the OEM, clutch type, rear differential. Since the switch, we couldn’t be happier with the reliability of the drivetrain and the balance it helps give the car. Diving into what puts the power to the ground, we’ll start with the clutch, head to the transmission, stop at the transfer case and work our way back to the differential.

 

Here's our custom Exedy twin disc clutch getting installed. We've solely used Exedy clutches in our car since the beginning of our team's time attack racing career. Reason being is that Exedy makes the OEM clutches for Evos and I personally prefer the design of the stock pull-type pressure plate over aftermarket push-type options. This has proven extremely reliable in our setup, with the addition of a MA Performance clutch fork stop and ACT Monoloc to prevent the clutch fork from over-returning and disconnecting itself from the pressure plate. This is the one major downside to pull-type clutches, but one that is easily overcome.

The clutch is a special unit made for us by the fine folks at Exedy Racing Clutch USA. We had been running an off the shelf triple solid disc cerametallic unit that was purchased in a pinch many years ago. This clutch worked flawlessly for us, but we didn’t need a clutch with a capability of holding 923 wheel torques. Due to the massive load this clutch could handle, it also weighed more than needed and could potentially apply more stress during shifts than a twin disc.

 

Our fully assembled Exedy twin weighs in at 23 pounds on the dot. Note the machining of the flywheel to reduce inertia.
Here's our beloved Exedy triple disc we used for many years. The weight savings going to the twin is a pretty healthy 6 pounds and 12.5 ounces. This clutch is can hold nearly 1,000 lb-ft of torque and driveability is good enough for street usage.
Here we can see a direct comparison of the weight of the flywheel with and without the machined holes.
Most of the weight savings of the entire clutch assembly comes from the deletion of the extra disc and center plate required on a triple disc. This all adds up to improved engine response and reduced shift times. Exactly what we were looking for when making the switch.

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