Imagine a clutch that seems to magically know how much HP you just added to your ride. Imagine that it could automatically increases the pressure at the pressure plate to harness that explosive HP at high RPM. What would this clutch do for your confidence off the line?
Welcome to the claims of ZOOM Performance Products newest clutch technology – ZVT – officially Zoom Variable Torque. In this editorial article and video blog on powerTV, we put the ZOOM ZVT to the test.
ZOOM just released this new ZVT technology for muscle cars and has started shipping their signature purple pressure plates with this latest improvement – a centrifugal force pressure actuator. This unique design adds pressure to the clutch disk as RPM goes up, and we all know that more pressure equals more torque capacity. In fact, ZOOM says that the ZVT will add up to 300 lb-ft of torque (on the clamp load) with organic friction material and well over 600 lb-ft with ceramic button friction material.
We installed the ZVT in our 2000 Mustang GT which makes about 330 hp with a 4.6L with full exhaust and the regular bolt ons. According to ZOOM, our stock clutch can support up to 290 lb-ft for our Mustang. The ZOOM Factor 1 clutch set starts at 366 lb-ft and increases to 450 lb-ft at 6,600 RPM. The Factor 2 starts at 471 and goes up to 667 lb-ft. We chose the Factor 2.
One of the reasons we chose the ZVT was that our car was owned by Melissa Lawrence, who, obviously by her first name is a girl. “We have had lots of excellent feedback, especially from men whose wives drive their cars, too,” explained Eric Waters from ZOOM. “The men get their race clutch that holds firm at high RPM and their wives get low pedal pressure when driving around town.” Now, of course, Melissa exercises more than we do, so her legs are plenty strong. That being said, even she didn’t want a HE-man clutch.
ZVT – An Overview of the Technology
ZOOM ZVT is, at essence, a technology which allows the clutch increased clamping pressure at higher RPM using a level arm which applies power to the pressure plate. There are three sets of arms placed evenly around the cover. These arms rotate on pivots to transmit the centrifugal forces to rollers that push directly on the pressure plate and add to the overall pressure.
This illustrates how the lever arm moves with different RPM. Now of course the arm will not move any noticeable distance when installed. Instead, it simply presses harder and harder on the pressure plate as RPM goes up. But the principle is sound. The arm is thrown away from the center of rotation by centrifugal force. The pivot rotates the force so that it pushes toward the clutch disc, increasing the pressure significantly. The amount of force that this simple lever creates is substantial. At 2000 RPM, it could add about 100 pounds. At 4000 RPM – up to 500 pounds and at 6000 RPM, possibly well over 1200 pounds.
For the Mustang, ZOOM offers four clutches which they refer to as Factor 1 through Factor 4. These are their equivalents to Stages 1 to 4.
Street upgrade uses Carbon/KEVLAR® composite materials with steel backing. Best for cars with bolt on upgrades.
This Stage 2 Street/Strip Upgrade has a four paddle design with KEVLAR buttons for added power over Stage 1. Clutch life is extended by the use of Kevlar and the torsion damper helps in daily driving. Elimination of the marcel cushions under the KEVLAR buttons offers faster engagement. Recommended for all vehicles with fuel system upgrades, ECU or performance chip upgrades, performance tires, short throw shifters, and more.
This Stage 3 Strip/Drift Upgrade offers a six paddle design with ceramic button material. Like Stage 2, the torsion damper makes daily driving smoother and the no-marcel (no-cushion) ceramic buttons offer a faster engagement. Recommended for serious vehicles that are turbocharged, supercharged, nitrous or have engine upgrades such as cams, polished ports, under drive pulley, fuel or ECU computers.
The Stage 4 Set is for competition only and uses a six paddle design with riveted sintered iron material to deliver extreme holding power. With a solid hub and no marcel this offers quick engagement through every gear and offers the quickest transfer of power to the wheels. Recommended for the serious road and track enthusiast. Used for drifting and drag racing in highly modified vehicles that have undergone motor swaps, larger turbos, high torque axles.
Choosing a Clutch Disk with your ZVT
There are four choices in clutch material based on what “factor” or “stage” you choose for your ZOOM clutch. In the calculations for torque capacity, µ is the coefficient of friction of the disc’s facing material. ZOOM is one of the first consumer clutch companies which publish their technical specifications in detail. “ZOOM stepped up to the plate and offered extensive technical data on our technology,” explained Waters. “We publish verifiable specifications on every part.”
The following numbers are published by ZOOM for their Products:
- Stock Organic Facing Material = 0.25
- Stage 1 (Carbon/Kevlar Material) = 0.28
- Stage 2 (Kevlar Material) = 0.36
- Stage 3 (Ceramic Material) = 0.38
- Stage 4 (Steel Material) = .40
In our case for our application, a 4.6L GT Mustang, we chose Kevlar, which provides a .36 coefficient of friction for Kevlar. According to ZOOM, our Kevlar disk can handle 471 lb-ft as the low range of torque, with additional torque available with the ZVT in the amount of 600+ lb-ft. This will be perfect as it will allow us to install a supercharger, nitrous, or a turbo kit down the road.
Below is the official ZOOM clutch chart to help you select your Mustang clutch:
Most ZOOM Flywheels have a replaceable wear surface bolted to the flywheel. This is perfect for those of you who are likely to thrash your clutch and score the flywheel. You can just unbolt the worn surface and put in a new one without the cost and trouble of replacing the whole flywheel.
[b]Installing the Clutch in our Mustang[b]
Our project car, the 2000 Mustang GT, had a badly worn clutch that was slipping badly. It was time for a replacement, and we decided to put the ZOOM ZVT to the test. We talked to Waters at ZOOM, and he recommended the Stage 2/Factor 2 clutch, which matched our power levels and our intended usage. We’ll walk you through the entire installation. So now on to the real work, removing the transmission to get to the stock pressure plate and disc….
The first action we took was to remove the shift lever and assembly from inside the interior. This is a pretty easy first step and required for any transmission removal.
We lifted the car and positioned our hydraulic jack under the transmission. First item underneath is to pull the drive shaft. First we put red chalk marks on the front and rear to mark the position so we can put it back in the same position. Here the shaft is loose at the rear and ready to be pulled out of the transmission
BJ always bags and tags every bolt, nut, and fitting to be sure he can get this all back together without having spare parts left over. Electrical system cables are detached.
The top bolt on the tranny is fighting back real hard. BJ spent 2 hours trying every tool in the shop. The bolt finally gave up and came out. Clutch cable is ready to be unhooked from the lever. Turns out a well placed crow bar at the back of the lever will relieve the tension just enough to easily disengage the cable end.
So there are no more bolts to be seen but the tranny fought us a bit. We tried to be lazy and not remove the h-pipe. That isn’t a good idea. We finally took the dual exhaust system completely off to fully expose the tranny. We taped the shaft opening because oil will drip without the drive shaft in place.
BJ has removed the pressure plate cover bolts and is pulling the cover off the positioning pins.
What we find is a very badly discolored flywheel that has seen a lot of hot spots. This is the result of too many burnouts, launches, and abuse on a stock 8 year old clutch.
BJ brings out the impressive new ZOOM flywheel with its removable friction plate and finds he has a 6 bolt flywheel and an 8 bolt crank. We ordered the wrong parts. Darn.
So it is back to ZOOM for the right flywheel. ZOOM is very helpful and gets it off to us overnight. Here it is Friday afternoon and the new 8 bolt flywheel just arrived.
BJ lines up the flywheel for installation. Note that the flywheel bolt holes will only align at one position of rotation. This is to ensure you don’t screw this up. Be sure to put thread locker on every bolt for the flywheel and pressure plates.
Place the clutch disk centering tool and the disk in place to position them for installation of the pressure plate. Be sure to follow ZOOM’s installation instructions to the letter. They recommend not adding lubricant to the pilot bearing and no lubricant is needed for the pressure plate.
Place the pressure plate over the disc with the alignment tool still in place to be sure the disc is centered after the plate is bolted on.
With the tranny chained to the lift shelf, get ready to lift it and “stab” it in. Take out the alignment tool first! Put the rear mount back in place. You’re getting close to completion. Be sure to use your alignment marks that you put on the drive shaft to align the shaft.
Once everything is installed, and new transmission fluid filled, start up the car and inspect for exhaust leaks. Then drive it without putting any stress on the clutch disc for the first 500 miles. Keep the RPM low when shifting and give it smooth re-engagement. ZOOM says to give the clutch 2 cycles of heating and cooling periods. Drive around using the clutch for 30 minutes to let it heat up, then park the car until the engine and exhaust are cool to the touch. Drive it again for 30 minutes and park it again until cool. Then go easy on it for 500 miles in which the break in will be complete.
The Driving Impressions – ZVT in the real world
The ZOOM ZVT clutch bites very solidly but smoothly. In comparison to our stock clutch, it’s bite is confident, firm, and sure. Probably due to the Kelvar material, there is an extremely confident feel to the clutch and as you apply the power to the car, no slip yet no sense of an over aggressive bite. We have no doubt this clutch is capable of handling all the power we can throw at it, including dragstrip launches.
Street manners for our ZVT Stage 2 were good. Pedal effort was higher than stock by a good degree. Although very reasonable for a 600+ lb-ft clutch, it was more than the stock unit by at least 40% by our estimation. For a daily driver, the ZVT passed with good colors although it might be a bit much for a total OEM vehicle and rookie driver. For our application, we were very happy.