Tech Article: Everything You Wanted to Know About Z Flywheels and Clutches But Were Afraid to Ask
by Ben Pila Jr., Member at Large
For this months tech article, I will touch on two areas of performance often forgotten by the average Z owner. A lighter flywheel and the installation of a stronger clutch set-up can help improve your Zs performance. Only manual transmission Zs have flywheels and clutches, so you with automatics can read but none of this applies to you. The flywheel is a rotating plate that is attached to the back of the crankshaft by bolts. What does it do? It provides inertial storage and holds the starter gear and the clutch assembly. The clutch disc friction material makes contact on the flywheel as you let the clutch pedal out to get the car moving.
The reason Nissan chose the weight of the stock flywheel as it is, was to come to a compromise between ease of clutch engagement without stalling the engine and at the same time not being a boat anchor (heavier than needed.) When the flywheel on the engine is lighter than stock, it allows the engine to accelerate and decelerate much more rapidly. The benefit to this is a Z that accelerates more quickly and has crisper throttle response (which is great for back roads and autocrossing.) Another benefit is turbo Zs gain boost sooner with lighter flywheels. The only drawbacks might be in real heavy stop and go traffic, parking lots or on a steep hill. A little more rpm will be needed to get the car moving from a stop. With a lighter flywheel, it doesnt take long to make the adjustment to its new weight and the performance is noticed immediately.
There are many ways to get a lighter flywheel. One way is to remove material from the backside (block side,) of the flywheel. Ive seen this done before but it must be done properly. Generally 5-10 pounds can safely be taken off and total end weight should not be less than 17-18 pounds. Early 240Zs and 1984-89 non-turbo 300s have fairly light flywheels so not much can be removed from them. Another way to lighten the flywheel is to purchase a custom made light flywheel. Most custom flywheels are 11-14 pounds while stock flywheels are 19-35 pounds depending on the model. The last choice is probably the best as you get a light flywheel that is very strong and it bolts to the stock location. Custom flywheels are usually made of either aluminum with a hardened steel insert, ductile iron, or chromoly. The advantage of the aluminum flywheel is that the weight of the hardened insert is more toward the center rotation and that helps keep the inertial rotating weight down. The chromoly and ductile iron flywheels are the solid material all throughout like a cast iron flywheel.
Years ago, I used stock clutch replacements on one of my Datsuns. At that time as I made more upgrades, I found that I would break my clutch more easily. I was rough on equipment then (drag racing.) Later, I invested in a heavier duty clutch and my problems were gone. The 2 seater Zs from 1970-1983 used a 225mm diameter clutch disc. The 2+2s from 1974-1983 and 1982-83 280ZX Turbos all use a 240mm diameter disc. If you put the 2+2 or turbo flywheel with the 240mm disc onto a 2 seater Z, then you can use the larger disc which in effect gives you a heavy duty clutch. What you are looking for if you buy a performance clutch, is higher clamping force without significantly higher clutch pedal pressure. You also want to stay away from discs that have metal facings (especially the ceramic puck styles or button discs,) and opt for the organic facing if you use your Z primarily on the street. Metal disc materials can chatter and grab making them a chore to use in city traffic. There are other new materials on the market like carbon-kevlar. These work better when they are hot which makes them better for racing but when they are cold, chattering or rough engagement is likely.
The latest trend in racing discs are using discs with an unsprung hub. These types of discs are the ultimate in grip for drag racing due to the lack of hub springs and instant engagement. The problem with them is that they engage so well that the shock of the engagement often breaks parts like transmissions and driveshafts. I recommend avoiding any disc that doesnt use hub springs as they should be used to cushion the engagement. Performance clutches and light flywheels can be purchased from speed shops that sell Nissan performance parts. Next time you need to replace your clutch, think about what was said here and make the upgrade. If you have further questions or are unclear on anything feel free to e-mail me (firstname.lastname@example.org) with any questions.
Sources for Z flywheels and performance clutches:
Jim Wolf Technology
90+ 300-TT flywheels, clutches for 81+ turbo and non-turbo Zs
Flywheels and clutches for many Zs
Flywheels and clutches for many Zs