1997 Mazda MX-5 Miata: Flyin' Miata Clutch And Flywheel
March 22, 2011
After Project Miata's tired stock clutch scuppered our plans to run acceleration testing, it steadily worsened. We needed a solution, so we tapped the fine folks at Flyin' Miata, the universe's single largest player dedicated to the Miata aftermarket.
Hit the jump.
A few days later, a box arrived containing what you see above -- a Flyin' Miata Level 1 clutch and lightweight flywheel along with new pilot and throwout bearings, a clutch interlock override doohickey and an alignment tool.
"Level 1" might sound tame, but consider the specs: this clutch is rated to hold 318 lb-ft of torque (as measured at the flywheel). Project Miata in its current guise is twisting out 141 lb-ft at the wheels (Dynojet), so Level 1 gives us a wee bit of margin. Plus, it's purple.
The clutch disk itself is an organic friction material with a heavy copper loading that increases torque holding capacity. Here are some words of wisdom for the noobs in our midst: if you want to drive your car on the street, you want an organic clutch lining and not some ceramic puck-type nonsense. Non-organic clutch linings provide engagement that is like a lightswitch and/or very juddery and you will hate (and I mean HATE) your car. Track-only cars that don't need progressive engagement can get away with the more aggressive friction materials.
Barney the purple pressure plate is a unit with a relatively high clamping force. Clever detail work within means this clamping force is achieved without ridiculous pedal effort. By using more of the available pedal travel, the Flyin' Miata clutch can pile on more total clamping force with little change in effort. Flyin' Miata are smart like that.
A lighter flywheel is one of those decisions that seems like a no-brainer but is easy to overdo and then regret. Like the clutch lining question, prudence should rule here. On a race car, sure, make the flywheel as light as you can. We're building a true dual-purpose car, so it's got to be streetable. Go too light and it will be tough to modulate engine speed every time you leave a stoplight.
Really, talking about flywheel mass is incomplete. We should be talking about rotational inertia if we're to be totally accurate, as two flywheels of identical mass could have radically different inertia, depending on how that mass is distributed. This is because inertia changes with the square of the radius. But until flywheel manufacturers start publishing product data in units of lb-in^2, we're stuck with mass.
You've probably seen claims of increased horsepower for lightened flywheels. There's a big asterisk here -- the amount of power sucked up by flywheel inertia depends entirely on its rate of change of the speed. The faster the revs climb, the more difference a lighter flywheel will make in power delivered to the wheels. Hence, light flywheels make a bigger difference when accelerating in the lowest gear (first) since it is here the revs can change quickest.
But hang on -- the revs can change even more quickly when you're not accelerating at all. Think how fast the revs climb during a gearchange when you blip the throttle to match revs. Here, light flywheels shine brightest, making your engine feels less trucky when shifting. They're about a snappier driving experience.
The FM flywheel weighs 13.5 pounds to the stock 20-pounder. You can see the holes near the center of the FM unit, but the bigger deal from the all-important inertia standpoint is probably the FM's flywheel's lack of a giant inertia ring waaay out at a large radius. Note the large, fun-sucking flange protruding from the stock flywheel here.
Another thing we like about the FM flywheel -- it's made of steel. The whole thing. Aluminum flywheels with their fussy multi-piece construction, delicate threads and inherent fatigue limitations are an unecessary can of worms. I'll only ever use an all-steel flywheel on cars I build.
Mark at MD Automotive helped out tremendously with the installation, applying his decades of Miata experience to make the process inhumanly smooth. You rock, Mark.
We'll have driving impressions of the new getup in the coming days, and then (in a few weeks' time due to a convoluted testing schedule, unfortunately) we'll run numbers on this little green supercharged Tic Tac.
--Jason Kavanagh, Engineering Editor
970 464 5600