What Lightened Flywheel? EcoBoost TVR content

I'm shopping for a new clutch and flywheel for my TVR project.  I attempted to use a stock Focus ST combo inside the NC 6-speed transmission, but it would seem there are clashes.

I have verification that the Miata units work fine, so I'm going to splurge on some shiny stuff.

I've pretty well decided on a Clutch-Masters FX350, that'll hold 400 ft-lb. 

What's the wisdom on lightened flywheels?  ACT has a one-piece chromoly piece that is 10.4 lb.  Exedy has a forged steel one that's 13 lb.  Or Fidenza sells an aluminum version that's only 7.6 lb and has the replaceable inserts.  Prices are similar, but lighter seems to cost more.

Any sweet spot here as far as weight goes?

I'm assuming the chromoly parts are less likely to explode and remove my ankles?

All of those are reputable brands and probably pretty darn unlikely to explode without a major mechanical overrev.

What are you using the car for? I'd probably go as light as possible on the track, and even the 13 pounder isn't really all that heavy so I would probably go with it for street use. Too light on the street can get annoying (my opinion) especially with a 4 cylinder that doesn't have a ton of inertia or unboosted torque anyway.

I vote for the forged steel unit. Strength is good, and for me a flywheel can be "too light" on the street. Wait - are you planning on this being primarily a street car? That was my understanding; if not and it's mostly a track car then lighter is better! ;-)

Street car for sure.  Definitely will get some autocross time too, but almost certainly no track.  I couldn't bear to ball it up.

At this point, the harmonic balancer is still on the engine.  That should help some with the smoothness.

The only downside to lighter is if you have camshafts that prevent a smooth low load drivability.  If you have stock cams, so the engine doesn't buck and snort and be unhappy at low load, lighter is better.

I don't understand how it is bad for engines with poor low end torque.  Reducing rotational inertia allows the car to accelerate faster no matter what.  Would you install a group 94 battery to increase low speed acceleration? Same thing.

Stock engine, with the high-octane tune.  Torque will not be in a deficit on this one.

I do like how my Focus ST is pretty docile in stop-and-go traffic.  It doesn't buck and carry on.  My old Protege5 was awful in traffic.

BTW, for comparison the stock NC flywheel is 16 lb.

FWIW, I liked a puck clutch and a 9lb flywheel on a rotary. So grabby clutch and low inertia.  Would often take off from a light in 2nd gear to save a shift, too.

Pete. (l33t FS) said:

I don't understand how it is bad for engines with poor low end torque. 

Not bad, just may be trickier for takeup. Like if you don't like to use the gas without releasing the clutch. Yes I know those people.

In reply to Paul_VR6 (Forum Supporter) :

That I understand, but that is also poor technique, not the flywheels fault 

High stall speed torque converters also creep less when in gear, some people think this makes them unstreetable.

So you're using NC miata parts in a car that weighs similar to an NC Miata? A stock Miata flywheels is already only 16 pounds, so I'm not sure I see the value in the 13 pounder. I'd be looking between the 10.5 and 7.5. flywheels. Especially with the street friendly (slippable) clutch you note, I'd be leaning towards the 7.5 route... Or 8.5 from Flyin Miata if you prefer one-piece steel.

In reply to Driven5 :

Yeah, the car should weigh about 2000 lb when done.

I'd somehow forgotten the Flyin Miata steel flywheel.  They don't really have any high-torque clutch options, so I think I just moved on from them.  I do like that flywheel though - lots of upsides.

I recently put a Fidanza on a Mazda3 with the 2.5 MZR that we now use primarily for Lemons and HPDE.  Zero issues on track and for low speed maneuvering it only requires a slight bit more care with careful clutch work than with stock.  For a use case like yours I don't think you'll have any problems going that light.  

I have owned two light flywheels one was behind a 5.0 in Ranger one was on a RX8 both were Fidanza and neither created any issues for me.

Ordered an 8.4 lb steel flywheel.  I feel pretty good about that.  Thanks everyone for the advice!