Lightweight flywheel - is it worth it?

  1. My model of MX-5 is: __Mk1/Eunos 1.8 S-Special
  2. I’m based near: __West Norfolk
  3. I’m looking for technical help or recommendations on: __Lightweight flywheels

Hi,

The rear crank seal on my MX5 is leaking, so the gearbox needs to come out and changing the clutch at the same time is probably a no brainer - it seems fine, but I have no idea when/if it has ever been changed.

However, I’m also wondering about having the flywheel changed for a lightweight one. I’ve spoken to a couple of people who have them and like them, although 1 did say it took some getting used to, especially with stalling etc. I don’t do track days, just normal, occasionally spirited, driving so I’m thinking it might actually be a waste of £3-400 plus the additional labour to fit.

I’d be grateful for any input from anyone who has one, especially if you use MX5 in a similar way to me.

Thanks

Phil

On a 1.6 Roadster, I went from a 1.8 standard factory flywheel (8.75kg) to a Mk2 1.6/UK Mk1 1.6 factory flywheel (7.15kg), I had a huge improvement in drivability, no stalling issues.

There were a variety of flywheels fitted.

Japan and US 1.6 models got a flywheel that weighed 8.3kg (P/N B61P11500A). For some reason, EU spec cars got a lighter flywheel, 7.15kg (B6S711500A). The same part number appears in Mazdaspeed catalogues at the time, and was fitted to the M2-1001 clubman special.

For 1.8s, Japan upto 1994/5, and all UK mk1s, a 8.75kg flywheel was fitted (BPE811500).

In Japan, for the RS-Limited onwards, and all 5-speed 1.8 Mk2/2.5s, a 7.9kg (BPR711500A) fywheel was fitted.

The Mk2 1.6 used the old Mazdaspeed lightweight flywheel.

Getting hold of a used Mk2 flywheel might be a shrewd low cost upgrade; the garage fitting mine charged an extra £50 for it to be balanced at an engineering shop.

Even shrewder, a 1.6 clutch can be fitted to a 1.8, with a 1.6 flywheel. The 1.6 clutch is more than adequate for a 1.8. Some of the cheap lightened flywheels are alumnium, and can give no ends of trouble, and trouble thats not easy/inexpensive to sort out.

I went from a 9kg flywheel to a 4.2kg one on a track car. It was still very civilised surprisingly. I raised the idle revs around 100rpm to smooth it out but apart from that I loved it. It needed a few more rpm to pull away but you adjust in no time, it’s like driving a 1.2 or a 1.8 engines car, just rev a touch more as you slip the clutch.

The upside was the way it reved out, was much better than standard, from idle to redline much faster. Sounded ace too as the revs rose and dropped rapidly, one of the best things about a bikes engine sound IMHO.

2 Likes

Hi The S special has the JDM lightweight flywheel already fitted, This flywheel became the standard fittment from the Mk2 onwards. You will notice better pickup with a lighter flywheel and better acceleration. Heavy wide wheels and tyres will ruin any advantage of a light weight flywheel.
I drive an ITB 1800 with a lightend stock JDM flywheel and a stock 1800 eunos with the same flywheel as yours, Its hard to notice the differance in gearchange as the synco is what slows down the gearchange
.I think your flywheel will be 7.6 Kg
My ITB car has a 7 Kg flywheel which is the 7.6 KG one with the inertia ring removed.
The ITB car is quicker as it is running at 169 Bhp. I sprint and hillclimb both my cars and both are used on the road,
Until you start to do track days and racing do not fit a very light flywheel but a lighter one will be of benefit. Making sure you have light wheels and tyres will improve the car more.
Think of each wheel Tyre as being a flywheel which has to be accelerated and braked.

2 Likes

For Series 1 NA8C, all Roadsters had the same flywheel (BPE811500). Parts listing:

http://do-da.co.jp/sun-mec/na8s1/na8s1_1100.html

The Series 1.5 NA8C (from NA8C-300000)introduced the lighter flywheel (BPR7-11-500)

Parts listing

http://do-da.co.jp/sun-mec/na8s15/na8s15_1100.html

Note, same part whether or not RS, R Limited, S-Special, S-Package etc.

Series 2 NA8s (from NA8C-400000) kept the same lighter flywheel

http://do-da.co.jp/sun-mec/na8s2/na8s2_1100.html

When it comes to the NB1 1.8, two flywheels are listed

http://do-da.co.jp/sun-mec/nb1/nb1_1100ab.html

BP5V-11-500
BPR7-11-500

One is for the 6-speed, and is the same flywheel as used on all Series 1.5 and Series 2 JDM NA8Cs.

1 Like

Many thanks for the replies. I think I will probably go ahead if the cost isn’t too prohibitive :+1:

Regards

Phil