Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Light Weight Flywheel - One For The Geeks!

WARNING - THIS ONE IS LIKELY ONLY FOR THE TUNING GEEKS AMONGST YOU!

A couple of years ago I bought this very light 3.2 kg Titan flywheel for Monty.




It'll certainly make Monty's engine spin up and gather revs at a rapid rate delivering increased throttle response and an even more exhilerating drive. However, I have to admit 3.2kg is on the very edge of being too light for street driving so I've held off from fitting it.

As all us engine tuning geeks know, a lighter flywheel can often yield many benefits, during the early 1990's when I was in the restoration game one of the first things we'd do to improve the way an Austin Healey performed was to machine quite a few lbs out of the flywheel. The crank alone in that big Austin six weighs an absolute tonn revealing the engine's commercial vehicle origins, so taking any mass out of the bottom end was a no-brainer that only yielded benefits.

However, a Ford Duratec is a very different engine, the potential benefits of a lighter flywheen are the same as those we enjoyed with those big Healeys we restored, but the margins that seperate success from failure are a lot tighter with Monty's little four banger Duratec. Flywheels exist for a reason, if you go too light the engine will complain letting you know you've gone too far by delivering a lumpy idle and poor low speed driving characteristics.

So how do we understand and define what's just right, from too light?

Well, one way we can check such things is to make use of the internet, I've been researching the subject for some time now making use of a few Caterham forums where it's commonplace to fit a lighter flywheel to a Duratec powered Seven, and the many MX5 forums where the Duratec powered Mk3 (NC) MX5 is often fitted with a lightweight flywheel. Excluding idle quality for a moment, one area of consideration is the vehicle's mass, the lighter the car the less flywheel mass you need to retain a smooth pull away at junctions and low speed drivability.

Monty's mass sits somewhere between a Caterham and an MX5 so with Seven owners fitting flywheels as light as 3kg and the Mk3 MX5 community generally agreeing its unwise to go lighter than 5kg, it seems likely Monty's flywheel weight sweet spot is somewhere between the two. That's a 4kg flywheel then, so my basic initial research does point towards my 3.2 kg Titan billet steel flywheel being a bit on the light side.

However, these days a lot of what I now do for a living heavily leverages the truly mind bending powers of artificial intellegence, so while I've completed my own old skool internet research and the results point to 4kg being Monty's flywheel sweet spot, I do have some engine management tricks up my sleeve that may just mean I might get away with 3.2kg?

The secret to getting good results with AI is to provide it with all the facts, we call this 'prompting', once 'trained' a correctly prompted AI engine is a very powerfull tool indeed, with its capacity to absorb all the facts it's a way more effective way to sense check a theory than simply searching a few forums.


So let's give AI the facts and see what it comes up with, here's my prompt....

I have a Titan 3.2 kg flywheel that I'd like to try in my Duratec powered Morgan Plus 4, my hope is I'll achieve an even more exciting and rev happy engine but I don't want to introduce poor idle quality and an overly sensitive throttle in the process.

The car must remain nice to drive in town, and it must retain a smooth idle.

The car only weighs 950kg so is quite a low mass to move, I also have an EMU Black ECU which gives me lots of control.

To hep with idle quality and reduce the effects of my 3.2 kg flywheel introducing overly sensitivity throttle behaviour, I plan to use the following ignition timing stratergies.

1. Advance my ignition timing at idle from 10 degrees to 16 degrees to help smooth out idle quality.

2. Retard my ignition timing on tip-in from 16 degrees to 7 degrees to dull and smooth out any unwanted overly sensitive throttle behaviour as I first pull away from a standstill.

Given the light weight of the vehicle, and with my above ignition timing stratergies, do you think I can still retain my stable idle at 970rpm, and the car's smooth street drivability after I've fitted my Titan 3.2 kg light weight flywheel?

And here's how AI responded....

Yes, with a Titan 3.2 kg flywheel, the lightweight 950 kg car, and your planned ignition timing strategies on the EMU Black ECU, you have a very strong chance of achieving both a smooth idle at 970 rpm and a well-behaved street car.

Analysis of Your Strategy
Your approach directly addresses the primary challenges associated with a very lightweight flywheel: idle stability and off-throttle jerkiness.

*1. Advancing Idle Ignition Timing (10° to 16°)*

Benefit: The advanced timing (closer to the point of peak cylinder pressure development) will make the combustion process more efficient and powerful at idle speed. This provides a more consistent "push" for the engine's power strokes.

*Result:* This added stability helps overcome the lack of rotational inertia that the lightweight flywheel would otherwise cause. The engine will "fire" more strongly, helping it maintain a steady rpm, which is crucial for a smooth 970 rpm idle.

*2. Retarding Tip-In Ignition Timing (16° to 7°)*

*Benefit:* Retarding the timing on initial throttle application reduces the initial, sharp torque output (torque "spike"). This effectively "softens" the engine's response when you first press the accelerator pedal.

*Result:* This directly counteracts the "overly sensitive throttle behavior" you anticipate. It smooths the transition from idle to acceleration, making pulling away from a standstill much less jerky and easier to manage in traffic.

*3. Car/Flywheel Weight Combination*

*Benefit:* The car's extremely low weight (950 kg) means the engine doesn't have to overcome much resistance to get the vehicle moving. A heavier car would struggle more with a 3.2 kg flywheel.

*Result:* This low mass works in your favor, reducing the demands on the engine at low speeds and making it less likely to stall compared to a heavier vehicle with the same flywheel.

So it looks like it's game on for the Titan super light weight 3.2kg Flywheel

I only paid £125 for it, OK so it needs a light reface and I will also need a clutch as It'll be mad not to change it when I fit the flywheel, but a really good clutch kit is only £350 so that's not the end of the world. For roughly £500 I'll be giving Monty even better throttle response and making the engine even more rev happy, the result being a car thats more fun to drive and in theory without risk of introducing any idle or drivability downsides.

For Monty, fitting the 3.2 kg Titan flywheel is therefore the best value for money modification going, I'll be achieving a real change in engine behaviour that I can genuinely feel, and for the very lowest possible financial outlay. It's also very rewarding to have my ignition timing stratergies validated by artificial intelegence proving what I already own up to, that I am a proper engine management mapping geek

As you can imagine, I'm great fun at parties

Of course the proof of the pudding is in the eating, if it turns out I don't like the results I can easily return to the standard flywheel, or simply fit a 5Kg light weight one designed for a Mk3 MX5 that are proven to deliver great results in the much heavier Mazda, so it'll definitely be fine in the 950kg Monty.

But following my extensive research I'm confident with some ignition timing tricks my Titan 3.2kg flywheel will be just fine, watch this space for an honest review at some point in the New Year!

Should be interesting watching you at Prescott next year!

Always Graham

That really is a good looking car. Fabulous picture.

Thanks Paul, Monty loves Prescott

https://youtube.com/shorts/gUo4uDXvOXo?si=yM07nsHZwQjvJfYC

https://youtube.com/shorts/5cIbIam1Woo?si=V38bTr1Fh73uImX_

Wonderful exhaust note...Music to my old ears... Thanks for posting.

Excellent write up, it will very interesting to hear how the lighter flywheel improves the car.
Bob.