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?