Lightened flywheel options

[DerekJ]

Demos

You are correct. The Peak torque on my car is at about 4700 revs. Peak power of 160 bhp came in at 5500 revs and then dropped off as I revved the car up to 6000. At 5800 revs torque had dropped to about 137 ft/lbs.

I have a flat torque curve from 3000 to 4700.

I think the lightened flywheel will be very useful for the tight and winding hill climb courses.

 

[Bob_Spidell]

... I think the lightened flywheel will be very useful for the tight and winding hill climb courses.

Get some before (flywheel lightening) and after numbers and let us know.

The technical explanations and anecdotal reports are compelling, but I've never seen any 'my track/strip/hillclimb numbers improved XX% due to flywheel lightening' statements anywhere.

 

[DerekJ]

Bob

I think you'll find the answer in every racing car. F1 cars don't even have flywheels.

Power is torque multiplied by revs. With a lightened flywheel you get the revs quicker therefore you get the power quicker. Overall, at peak power and optimum revs there is no overall power increase. It is just that the power is delivered quicker and it is shed quicker which provides better engine breaking, and that is why it is used in motorsport.

 

[HealeyRick]

Bob

which provides better engine <span style="font-weight: bold"><span style="font-style: italic">breaking</span></span>, and that is why it is used in motorsport.

Probably not quite the result you're looking for

 

[Bob_Spidell]

Another compelling argument, to be sure. But I'd still like to see credible comparison numbers (in all the lightened flywheel discussions and data I don't recall seeing any before/after numbers--usually you do for 'speed' mods). I thought since you're doing (presumably) timed hillclimbs you'd have some numbers to compare.

It's clear to me that an engine would rev/'unrev' freer in neutral with a lighter flywheel; what isn't intuitive is why six pounds--even at the periphery of a 18"(?) disk--would make much difference when you're pushing a 2,400 pound mass (the mathematical explanation is compelling, but my calculus is way too rusty for me to totally verify).

Flywheels are (sometimes) used in F1--in a different way:

https://en.wikipedia.org/wiki/Kinetic_energy_recovery_system

 

[Randy Forbes]

I think the only way to get Bob on board with this, is if we all chip in and get him a turned down flywheel.

It would be difficult to "prove" with quantative numbers, because there are too many variables on any given track; just the barometric pressure from one day to the next could affect lap times. A tester would have to run several laps to get a baseline, then instantaneously pull the trans/clutch swap flywheels and put it back together and get back on the track before conditions changed (like shade replacing the direct sun in a corner...).

How about this for a test; take your 9" Milwauke grinder with a Pipeliner (9") disc and "feel" how quickly it comes up to speed when you pull the trigger and coasts to a stop when yu release it. Now put your 4-1/2 grinding wheel on the motor and do the same test.

The key element is "feel" and it's uncanny at first, but of course you get used to it. Whenever I drive someone elses Healey, it feels very sluggish and lazy climbing the revs. You need someone in SoCal running a lightened flywheel to give you a demonstration :wink:

 

[Bob_Spidell]

...

How about this for a test; take your 9" Milwauke grinder with a Pipeliner (9") disc and "feel" how quickly it comes up to speed when you pull the trigger and coasts to a stop when yu release it. Now put your 4-1/2 grinding wheel on the motor and do the same test.

...

... except, in both cases strap a 5lb weight to both discs--analogous to the 2,400lbs you're pushing--and see what the difference is.

Don't get me wrong, I believe the testimonials from experienced people like you and Richard. I just can't wrap my head around how lightening a flywheel making a difference with the clutch engaged and pushing the weight of the car. But, it's obvious the unloaded engine would rev and decelerate quicker.

If a stock flywheel makes a Healey feel sluggish, I would think that would be evident in, say, 0-60 or quarter-mile times, even with some changes in barometric pressure. Has anyone gotten the average of, say, ten 0-60 runs on one day, then installed a lightened flywheel and done the same a day or two later, on the same track or piece of road in similar atmospheric conditions?

I have a 3.54 rearend in my BJ8, which makes engaging the clutch more touchy, so I think a lightened flywheel would only make it worse.

 

[HealeyRick]

I'm still looking for hard data; i.e. 'my track/quarter-mile times improved 3% after I had my flywheel lightened.' I don't think you'll see any difference on a dyno, unless there is an actual increase in rate of acceleration and the dyno can compute that.

Bob,

You're right, there's a lot of seat of the pants impressions but not a lot of real data out there. But David Vizard (probably the best known BMC "A" series engine tuner out there) did some back to back testing on Mustangs here: https://www.popularhotrodding.com/tech/0602phr_rear_wheel_power_increase/

 

[Bob_Spidell]

Wow, excellent article. Finally, we put some numbers to the theory. Interesting side point about removing the damper actually reducing power.

I think I'll stick with the stock manhole cover in my BJ8--mostly because of the taller rearend--but now I want a Fidanza flywheel in my Mustang!

 

[HealeyRick]

I think I'll stick with the stock manhole cover in my BJ8--mostly because of the taller rearend--but now I want a Fidanza flywheel in my Mustang!

I put a Fidanza on the 5.0 in my Nasty Boy when I was putting it all together. It revs really nice, although I don't have anything with which to compare it.

 

[Patrick67BJ8]

Wow, excellent article. Finally, we put some numbers to the theory. Interesting side point about removing the damper actually reducing power.

I think I'll stick with the stock manhole cover in my BJ8--mostly because of the taller rearend--but now I want a Fidanza flywheel in my Mustang!

IMHO, I think removing the non-clutch engine fan blades and replacing them with a temp-clutch type might do more for HP or, completely removing the engine fan and just running an electric temp controlled fan would also help HP. Then there's the "crossover" pipe between the front two header pipes that could help. These mods actually do work.

 

[Hoghead]

I see that Randy has cut his down at the outer rim to ring gear thickness extending to the clutch mounting tabs, resulting in a 4.6 lb reduction in weight. Note that this is removed from the outer rim of the flywheel for max effect, and easy to do

Presumably more weight could be removed from the rear or even front of the flywheel, to a lesser effect that if taken from the rim, but still an effect.

Assuming that one chooses to do this, how much weight removal is "right" for street use in a BJ8 with overdrive

 

[HealeyDave]

I'm late to this thread but thought I'd throw in my 2 cents: The physics being talked about here is change in rotational inertia, not change in vehicle mass. In the linear domain: Force = mass x acceleration. In the torsional domain, which is what we are talking about here: Torque = Torsional Inertia x alpha (torsional acceleration). So, for a given torque coming in from the crankshaft (pistons firing force (lbs) at a crank throw distance (feet) = torque (lb-ft) on the crankshaft) a reduced flywheel inertia will result in increased torsional acceleration available to go down thru the propshaft thru the diff and out to the wheels. Everything will spin up (and down) faster.
Flywheel inertia is a large part of the rotating inertia of the vehicle powertrain. Inertia is the tendency for an object to remain at rest, or in motion. Some guy named Newton may have proved that. Reducing it will improve vehicle response to a given torque input from the engine.
Downside can be less inertia to smooth out engine firing pulses, so some compromise is probably best for a road car. Go too low in flywheel inertia and you may run into driveline durability issues due to the engine firing pulses beating everything up faster (clutch springs, trans dog clutches, synchros, u-joints). Probably why Harley's have such big flywheels - to try to reduce the torsional vibration from the uneven firing pulses from getting into the system. But it doesn't work to well
I think ..........

 

[Patrick67BJ8]

I see that Randy has cut his down at the outer rim to ring gear thickness extending to the clutch mounting tabs, resulting in a 4.6 lb reduction in weight. Note that this is removed from the outer rim of the flywheel for max effect, and easy to do

Presumably more weight could be removed from the rear or even front of the flywheel, to a lesser effect that if taken from the rim, but still an effect.

Assuming that one chooses to do this, how much weight removal is "right" for street use in a BJ8 with overdrive

A link to an magazine article I sent to John for his website. There are also more articles on his website.
https://www.healey6.com/Technical/Competition.pdf

 

[BoyRacer]

Bob,
If you want to drag race your Healey then you should keep your 30 lb flywheel. Because, as you are reving your engine to 5000 RPM, that massive flywheel helps launch your car out of the shute, as you dump your clutch.
But Bob, most of us are not drag racers. Some of us are actually sports car racers, that accelerate, decelerate, brake hard, downshift, upshift, and drive deep into and out of turns. With a lighter flywheel, all of these changes can be effectuated much more quickly..... which makes us go faster ...and have more fun.
On the other planet, a 30 pound flywheel is great for a big Austin sedan. It's smooth, slow, no jerkiness. Good for old people.
Not to beat a dead horse here.... BUT.....I hold the track record at Road America for the fastest Austin Healey. I use an aluminum flywheel that weighs 10 pounds. That is not anecdotal. I have the time sheet.
One last point, if you are having problems moving off the line with a 3.54 rear end in your BJ8, then I think you need a tune up or a rebuild. Our engines make lots of torque if they are running right. The 3.54 was the factory offering for a non-overdrive BJ8.

 

[Randy Forbes]

I see that Randy has cut his down at the outer rim to ring gear thickness extending to the clutch mounting tabs, resulting in a 4.6 lb reduction in weight. Note that this is removed from the outer rim of the flywheel for max effect, and easy to do

Presumably more weight could be removed from the rear or even front of the flywheel, to a lesser effect that if taken from the rim, but still an effect.

Assuming that one chooses to do this, how much weight removal is "right" for street use in a BJ8 with overdrive

Material was also removed from the backside (in reality, the forward-facing side when bolted to the crankshaft...), and the entire face (contact surface) was skimmed .125" for clearance with an MGC xmsn setup__this reduced height is currently working just fine with a Healey side-shift box as well.

 

[John Turney]

Back to the original question, since you're in the UK and have a DWR8 cam, have DWR lighten your flywheel. They did mine.

 

[Hoghead]

Randy
You seem to have a pic of everything - do you have one of the back side of the flywheel or can you post a drawing on where and how much to remove?

 

[Patrick67BJ8]

Randy
You seem to have a pic of everything - do you have one of the back side of the flywheel or can you post a drawing on where and how much to remove?

There's a link to www.healey6.com that I previously posted earlier in this discussion that shows how much to remove from the backside using a "quarter" as a measuring tool. The picture of the mag article is clear enough to use. BTW: For BJ8 Healey engines the flywheel dowel pins are different than the ones from earlier cars and are no longer available. I found out the hard way when the machine shop lost mine when they resurfaced my flywheel. I did end up making a drawing for them for the next time.

 

[Hoghead]

I am loath to give a machinist the photo with a quarter as a measurement reference and cannot find a proper drawing
I did however find this for a BN1
https://www.britishcarforum.com/bcf/showthread.php?73613-Lightening-BN1-Flywheel

Anyone have a drawing for a BJ8 flywheel?