What do you think about lightening a 1.6 Flywheel?

[RoadsterTech]

I was looking at the Spec Miata forum and it looks like there's some rumbling to allow the 1.6ers to remove the back inertia ring from their flywheels.
Looks to be around $100.00 for the ring removal, surfacing and balancing.

What do you guys think about doing this?

[SM16RMSM]

I never heard that one before. Then again, I run a 1.8L.

[RoadsterTech]

Sorry I just checked. It was an old thread.
I am more interested in lightening the Flywheel. Since it appears hi have been somewhat endorsed.
Good idea or not.

[RoadsterTech]

Here is the old link.
http://forum.specmiata.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=44;t=002885;p=0

I guess my biggest question is that if safety. I haven't heard of any broken flywheels on a Miata.
What do you guys think. Any one running a lightened OEM flywheel?

[kung fu jesus]

That is my biggest fear too. I think the pricing on good chromoly flywheels is an extra $100-$200 more. Hard to put a price on peace of mind.

[Demon I Am]

I've had nothing but good experiences with the F1 lightweight flywheel on both of our cars.

[maharaj]

I wouldn't lighten a factory flywheel. The tolerance will be compromised. If a lighter flywheel is what you are wanting then I'd suggest a lighter aftermarket one but make sure it isn't made in China!!!!!!!

[Phatmiata]

I had a racing beat flywheel in mine, it took a couple days to get used to, but it was fine after that. I don't have experience with the stock one being lightened other than regular maintenance (like getting it turned) when you replace the clutch.

[RoadsterTech]

After reading a lot of threads on this from multiple different forums I have come to believe that the only safe lightening is to only remove the inertia ring on the back side of the flywheel. Any additional removal of structural material in my mind is unsafe. I value my ankles too much!

What can one expect to remove from the back side of the Flywheel?
We are talking about a cylinder with an ID of 235mm and an OD of 245mm and a height of 9.5mm. If I am overly optimistic I would say that I could remove 3 lbs this way in reality I think it would be more like 2.5 lbs or 1.134Kg.

This is a rotating cylinder so the inertia is 1/2M(a^2 +b^2) a = inside diameter and b = outside diameter.

This gives us and inertia of 0.0679 KgM^2.

Inertia is an interesting beast in that it effects torque only on acceleration and is based on the acceleration component. So, we are looking a an effect that only occurs during acceleration the faster the acceleration the more negative effect on torque the inertia will have.

Logic would tell us that the acceleration on first gear will have the greatest parasitic effect (at least on a 1.6 Miata). First gear gives us the greatest acceleration.

I have some handy force calculators I use when sizing servo systems. I decided to use these here.. I only needed a viable Idle to red line speed in first gear... One of the TBM members published a chart in his Megasquirt thread that gives me that acceleration time.

For first gear we see it taking ~4 seconds. to go from 650 to around ~7650 RPM... I will use a rise of 7000 rpm over 4 seconds.
this gives us an acceleration time of 1,763 RPM/Sec.

Pluging this into my calculator I get a required torque of 3.72 NM or 2.75 lbf-ft. This reduced with every gear change. So that is about the maximum torque saving we would get on a safe lightening of an OEM 1.6 flywheel.

Assuming a max torque of ~90lbft we would effectively get 92.75 lbft, a savings of less than 1% I think I will spend my money elsewhere.

I am not bashing Aftermarket Flywheels these reduce the spinning weight by a significant amount, but safely shaving an OEM Flywheel just doesn't get you much and is not worth the $100.00 to lighten and balance.

[Phatmiata]

Well you can always install a scatter shield if you are worried about it exploding, but then that kinda defeats the purpose of shaving the weight in the first place.

[kung fu jesus]

A lighter flywheel can add more chatter from gear lash. My aluminum FW was ~8# and chattered quite a bit. My Chromoly FW weighed ~10# and was much quieter. I don't recall much, if any gear lash heard on that one. Both were 1.6 sized.

You can expect inertia to fall off much quicker between shifts, which can be a little wearisome in stop-and-go traffic. You can also find heal/toe maneuvers much easier because of quicker RPM response. Personally, it was one of my favorite modifications I did to my Miata for enhancing the driving experience.

I don't like lightening the flywheel because it is cast iron. It just worries me about eliminating the material and exposing a flaw or stress fracture in the casting. I like my ankles too much to risk a spinning guillotine should it let go. $.02

[RoadsterTech]

right now goodwin has the 1.6 F1 for $184.00 "Demon I am" did you have any issues with the F1 flywheel? Kung fu do you have the F1? BTW I calculated a 10lb wheel and in first gear it gives around an 7.4 lb-ft increase in available torque... not too shabby for a $184.00 investment. This or a header? I think the Flywheel might actually be of more benefit.

[Demon I Am]

I love my f1 flywheel. I have one the an OE Exedy clutch in the Miata, and one with an ACT Stage1 in the SpecV. Car spins up much quicker and makes rev-matching a breeze.

KFJ saw mine when we did the engine swap, so he knows more about how it looks after 2 years than I do.

I would suggest the flywheel, and a new clutch, if you think yours is in need of replacement. It's a big job to replace. Bang-for-buck though, it is pretty awesome.

[RoadsterTech]

I actually have a exedy stage 1 waiting for the engine to be swapped out. So now is the perfect time to do this.

[kung fu jesus]

Rick, I bought my F1 FW from Goodwin. It is a nice piece and a good price. Be warned the pilot bearing bore may need a little clearancing to get the bearing in properly. A little time with some emory cloths will do the trick. That was the only issue I had with it. I would do this before the header. It just makes the car far more entertaining to drive.

[RoadsterTech]

Just pulled the plug and ordered the F1

[Demon I Am]

sweet.

[kung fu jesus]

Don't know if you have done this or not, but I strongly recommend the long braided clutch line 949 Racing sells. You can remove that hardline between the firewall to the clutch slave. Makes swapping out slaves SO much easier. I would even go so far as to recommend the slave AND the clutch master if you haven't done either in a while.

[RoadsterTech]

Are both ends if the flex lines the same? I might have our local Goodyear rubber make me up one.
Yea, I was planing on swapping out the clutch Slave and master didn't think about the flex line.
Thanks!

[kung fu jesus]

Not sure. IIRC, the connection at the firewall is female, the other end at the slave is male.

[RoadsterTech]

Here are a few pic's of the old flywheel vs the F1 Racing flywheel

http://rabrillhart.smugmug.com/Other/miata/i-S88Sm9f/0/M/CA_03241320573545-M.jpg

http://rabrillhart.smugmug.com/Other/miata/i-bN737Lp/0/M/CA_03241320592219-M.jpg

http://rabrillhart.smugmug.com/Other/miata/i-ctMDpDN/0/M/CA_03241321020219-M.jpg

[kung fu jesus]

Nice

[RoadsterTech]

I got it on and its running very nicely. My pilot bearing was tight but the hole did not need reaming. I expected a little bit more out of it but there is definitely a difference in acceleration. There is no additional transmission noise and down shifts were not a real issue, but if I let the rev's die even the slightest on start-up it will stall. The wildest thing is when I turn off the engine it dies almost instantly... No more wind down.

All in all well worth it.

[kung fu jesus]

Reset the ECU, it should help with the stall. I think the F1 version is the best compromise. The 7 or 8# Fidanza is loud and takes a little getting used to for daily driving.

Still my favorite driver's enthusiast mod for this car.

[Flyin 92]

I have the ACT 10# and love it. Like KFJ said, it takes a little getting used to. I'd love to have the benefits of a light flywheel without all of the noise.