The mythical GX390/420 grenading flywheel

[Brian Boyer]

Originally Posted by Streetbu

My buddy raced cage carts with clone engines for years. Long before there were many performance parts available. He actually took a stock flywheel and machined it down on a lathe to lighten it. Dropped almost half the weight. Then sent it out to be balanced. Ran the same flywheel for 6 years, spinning a max of 8800 rpm. No issues.

[TJL]

Yes you can balance a stock flywheel and it will be safer to a higher rpm. Find some pictures of a fragged cast iron flywheel. The tractor pull guys have had it happen and the results are quite nasty. A chunk of cracked cast iron flying at a high rate of speed does some serious damage. If it were to hit you you could easily be killed. For the relative cheap price of a clone billet flywheel i think its a very good decision.

[Brian Boyer]

I just simply cant find any, none.. They are all GX200/ Predator 212 class wheels. (And i have not seen a wheel i didnt think was way over-priced..)

I'm not faulting guys for using them/ its your motor.. I just need the limited play money i have to go directly to helping the motor make power.. (Does the flywheel "free up" some power,.. Ehh,.. Guys claim so, in theory i know it ~SHOULD~,.. But in real world applications for us does it free up anything?.. (Not really,.. They do look cool though)

Guys like me running the 18ah charging Lifan there really needs to be a true reason to go billet and i just dont see any. Thats a LOT of money to go for parts that REALLY help make more power.

[raydhd]

Vegascarts and ARC both have billet flywheels for the 390-460 engines.

[sho305]

I was told you can make some good power under 6K rpm, especially if you don't want a radical race motor in your GC as well. Was told you can run it to 6K and even if it does break in a GC you should have a guard/etc. My G9 has a steel plate under the seat. I don't run 6K anyway and plan to stay under that. If you go big rpm you have to pay to play, the flywheels create force to the square iirc, way more forces at higher rpm. You can also get honda flywheels, you can get other wheels cut to this taper from other racing mower engines though you will have to remount the coil. Others say a heavy flywheel is not good on the bearings at high rpm either, in particular if its out of balance at that high rpm.

If you can't afford the performance parts you may be better off swapping to a bike engine, or get a used v twin to build up. There are many ways.

[Brian Boyer]

Originally Posted by sho305

I was told you can make some good power under 6K rpm, especially if you don't want a radical race motor in your GC as well. Was told you can run it to 6K and even if it does break in a GC you should have a guard/etc. My G9 has a steel plate under the seat. I don't run 6K anyway and plan to stay under that. If you go big rpm you have to pay to play, the flywheels create force to the square iirc, way more forces at higher rpm. You can also get honda flywheels, you can get other wheels cut to this taper from other racing mower engines though you will have to remount the coil. Others say a heavy flywheel is not good on the bearings at high rpm either, in particular if its out of balance at that high rpm.

If you can't afford the performance parts you may be better off swapping to a bike engine, or get a used v twin to build up. There are many ways.

I don't ever ever plan on spinning over 6,000 rpm.. This thread was a study for me, one forum to the next there are so many folks passing the kool aid around/ its refreshing that the billet kool aid mentality isn't dominating this forum..

I want to post a link to this thread on my mud motor forum but nahh, let them fellas keep spending money on billet ARC flywheels and ARC rods (the wrong length lowering CR) and then run 4,700 rpm.. I look at it as a leg up for me financially in parts that actually help make more power WITHIN the rpm range our muddies operate in.

This forum is a huge big block resource.

[sho305]

We try to help, I mean fun is the name of the game and if your cart can run better its more fun right....lol!

Billet flywheel can have other advantages, it will lighten the entire engine some since that is the only huge iron part other than the crank. It will rev quicker. It may start harder and idle faster though. You don't have to worry about failure at high rpm.

Its one of those things, do you need it for those reasons or not? Depends on what you are trying to do. You don't want to toss the usual list of go fast parts on an engine if you don't need certain ones....better to use those funds for something that matters. You don't need a flywheel for lower rpm, though it can help on a kart because it is more weight sensitive, and you may come off the corners faster with a quicker rev and one gear drive. But in my 600lb dry GC with a CVT drive, I doubt it changes real performance that much for a <6K rpm engine. I could buy a big cam and valve parts that would make real power instead, for example.

[rose88]

Originally Posted by Streetbu

My buddy raced cage carts with clone engines for years. Long before there were many performance parts available. He actually took a stock flywheel and machined it down on a lathe to lighten it. Dropped almost half the weight. Then sent it out to be balanced. Ran the same flywheel for 6 years, spinning a max of 8800 rpm. No issues.

Who can turn stock 420 predator flywheel and balance it?

Thanks

[slonomo]

Originally Posted by rose88

Who can turn stock 420 predator flywheel and balance it?

Thanks

Any engine machine shop can do it.

[raydhd]

Brad Porcellato of the engineering company of that name did flywheel weight reduction and balancing for Club Car . BUT he Warned against using just any machine shop to do this as they do not know what critical areas not to remove. They did extensive testing of flywheels after weight reduction. They spun them a high rpms in containment chamber and see what machining caused failures. P.S. Many of his videos are still on youtube under " Brad Porcellato DBA Porcellato Engineering "