Jersey Posted April 5, 2005 Share Posted April 5, 2005 I'm going to be swapping the blown T5 out soon and thought about lightening the 240mm flywheel up a bit while i'm in there. The Fidanza unit is real nice but @ 10-11lbs, it's too light for me. AZC has lightweight steel ones @ 13.5lbs but i remember Jon (Jmortensen) saying that a bunch of machinists looked at this flywheel and were concerned about thickness. I think the 240mm in it's stock form it weighs 23lbs (?) so i was figuring to reduce it to around 16lbs which should show a good improvement in rev speed. I'm just curious to know if you guys think this is a safe weight to shave the stock cast unit down too? Anyone know of a 240mm flywheel that's proven safe that weighs in at around 16lbs? I'd like play ball with my son on both feet when he's older Quote Link to comment Share on other sites More sharing options...
Clifton Posted April 5, 2005 Share Posted April 5, 2005 The AZC flywheel is fine. One machinests opinion on a flywheel is like one mechanics opinion on turbo L28's at 20 psi. My HKS flywheel is lighter 10 lbs and just as thin, I don't know why you don't want it that light. It isn't any less drivable. The Greddy ones for 7M's are just as thin too, only the ring gear is cut in and not pressed on. Cast iron is alot weaker than billet steel if you are worried about your feet. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted April 6, 2005 Share Posted April 6, 2005 I took my stocker to 17.75lbs from 23lbs, with most of the material removed from the outside. Make sure that there are no sharp edges when it is machined out, it should have a nice radius to it. This mod made a huge difference in my car and was well worth doing. I am not sure I'd take the stocker any lower than 17lbs though. If you want to go lighter get an aftermarket unit. Quote Link to comment Share on other sites More sharing options...
Jersey Posted April 6, 2005 Author Share Posted April 6, 2005 Thanks Drax. 17lbs sounds good. Trust it fully? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 6, 2005 Share Posted April 6, 2005 Just to clarify--the issue stated by all 3 machinists who questioned my flywheel was the outer rim. It is cut sharp on the backside, no radius, and that sharp cut goes straight through all 6 pressure plate mounting holes, which are threaded. This supposedly is a great way to get a stress riser. They all said that the threaded holes should not have been cut through. They were the only 3 machinists who had ever seen my flywheel, so it was 3 for 3, and it was seen years apart by machinists who did not know each other. The other big deal was that it took a LOT of balancing, despite the fact that it had balancing holes in it from Dave. I haven't seen the HKS unit up close in a number of years, but somebody posted a picture of one and it's backside was radiused, not cut in sharp corners. With that said, I've inspected if for cracks twice and no problems yet, and I've had it on for maybe 7 or 8 years with no troubles at all. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted April 6, 2005 Share Posted April 6, 2005 No sharp edges, no cutting through bolt holes. (especially threaded ones!) Couldn't agree more with those machinists. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 6, 2005 Share Posted April 6, 2005 If anyone cares to see exactly what we're talking about here, here are some pics: http://www.arizonazcar.com/fly.html Quote Link to comment Share on other sites More sharing options...
Jersey Posted April 6, 2005 Author Share Posted April 6, 2005 Clifton, Drax, Jon.. Thanks for the replies. Clifton, My Z is basically a "sunny day" driver but i'm still going to dragrace it a bit just to (hopefully) get it into the 11's and then i will focus on more open track type racing which is why i'd rather not go as light as 10lbs. If the 17lb weight shows a good improvement as Drax says, and is 100% safe, i think that would be a good compromising weight for what i'm looking for. I'll make sure the machinist i take it too doesn't shave down the bolt hole edge and makes a radius cut. Appreciate the info all. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 6, 2005 Share Posted April 6, 2005 If you've got the cash I really like the light flywheels. There is a noticeable difference between a 10 and 12 lb IME. Might not be the best for drag with a turbo, but would kick butt on a track. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted April 6, 2005 Share Posted April 6, 2005 If you want to be 100% safe.... well... sell the car, buy a bombshelter and never come out. As always, modifier beware! Quote Link to comment Share on other sites More sharing options...
Jersey Posted April 6, 2005 Author Share Posted April 6, 2005 Thanks Drax. Quote Link to comment Share on other sites More sharing options...
Clifton Posted April 6, 2005 Share Posted April 6, 2005 Here's a Greddy/Trust flywheel. I'm hosting it so it may not show up at times. Here's AZC Quote Link to comment Share on other sites More sharing options...
Jersey Posted April 7, 2005 Author Share Posted April 7, 2005 Thanks Clifton. Appreciate the pic comparison, Quote Link to comment Share on other sites More sharing options...
Jersey Posted April 13, 2005 Author Share Posted April 13, 2005 Welp, after all this, i decided not to lighten up the stocker. I took it to a few machinists today and they said it was do-able to bring it down near 17lbs, but they all showed reservations about the safety issue. Good enough to change my mind. I'll guess i'll just use the stock 24lb'r for now. If i could find a used light (10-13lb) aftermarket wheel, id try it i guess. I would just hate to spend over $300 on a piece that i may pull out in a short amount of time. It's tough being budgeted Thanks again for everyone's input. Quote Link to comment Share on other sites More sharing options...
Forrest Posted April 13, 2005 Share Posted April 13, 2005 Keep checking on ebay. I just saw one on ebay for 240$ shipped buy-it-now. The fidanza is nice because it has a replaceable friction surface. If you're using grabby clutches you'll appreciate that feature a LOT. They are only like 54$ from Summit, so keep in mind that any used fidanza you can find with good teeth can be put back to new condition for that price. I love the engine response you get from the 10lb flywheel. Quote Link to comment Share on other sites More sharing options...
BillZ260 Posted April 14, 2005 Share Posted April 14, 2005 Good call on modding the stocker. I am sure it can be done but I would have to say the aftermarket FW would be the way to go, since it was designed to be light and on your engine. Quote Link to comment Share on other sites More sharing options...
Jersey Posted April 14, 2005 Author Share Posted April 14, 2005 Thanks Forrest, Bill. I had a lightweight in my first Z (below) back in 1987 and loved the response as well. Check out those fog lights and that off-road ground clearance! lol... Quote Link to comment Share on other sites More sharing options...
Guest tony78_280z Posted April 14, 2005 Share Posted April 14, 2005 Does a lighter flywheel make that big of a difference. One is only shaving off 5 to 7 pounds, althogh I see it is rotating mass. But how much of an improvement can be made? "I love the engine response you get from the 10lb flywheel." and "There is a noticeable difference between a 10 and 12 lb IME." Are there any drawbacks to a lighter fly wheel? I supose I should have looked into that when I was putting in my tranny a few weeks ago! Dang it! Quote Link to comment Share on other sites More sharing options...
arizonazcar Posted April 29, 2005 Share Posted April 29, 2005 The azc (arizonazcar.com) flywheel is made from hot rolled steel not cast iron like a stock one and is fully CNC machined. My flywheel is exactly as thick as the HKS ones we used to sell until they were discontinued (we sold hundreds of them). I know of no failures in the 8 years or so we’ve been making them. The ring gear land sees no load except for the torque applied during starting, and centrifugal force . The centrifugal loads are offset by the steel ring gear that is interference fit (heat shrunk) into place. John's 3 machinists are wrong and have obviously never seen the flex-plates used as flywheels on stock cars. Also the factory pressure plate bolt torque is 12-15 ft/lbs. , you'll break the bolts off long before they ever strip out. A stock cast iron flywheel is way more likely to fail than my billet steel one Especially if lightened . I would NEVER take a significant amount of material off a cast iron flywheel. Dave Quote Link to comment Share on other sites More sharing options...
Drax240z Posted April 29, 2005 Share Posted April 29, 2005 The question is when it is a matter of adding a negligible amount of weight to the unit, why have sharp edges at all when a small radius edge is far more resilient to failure? The normal loads might be small on this portion of the flywheel, but abnormal things do happen. (someone trying to engage the starter when the engine is running, for example) As for the three machinists being wrong, are you disputing that a sharp edge creates a stress riser? Or that threads can create a stress riser? Or are you simply saying it's not something you worry about? I wholeheartedly agree that a billet flywheel is far superior to a cast one. Quote Link to comment Share on other sites More sharing options...
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