Doc Hawk Posted August 9, 2008 Share Posted August 9, 2008 I have a turbo flywheel that I would like to get shaved (lightened) before dropping it behind my L28 (NA Maxima head). I have a six puck ACT HD turbo clutch set that I want to use, which is why I am converting. The info I found through searching mostly had to do with 225mm flywheels, so I want to be sure I have the right info. I will take it to a reputable shop, but in order to be educated when I do so, what part(s) of our flywheels are typically shaved to reduce weight, and how much should I have them take off? The back side ring running around near the outer edge? This is primarily an autocross car which I occasionally take out for an exhilirating run somewhere. Definitely not a DD, but I don't want to be forced to launch from the neighborhood light at 6K either. Edit: I saw that Bastaad525 runs/ran a similar setup. Does ~19lbs sound right for a reliable/safe/resurface-able turbo flywheel? Bastaad, how did your setup work out for you, long run? Thanks, Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 10, 2008 Share Posted August 10, 2008 Removal of the "Inertia Ring" is what pays the most dividends. Regardelss of 225 or 240mm, the flywheel is the same, they just have holes drilled in different spots to accomodate their respective flywheels. REMOVE THE DOWELS ON THE FACE! If you don't, chances are good they will be surfaced flat with the face of the flywheel and then...er...yer screwed... There are other tricks that can shave more weight, like cutting down the ring gear, drilling the outer edges ala Kameari's Cr Moly Flywheel, etc... But the big improvement comes form the removal of the inertia ring. I have one that was done in Japan, and it's 15#. It acts snappier than the 13# aluminum units sold today. Closer to what my old Tilton 11# unit did... As for now, even with a Kameari Flywheel, I'm not running to 6K to get a start. If you have a grabby clutch, you will get away with slipping it to get it moving smoothly a couple of times, but once you are hot, it's going to be on-off engagement and you better get the feel of the launch/bog point or you will stall embarrassingly. I don't think I have to go over 3K for a launch...but I've driven nothing but lightened flywheels in Z's since 1985. On stock clutches I can slip it off idle and get the car moving. IMO the light flywheel drivability issue is overblown...what clutch disc material you have is what makes it untoward. And that goes with any weight flywheel! Quote Link to comment Share on other sites More sharing options...
Challenger Posted August 10, 2008 Share Posted August 10, 2008 I dont think the weight matters as much as where the weight is. Like you said the 11 lbs ones didnt work better than the 15 lbs one. Is that because the weight was removed from the outside? Quote Link to comment Share on other sites More sharing options...
Doc Hawk Posted August 10, 2008 Author Share Posted August 10, 2008 REMOVE THE DOWELS ON THE FACE! Thanks Tony, this kind of warning is exactly why I posted. I will remove the dowels and have the inertia ring turned down. I am not looking for extra ounces of savings and I want it to retain as much strength as possible, so I won't bother with the additional lightening options. Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 10, 2008 Share Posted August 10, 2008 Like you said the 11 lbs ones didnt work better than the 15 lbs one. That is not what I said. What I said was my Japanese lightened flywheel felt more like my old Tilton 11# aluminum one, and was considerably more 'snappy' than the 13# units currently being marketed. The Tilton 11# unit was a very nice unit, and IMO the 13# unit that is out there today is kind of disapointing the way it reacts. Yes, where the weight is removed is very important, but simple physics says the more you can take off the better. The Japanese units concentrate on maximizing the weight reduction at the furthest portions of the flywheel, and as it was explained to me, once you get within about a 125mm diameter from crank centerline you won't accomplish anything of significance anyway. Curiously the Japanese Machinist pointed out that this number depends on which crank pulley you have installed, and if you have a larger diameter pulley, you can leave more on in the center of the flywheel. Their opinion was that metal left there contributed to strength, and as such paid a double dividend. Though they did completely machine the back of the flywheel to remove rough casting. They looked very nice indeed. And behind the frictional face the tended to leave a little more material. The bad thing about a 240mm flywheel is that you need the facing thickness at 240mm diameter meaning any 240mm flywheel will rev slower than the comparable 225mm flywheel as the intertial effect of that ring will be more at 240 diameter than it will at 225... But it's splitting hairs. You cut your flywheel down to 15#, and you still have a 24# pressure plate! Get someone to disassemble and cut THAT down comparably and you will REALLY see some more snappy acceleration! For some reason the flywheels I have had lightened in the USA don't seem as snappy as the one I have in the car form Japan. I still have to pull it down to compare the cuts. It makes me curious as to the difference in cut-down they did. I notice differences, but haven't had that Japanese Flywheel off the car since 1989, and the last time I had to put a clutch in it was late 1989 or early 1990... (first NISMO Clutch assy smoked...yeah, 250HP 250ft-lbs capability my butt!) Quote Link to comment Share on other sites More sharing options...
spork Posted August 10, 2008 Share Posted August 10, 2008 It is also wise to have the flywheel re-balanced when you're done. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 10, 2008 Share Posted August 10, 2008 I can feel a distinct difference between my 12 lb AZC flywheel and my friend's 10 lb HKS flywheel. Hers revs a lot faster than mine. As Tony said, where the material is removed makes a big difference. I also have never had any trouble with stalling, even when I had a stock compression engine with a big cam, triples, the AZC flywheel and an ACT pressure plate, I stalled it maybe once a year if that. The long heavy crank in the L6 is helping for sure. I used to stall my friend's 510 with an L16 running 44's, a Tilton flywheel and roadster comp pp all the time. There is just a lot more inertia in a L6 spinning 1000 rpm than there is an a L4 at the same rpm. Quote Link to comment Share on other sites More sharing options...
Doug71zt Posted August 13, 2008 Share Posted August 13, 2008 I'm running a shaved 240mm flywheel, down to 16lbs. most came from the inertia ring. Behind the friction surface was just cleaned up to remove the casting imperfections. I didn't remove too much off of the face. The flywheel needed a rebalance after - it was quite far out of balance due to the irregular casting surface. I'm running a sprung 6-pick Kevlar-Ceramic clutch with a no-BS rating of 480 ft-lbs. I'm quite happy with the streetability of the combination - not stock, but much better than I was anticipating. Doug Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted August 14, 2008 Share Posted August 14, 2008 Do you guys have any pictures of the lightened stock flywheels? This is the first I've read of lightening the OEM units. I have a spare one that I might be interested in getting lightened. -Ed Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted August 24, 2008 Share Posted August 24, 2008 bump.. curious about some pictures Quote Link to comment Share on other sites More sharing options...
Doc Hawk Posted August 25, 2008 Author Share Posted August 25, 2008 I'll post a before and a few afters of mine once I'm done. Remind me next month if you don't see them. Quote Link to comment Share on other sites More sharing options...
Doc Hawk Posted August 25, 2008 Author Share Posted August 25, 2008 The flywheel needed a rebalance after - it was quite far out of balance due to the irregular casting surface. Doug, did the same shop rebalance the flywheel after shaving it, or did you have to take it somewhere else? Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted August 25, 2008 Share Posted August 25, 2008 I just bought a new Fidanza Aluminum flywheel... 10.5 pounds.. let's see how it'll do!! $300 shipped.. i got deal Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 25, 2008 Share Posted August 25, 2008 There was a guy selling lightened stockers out of Japan. A Friend bought one, then took measurements and did a 'half diagram' with radisuses, dimensions, etc... It's buried on my desk someplace. I don't know if he ever had photos taken of it, but I suspect with his diagram and taking it to any competent machine shop you could replicate it for around $40-50. That was the going rate in L.A. at Griffins Machine in Paramount when I last did a run. Some guys on another board did theirs mail-order through the same place...and with postage it was still cheaper than for the one being sold on e-bay. A photo won't show you much unless it's the front side of the flywheel, that faces the engine. That is where all the work is done. Instead of being 'ring gear thick' or thicker, it's undercut to where the ring gear is on a small teat of metal attached to a flywheel that is cut down to a fraction of it's former thickness. Looks like an HKS, Fidanza, or Kameari flywheel, only slightly thicker near the crankshaft mounting area, and in the frictional area. Quote Link to comment Share on other sites More sharing options...
Nigel Posted August 26, 2008 Share Posted August 26, 2008 Here's a picture of mine... This brought it down to around 17lbs as I recall... Nigel '73 240ZT Quote Link to comment Share on other sites More sharing options...
Noddle Posted August 26, 2008 Share Posted August 26, 2008 There was a guy selling lightened stockers out of Japan. A Friend bought one, then took measurements and did a 'half diagram' with radisuses, dimensions, etc... It's buried on my desk someplace. I don't know if he ever had photos taken of it, but I suspect with his diagram and taking it to any competent machine shop you could replicate it for around $40-50. That was the going rate in L.A. at Griffins Machine in Paramount when I last did a run. Some guys on another board did theirs mail-order through the same place...and with postage it was still cheaper than for the one being sold on e-bay. Could, would you share this with us please Nigel Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 26, 2008 Share Posted August 26, 2008 If I had the time to find it, gladly. I'll put it on the list of things to do. I was looking at the 2+2 Roll Bar up in the rafters just the other day thinking "I got to get that down and snap those photos for Stealth Z and the bunch..." From the photo published, I can say that I believe it is 17#...it has a very heavy ring under the flywheel. The Japanese will cut right under the flywheel at a 30 or 45 degree angle with a radius at the 'flat back' of the thing---they will not leave all that metal at the outer edge of the flywheel. I have seen some that cut the ring gear in half from the non-lead-in-edge for even more weight reduction... That you can see 'Japan E30' is also a sign that they didn't cut nearly as much as they could have. But in that area there isn't much advantage---what the Japanese Machinist explained to me back in 86/87 was to leave that area relatively thick (behind the friction face), but make sure you get ALL the casting roughness off to preclude any chance for stress risers. So they skim cut till smoooth, then a little deeper to get some weight reduction. They would also get rid of the 'hump' transition to the centermost part of the flywheel around the crank flange, using a straight angle cut and generous radius. On the crank mounting area, they would skim cut to remove the casting irregularities. The pictured flywheel would be considered 'heavy' basically they machined off the inertia ring, but not very agressively at all. They left a lot of metal there that does nothing but slow down acceleration. They could have done this to it as well: Quote Link to comment Share on other sites More sharing options...
Nigel Posted August 26, 2008 Share Posted August 26, 2008 Well, after seeing the aftermath pictures of a few flywheels that have grenaded after lightening, I'm not disappointed that the shop that did mine didn't try to go further... Nigel Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 26, 2008 Share Posted August 26, 2008 The issue of grenading is as much from extra weight at the outermost edges as an unseen structural flaw. Let's not kid ourselves here, you can't do stupid things like try to make a stock flywheel 5Kg. You can make it 7KG, though. And when you do this, it's always wise to do magnaflux inspection of the core you intend to use to make sure nothing is latent in there to cause a failure. My 7Kg (what I refer to as a 15#) lightened stocker has seen upwards of 7500 rpm on occasion, though usually it's shifted by 6500. It was on the car when the Nismo Clutch and Pressure Plate failed, and I had to take a chisel to break the marcel off the face of the flywheel to remove the clutch disc. It has taken over 40K miles of my abuse, 5 MSA Auto-X weekends (the first five, when you were getting in some cases 30+ runs per day!!!), and dyno time that checked RWHP to the 350 range. Does that mean I would keep it on there in real competition? Not on your life! SFI 3.1 rated flywheel would go on there in a heartbeat! For me, the above conditions are what I am terming 'street use'---if I'm going to go racing, I'm spending the $1000 and getting a proper competition clutch and flywheel assembly. But just because a stocker is lightened doesn't make it inherently any less safe than the stock unit. And given the way you lighten them at the outermost edges, one can make the argument that a lighter flywheel with no inertia ring is safer than a stock unit simply because of less stress risers and exponentially reduced centripital loads on the core metal. For the load imparted to the flywheel from the ring gear during starting of even a diesel motor, do you really think that ring needed to be that thick? When I see it, all I see is extra weight at the worst possible place on a flywheel. And the exponential forces it will generate compared to one cut as I described. Again, it's not how much weight, but where! Those rough casting surfaces make me shudder. If they are going to cut it, make it safer at the same time. Leaving rough unmachined surfaces seems anthema to a professional machinist given the little time they would take to do that cleanup. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted August 27, 2008 Share Posted August 27, 2008 Thanks for the responses guys, learning alot on this one. So what would you say the min safe thickness would be around to safely shave down 2? I know if I bring it to my shop they are going to want to know what I want it taken down to. -Ed Quote Link to comment Share on other sites More sharing options...
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