mark Posted August 2, 2007 Share Posted August 2, 2007 No functional speedo here, but according to the datalogger 152 on the front straight, don't know on the back. Mark is faster than I am. jt Top speed at VIR is limited by testicular size. 4th is good to about 140. If I short shift into 5th 150 comes and goes, I'm too busy finding my nuts, braking, down shifting, watching jt1 go by me in the braking zone, and remembering to turn left to check the speedo. Tranny is t56, diff is q45, rear tires 245-40-17's Quote Link to comment Share on other sites More sharing options...
johnc Posted August 2, 2007 Share Posted August 2, 2007 I wonder if the solution to these issues along with a lower PMOI might be obtained by moving the diff forward. Take a look at a 911 and the transaxle outputs are 2-3 inches ahead of the companion flanges. No reason we shouldn't be doing the same thing. Ding, ding, ding ding! Nissan had the diff position optimized on the early 240Zs but there were enough vibration complaints from customers that they de-optimized the position to eliminate that warranty complaint. Putting a R180 or a R200 back in the forward position helps driveline angles. Quote Link to comment Share on other sites More sharing options...
mark Posted August 2, 2007 Share Posted August 2, 2007 John, Could you provide a little more info on the effect on drive line angles that moving the diff forward would have? I understand the PMOI effect. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 2, 2007 Share Posted August 2, 2007 What John means by "helps driveline angles" is that there would be more room for the CV's and they wouldn't bottom and the cage on the drivers side wouldn't need to be flipped. This is contrasted to the moved back position where the CVs and halfshafts are near bottoming. John covers this issue in the "R200 Handling Issues" article in the bench racing area of his site: http://www.betamotorsports.com/benchracing/index.html Quote Link to comment Share on other sites More sharing options...
mark Posted August 2, 2007 Share Posted August 2, 2007 Thanks for the clarification. That makes perfect sense. So if the diff is moved forward to the early 70 car position it may eliminate the need for the custom shaft route that Tom went on his set up. Makes me wish I had kept all those early Z parts. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 2, 2007 Share Posted August 2, 2007 I wonder if it would be possible to flip the R200 bar and maybe hook the front diff mount on the rear set of holes... Quote Link to comment Share on other sites More sharing options...
rudypoochris Posted August 2, 2007 Share Posted August 2, 2007 Just out of curiosity, what is the PMOI? Something moment of inertia? Permenant? How does moving the diff a little forward help? Does it reduce the chance of part faliure but increase the vibrations? It does not seem 240z specific (hence the mention of the Porsche) so it must not only be a way to help bottoming of the axles. Any insight appreciate. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 2, 2007 Share Posted August 2, 2007 PMOI is polar moment of inertia, which is essentially resistance to changing direction in a car. Moving weight in between the axles reduces PMOI, while hanging a 500 lb weight on the front or rear bumper would increase it. There is an argument that you don't want the lowest PMOI that you can possibly get, but that's probably a subject for another thread. The initial failures of U-joints with the diff in the forward position was due to the U-joints inability to articulate freely enough. Moving the diff back and in line with the companion flanges eliminated one source of angularity in the shafts, and then the halfshafts only dealt with the camber change. Quote Link to comment Share on other sites More sharing options...
rudypoochris Posted August 2, 2007 Share Posted August 2, 2007 So the sole benefit to having the diff mounted forward would be to increase the ease of turning the vehicle? In our case would there be a second benefit in that the shafts would not bottom out -> increased strength? Thanks for explaining the term, I just couldn't figure out the P in PMOI. Quote Link to comment Share on other sites More sharing options...
Mikelly Posted August 2, 2007 Author Share Posted August 2, 2007 So I'm pretty sure what I have will work, for me... But I still am unhappy with the "selection in gears"... We still don't have a solution that is not the norm fellas... Kick it around some more... MIke Quote Link to comment Share on other sites More sharing options...
johnc Posted August 2, 2007 Share Posted August 2, 2007 When tuning the suspension of the ROD I was not happy with putting power down and was having to very careful applying power at mid-corner before the apex. It was suggested by a 240Z ITS racer that I try moving the diff forward to the original factory location. I happened to still have the parts so I gave it a try. Suprisingly the car became more forgiving about power application and I could consistently give it about 10% more throttle before and past the corner apex. Lap times dropped by about 2% overall. As it was explained to me, dynamic toe change under power was reduced by have a slight forward angle on the halfshafts. To test this I reduced rear toe-in to 1/16", which was marginally stable under power before (and downright scary in Turn 9 at WSIR), and the car tracked better under power. Before I was running 1/8" of rear toe-in which was eating up stub axles. This was with a R180, Quaife, and halfshafts. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 2, 2007 Share Posted August 2, 2007 That was not what I expected to hear... What do you attribute the toe change to John? Seeing as how the suspension doesn't have dynamic toe change in the rear by design, are you thinking that having the halfshafts forward meant they could torque the bushings less or something? Were you running your Kevlar bushings at this point? Control arm deflection? Quote Link to comment Share on other sites More sharing options...
evtech Posted August 3, 2007 Share Posted August 3, 2007 Hi Guys If your interested I started a thread on the Uk Z club site for my conversion to a Subaru VLSD. http://www.zclub.net/forum/showthread.php?t=9013 Only bit of hind sight would be to get the diff stub shafts made up with UJ flanges and run the original Datsun shafts instead of making a whole new shaft with a CV end and a UJ end. Just another for the melting pot; by the way the new diff ratio worked so good it took 10 seconds off last years fastest time up our hillclimb course, but as I was enjoying the ride so much I forgot to hold the boost back and the rest as they say is history:cry:. New L28 build progressing. Cheers Nigel Quote Link to comment Share on other sites More sharing options...
JIM73240Z Posted August 3, 2007 Share Posted August 3, 2007 ok, so where is this "original location" that is being talked about. i have not seen anything on this ever. jimbo Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 3, 2007 Share Posted August 3, 2007 The 70 and 71 had the diff mounted about 1" forward of all the rest of them. They had a different mustache bar and a different transverse link behind the diff which was straight instead of curved back. After mid 71 or so they changed them and moved the diff back, and I think there was a recall at the time because of premature U-joint failure. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted August 3, 2007 Share Posted August 3, 2007 As it was explained to me, dynamic toe change under power was reduced by have a slight forward angle on the halfshafts. To test this I reduced rear toe-in to 1/16", which was marginally stable under power before (and downright scary in Turn 9 at WSIR), and the car tracked better under power. Before I was running 1/8" of rear toe-in which was eating up stub axles. This was with a R180, Quaife, and halfshafts.. I'm a bit puzzled by this as well. Was it mentioned that this is true only for U-jointed shafts and did not apply to CV-jointed shafts? Just fishing now. Quote Link to comment Share on other sites More sharing options...
tube80z Posted August 3, 2007 Share Posted August 3, 2007 As it was explained to me, dynamic toe change under power was reduced by have a slight forward angle on the halfshafts. To test this I reduced rear toe-in to 1/16", which was marginally stable under power before (and downright scary in Turn 9 at WSIR), and the car tracked better under power. Before I was running 1/8" of rear toe-in which was eating up stub axles. This was with a R180, Quaife, and halfshafts. I seem to remember Mark Ortiz debunking this in a column. I do know the back of a Z has a lot of toe compliance and fixing that may help all this. Cary Quote Link to comment Share on other sites More sharing options...
johnc Posted August 3, 2007 Share Posted August 3, 2007 I can only state what was told to me and the little experiments I did. This was running aluminum offset inner bushings and Hydlar/Kevlar outer bushings on 240Z LCAs. The diff and mounstache bars were solidly mounted. Simply moving the diff forward made putting power down a whole lot nicer. It also allowed me to reduce rear wheel toe-in by 1/16". Maybe dynamic toe was not affected. Maybe stiction in the strut was reduced. I don't have a clear answer as to exactly what was affected by this change but it worked in my specific application. Quote Link to comment Share on other sites More sharing options...
260DET Posted August 4, 2007 Share Posted August 4, 2007 There is always the Nissan multilink subframe setup in all its variations, Z32, Skylines, S13/14/15. Choice of the improved shortnose R200 and 230 diffs, various track widths, big brakes, 5 stud hubs, big CV axles. Multilink is an excellent suspension with heaps of aftermarket support, including suspension arms that change the roll center. See 30 secs in for multilink doing the job, turn the volume up Toyota double A arm subframe setup may be worth a look too. Quote Link to comment Share on other sites More sharing options...
smoorenc Posted September 27, 2007 Share Posted September 27, 2007 TitaniumZ do I need the V axels for our R200 LSD? Quote Link to comment Share on other sites More sharing options...
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