260DET Posted August 25, 2005 Share Posted August 25, 2005 Edited my last post to make it clear that the 280ZX half shafts being talked about were the CV type. Quote Link to comment Share on other sites More sharing options...
zredbaron Posted August 25, 2005 Author Share Posted August 25, 2005 thanks for the clarifications. rudypoochris, after my explanation do you still think it was decel that caused it? (i realize at this point i'm probably making a mountain out of a molehill...sorry) Ed - my jets right now would appear quite odd. Since installing an A/F ratio gauge, I've discovered I have a problem running extremely rich when the outside temp is above 85 and humidity is > 50% (east coast sucks i have to tune three carbs for temp AND humidity). It was really weird...even if I dropped my main jets as much as 30, it wouldn't lean out. After ruling out incorrect float levels, I finally determined my fuel pressure was too high (6 psi when it should be half that!). I have a pressure regulator on the way. But...when its nice out...75 degrees and low humidity...it runs beautifully with the following setup: 36mm venturis 140 main (trying to lean out my rich condition) 220 air corrector (i know, big jump...but it likes it) 55F8 idles My theory on the air corrector jet needing such a large jump is a resultant cross between fuel pressure being too high and the head flowing so well. And let's be honest, my 25 year old lead foot isn't helping any. Heres a pic of my guage install... Quote Link to comment Share on other sites More sharing options...
rudypoochris Posted August 25, 2005 Share Posted August 25, 2005 well it is hard to explain and obviously since i wasnt there i cant tell you. But on my explorer when i go from 65mph at 5 to 65 at 3rd (a much mroe extreme case then yours) the engine obviously will take time to match the road speed. Now if i let the clutch out too fast, the traction in the rears will break away for just an instant (because the engine was at 2000 rpm and now is trying to jump to 4000 rpm), but since i have my foot on the gas it is quickly followed by acceleration. This is bad for the car. Now i am not sure if that is what happened. I don't know what your throttle response is, and a jump from 5 to 4 isnt that much, maybe you just got unlucky or it happened so fast that you don't realize it happened Don't worry about it new u-joints should be sufficent btw... are you sure, since you are running rich and all, that when u dumped all that gas into the engine that it didnt bog at all even for a split second, because that has happened to me, never broke a u-joint off it but it can happen when you dump alot of gas in at once, especially if you are going lean. (but it probably isnt this) Quote Link to comment Share on other sites More sharing options...
johnc Posted August 25, 2005 Share Posted August 25, 2005 there was never a decel, the shift was as instant as it gets...i think any decel would be negligible: i pushed in the clutch, and yes, im sure there was a *slight decel* as the shifter went from 5th to 4th, no slip in traction yet...the clutch is still in, then i simultaneoulsy let off the clutch and mash the pedal. this is where the chirp occurs...definately under accelleration, not decelleration. this all happened in less than half a second. not much decel can happen in half a second with the clutch pedal in. drop in torque felt on the rear drivetrain, sure, but decel? any decel would be from drivetrain friction and road friction (wind resistance slowing car speed and therefore wheel rpm), the engine would not be doing a forced decel. this decel wouldn't be anything more than negligible for all intents and purposes. not in my train of thought, anyway. OK, look at the loadings: 1. Forward torque load from acceleration in 4th. 2. Reverse torque load when clutch is depressed. 3. Shock forward torque load from speed shift. There were two torque reversals while the halfshaft was spining at around 2,000 rpm and the second was a shock load. It doesn't matter that the reverse torque load was less the the forward torque load, what matters is that the reversal occurred and then you shock loaded the halfshaft. In a sense the u-joint "wound up" before it had to apply the forward load and that's what made it fail. And, BTW, U-joints are generally stronger then CV joints as long as the angles are kept to a minimum. In high horsepower Viper race applications (GTS-R) they replace the CV joints with u-joints and pickup reliability and about 45 horsepower on the chassis dyno. Quote Link to comment Share on other sites More sharing options...
mom'sZ Posted August 25, 2005 Share Posted August 25, 2005 I always thought it meant in my HUMBLE opinion? Quote Link to comment Share on other sites More sharing options...
zredbaron Posted August 25, 2005 Author Share Posted August 25, 2005 thanks, john. perfect explanation...understanding why will help me prevent future mishaps. so...the intended use of this car is autocross. i may go to the drag strip a few times, and I also drive the car to work frequently. if this were your car, john, would you keep the u-joints or would you go with CVs? i would like the less vulnerable solution, i intend to jump hard on the pedal after coming out of a turn. and in the case with the gts-r viper, how are u-joints more reliable, and why is there a power difference at all? (and yes...rudypoorchris, sure it was possible the engine bogged. it was very fast. my logic would agree that it likely did from the rich condition. my butt just doesn't think so.) thanks. Quote Link to comment Share on other sites More sharing options...
johnc Posted August 25, 2005 Share Posted August 25, 2005 the intended use of this car is autocross. i may go to the drag strip a few times, and I also drive the car to work frequently. if this were your car, john, would you keep the u-joints or would you go with CVs? Ran only u-joints for years in the Rusty Old Datsun - 320hp, 275ft. lbs. - on autocross courses and race tracks all over California, Nevada, and Arizona. Never, ever had a problem with them. and in the case with the gts-r viper, how are u-joints more reliable, and why is there a power difference at all? More reliable because there are no boots or grease to worry about and much easier to rebuild. Don't know where the power difference came from but it most likely wasn't an actual horsepower increase, just a reduction in weight and MOI. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 25, 2005 Share Posted August 25, 2005 If you're going to drag you might still want to consider the CV upgrade. Start searching for threads on broken U-joints and you'll see why. Common consensus from the drag racers is that the U-joints are the weakest link, followed by the stub axles. What John is saying about U-joints may be true in a Viper, but it is apparently not true in a Z when comparing the commonly available U-joints to the commonly available CV joints. My understanding on the Spicer U-joint issue is that the threaded hole for the zerk fitting in the U joint cross is the weak link. The Nissan U-joints are not greaseable, so they don't have that hole in the cross. I have a couple halfshafts I want to get rid of which both have Nissan joints in good shape. Drop me a PM if you're interested... Quote Link to comment Share on other sites More sharing options...
johnc Posted August 25, 2005 Share Posted August 25, 2005 What John is saying about U-joints may be true in a Viper, but it is apparently not true in a Z when comparing the commonly available U-joints to the commonly available CV joints. Correct. The halfshafts in the 240/260/280Z were designed for the expected torque loadings of the 2.4L and 2.6L engines. There was enough designed in strength to handle the 2.8L engines. Once power went up with the turbo engines Nissan redesigned the halfshafts to increase the strength and they went a step further by specifying CVs to reduce vibration. CVs product less vibration then u-joints and work at higher angles of deflection. In the turbo CV halfshafts they are stronger then the u-jointed halfshafts because Nissan designed them to be stronger, not as an inherent function of the CVs themselves. Quote Link to comment Share on other sites More sharing options...
zredbaron Posted August 25, 2005 Author Share Posted August 25, 2005 ah hah. so while u-joints should be ok for me at autocross (i'm definately not making over 300 hp), the drag strip may tear them up. the zxt CVs would actually be stronger than the u-joints, and smoother, too. so basically unless i do the conversion, stay away from drag or take it easy if i do go there. the last time the two of you tag teamed a thread of mine (head discussion) i learned a lot (and got a sunbelt head!). thank you both so much. again. john, that is a sexy picture of that Z with that front tire just off the ground. somehow i think i'm just a few thousand dollars away from that level... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 25, 2005 Share Posted August 25, 2005 Hey, no problem! I'm glad to see you finally started getting some power out of that engine. Still think there would be more in a set of 45's though... Quote Link to comment Share on other sites More sharing options...
johnc Posted August 25, 2005 Share Posted August 25, 2005 john, that is a sexy picture of that Z with that front tire just off the ground. somehow i think i'm just a few thousand dollars away from that level... Nope, you're closer then you think. Its all about putting power to the ground from mid-corner to corner exit - amazing what a Quaife can do if the suspension is designed to work with it. Quote Link to comment Share on other sites More sharing options...
zredbaron Posted August 25, 2005 Author Share Posted August 25, 2005 it IS nice to finally get some more power. and i think 45DCOEs would realize more, too. the weber chart says i should be at 38-40mm venturis, but i suspect 42mm may even be in order since the sunbelt head probably flows a little more than that graph is figuring... johnc, interesting you should mention that bit about suspension being setup to match it. i was just having a conversation with my old mechanic (who raced Zs in the 70s) and he told me that he once saw on a videotape that his rear inside wheel was coming off of the ground (obviously welded diff....i doubt quaife existed back then) (i sure as hell didnt! ). he said he fixed it by taking the rear sway bar out completely and having a 1" bar up front. any experience on that matter with the quaiffe? whats your setup? im taking an autoX class next friday and the instructor will help me tune my setup a little... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 25, 2005 Share Posted August 25, 2005 I lift inside rears in slaloms or so I'm told, but I think that was due to a swaybar binding issue that I've hopefully gotten fixed. You didn't ask me, but the issue with the Quaife is that it tends to spin the inside tire. You need to run softer in the rear with the Quaife than with a clutch type LSD. Try loosening up the sway bar end links if you get wheelspin on tight turns. If that isn't enough just take one end link completely off then it will be like running no rear bar at all. More important than a little wheelspin IMO is getting the front end to hook up. Increasing caster and negative camber helps, and a whole lot of toe out on the front can be good too. Might try something like 1/4" toe out. Don't leave your car like this for the street though, unless you have an unlimited tire budget and don't mind a twitchy car. If this is a school though your first autox experience you might want to concentrate more on your driving than the car setup. Quote Link to comment Share on other sites More sharing options...
260DET Posted August 26, 2005 Share Posted August 26, 2005 Nope, you're closer then you think. Its all about putting power to the ground from mid-corner to corner exit - amazing what a Quaife can do if the suspension is designed to work with it. Must agree with that, an ATB (Quaife type) diff is a revelation in power down through and out of corners. Not that the stock clutch type LSD is bad, its not, one of the Zed's strong points. On stock universal type half shafts, they do break even with a moderate power increase, mine tended to have the caps come loose, ended up welding them into the yoke. I bet yours, John, on the ROD were well maintained and inspected, the 280ZX CV type is more fit and forget. My 280ZX ones are part of a 300RWHP drivetrain, would not rely on the stock universal ones for that. Quote Link to comment Share on other sites More sharing options...
johnc Posted August 26, 2005 Share Posted August 26, 2005 any experience on that matter with the quaiffe? whats your setup? im taking an autoX class next friday and the instructor will help me tune my setup a little... My setup is irrelevant because it was caused by a touch of madness and a fat wallet. There are basically two schools of thought regarding the 240Z suspension, East Coast and West Coast. East Coast tends to run most of the roll stiffness up front (big front springs, big front anti-roll bars) with a softer rear to apply power. A lot that might come from their smoother and faster tracks. West Coast tends to balance roll stiffness with close to equal size springs and medium front and small to medium rear anti-roll bars. Both setups work, although the East Coast setup tends to push in tighter corners. Since an autocross is all tight corners (compared to a road course) I would run a West Coast setup but try to keep the rear as soft in roll as I could without inducing understeer in front. FYI... Bryan Lampe, a local ITS champion and a West Coast setup proponent, ran a VARA vintage event at Willow Springs a couple months ago. He experimented by removing his rear anti-roll bar on his ITS 240Z (that he had just sold) and ran a second per lap faster then he had ever run at WSIR before. He said the car pushed in 3, 4, and 5 but being able to put the power down earlier in 9 and 2 helped his lap times. Quote Link to comment Share on other sites More sharing options...
zredbaron Posted August 26, 2005 Author Share Posted August 26, 2005 great feedback, as usual guys. that was exactly what my old mechanic said... that his lap times dropped about a second and a half (he also added that it felt weird to drive, but it worked). i think Jon is right though, i'm probably getting ahead of myself. i've never autocrossed before, and i should start learning how to drive before i start experimenting with my car. i'll definately keep all of this in mind when that time comes, though. one variable at a time, please. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted August 29, 2005 Share Posted August 29, 2005 Just wanted to put my 2 sense in. I think the main reason for halfshaft U joint failure is extra torque with weak suspension through a turn or hard shift/launch. Just what I think anyways. -Ed Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.