SleeperZ

Welcome!

Cool! Problems like this are what remind me of how much I hate carbs. I've been a hardcore FI guy for a while now, I'll never go back to carbs. I had a lawn mower carb go bad on me, and I couldn't fix it Bought a new mower instead.

Jason - I was having your same problem with the ECU, but I switched to the 300ZX one and still had a problem with it that I traced to bad plug wires. If you are totally sure your plug wires, cap and rotor are good, it must be the ECU, and I will refund your money. I was sure the ECU was good once I found the bad wire I had, but it sounds like I was wrong. I can't imagine what in the ECU would go bad to cause this problem; I just assumed if ECUs go bad, they just stop working. Let me know what you think is fair.

I disagree with the idea the contact patch of the tire is the same for the same car (and same weight). A wider tire may indeed have a narrower patch front to back than a narrower tire, but just because the patch is differently shaped, doesn't make the surface area equal. Most tires have fairly rigid structures, slicks excepted, and just need to be properly sized to the vehicle to work optimally. Actually, I think the area point is moot, because the normal force (weight) obviously distributes through the entire contact patch (more or less). So any gain or loss in launch capability from a diffently sized tire is entirely due to the tire compound and how much weight per unit area you are putting on it - hence the increase or decrease of the frictional coefficient that affects launch capability. I know, I should just go to bed.

Boy, I sure hope not...He bought my old stock ECU.

Beautiful car! That is a very good article. He has very clear reasoning, and I often wondered what the deal was with the wider tires. I took physics in high school and college, where they taught the friction force (ability to launch) is generated as a product of the frictional coefficient (tire compound) and the normal force (weight of the car). I always followed this reasoning, and saw most folks get wider tires to get better grip, which made no sense to me. If you increase the contact patch (wider tire), you spread the weight over a greater area, and the normal force is spread over a larger area, and goes down (per unit area). Therefore, in the theorectical sense, you gain nothing by going to a wider tire. The author claims a wider tire will slightly increase the frictional coefficient, which is evident in his data. Once again, I am sticking to my "sleeper" look, by not going crazy on tire width, and am sticking (pun, hehe) to quality compound tires.

I got a donut off a Hyundai Excel for my '78 -- I'm sure this will work for a ZX as well. There are literally 1000's of these wrecks in every scrapyard in America.

Okie - I think I have found the source of the vibration... I checked the angle of the tailshaft yoke and the diff yoke the best I could. I used a tape measure and compared the length between the joints at the top and the bottom of the driveshaft. Nuts-on. Hehe, what the heck is it??? Pushed up on the ujoint at the diff...click, click. I have a bad u-joint on my driveshaft. I have no idea why I didn't notice before, but there it is. Maybe the new urethane diff mounts allowed me to hear it now, the rubber ones masked it. I should be able to get it repaired before Test and Tune at the strip on Wednesday evening. I will post a timeslip, good or bad. Wish me luck!!!

If you wanted the IC to absorb more heat, it should be painted on the inside On the outside, you don't want it to absorb heat, you want it to reject heat, avoid heat-soaking it. As far as I know, the only turbo that bolts up to the L28ET is the T3 turbine housing. A hybrid T3/TO4 will bolt to the exhaust, but the intake needs to be modified to accomodate a larger compressor. The turbo does build backpressure, and how much depends on the A/R of the housing. The bigger the A/R, the lower the backpressure, but the lag increases. A larger A/R will produce more top-end power at the expense of throttle response.

I'm confused. Scotty MIZ is running an L28ET. Are there clutches for V8s available for the Nissan motors/trannies? I haven't run into the limitations of my Centerforce II clutch yet...I am very happy with its performance - it's never slipped and it's well behaved on the street, but I'm only putting 170hp to the wheels.

Yup, what he said.

I got the 3.90 from an '81ZX 5-speed. I also got one from an '84 200SX turbo, and compared the two. The one from the SX was baked inside, and had as much backlash as my old 3.54, so I was pretty sure I had another whiner. The ZX had very little backlash, was very clean inside and had no metal in the plug. Both 3.90s came from the local pick-n-pull. I drove the car again today, and the vibration is hardly noticeable...I think I will drive it some more, just check all the driveshaft and halfshaft bolts, and see what gives out on me. Thanks for all the ideas and advice.

My driveshaft is custom made with replaceable solid spicer joints. It was very smooth before with the 3.54. I re-used the stock front diff mount, as it was still solid, and I secured the nose with a plastic-coated piece of 3/16" cable. But the mounting in the rear has changed to the urethane mustache bushings. I guess I can try to measure the distance from the bar to the body at the loops - I have no capability to measure the u-joint angles with any accuracy. I was just wondering if anyone else had this problem with stock stuff...? Maybe it's just a halfshaft (although I've had those go bad on me, and they clunk, not hum).

Hmmm, OK. The 3.90 is a serious demon now, got a 6.9 second 0-60 on the street with G-tech, and that's with bad tires and a 2.7 60'. Problem is, I have a vibration, or growl, in the rear now, with new diff and new urethane bushings in the mustache bar. It makes noise over 80mph, and it sounds like what folks talk about being a problem in the V8 swaps. All I changed was the R200 3.54 with an R200 3.90, the mustache bar bushings (used the thick washers on top and bottom), and I swapped some halfshafts because my old ones had grease fittings in the "stretch" part of the u-joint instead of the compression part. The halfshafts seemed to have good joints, and I just greased them up good. What do you think? Is my diff mis-aligned from the urethane bushings? Or do I have potentially bad halfshafts, and I should focus on replacing those? Any guidance?

Thanks for the comments folks. I used the copper washers on the front caliper lines, and I don't see any seepage in the connections, but I should check again. I did intall the calipers with the bleeders in the top position. I haven't adjusted the rear brakes, but I use the parking brake all the time, and it only comes up to about 60 degrees - can they be adjusted manually?

By the way, who'd a thunk the 14x6 6 spoke wheels would rub on the ZX calipers.. Looks like a tiny bit of grinding can clear them...

I converted the front brakes to 280ZX calipers this weekend. I bled them well using my Russel speed bleeders on all four corners, but I still have lots of pedal travel. I still have the 7/8" master cylinder, and I was wondering whether the 15/16" cylinder from the ZX would help this. I bled out the master a few weeks ago, could replacing the front calipers and rear lines have got air up into the master? (I didn't bleed the master out again after the swap) The brakes don't pump up much, so I'm not sure it's air in the system... I'm still running the stock drums in the back, will the ZX proportioning valve work better or worse than the Z valve? I haven't broken the pads in yet, so I don't know whether the front/rear bias is messed up or not. Thanks in advance for your informed comments.

I get 9" of vacuum, but I am running an aftermarket cam in my L28ET. 12" sounds a bit low, but will a small vacuum leak cause a low manifold vacuum reading? I'm not so sure about that. Camshaft timing will certainly affect manifold vacuum, have you checked your cam gear and timing chain?

Wooooo.... Drove the Z with the 3.90 installed today. What a difference compared to the 3.54!!! Keeps the turbo in the power band, very lively off the line (T5 ZX tranny), I love it. It's also nice to have no more gear whine I've seen discussion that the lower ratios may be faster as they help the turbo make boost -- I've seen no evidence of that -- I get full boost in 2nd gear, just like the 3.54, and it pulls harder. So for anyone that was wondering, 3.90 is amazing behind the T5. I installed the urethane mustache bar bushings, no problems, thanks to all the advice about burning out the old rubber - if I'd tried to take out the bushing shell I'd have been po'd at a tremendous waste of time. The diff bolted right in, and I got a white tranny gear for the speedo - I was surprised it fit the T5. So bring on the 5.0s!

ROFL SuperDan! "I also made a nice background image for my portable, red with white letters that says 'Danger to manifold'" Getting inspired by F&F??

I'm putting on 280ZX calipers, 240 hubs and '84 300ZX rotors this weekend. I'm having the rotor diameter turned down 1/4" so I can fit the caliper on the stock mounting ears. The calipers are from an '81 turbo and are identical to the set of '79 calipers I also have. The ONLY brake pads the local parts stores carry are OEM type pads, and I want something that will withstand a bit more heat. I will eventually buy a set of Porterfield pads for road racing, but I want some good street pads. Anyone have any recommendations or brands to steer clear of? I have used semi-metallics on my Toyota calipers and am very happy with them, but none seem to be available for the ZX calipers.

Couple ideas come to mind. I don't believe you can get an adjustable fuel pressure regulator that will go below 30psi, but it's questionable that the injectors will perform that low anyway. Further leaning out of the AFM may result in much more intake restriction, as you will be tightening the s**t out of the AFM spring. Last idea before going to a different ECU is a metered air bypass. Get a small air cleaner and adapt a 1-1/2" or 2" PVC pipe to it, run it through a ball valve, than insert it into the intake before the turbo. Then adjust the ball valve until you get somewhat close to a good mixture, and fine tune it with the AFM. Keep in mind, I have NOT done this -- it should work, but it will be ugly. My solution to this, once I install my 370cc injectors, is to reprogram the chip in the ECU with a different injector table. But I am running a 300ZX ECU.

Superchargers can give boost right off idle, but in a V8's case here, with the limited traction of a Z car, it seems that turbocharging a V8 would work very well, as the boost will build once you've left the line and hooked up. A supercharged ZV8 has a better chance of just smoking and sitting there. Sorry, off the topic, but I've not posted anything for a while and I just wanted to jump in.

That sounds great - I don't remember what engine management you are using, but you will run a bit rich (quite a bit of difference between 260cc and 370cc - 43% more flow). I'm not sure if the AFM has that much adjustability in it, but you may have the opportunity to find out That said, I'm all ears to what you do to tune it, as I have my injectors and a stock ECU (stock for '87), and will need some tuning tips when I hook it up. I would think you will be better off with a stock pressure regulator - your crushed one will only aggravate the richness of the bigger injectors. You will not need the higher pressure to inject the fuel, and you will only load your fuel pump un-necessarily. If you don't have a mixture meter or a fuel pressure gauge you can read inside the car, be careful that your fuel pump doesn't run out of gas on you, as that is going to be the next weak link.

That is the swap I fantasize about. The 2JZGTE motor is one of the most amazing turbo engines ever. With tweaking and a single turbo conversion, a (relatively) lightweight first generation Z would be mind-blowingly fast - it would certainly be the equal of a GN conversion (probably a bit more money, but a 6 speed )