130mph floating issue

[josh817]

My speedo use to read right but lately you will see it jump from 60 to 80 and it won't go back to normal unless you hit a massive crater of a pothole or if you come to a complete stop and accelerate slowly. All my cruising speeds (20, 30,45, 60, 70, and 90) are conveniently placed at RPM's like 2000, 2500, 3000, and 3500.

 

Or I guess you can just follow the flow of traffic... When I do 300+ mile trips I find a few ridiculous speeders to tag along with so if there is a speed trap they get owned, before I do. If its a nice car, and you see that he brakes before a cop is in sight, its safe to assume that he may have a radar detector so just follow his lead. :]

 

Back to the initial topic, like I said I've done 145 and it did feel very jittery. You definitely have to choose your location wisely. Make it a track, not a street road. The highway I did mine on was a fairly stupid idea. Deer can jump out, cops and jump out. I did pass a state trooper but he was going the other way, didn't seem to turn around. If there is any change in the surface of the road it can get ugly. Doing just 45mph down a certain road over here where it has a groove with slight change in elevation going across the lane, it will try to suck the car into that direction.

 

I'm unsure about other airdams but the zenon one may fold back on you after like 70 or 80, someone asked about how to fix it a while ago. Fiberglass BRE style airdams may be fine but to me they don't hold onto enough meat. I would worry that they may break off, if they're thin fiberglass. Right now I use an MSA Type III airdam. Mounted with 5 bolts on each headlight bucket, where the stock turn signals go. Then I made two brackets which bolt to the bottom from the airdam to the chassis. Makes it very solid! It should withstand a small tap, like if I pull forward a little too much or something slowly. If I hit anything like a tire carcass on the road, I don't think it will the airdam. I don't have a picture but these supports would go where the metal pan/tray would be from the bottom of the airdam to the radiator support. My brackets won't get in the way if I ever choose to do that. The thing I like about the Type III is that is has a big 3" lip on the underside, good for bolting things on.

[getoffmyinternet]

I like the urethane airdams, the fiberglass ones seem to enjoy exploding on you if they tap something. I had one that looked like they took a plastic one or a cheesy glass shell and backed it with boat cloth, making it over half inch thick, and it snapped in two when I scraped the ground coming out of a driveway. My car resonates a little at about 80, but I suspect it's the wheel hubs or the rims don't want to stay balanced. I've seen it before where a car will vibrate like crazy at a certain speed and after a tire change the problem disappears. At high speeds a tiny misalignment could turn into a pretty significant unbalance. Does anyone know of hatch louvers causing buffeting at high speeds? I bet they create a decent amount of turbulence behind the car, although since I got them my mileage hasn't noticeably gone down.

[lilesrebel]

Ive read over this thread alittle bit. And i too have a (close to stock) 1978 280z (black pearl edition) was a 4 speed car, now a 5 speed. before i had just took off the huge bumpers and just had nothin but the big open mouth in the front. i ran my car 4th gear pinned speedo bouncing between 135mph and 140mph. it felt like it was floating pretty good. lol. kinda shakey.

i put the msa type 2 air dam on it and i havent tried those speeds in awhile. but 90mph is a breeze. rides smooth as ever.

 

but i do gotta say that i dont have fuel injection. i converted to the bob sharp 4 barrel intake with a 390cfm holley. maybe this adds alittle power to help me get to those higher speeds. lol. not sure.

[Tony D]

But does your tach go up to 10k?? HMM??

 

Actually, mine does!

 

 

This was not 300Kph, though...

 

Watch out for Urethane at serious speeds---unless you reinforce it the damn things will fold under and deform like crazy on a hot (or not so hot, if you are going fast enough!) day!!!

Edited April 20, 2010 by Tony D

[Two80z4me]

to a couple things ive read in this thread.

 

I removed my bumpers, and yes the car raised up because of the weight loss

I have cut tokico HP springs, and the rates are in the 200 in/lb area, if my memory isnt lost.

 

at the airforce base, I hit 133 on a speed trap on a level surface on the launch pad (I literally left brown spots in my seat )

the car felt light, but not like it was going to tip over if I need to do any offensive driving, but I can attribute that to my ride height...

(yes my exhaust, is bent by the diff making it extremely low and rusted)

I cant wait to get an airdam set up on my car, Im thinking MSA type 3, because I dont really want to keep any front bumper.

and from other threads discussed, a rear spoiler can do miles for your traction.

[cannonball55]

The 240z have better aerodynamics than the 280s? My 240 has bumbers removed. No rear wing. No airdam the nose open and I've had it to 147 mph (listed by my Garmen gps). The LS3 and 700r4 trans add a little weight. I guess that would help some but I had it on a friends dirt track car scales recently and it weighed 2400 lbs so not like its heavy or anything. Never felt any lightness. I recently switched over to a t56 trans and will be installing a new autometer electronic speedo to go with it. It goes to 160 mph and with that double overdrive in the T56 it should be pretty easy to peg it.

[getoffmyinternet]

Actually, mine does!

 

 

 

[vega]

any updates? i just got my cast off i broke my thumb from a hit and run motorcycle accident so i havnt touched my z. boy its hard to even lift things less than 5 pounds with my left hand let a;one put in a control arm in the bugger.

[jc052685]

Wow, 130mph. That must be speedo-indicated. I hit 135 indicated, (redline in 4th, 125mph actual) at 9500' elevation (years ago, old man!) with no front end lightness. Thanks to the air dam I have.

 

Not sure how correct this is but with 3:54 diff, 225/50/16 tires, and a '79 5spd the Z design studio shows me at 167mph @ 6900rpm.

 

That is where I had the hard cut limiter set and I hit hit pretty hard in fifth gear several times. I have had not problem with the front end floating. I have a molded whale tale and a fascia of some sort. That along with nearly everything you can buy for the suspension. Solid as a rock.

Edited May 24, 2010 by jc052685

[vega]

i'm not positive but, i don't think there was a 5spd in 70'...

[Tony D]

Non-North American Models were available from the beginning of the model run with a five speed. They were also available through Nissan Comp (Z or Roadster Box).

 

It is possible a 70 has a five speed, either from it's non-US origin, or a previous swap with available Nissan Factory Components.

 

Many dealers would install the Nissan Comp Parts before you took delivery.

 

Obviously there was a five speed in '70, you just had to work a bit to get one in a car here in the USA. Not so elsewhere.

Edited May 24, 2010 by Tony D

[jc052685]

i'm not positive but, i don't think there was a 5spd in 70'...

 

 

Fixed it. Was 79 not 70.

[Tony D]

everything, everywhere was avaialbe with a five-speed in 79!

[vega]

yup

[Dan Baldwin]

everything, everywhere was avaialbe with a five-speed in 79!

Not the Corvette

[JMortensen]

Or the 911 Turbo.

[vega]

back in the late 70s was cars were considered competition for the 280z race cars anyhow- like in the class c racing stuff and the rally and whatnot.

[LowCarbZ]

The G-Nose front end on my car has provided ample downforce. Coupled with a belly-pan that runs basically to the back of the oil pan there is no noticeable lift at speed. I don't even have a lower valence or splitter to speak of, however I do plan on adding one. Sounds like your car is simply sucking in air like a catfish and creating a ton of lift.

[260DET]

On top speed claims, a basically stock S30 did 131MPH over a long salt lake course recently. It was allowed to have minimum aero assistance in its stock class, according to the driver it was moving around a lot at 130, I think the course was seven miles long, it needed a long run to get to that speed which was accurately timed of course.

[vega]

i will say it took me a while once i got to 110 to get up to 130ish however accurate the gauge.