130mph floating issue

[JCan]

Vega's car is 40 years old. I am sure during its 40 years somebody got ahold of the head and added a mild cam and possibly increased the compression ratio. 130MPH should be easily possible on the car. Regarding how a z handles at 130MPH well it is my experience that the car floats. I am also very interested in learning how to better handle air around the front of the car.

 

Referring to the below picture. Notice how the aluminum is fitted ontop of the air dam and (if you look closely) runs all the way back to the radiator.

 

I think this is what people are talking about.

 

On the car my son and I are working on, we are planning to put the aluminum underneath the top lip of the air dam as I believe it will make mounting the aluminum (sides) onto the bumper brackets and center bracket easier.

 

Jim

[HowlerMonkey]

I know this isn't a Z car but it does have a L28et in it and I did some high speed testing in it.

 

I was aero testing at Kennedy Space Center these last two weeks and managed to get my M30 onto the runway and run it right up to the rev limiter of the M30 ecu.

 

The car has a stock L28E with P90 and stock turbo injectors running on the M30 ecu with a supra intercooler at 7 psi boost and a 280zx turbo 3 speed automatic behind it and a 3.54 gear with brand new 215/60-15 tires and I'm pretty sure it was going around 130+ when I ran it.

 

Here's a timeslip to help computing the power level knowing the mods above.

 

 

The runway is 3 miles long so I pussyfooted it most of the way and still bounced it off the rev limiter before a mile had come up.

 

It will definately go faster with more gear.

 

A week earlier, I had run it up to 120 on the highway and experienced the "floaty" feeling and simply cranked in a bit of toe in which completely settled it down as it was rock solid after that.

 

It was probably more toe in than needed but I only got one run.

 

The M30 toes out when the nose is lifted at speed because the rack is behind the crossmember.

 

While it has a pretty sweet CD and relatively small frontal area, it's stock ride height and front aero is not optimal for high speed driving.

 

 

Any toe out will make the ride spooky and it is amplified greatly if you have anything loose such as ball joints or inner/outer tie rod ends.

 

Your stance at speed and the toe changes that accompany the stance change are very important.

 

I've got slightly loose inner tie rod ends and the toe in made it completely stable but I returned it to a less severe toe in for my daily driving for the sake of tire wear.

 

All of our runs were quickly put into perspective when a F104 took off, went into a vertical climb near our viewing station at midfield, and performed a few low passes at mach .96.

 

Edited October 19, 2012 by HowlerMonkey

[SUNNY Z]

 

I later went near 240mph in a twin turbo corvette while the owner of the ford GT may have gone over 280mph in the standing mile driving the ford GT.....

 

I know this is the internet, but really? 280 mph? The current record is 257, but it is in a GT, just not that GT.

Edited October 21, 2012 by SUNNY Z

[HowlerMonkey]

I want to stay on topic here so I will delete references to our other cars.

Edited October 19, 2012 by HowlerMonkey

[JCan]

I will add the air dam and aluminum ducting from the air dam to the radiator.

 

However your comment on running the front suspension toe in resonated with me. Once the car is assembled, (March 2013) I will attempt to try running it toe in a bit and testing it at high speed.

 

Thanks

 

Jim

[HowlerMonkey]

Remember that the 240z through 280z have the rack in front of the crossmember which would have the opposite effect by inducing more toe in as the front comes up.

 

An extreme amount of toe in can induce similar wandering/instability as does toe out but in a less drastic fashion.

 

Also, you might find that non-stock ride heights could cause tie rod angles that would yield toe change in the opposite direction as a car at stock ride height.

 

We use a data acquisition unit that uses linear potentiometers to measure the ride height at all 4 shocks and then put it on the alignment rack.

 

Before we perform the alignment, we load or lift each end of the car to duplicate the data we had during the run on the linear potentiomenters and then set the alignment such that it is optimal at our target speed.

 

We actually had to deviate from those settings to find a solution that worked for all accelerating/braking states because you can easily set your car to feel great while acccelerating and then end up not being able to control it once you let off.

 

If you don't have datalogging, you could take a picture or video of your car from the side at speed during acceleration and another as it brakes from speed and use weight or lifting to duplicate the fender to wheel gaps you see in the picture.

 

If you observe compression/squat or lift/downforce change the car's stance enough that the alignment has to be put to settings that favor one condition at the expense of another, you might want to go with high spring rates and eliminate the movement you are compensating for.

Edited October 20, 2012 by HowlerMonkey

[JCan]

WOW!

 

This is a great idea. I could place a camera and focus it on the shock and add a measuring stick to look at what each shock does as a function of speed.

 

Regarding alignment, you suggest I align all 4 wheels to stock specifications at speed? (50MPH for street and 100MPH for racing ?)

 

thanks

 

Jim

[HowlerMonkey]

Everything I mentioned is for extreme top end speed and I'm not sure the optimum settings for those speeds would be good for all around driving.

 

I'm sure there are some here who have lived with a good trackday car they also drive on the street and could give better advise for that kind of usage.

[JCan]

Regardless.... What you prescribed (in my mind) should work no matter what speed you travel. Cameras are so cheap right now.... Once our car is assembled, I'll do an experiment and add it to this thread (I do not expect to have the car assembled till march) FYI.

 

You have given me great things to think about.

 

Jim