Well I took my sister to the train station today. I took the car across the Howard Franklin Bridge into Tampa (I-275). Traffic was light so I decided to get her there quick. 30 minutes of driving with the needle buried and the tach steady at almost 5 grand. I really wish I could get the correct size tires for this thing so the rpm's will drop at interstate speeds. My sis was scared but the car felt great, oil pressure was beautiful, temp never touched half and the car was steady pulling at almost 5 grand with light touches of the throttle. In between the red arrows was the cannon-ball run...man it felt good to open up the Z. It wasn't without it's problems though...the left rear suspension is squeaking now for some reason but who really cares...I am sure I hit 100mph a couple of times. Do you all think the car has a problem running near 5,000 rpm like that for that long? It seems to be fine, like I said oil was great as well as the temp.

 

lol sounds like you had fun, its always nice to open em up every now and then...i think you car should be fine i run my z hard every time i get in her after all there sports cars thats what they were made for.

 

It's colder this time of year, so its not much of a problem, but during the summer, thats when you will have problems.

My Z hits 100 like nothing, but i never take it past that, untill I get better speed rated tires lol, and new suspension is a good idea though, will help you keep stability at those speeds, which is very important for highway driving. I was going to ask what gear you were in to be doing 80-100 mph and at 4900 rpm, but saw you have a AT, thats why, I Was like you should of been at like 110 with that rpm range in 5th (just estimating from inside of my head here lol)

UPDATE
http://www.geocities.com/z_design_studio/

Oh **** I have been doing 124 mph !!!!

5th on the 5spd at 4900 is 124

No selection for AT though

 

well i do 3500 rpm in th at 75 mph. ususally run about 4000 doing about 85 mph summer or winter and she never has a problem. im also runnin 3.90's but either way ive held her at 5000+ for long peroids of times and she never has problems. im also a 5 spd

 

man... the gearing in those cars must be small... in my N/A Z32 i hit 145.

 

ive run my car at 6000 with no problems, 1st gear thru town, just cause i can, plus i was out doing a ricer! your tires/ gearing must suck for that combo of rpm/ speed. i can do 220kph at 4700 rpm thats aboot 140 mph

 

I have the factory 3.54:1 gear but not factory sized tires or rims.

http://ctny.audiworld.com/mark/s4/gears/

According to a site that I found where I can input my tire size, gear ratio and speed, to find my rpm's my specs are such:

Current Setup Engine spinning 245rpm faster than stock at 70mph
Tires: 205/50/15
Gear ratio: (tranny 3rd gear) 1.00
Final Drive: 3.54:1
Speed: 96 mph - at 70 mph
Rpm's: 4951 - 3610

Factory Setup
Tires: 195/70/14
Gear ratio: (tranny 3rd gear) 1.00
Final Drive: 3.54:1
Speed: 96 mph - at 70 mph
Rpm's: 4615 - 3365

Future Setup Engine spinning 55 rpm slower than stock at 70mph
Tires: 215/60/15
All else same as above
Speed: 96 mph - at 70 mph
Rpm's: 4540 - 3310

Future Setup with 81-83 N/A 5 speed Engine spinning at 899 rpm slower than stock at 70 mph and within 1 mph accuracy on the speedometer. Now we are talking killer gas milage and good off the line performance.
Speed: 96 mph - at 70 mph
Rpm's: 3382 - 2466