So does the limiter cut you off based on what the speedometer says or what your actual speed is?

It can work a number of ways. Not exactly sure how it works in the Z, but it could just simply be a rev limiter in top gear, or based off of the wheel speed sensors.

I know for a fact I was going faster than 150, because I've been that fast in my last car and this felt way faster. Tires and wheels were stock with 20mm spacers all around, and the tpms were also removed. Awhile back I noticed it has a green bolt on the front of the engine.. looks like a ground. Thought maybe a grounding kit? I'll have to take a picture of it and see if you know what it could be. That was the only indication that it had be modified.

that's not really the most scientific way to establish speed

That's true. 100 MPH in a Buick LeSabre feels faster than 140 in a 370Z.

Well I'm assuming a 350 and 370 feel very similar at that speed. I'm not trying to be scientific. I'm just sayin..

they don't. the shorter wheelbase on the 370 is going to make it feel notably different, not to mention the fact that your car is slammed.

Oh..I see. Well my 350 was slammed as well...had a little more done to the engine too. I guess i'll get my friend to stand on the edge of the road and use my Hotwheels radar gun next time so I can get an accurate speed and prove myself.. :rofl2:

It's safer just to sit here and theorize. :icon17:

When I had my G37.. I saw 173 on the speedo and it was not tuned... Wondering if the governer is not always set from the factory? I have been in some BMWs that have blown past the governer as well untuned..

The speedo can be WAY off so I wouldn't go by that. It's possible the governor is RPM based and you weren't quite at that RPM, but the speedo was reading much higher.

You really need to be looking at your RPM and use your gear ratios and tire heights to back your way into your speed. And verify things with GPS (which also has a margin of error).

This is what Tire Rack has to say about speed ratings:

Speed Rating

In Germany some highways do not have speed limits and high speed driving is permitted. Speed ratings were established to match the speed capability of tires with the top speed capability of the vehicles to which they are applied. Speed ratings are established in kilometers per hour and subsequently converted to miles per hour (which explains why speed ratings appear established at "unusual" mile per hour increments). Despite the tire manufacturer's ability to manufacturer tires capable of high speeds, none of them recommend the use of their products in excess of legal speed limits. The maximum operating speed of a vehicle must be limited to the lowest speed rated tire on the vehicle.

Speed ratings are based on laboratory tests where the tire is pressed against a large diameter metal drum to reflect its appropriate load, and run at ever increasing speeds (in 6.2 mph steps in 10 minute increments) until the tire's required speed has been met.

It is important to note that speed ratings only apply to tires that have not been damaged, altered, under-inflated or overloaded. Additionally, most tire manufacturers maintain that a tire that has been cut or punctured no longer retains the tire manufacturer's original speed rating, even after being repaired because the tire manufacturer can't control the quality of the repair.

Over the years, tire speed rating symbols have been marked on tires in any of three ways shown in the following examples:

225/50SR16 225/50SR16 89S or 225/50R16 89S


Each of these was an acceptable method of identifying speed ratings.

Early tires had their speed rating symbol shown "within" the tire size, such as 225/50SR16. Tires using this type of branding were not to have been produced after 1991.

225/50SR16 112 mph, 180 km/h
225/50HR16 130, 210 km/h
225/50VR16 in excess of 130 mph, 210 km/h


Beginning in 1991, the speed symbol denoting a fixed maximum speed capability of new tires must be shown only in the speed rating portion of the tire's service description, such as 225/50R16 89S. The most common tire speed rating symbols, maximum speeds and typical applications are shown below:

L 75 mph 120 km/h Off-Road & Light Truck Tires
M 81 mph 130 km/h
N 87 mph 140km/h Temporary Spare Tires
P 93 mph 150 km/h
Q 99 mph 160 km/h Studless & Studdable Winter Tires
R 106 mph 170 km/h H.D. Light Truck Tires
S 112 mph 180 km/h Family Sedans & Vans
T 118 mph 190 km/h Family Sedans & Vans
U 124 mph 200 km/h
H 130 mph 210 km/h Sport Sedans & Coupes
V 149 mph 240 km/h Sport Sedans, Coupes & Sports Cars


When Z-speed rated tires were first introduced, they were thought to reflect the highest tire speed rating that would ever be required, in excess of 240 km/h or 149 mph. While Z-speed rated tires are capable of speeds in excess of 149 mph, how far above 149 mph was not identified. That ultimately caused the automotive industry to add W- and Y-speed ratings to identify the tires that meet the needs of new vehicles that have extremely high top-speed capabilities.

W 168 mph 270 km/h Exotic Sports Cars
Y 186 mph 300 km/h Exotic Sports Cars


While a Z-speed rating still often appears in the tire size designation of these tires, such as 225/50ZR16 91W, the Z in the size signifies a maximum speed capability in excess of 149 mph, 240 km/h; the W in the service description indicates the tire's 168 mph, 270 km/h maximum speed.

225/50ZR16 in excess of 149 mph, 240 km/h
205/45ZR17 88W 168 mph, 270 km/h
285/35ZR19 99Y 186 mph, 300 km/h


Most recently, when the Y-speed rating indicated in a service description is enclosed in parentheses, such as 285/35ZR19 (99Y), the top speed of the tire has been tested in excess of 186 mph, 300 km/h indicated by the service description as shown below:

285/35ZR19 99Y 186 mph, 300 km/h
285/35ZR19 (99Y) in excess of 186 mph, 300 km/h


As vehicles have increased their top speeds into Autobahn-only ranges, the tire speed ratings have evolved to better identify the tires capability, allowing drivers to match the speed of their tires with the top speed of their vehicle.

most speedos read 12-25% high. pretty easy to verify with a GPS unit.

Wait i dont get it... I read your posts after and you are saying it is rev limited, yet you also say its drag limited.... Every car is drag limited once the rev limiter is off... If it is drag limited then why were my rps not even close to redline at 154MPH?

electronically limited from the factory to ~155mph.

It is drag limited to about 165, give or take.

to the bolded part--drag limited means you can't run the car to redline because there isn't enough power to overcome the drag....

I think you're just misunderstanding me.

In terms of real world top speed (with the speed limiter removed) it is drag limited to around 168 mph. At that speed there is simply too much drag for the engine and gearing to overcome.

In stock form, the car is limited to around 155 mph. This could be a rev limit *IF* that's the type of governor used... where the ECU says "I'm going to cut fuel at X RPM in top gear where X RPM = 155 mph or thereabouts."

okay gotcha, i see what you mean now

I've only hit 110mph in my Z, so Im still a ways away from finding out what she'll do, theres not many roads around here to open her up..

ive hit 150 in my auto, forgetting to upshift in manuel mode to the 7th gear lol

Come visit Maine, ill show you some! :driving:

Not that I ever would outside a track, or on a track for that matter, but it's nice to know the RE070s I got are (Y) rated. FWIW, a stock 370Z will do ~175mph on the old Mulsanne straight at Le Mans...in Forza 4 :driving:

:icon18: I love that track to test out all my cars.

This sunday after few weeks take my baby to highway. Outside temp were really low - 2'C and winter tires on 18" wheels.

The Vmax by speedo reached were 270 km/h!!!! the 255 km/h on 5th gear (but limiter is higher). It was first time with speed exceeding 200 km/h for longer time and I'm really nicely surprised :driving:BTW: RON95 used for few last tanks.

135 to 150mph is kinda slow to get to. The Z definately needs bolt ons for a smoother-quicker ride to 155mph. But this car sure feels crazy above 140mph in spite of the kinda laggy accel up high.

Went just shy of 155, and the car kept going.. Friend of mine said it would be limited to 110, but that was disproven :)

Hey guys. Im a "spirited" driver as much as thr next person, especially on the highways.

And i loveeeee speed.

But at speeds above 120mph, and even speeds at 140mph+, a simple BUMP, a simple dead bird on the road, a simple piece of garbage that fell off a truck, a simple MIScalculation in the steering wheel, and it can all be over.

For the sake of life, and ppl on the road....

Please guys, dont go these speeds on ANY public road...

Give me crap if u want... But i have had friends die becuz of speeds above 100mph.. So just my 2 cents..

Dont you tell me what to do!! *Runs to bathroom crying* LOL, but yea, totally agree.

lol...

It is factory limited at 155. if you see more or less on the speedo, it is a small variance in speedo calibration.. if you see a variance on gps, it is a question of calibration vs. wheel diameter (more diameter, faster travel vs. indicated.)

Removing the limit will give mixed results based on a lot of things... wind direction, slight descent or climb on the road, Things like air filter condition, oil, engine condition (is it a tired engine over 100k miles and more exhaust out of pcv than the exhaust, etc...)

The drag coefficient is also a factor... .29ish can be helped by adding in a full undershoud to limit under-car air turbulence, and dropping the car enough to limit under car channeled air.

"Tuning" the tires ( properly sizing front and rear tire diameters) to a near neutral cord line relative to path of the car will also reduce drag or in some cases remove float. (bigger rears making more downforce but creating much more drag, or front wheel large diameter causing float and increasing under car drag, and possible dangerous condition at high speed.

Other things like tucking the side view mirrors ( or removing them all together) drastically helps at those speeds

When at the track, ive gotten it to sit at 155 quite easily... when i removed limits and twin turboed it, i was up to 184 (gps).. but that wasnt a max out, just a quick top out on a pull. had i sat on it, i might have gone much quicker.

The car is quite stable, but not practically meant for sustained max speed.

that said, ill throw in the disclaimer..
you should never drive faster than the speed limit on public roads. Any driving of this nature should be considered unsafe without the express consultation of a professional in this field and in an approved venue for such activity. high speed driving requires reinforcement of the vehicle to avoid catastrophic failure of oem components.

when I shop for a car, I do pay attention to how much power does it make thus knowing is it a good engine..

but I don't really pay attention on how fast it can go or what's the max speed...

cos I know 1) I won't be able to reach that speed, and 2) it's too dangerous to reach that speed.

:icon17: