flynnibus

So, we all have seen the 'how fast have you gone threads'.. and talk about a speed limiter at 156mph (Nissan's posted top speed I believe)..

But we haven't heard anyone talking about hitting a fuel cutoff, etc... (that I've seen).

So today on my cruise into work.. I realize I'm doing 80mph in 6th gear.. and the tach is RIGHT ON 3k RPMs. Based on that.. our gearing top speed should be ~176MPH..

So which is it.. drag limited.. or has anyone actually hit a electronic 'ceiling' yet?

OC_350Z

All I know is I would hate to hit that damn fuel shut off at top speed. If the back tires break loose at 155+ it's never a good thing

ares

iTrader: (2)

ok, few things, yes theoreticly I think our gearing would allow us 180 or so. however, there is no way 287hp will get us there. if it isnt electronicly limited, you would hit drag limited somewhere in the 160 area. but its sposed to be electronicly limited at 156, doesnt matter what the RPMs are, thats when the car wont accelerate any more.

it also wont just shut it down like it does when you hit redline, it will just not let you accel anymore,.

flynnibus

I've seen someone post they saw 159 on their digital speedo.. which lead to a discussion about accuracy of digital vs analog speedo.. but its moot really because they are both fed from the same electrics in our car (though the refresh rate on the digital speedo seems lower-> slower to update).

So if there was a electronic speed limit.. the ECU would have known the reported speed and not let it happen. So either it doesn't, or the poster was full of crap

350zroadster

iTrader: (1)

to bypass the speed limiter, just strap on larger diameter tires, and put a gps unit on

350zroadster

iTrader: (1)

to bypass the speed limiter, just strap on larger diameter tires, and put a gps unit on

toykilla

iTrader: (1)

I think this discussion calls for my comments..

As you can see in my sig, I have hit 160mph. This was read on the digital speedo and the analog one was topped out as well.

If you want to talk accuracy of the speedometer, you have to realize there is a +/- tolerance to ANY electronic device. Which means 160 could actually be lower or higher than what i was going. You would think that Nissan would use the same computer readings to display the speedometer as well as a fuel cutoff/speed limiter. So if there was a cutoff at 156, I would have hit it.

When I saw the Z at the Dallas Autoshow before production, they stated ESTIMATED top speed of 156. This is how most vehicle top speeds are rated i think. They probably factored weight/drag coefficients/power/gearing/etc.. into that estimate. It is damn close to what I saw.

I held 160 for about 5-10 seconds and still had it floored. It did not want to go faster and actually took awhile to get from 150 up to 160. I think the wind drag on the car is what is limiting the speed. I believe with more power, we will see higher top speeds. No speed limiter or fuel cutoff exists IMO

I have done no mods to my car yet and have not had it dynoed.

PS. i dont encourage speeding

flynnibus

Thats my point too.. if it were a cutoff.. they'd obviously feed from the same info as the guages.. and accurracy to 'true' speed isn't an issue, because again, its looking at the same source.

Wonder what the ECU hackers think..

ares

iTrader: (2)

yeah tho no "proof" is shown of higher speeds, tho we do have a photo of 156mph. lots have said theyve done higher, which leads to speculation that there is no limit.

also remember, this depends on up and down hill, wind ect. at these speeds, if you were driving with a 20mph wind, 180mph wouldnt be unusual. and if you were going down hill you might get a little extra.

question is, will the fuel cutoff, limit power, or just limit acceleration? perhaps it cant accel past 156, but if your going down hill, that same power might take you a bit faster unless it starts doing engine braking, which they should be hesitant to have a car do at such speeds.

toykilla

iTrader: (1)

i was going on a looooooonnggg flat highway with close to 0mph winds.... for those that need "PROOF", i will offer rides at $10/ticket

FLY BY Z

I would assume that the speedos are fed by a signal from the ECU. This would mean the ECU would know the speed before the gauges/us. If there is error, it is very easily possible that it is greater than the difference of 156 and the top of the speedo reading. The faster you go the greater the error. I would not believe any top speed claim unless it was measured with a GPS. Cars electronics and mechanicals are not reliable enough.

flynnibus

Who cares about the 'true' accuracy of the car's measurement of speed.. the only thing that matters is what speed the car THINKS its at.. because in this discussion that is all that matters.. what the car (ECU) is going to do.

And GPS measurements aren't all that either.. the frequency of updates and their location accuracy aren't all that. Even with 3 meter accuracy.. thats a big margin when measuring speed.

FLY BY Z

Who cares about the true accuracy? How about if the car has a 156 MPH limiter but it reads 165 to us then we think there is no limiter when there is one it is just that the speedo is off. How do you know that ECU doesn't measure speed independently of the speedometer? Tell you what, you don't know.

ares

iTrader: (2)

they could very well be running the limiter off the RPMs... sensing gear and rpm to get speed. that would be seperate from the tranny sensor giving the speedo a reading. its possible..

also my speedo reads about 2-3mph high at 60mph(this was on stock tires) compared to GPS.

Rob Nance

Amusingly enough this has been a topic of discussion on a message board myself and a bunch of old friends from when I was in the Air Force post on. I had made a joke post saying I got arrested for going 165 on the way to work because nobody was posting and I was trying to stir everyone up. Well this big debacle unfolded about how the Z can't go 165. Basically the fact that Nissan says it is limited means so little to me. I don't doubt it is limited, or that it isn't, I do doubt that many people at Nissan know. Even within a company as big as Nissan, the communication breakdown from engineer to marketing/sales, whatever, is a huge breakdown. Tie the fact that it is a Japanese company in and you can cut the validity of info we get by half or more.

Anyhow, against my better judgement I made an attempt at this two nights ago. There is this hill here in Austin that I topped my Eclipse out at once, and now I have done it with the Z once. It's unnerving going that fast, especially at night, so it was a one shot deal. I must say the car is scary smooth, and I have been 150+ in several cars and on bikes. As smooth as any german/european car I have been in at those speeds, supebly stable and smooth. I was well past 160 on the analog speedo, pegged basically. As I shut down because it was just to unnerving to push it any further, I looked at the digital speedo and it said 157. I was still accelerating when I backed off, it had more.

As for comments about being on a decline. The only things that effect top speed are aerodynamics and power for the most part, and even then the power is just the ability for the car to overcome your Cd (drag coefficient). There are other minor variables like rolling resistance of tires, wind, and probably least of all forward momentum. The forward momentum would be the only thing really coming into play when going down a decline. The thing is, your forward momentum even going down a steep decline might net you 1 or 2 miles an hour at best. The wind resistance at these speeds is so great that the ability to hold a top speed higher than you are drag limited would be tough, and the rate your speed would be increasing would be so minor that it is not likely a decline would net you any higher of a top speed, it's just going to get you there a little faster.

Also, the argument about engine braking, etc, when dealing with a decline is a moot point. The car, if speed limited, would just continue to cut fuel more and more if you gained more speed. The wind resistance at those speed you could be going down a 45 degere incline (no such road in the world) and if you let off the gas and pushed in the clutch at 150 you would slow down most likely, so at a steep real world decline 20-30 degrees, this would definitely be the case.

Anyhow, I really don't think it's speed limited, but we'll see. Someone will prove one way or another eventually, but I honestly don't really care. Going that fast is insane, and I don't plan on doing it ever again, at least on the street.

flynnibus

Look in the service manual.. the same signal feeds the entire guage cluster.. our guages are purely digital (the analog speedo just is a analog representation).

Now do I know what the ECU looks at for a cutoff/rev/speed limit? NO.. because thats the whole f'ing point of the thread.. IS THERE ONE AT ALL? If I knew what the ECU did use, that would infer I knew the limit existed, making this thread pointless to start in the first place.

We know the ECU monitors revs, but I don't know why they would calculate gear and rpm equation to come to a conclusion when they already have a speedometer reading at thier disposal. Such a calculation would not be any more accurate, it would actually be much less.. given we already know that 6600RPM would give us a theoretical speed of ~176mph, which it hasn't.

And yes, the ECU has access to the speedo reading as well.. the speedo taps into the bus system of the ECU (go read your service manual). I don't know if it uses it, but its there.

SD350ZEE

I read in C&D that it's Drag Limited, so they couldn't get the car to go any faster in 6th gear.

Daytona Blue Z in Bo

Estimated Manufacturer or Magazine top speeds (estimated and tested) mean close to nothing to me unless it specifically says its "electronic limited". I have driven many cars that I have known the supposed "top speed" by drag limited or whatever and gone way beyond it. Way back my friend's new 96 4MT Toyota Tercel (93HP but 2000 LBS) was rated at a top speed of 110. He has seen 120+ in it, and 115+ UPHILL on highways. In countless rental cars I had I regularly get the top speed 5-10 Mph above "top speed" (I had a 3-speed auto Dodge Neon up to 130!).

I am not saying the Z will do 165-170, I am saying that I bet on any given day I can hop on the interstate and get my Z up to 160 and snap a picture of the speedo but I choose not to at this time for many reasons (safety, stress on car, paint chipping, legal etc.). My friend's 2000 Celica GTS was tested to have a top speed by C&D of 129 and he has gotten it well above 140 stock. I am pretty sure I seen a photo of a 350z doing 162 in a pic that showed the analog speedo just beyond the 160 mark and the digital speedo at 162 in the same pic with just a CAI. I wish I had kept the picture but it was before I got my Z and was not so interested at the time.

tbcz

I'm not sure how much it comes into play here, but it has been tested and shown that manufacturers usually calibrate their speedos to err on the conservative side...i.e. the speedo says you're doing 160 but you're really doing 150. From what I recall reading about this, the chances are that anyone seeing 160 on their speedometer was probably doing much less than that.

The question is does the manufacturer take this into account when calculating the exact cutoff point? I sure as hell don't know...

uklooney

My friends M5 is speed limited by the ECU changing the rev limit when in different gears (noteably 5th & 6th). Does the Z ECU know what gear you are in? If so, why?