lionking

Lionking, can you verify these numbers? Easiest way to do this is put the car in 2nd gear, do exaclty 3000rpm and your speedo should be reading 49kph. If that is what you're seeing then my calculations for the auto are correct. I know that the manual calculations are correct as they match the published numbers and my revs/speedo.

Ok, had a play. In first gear on the limiter (7000) was 69 kph - which matches your calculations at 6600 revs. Hmmm.... my tacho definately said (well it didn't actually SAY - I had to look at it) 7000.

In second gear, at 3000 revs the speed was 46 kph.

I did a couple of runs in both gears and the results were identical.

I wonder if the gearing ratios that I found are accurate??? Are the rear end gearings the same or is that already taken into consideration? I'm new at this.

I should be able to work it out from that as it's the speeds in gear that tell the story. What is are the numbers that I underlined above?

Will try to find out what the mystery numbers are.

Update: I found the source I used http://350zmotoring.com/2003_nissan_...fications.html

Z350Lover

iTrader: (2)

that's pretty close to David's calcualtions though! well done David!

Btw David... do you know how to improve 2nd gear end speed on the manual Zed? as I notice that we cannot be able to break 100 km/hr or even more in 2nd gear and that will definitely affect our acceleration timing!

I presume that with our exhaust mod, our car SHOULD do around 100 km/hr now at the end of 2nd?!

cheers and thanks in advance!

richie

DavidM

Ok, had a play. In first gear on the limiter (7000) was 69 kph - which matches your calculations at 6600 revs. Hmmm.... my tacho definately said (well it didn't actually SAY - I had to look at it) 7000.

The numbers I worked out could be close. One thing I did not take into account is that your rear tyres are 235/50/17 while mine are 245/45/18 (all calculation were made with 245/45/18). I just worked what difference it makes and:
- 245/45/18 = (11.025cm x 2) + 45.625cm = 67.675cm
- 235/50/17 = (11.750cm x 2) + 43.090cm = 66.590cm

That means that the 'real' numbers should be 98.3972% of what I originally posted. ie.

Auto 350Z @ 7,000rpm:
- 1st gear = 71.8kph
- 2nd gear = 112.5kph
- 3rd gear = 173.0kph
- 4th gear = 254.6kph
- 5th gear = 320.7kph

Auto 350Z @ 6,600rpm:
- 1st gear = 67.7kph
- 2nd gear = 106.1kph
- 3rd gear = 163.0kph
- 4th gear = 240.1kph
- 5th gear = 302.3kph

Still, all the 'speeds in gear' are very sensitive to tyre wear and I'm working them out with brand new tyres. Though, this does not affect your speedo reading, but only your real/true speed ie. your speedo will show 70kph either way, but the radar will catch you at 70kph with new tyres and at 68kph with bold tyres.

Still, that does not make any difference to your speedo reading. so if the specs for the gearing I got here are correct, then my calculations should be correct (as my 245/45/18 manual calcs are spot on). One last 'element' that could be variable is that I'm pressuming ~3% tyre elasticity (ie. the tyre is sqashed by 3% when on a car and pumped up). From the look of it, this works for the 245/45/18 tyres, but maybe it's not for the higher profiled 235/50/17s? I'll try to see what happens when I 'scale' my calculations to fit in with your observation of:

"In second gear, at 3000 revs the speed was 46 kph."

This implies that if the auto limiter is set aty 7,000rpm, then you should be able to reach 107.3kph in 2nd gear. This is 4.6% lower then the numbers I've got above, but when I scale everything to 95.4% then this is what we get:

Auto 350Z @ 7,000rpm:
- 1st gear = 68.5kph
- 2nd gear = 107.3kph
- 3rd gear = 165.0kph
- 4th gear = 242.9kph
- 5th gear = 306.0kph

The numbers for the 1s two gerars match your observations, but at the moment I have no idea where the -4.6% is coming from ... I'll re-check my rolling tyre calculations later. If my calculations are valid then another option is that the rev-limiter is not at 7,000rpm, but 4.6% lower ... which would mean 6,700rpm for the auto. That is damn close to the 6,600rpm then the manuals have set and the redline.

So can you verify these numbers? The 1st two gears match so can you do:
- 3rd gear 3000rpm and your speed shold be 70.7kph.
- 4th gear 2000rpm and your speed shold be 69.4kph.
- 5th gear 2000rpm and your speed shold be 87.4kph.


Btw David... do you know how to improve 2nd gear end speed on the manual Zed? as I notice that we cannot be able to break 100 km/hr or even more in 2nd gear and that will definitely affect our acceleration timing!

Your only optinos are:
a) Raise the rev-limiter to around 7000rpm (or just under).
b) Get taller gear-set for the 2nd gear (very expensive)
c) Get taller final drive gear (that will increase speed in all gears and your speedo will need to be recalibrated)
d) Get tyres with higher profile on the rear instead of the OE sizde. ie. 245/50/18 will allow oyu to reach 101.5kph in 2nd, but your speedo will still be sahowing 98kph so it will need recalibrating if you want accuracy.

Best thing to do is to raise the limiter to 7,000rpm.

I presume that with our exhaust mod, our car SHOULD do around 100 km/hr now at the end of 2nd?!

No, no amout of bolt-ons to the engine (or power output) will allow the car to reach different (ie. higher) speeds in each gear. This is set purely, but wheels/tyres, gearing and rev-limiter ... nothing else.

So you need to change one of the above (ie. limiter) to change the speeds-in-gear.

mchapman

iTrader: (1)

I dont think that recalibration is needed for the Z, as 350evo are selling a shorter final drive ratio and that didnt need recal. I think the 350z gets its speed from someother non-conventional manner which isnt affected by these changes. I could be wrong, but im sure the 350evo final drive didnt need any recalibration.

Z350Lover

iTrader: (2)

Thanks David... the only thing that I concern about is HOW SAFE is it to raise the rev limit up to 7000 rpm and who can be able to do that? By using Uni-Chip or any other after market computer/electronic devices? I just know that Uni-Chip should be able to raise the fuel cut, but not too sure about how safe that will be though!

cheers,

richie

mchapman

iTrader: (1)

The unichip on my last car couldnt rasise the rev limit. Only one piggyback can raise rev limit, and that the motec unit. Or the reflash from powerchip.

DavidM

the only thing that I concern about is HOW SAFE is it to raise the rev limit up to 7000 rpm?

'How safe' is not something that I'm in position to say as I only know what I read about stuff like that. Peter/Nathan went into a fair bit of detail about this in a different thread and it sounded like low 7k rpm should be OK for the engine.

On the other, if the auto Zed has a 7,000rpm limit then it should be totally safe ... afterall, Nissan puts warranty on the engine in the Auto Zed.

...and who can be able to do that?

Again, I'm no expert, but connsidering that the rev-limit is set by the ECU in the engine, then an afetrmarket ECU (or the current one re-programmed) should do it. I know that in the US they sell a chip that raises the limit to 7,200rpm. I'd pressume that there'd be something localy as well, but I have not been following many things like that.

Oh, I think that Nathan's GTP 350Z has a 7,200rpm limit (or is it 7,5000rpm?), but I think they are doing it via Motec.

ottonove

Oh, I think that Nathan's GTP 350Z has a 7,200rpm limit (or is it 7,5000rpm?), but I think they are doing it via Motec.

you might want to fix that

lionking

Ok DavidM,
Here are the latest test results.

2nd 4000rpm 62 kph
3rd 3000 69
4th 2000 67**
4th 3000 105
5th 2000 **

**2000 revs is too slow to get an accurate reading. The needle floats too much and the slope of the road can vary speed substantially at these revs. I checked on a steep downhill and got 3rd gear 3000rpm 72kph!

For the other tests I tried to find a flat peice of road and do several runs in different directions.

David, I'm wondering if 3000 is even too slow to get an accurate reading. Could the tranny still be slipping slightly at these revs? I'm new at this and have no idea at what point you get 100% drive from an auto. I was told that some street legal drag cars won't even move 'till you get them to 3000-4000.

Anyway, hope you're enjoyin' all this homework.

ps. Wouldn't you know it. As I was pullin' onto the freeway for the 4th/5th gear 100+ test there appeared next to me a hooned up Skyline. I must be a magnet for these friggin' things. I recon they're waitin for me under the overpass and take off when they see me comin'. It happens like every second time I get on! There was a little bit of chest beating and a little bit of showin off but couldn't get a proper race. Sounds pretty cool when the turbo winds up though. How awesome would it be to have the big-a$$ Nizpro set-up! Then you'd have no need for 7000 - that thing gets boost at idle!!!

zuff

I was under the impression that they just removed the rev limiter....not lift it.

I do know they did it by ECU reflash from Japan.

They don't use Motec due to ABS/VDC incompatibility and the bloody price tag... ...ouch!

mchapman

iTrader: (1)

These AU threads have info on reving strength of the engine and its internals, check page 2 etc

https://my350z.com/forum/showthread....6&pagenumber=2

https://my350z.com/forum/showthread....0&pagenumber=1

DavidM

2nd 4000rpm 62 kph
3rd 3000 69
4th 2000 67**
4th 3000 105
5th 2000 **

That looks like it's close enough to confirm the numebers I posted. Taking the numbers you listed would indicate:

Auto 350Z @ 7,000rpm:
- 1st gear = 68kph
- 2nd gear = 108kph
- 3rd gear = 161 - 168kph
- 4th gear = 245kph
- 5th gear = ????kph

I'd call that a match for the calculated figures as we can't read the revs and speeds accuratelly enough. Still the numbers are within reasonable error margin so that would confirmn that the gears in speed are as previously calculated:

Auto 350Z @ 7,000rpm:
- 1st gear = 68kph
- 2nd gear = 107kph
- 3rd gear = 165kph
- 4th gear = 243kph
- 5th gear = 306kph

Of course, speedo error will squeue the numbers read of a speedo a bit, but I'd say this is what we should go by as the 'true' speeds will be somewhere close to it. The 'true' speed is directly affected by the tyre pressures as well as the tyre-wear. ie. both of these will influence the rolling circumference of the tyre. I'd say that there is a good 5% variance depening on the pressures and tyre conditions (eg. brand new tyres at 40psi comapred to bold tyres at 28psi).

ps. Which brings me to one other way to reach 100kph in a manual Zed. New (ie. a lot of thrread) tyres over-inflated (ie. 45 - 50psi) and you would hit around 102kph in 2nd ;-) Not that I recommend it.

David, I'm wondering if 3000 is even too slow to get an accurate reading.

The higher the revs, the more accurate the readings will be and so will the 'interpolated' numbers. Though, the higher the speeds, the less accurate the speedo will be ... so it's a bit of a catch 22. Still anything bellow (or around) 100kph should still produce pretty accurate speedo readings (ie. 1 - 2% error).

I'd say that 3000 - 4000rpm should be good enough to give us an idea whether the calculated numebrs are correct - which they seem to be.

I'm new at this and have no idea at what point you get 100% drive from an auto.

I'm no expert on auto-gearboxes, but I'm pretty sure that there is no slippage over 3000rpm in 1st gear and I'd be even more surprised if the higher gears were slipping at all.

As far as I know, the only 'slippage' you'd have with the auto is when you are taking off from stand-still and then on the gear-changes.

...you might want to fix that...

I would love to, but this board is telling me that I can't edit my posts anymore. Since yesterday it's been telling me that I only have a 10min window after a post to do so. Not sure why that is as I rarely get to read my post within 10 minutes ... it's usually a day or two later :-(

lionking

DavidM,
Thanks for the analysis. We need to do some practical testing now. Check your PM's.

LK

lionking

This may be because you have a 'silver' auto. Because an auto is slower, nissan may have made it stay in gear longer by reving higher to make it quicker. So when you shift your starting higher up the power band.

Had a testing session with DavidM. The results might just surprise you!!!

DavidM

The Auto has the cut-out set at 7000rpm. Definatelly it's a lot higher than the Manual. The manual bouches of 6,600rpm while the auto bounches of 7,000rpm.

Maybe all that is needed for a 7000rpm redline in a Manual Zed is the chip (or ECU program) from the Auto Zed? I wonder if Nissan would do that for us in the nextservice? Obviously they warranty the engine in the Auto with 7000rpm limit.

mchapman

iTrader: (1)

Originally posted by DavidM
Maybe all that is needed for a 7000rpm redline in a Manual Zed is the chip (or ECU program) from the Auto Zed? I wonder if Nissan would do that for us in the nextservice? Obviously they warranty the engine in the Auto with 7000rpm limit.

I cant really see Nissan doing this, but good find guys! I guess its completely safe to rev to 7grand then

mchapman

iTrader: (1)

Originally posted by DavidM
Maybe all that is needed for a 7000rpm redline in a Manual Zed is the chip (or ECU program) from the Auto Zed? I wonder if Nissan would do that for us in the nextservice? Obviously they warranty the engine in the Auto with 7000rpm limit.

I cant really see Nissan doing this, but good find guys! I guess its completely safe to rev to 7grand then Just need to get the car to make some more power up there first.

lionking

I guess its completely safe to rev to 7grand then


Don't know how safe it is but I'm sure that DavidM will tell you that I rev there too much! With the auto if you push it right to the edge and the limiter kicks in bfore the gear change it'll hang there for a couple of seconds. A REAL pain! I'm no pro driver so a few of our runs were useless because I ran too far in the red and the limiter slowed the gear changes. Anyway, I rev there a lot (almost every time I drive the car) and I'll be strait on the forum to let you know when she blows.

mchapman

iTrader: (1)

Thats the spirit!

mchapman

iTrader: (1)

Those are some great results, but if the auto changed at 6600 would it be slower than the manual?

Probabally as you only have 5 gears to our six, depending on gearing of course. So Nissan have made those rev limit changes to make the car quicker by making most from the 5 gears it has.