9kFever

iTrader: (9)

Ok, well i was doing a little browsing tonight when I came across a fellow revup owner with the technosquare reflash revving out to 7500 rpms. In the thread people were commenting saying that there was no need to rev the motor that high due to the fact that it stops making power at 6200ish. I am not intrested in raising my rev limiter as I wouldn't do that without a built head and cams to actually make some more power up there. Anyways, coming from an s2000 with a 9000rpm redline where the stock peak power was at 8200rpms I am somewhat familar with this situation. In the s2k if you shift anything short of 9k the car loses steam and falls on its face. Anyways, other members including Alberto (who I have grown to respect on these boards) was pointing out that even in a stock revup motor (in gears other than first and second) it is beneficial to shift somewhere around 6500 to get the most out of the car. I am waiting for an s2000 buddy to re race me so I can see if shifting a little short in some of the taller gears will make a difference. After looking at this dyno as well as playing around with a gear calculator I am pretty much convinced that it is still best to rev it out because you are making more horsepower above 6500 than you would be if you shifted and fell into the lower 5000 rpms region. However, due to alberto's opinion I am unsure of this. Anyone have any thoughts on this? I took my car out and tried shifting into fourth at 6500 (open highway) and it felt just as fast but I do not know if this is the torque decieiving me.

Anyways here is the thread I read:
https://my350z.com/forum/showthread....lash%26quot%3B

And here is Alberto's quote:
"What I should have said was on REVUP's, shifting at even 7000rpm's (besides 1-2 shift when dragging) is dumb. No need to shift at 7000rpm's or more on a revup seeing as how they peak the same as standard Z's but have an increased redline. That was what I should have said"

Any thoughts guys? i will try to make a video tomorrow night showing the difference at various shift points. My personal hypothesis is that staying in the lower gear till redline will put you that much closer to peak power when you shift. This is pretty similar to how the s2k is minus the added torque =).


The dyno I am using is taken from rwalton1129's stock 2006 MT

Nitrouz

iTrader: (27)

shift at 9k rpms to get the most out of the vtec.

j/k...when I was stock, I used to shift at around 6500 to 6800rpms... Usually get the best times from shifting around the 6600rpms mark.

9kFever

iTrader: (9)

Sounds interesting. Did you do this in first and second as well?

Nitrouz

iTrader: (27)

first and second I was hitting more towards the 6800rpms mark. As the gears go up, I started shifting just a little sooner.

davidv

iTrader: (2)

Redline is a number determined by the manufacture. It takes into consideration peak horsepower and safety. If we are talking about maximum acceleration (drag racing) lets set aside safety and use the term peak horsepower. For maximum acceleration, shift at peak horsepower. After peak horsepower, the Z is no longer accelerating so shift.

Now the real world with different staging pad conditions and different weather (temperature, humidity, barometric pressure). For the best ET, a respectable 60-foot time is essential. If I am spinning tires in first gear, I will often short shift to second gear. The engine is not at peak horsepower, but the car is no longer accelerating so why push it.

Shift points are important, but just as important is Where do you come into the next gear? I like to push the motor just past peak horsepower so that I can come into the next gear as high as possible.


There are days that I am on top of my game, and wont hesitate to dial-in 13.47 seconds.


Then there other days when I may have just as well as stayed home.

roast

iTrader: (2)

Sorry david, but that is very incorrect.

Just because you pass peak HP doesn't mean you mysteriously stop accelerating. Look at the dyno. The engine is clearly still making power. Just because it's not at its peak anymore doesn't mean you no longer accelerate. Simple case and point, in any gear, hold the engine at peak hp and then add throttle for the remaining few hundred RPM. You will clearly accelerate.

The question comes down to whether short shifting (shifting early) will accelerate faster than holding the gear out to redline. Luckily this is not the case in a stock Z because it is geared well.

Gearing is torque multiplication. The engine outputs torque. Low gears amplify the torque. 5th gear is a 1:1 ratio, and 6th gear reduces torque since it's overdrive.

Take your gear ratios and multiply them by the torque numbers on the graph. You will see that in no circumstance does short shifting increase torque to the wheels. With a stock Z, there is always more torque to the wheels at redline than if you had shifted to a taller gear earlier.

The Z has a nice torque curve so shifting early is not going to punish you, but it's certainly not going to do you any favors in the accelerating department.

davidv

iTrader: (2)

Thanks for the clarification.

trentor

many cars don't allow it due to a rev-limiter, but the optimum shift point is always the point where you're making the same hp BEFORE the shift as you are AFTER the shift.

from a dyno graph standpoint, look at it this way... if you draw a line from your shift point in the lower gear to the point on the graph where you end up in the lower gear, this line needs to be as horizontal as possible. if shifting at a lower rpm creates a bigger angle of the line, then you're not maximizing power in the shift.

Miko

iTrader: (2)

Very nice write up roast.

9kFever

iTrader: (9)

I guess a video is going to have to solve this, or not if its the same for both.

mavtais

iTrader: (12)

I'm glad that we can all agree that if you hold it all the way to redline before shifting, then it will land in a higher RPM to start the next gear. As you can see from the power curve on the dyno above, it would benefit to hold all the way to redline before shifting any gear because the drop off after peak power is not as rapid as the climb in power before reaching peak rpm. Shifting at peak hp will put your motor at a lower hp than leaving it in gear all the way to redline. If you have more instances where you have less hp, then you are not maximizing output, therefore slower.

Got Me WORKIN

Jus rev that biznatch til it wont rev no mo