Kwame

iTrader: (78)

I'm going to see if I can answer your question "better" when I'm free later on tonight.

For now, try plugging in your information in a program like Cartest (I know its kind of cheesy and really old-school but it is still helpful in some situations) for now and see if it gives you what you're looking for.

Z1 Performance

iTrader: (564)

I'd have to see the math you are working with to better be able to tell where you're making your misunderstanding things. It defies the laws of physics to have a longer final drive accelerate quicker than a shorter final drive assuming the torque curve has not changed, and traction has remained consistent and the road is level.

onagao

Within a single gear, I'm totally with you. 2nd gear versus 2nd gear, and it's no competition. The difference comes into play when you look at all gears in series and consider the fact that you're shifting out of a gear with more torque than stock and into a gear with less torque than stock. Until the stock gearing requires a shift into the next gear, it will be developing more torque than 4.08s, 3.9s, or what have you.

In playing with CarTest a little bit - which, Kwame, I really appreciate you linking me to - it seems to confirm this to a degree. That program shows a significant advantage for the 4.08 car when starting in first gear, but when starting in second or a later gear, the stock gearing can actually be quicker (depending on the speed you start at). I'll play with the program a little more while I wait for Kwame to get freed up.

(On a side note: Vista sucks and will not work with CarTest, so I'm limited to using the online app. My car is now a modified Hayabusa.)

Z1 Performance

iTrader: (564)

It comes down to a very simple question that only you can answer for yourself. You are overcomplicating things

If you want better acceleration in every single gear, you get the 3.9 or 4.08 final drive. If you want more top speed in every single gear, you stick with your current 3.5, or swap to the automatic 3.3 with the automatic differential (since it won't work with your stock ring and pinion). That is what the ring and pinion options come down to. It depends on what you want, and the conditions you use your car in. Shifting from gear to gear is a different set of equations and you are now dealing with far more than just the singular ring and pinion change.

Kwame

iTrader: (78)

This is what you meant to say...

onagao

Not to sound combative, but I'm really not over-complicating things. I'm trying to look at the overall straight line performance outside of just one gear. The simple fact that in a race that spans longer than one gear, there are portions of it where the stock gearing will actually be accelerating faster than the shorter gearing, and that they will alternate over the course of the race, can be very significant.

In one gear, there is absolutely no disadvantage except the reduced top speed. But when you make the scenario more realistic (i.e. longer with more than one gear), there is a trade-off, and it's not one you should ignore. I've run the CarTest simulation with each gearing setup beginning at different speeds. Here, I'll post the results.

0 mph: Geared wins big.
5 mph: Geared wins big.
10 mph: Geared wins.
15 mph: Geared barely wins.
20 mph: Virtual tie.
25 mph: Virtual tie.
30 mph: Stock barely wins.
35 mph: Stock wins.
40 mph: Geared wins.
45 mph: Virtual tie.
50 mph: Virtual tie.

Now, of course some of it comes down to what RPM the cars are starting at, and at what speeds they needed to shift (the program set them at 45,73 for stock and 39, 63 for geared), and the only time they start at the same rpm (0 mph), the geared car toasts the stock gearing.

If you think I'm making things up or am somehow wrong, click on the link and test it for yourself. I'm not mistaken, misunderstanding things, or over-complicating it. I'm looking at it from a broader perspective that is arguably more practical.

EDIT:
I don't want you to feel like I'm trying to argue with you. I'm really not. I just feel the need to justify my approach. I began looking at this mod with a mistaken belief - that gears effectively take the car you have right now and increase its available torque by x%, and therefore it's quicker - when, in fact, the gears transform the car entirely. With that transformation are some huge improvements as well as a few drawbacks. One of those drawbacks happens to be the fact that there are portions of a straight-line race where your stock gearing will actually be superior. Nonetheless, I really appreciate you entertaining my questions - it would be very easy for you (like some other people) to completely dismiss what I'm saying as ridiculous or stupid, and I thank you for not doing that.

Z1 Performance

iTrader: (564)

I wish you luck on whatever route you decide to go - we're going around in circles at this point.

If this were a true race car, you would have a multitude of ring and pinion ratios, tire staggers, and even individual transmission gears to suit all possible race conditions you may encounter at all the tracks you run at. You would also alter balast, differential locking, brake bias, and other aspects of the car to maximize each lap. But you don't have a race car. You have a street car.

Again, the effect the gears have is indisputable - it is up to you to decide for yourself whether these effects benefits you, or does not benefit you, given the conditions under which you operate the car.

Kwame

iTrader: (78)

In those comparisons above, what factor determines who wins or doesn't win? I understand the post above are the starting speeds but what type of competition are we talking about here? 1/4? -60 mph? Top speed?

onagao

I was going off of the various time-to-distance benchmarks in the application, with the farthest being 1/4 mile. Sorry, I meant to specify that.

Z1 Performance

iTrader: (564)

Which is what we come back to - all this info can easily be extrapolated from the info on page 1 of this thread. No one said the gears are for everyone - it is up to the user to decide if they are a proper mod for them, given the situations under which they use the car, and the properties of their car.

onagao

I completely disagree with your first statement. I consider myself a fairly intelligent and intuitive person, and all this info could not be easily extrapolated from the info on page 1. On the first page are basic pieces of information, and much can be extrapolated from it. But to say that such extrapolation is easy is a tremendous understatement. Ever since I started posting on this thread, I made it clear that I was looking for *quantitative* performance gains. Quantitative"" refers to actual numbers, "performance" refers to more than just one gear, and "gains" refers to what your numbers look like in relation to the previous setup. I know that sounds condescendingly obvious, but if you consider what I've been asking about and compare that to what is offered on the first page, I think you can plainly see that they aren't the same.

With the info on page one, all you can do is roughly guesstimate without any real knowledge of the implications of shifting earlier. Whether or not there are any performance gains outside of the analysis of one gear is completely unknown without calculation, much less easy extrapolation. That first page isn't nearly as informative as you think when it comes to real-world relative performance.

And I'm not saying anything about the ultimate value of the mod. I'm simply trying to get a better picture of the full implications of its application. What you seem to be suggesting is that quantified relative performance results could easily be gleaned from a chart of gear ratio numbers, top speed in each gear, and percent torque gained in each gear... all topped off with the qualitative opinion that it's a great mod.

The first page is informative as heck, but it absolutely did not answer my questions.

Kwame

iTrader: (78)

I was going to attempt to answer your questions last night but I got sidetracked by the Yankees game and after their loss I was not in a mood to go online. After reading what you have written over the last couple of days up to and including today I'll come out and say that I simply do not know what exactly it is that you are asking. If you could clearly list your exact question(s) I would love to take a stab at answering them individual if I can.

onagao

Well, my initial inquiry was into how the swap from 3.54 gears to 4.08 gears would translate into real-world performance. Obviously it makes each gear shorter, cuts down your top speed, marginally hurts gas mileage, and shortens each gear. It also adds 14-15% torque at the wheel for each gear versus what it was previously. All that I understood/understand.

What gave me pause was a video (oddly, the ONLY video I could find showing direct before-after gear comparison). In the video, the time it took to accelerate from 25-100 mph in the Z was virtually identical. I had thought that a 15% increase in available torque would yield HUGE gains, but it seemingly didn't. So that was my first question:

1) What sort of quantifiable results could one expect in terms of straight-line performance overall (i.e. not just 2nd gear versus 2nd gear, but all gears in a distance race)?

My second question was effectively:

2) Why does the only direct video comparison I can find apparently show no gain despite the addition of all that available torque?

Now, thanks to you linking me to CarTest and a lot of the calculations I was doing on my end, I feel like I've sort of answered those questions, but I would happily welcome confirmation or denial of the conclusions.

Possible answer to both questions:
1) Assuming you have good traction and start in first gear, there will be significant gains in the realm of 0.2-0.3 seconds in a 1/4 mile race, along with a similar gain in 0-60 time. Primary gains over stock will be limited to first gear even though all gears will pull much harder than before.

2) Beyond 1st gear, or a race beginning within 1st gear with good traction, there really is not much - if any - straight line performance advantage to having 4.08 gears instead of the stock 3.54s. The reason being that shifting out of a relatively higher torque gear in the 4.08s earlier means that the stock gearing will be putting more torque to ground than the 4.08s until it has to shift. This would lead to a sort of alternating advantage/disadvantage between the cars all the way down the road. So it seems that unless you start in 1st gear and have great traction, a distance race between stock and geared cars will be practically even.

---

So I'm left with two questions beyond those ^^^.
1) Are my conclusions correct?
2) If so, are there any reasons to get gears beyond (a) optimization of 1/4 mile time/finish, (b) more effective track racing gearing, (c) a car that feels more responsive even if it isn't ultimately quicker after 1st?

---

Thanks for taking the time to read all of this. I know I have a tendency to really get in the details of things. But the way I look at it - it's an exciting prospective mod that has me on the fence, and since it costs as much as it does (with labor), I had better do the research and ask the questions before making the investment.

hpro350z

iTrader: (4)

if i get the 3.9 gears do i have to get my ecu reprogrammed for the gears?

Z1 Performance

iTrader: (564)

no, the ecu is unrelated

hpro350z

iTrader: (4)

i didnt mean like a tune, i mean doesnt i mess with the speedometer? my dad was telling me some bs like that.... hes just an old hippie

Z1 Performance

iTrader: (564)

you're dad is right about some cars, but thankfully these are not one of those cars - that's mainly on older cars

installing the final drive does not affect speedometer accuracy one bit on these as speed is taken via the abs sensors

hpro350z

iTrader: (4)

thanks for the answer

onagao

Would it be possible to get answers to my last post? I don't want to bludgeon it to death, but it's incredibly difficult to find anything around the internet that addresses my specific issues/conclusions, and whether or not they are correct is critical in my decision-making process for whether or not I'm going to go in the direction of gears for my car. Thanks.

Kwame

iTrader: (78)

^ I think when comparing the two sets of final drive ratios you should be comparing torque as a function of engine speed as opposed to torque as a function of vehicle speed as you seem to be doing. What you are saying is correct in that there are going to be certain speed intervals at which the OEM Final Drive will be putting down more torque than the shorter final drive due to the lower maximum speeds per gear of the shorter final drive as compared to OEM. However if you were to compare the two final drives at each specific RPM (engine speed) point you will see that at each and every point the shorter final drive will be putting down more torque to the wheels than that of the OEM.

The only way to offset the loss of speed in gear is by increasing your engine's redline. Installing a shorter final drive and increasing your engine's redline would ideally give you the best of both worlds.