Close ratio gears?
 

Close ratio means that the first set of gears (1st through usually 4th) are VERY close to the same size. The reason they do this is to keep you in the power band.

Your motor will make all its power between 4000 and 6500 RPM. Close ratio transmissions will prevent your engine from dropping out of that range during hard accelerations. Before close ratio transmissions, every time you shifted, the engine would drop below it's power range and would take some time for it get back into that range. That would cause a serious reduction in acceleration time.

Close ratio prevents that by keeping the motor in its power range. This will - in affect - increase your acceleration time.

Back in the day, 4 speed transmissions didn't have close ratios due to the fact that they only had the 4 gears to get up to speed and even then, they didn't really have an over drive. Ratios would be around 4.0, 3.0, 2.0, 1.0 for 1st, 2nd, 3rd, and 4th gears respectively. Close ratio wasn't even a thought since they hadn't even figured out how to do an over drive (Any gear less than 1.0). But once an over drive was possible, close ratio transmissions were an option.

tvfreakazoid,

If you have any questions about how the mechanical parts of cars work, check out HowStuffWorks - Learn How Everything Works!
That will answer just about everything you need to know. The direct link to the gearing section is HowStuffWorks "How Gear Ratios Work"

Once you read that then read my following comment.

Close ratio gears just means that there is less of a difference between the size of the gears (gear ratios). The result is that gears are shorter and that translates to faster acceleration. There are two problems when gears ratios are too close. 1) You limit your top speed and 2) You have to shift more often and therefore any time you gained in acceleration is nulled out by the time it takes you to do all that shifting. The opposite occurs when the ratios are longer... you will have less acceleration, but a higher top speed.

Damn those 2 beat me to it info was good enough :D

Yes, exactly. But you can have the best of both worlds if you have enough power. For both top-end speed and fast acceleration, you can do 1st-3rd close ratio, then make the spread from 3rd-4th more drastic. From there 4th-6th (7th or even 8th in some cases) can be more drastic. In the end, your top speed will rely on these things:
How much drag your car creates
How much your car weights
How much power you have
Your final gear (the gear size of your differential)
And your last gear of your transmission.

Assuming that weight and drag didn't have anything to do with it, theoretically, to increase your top speed, you can make the ratio for the final gear smaller, or make the ratio for the last gear in your transmission smaller.

To give you an idea of why power, drag, and weight have to do with it, the 2004 Corvette has 6 speeds. It has 350HP and 365Lbs/Tq. The final gear is a 3.42, and the 6th gear is a 0.5 while the 5th gear is a 0.85 (I believe). In this case, the top speed in the Corvette is achieved in 5th gear, not 6th because the car doesn't have enough power to push it that fast when it's in 6th gear due to drag. If the car was moving at 190MPH and then shifted into 6th gear, it would slow down to about 150MPH even with the throttal at 100%. However, theoretically, if the car had enough power to max out the RPMs in 6th gear, the Corvette's top speed would be around 250MPH.

Good talk.

The truely ideal setup is to have a huge power-band. The C6 Z06 gear ratios:
First gear 2.66
Second gear 1.78
Third gear 1.30
Fourth gear 1.00
Fifth gear 0.74
Sixth gear 0.50
Reverse 2.90
Final drive ratio 3.42

This car will terrify you all the way to 60 in first gear. Now that is a power-band. So what you want is a huge power-band and longer gears.

First gear 2.66
Second gear 1.78
Third gear 1.30
Fourth gear 1.00

^^^^ That's pretty nice. I miss my LS1. :(

Some good info here guys.

Nissan 370Z gear ratio:

http://www.the370z.com/images/370zforum/spec3.PNG

:driving:

^^^^ WOW! 5th gear is 1:1!!!! These gears are DEFINITELY aggressive! I see how they got the Auto to good gas mileage though. The auto is going to pull nice between 2nd and 4th.

I'm so used to the tall GM gears where 4th is 1:1 with 5th and 6th both as over drives.

So, is the gear ratio set up good on the 370? What will need to be done to hit 200mph on the 370? I wonder if there is any video out for a 350 doing 200+?

Why do you want to hit 200 MPH, anyway? Our car speeds are limited by government. Some of the questions you are asking can simply be looked up in :google:. As much as I try to encourage asking questions, don't abuse the system.

no Z should be anywhere near 200mph... lol

Man, the past few days have been so rough for these forums...