Gear ratios

[Kreator]

Well, i haven't seen anything on this topic for the 2 weeks i'm here, so i thought i won't get flamed for asking.

Ok, i was driving with a friend and let him drive for some time and he said that the ratios for the car are pretty high. So i got online and checked some stuff. This is what i found:

s14/s15 MT s14/s15 AT
3.692 (turbo) 3.916 (turbo)
4.083 (N/A) 4.083 (N/A)

Notice the huge difference for hte manual transmission between turbo and the N/A..... Meaning that the difference between turbo AT and turbo MT is more than .2 while there is no difference between MT N/A and AT N/A..... Now my question would be, why is the ratio so high on the manual N/A? Like 300zx has the same ratio, but yet it's 400 something lbs heavier......

And as long as i'm asking this, I want to know what are the ratios for what amount of hp u are running and if you are going more than the stock turbo gives you, where can you get the lsds with this gear ratio?.... Or i guess you can tune them.... NM my last question.

Kre

[drift freaq]

Kreator,
you have voiced a good question. now you call the ratio high but when you start talking about gearing high is low and low is high i.e. 4.08 are considered low or short because it takes 4 turns of the driveshaft to turn the wheels once thereby giving you more off the line acceleration and torque. In turn if you had tall or high gears for instance say 3.70 then it would take 3.70 turns of the driveshaft to turn your wheels once. thereby giving you less off the line acceleration and torque in exchange for more top speed.
Now here is where we get into the mathematics and physics side. When you have a Turbo engine it puts out more horsepower . When you have a lot more horsepower with gears like our stock 4.08 you induce a lot of wheelspin which of course means you do not get traction you need to accelerate forward. When you go to a taller gear like a 3.70 you do not induce as much wheelspin and thereby get traction and move forward.
Now, the other side of this, specifically regarding Turbo engines, is the fact that you want to keep your Turbo spooled up as long as possible. If you run a lower gear like a 4.08 you rev through your gears very quickly thereby taking the Turbo through its boost very quickly meaning that you do not get as much benifit from the boost and the Turbo drops out of spool everytime you shift.
Now with a 3.92 or 3.70 gear you are going to keep your Turbo spooled up longer thereby by getting maximum benifit of the boost in each gear meaning more horsepower to drive the car.
Thats it in a nutshell and pretty much explains reasons for gearing.
About the only place people don't always follow these mathematics is some drag racers who run extremely low gears for launching at which point it takes a lot of talent and extremely sticky huge tires i.e. drag tires to keep the wheels from spinning and losing the torque and ruining the launch.
Though most of our street cars do not run these tires so running extremely low gears with high horsepower can be a disadvantage rather than an advantage.
whew : <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/tounge.gif" border="0" valign="absmiddle" alt=':p'> &nbsp;that was a long one

[Kreator]

Ok, sorry about my low ratio/high ratio mess up. I didn't know what considered high and low (but i do understand how the thing works) so i just thought of the numbers <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/tounge.gif" border="0" valign="absmiddle" alt=':p'> (meaning the bigger the numbers, the higher the ratio).

Ok, but i still don't get the idea behind 4.08 on a manual N/A tranny. I mean i hit 3.5K rpms when i get to around 80mph, while my dad's camry (V6, gr 3.93) only gets 2.7K rpm at the same speed. On the other hand, i spin tires quite often at the start because the first gear got alot of power. I was just thinking that if the ratio was just abit higher (i guess that's gonna be right?), like what J30 uses, on a stock N/A MT would be a bit more comfortable for daily driving (you lose some power, but your gears get longer, meaning that the ride becomes smoother, mpg goes up, and you aren't hitting 3.5K at 80mph)... Or should've added the 6th gear.... anyways, the J30 which we tend to swap the lsd from, got 210hp, but it weighs 3500lbs and it's an auto! I can see why it's low for that car..... But for ours i think it just a bit too low. I mean shouldn't the manual gear ratio be lower than the auto one at least?

Kre

[luey02]

yeah, I like to go 80mph too but I dont want my engine to rev at 35k for 3 hrs... &nbsp;every manual cars are like that I've noticed.. &nbsp;except corvettes which has like .53 for final drive.

[drift freaq]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">kreator....
Ok, but i still don't get the idea behind 4.08 on a manual N/A tranny. I mean i hit 3.5K rpms when i get to around 80mph, while my dad's camry (V6, gr 3.93) only gets 2.7K rpm at the same speed. On the other hand, i spin tires quite often at the start because the first gear got alot of power. I was just thinking that if the ratio was just abit higher (i guess that's gonna be right?), like what J30 uses, on a stock N/A MT would be a bit more comfortable for daily driving (you lose some power, but your gears get longer, meaning that the ride becomes smoother, mpg goes up, and you aren't hitting 3.5K at 80mph)... Or should've added the 6th gear.... anyways, the J30 which we tend to swap the lsd from, got 210hp, but it weighs 3500lbs and it's an auto! I can see why it's low for that car..... But for ours i think it just a bit too low. I mean shouldn't the manual gear ratio be lower than the auto one at least?
</td></tr></table><span id='postcolor'>
ok lets tackle the first question. Our cars are 4.08 NA here in the states with the manual and the auto.
Two reasons for this. One, is its considered by the manufacture to be a sports type car. So they want it to have some go . Two, Americans love Torque. So the low gears give that torquey feel. Of course the second reason is my own opinion. They also gave it an overdrive 5th gear so you could compensate for the low final drive ratio and still get good freeway speeds with reasonable mileage.
Now if you look at a Honda which are torque less wonders they have really low gears too. average final drive ratio on a Honda is 4.23 thats why they still manage to scoot off the line.
Nissan was looking at from the point of balancing acceleration for the cars with MPG . If you go higher geared on certain cars you do indeed increase mileage and top speed but you do that for a sacrifice in acceleration i.e. your car would feel doggy off the line.
Now the J30's gears are 4% higher. Meaning that Nissan looked at the car and said, ok we have a car that weighs 3500 lbs. Lets give it 210 hp and because its a luxury car gear for some go but also a little more mileage. So that is 700 lbs more than our cars, but it has 60 more HP. if &nbsp;we split the hp of our cars it would be 75-80 HP per 1400lbs. The J30 has about 105 per 1750lbs. So the respective HP to weight ratios are close on the two cars. Yet they gave it the J30 a little more freeway oriented gears becuase it is more luxury oriented.
Oh yeah you have to take into account transmission gearing in these equations too. If you found out what the gears on your dads Camry were you might see that in that particular gear it is actually geared more freeway . Which the Camry's final drive is indeed right in line with the J30 and sporting a V6 is going to be torqueier than our cars which explains you spinning tires.

In answer to luey's statement Corvettes are most likely running 3.53 gears which for a V8 sports car is a lower gear ratio.
You have to realize that V8's have gobs of Torque which means they can spin there tires easily. unless the Corvette was going to be a strictly drag car that is actually very good gears for it.
Most american V8 cars run around 3.36 gears.

[Kreator]

Thanx, drift, i think i got it now <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'>