rear end gearing for my particular setup

[White Comet]

I'm searched for the past few hours and have been able to find a lot of info on nico but not exactly what im looking for. im running a black top s13 sr with ka trans (im told 5th gear in the ka trans is a lower rpm, better for highway driving. is this true?) i also currently have a jdm vlsd gearing in the stock pumpkin with stock usdm (4.08) ring gear. im considering changing out the rear end gearing for something that would give better acceleration, from what i've heard skyline (r32, r33 and r34) rear ends have anywhere from 4.3-4.9 gearing. i'd like to go with maybe a 4.3 or 4.6 but im wondering how much my highway cruising rpms would suffer. woudl the rpms be 1k higher at the same speed? etc. as long as the increase in rpms at highway speeds isn't too great i think i'd like to go with this. I have been told though that a gearing like this will hurt the engine since the turbo won't be in boost as often. is this the case or will the wear be unnoticeable? if it makes a difference i have the stock t25 right now but plan on upgrading to the gt2871r in the future.

i do have a q45 ring and pinion gear which is 3.9 or 3.52 ( i think its 3.51 since the diff is out of a 94). from what i hear a lot of people that are turbo'd prefer gearing like this. i'm told it keeps the turbo in boost more often. shoudl i just through this gearing in? i really want shorter gearing for better acceleration but i dont want it if my gas mileage suffers to much or if it wears teh turbo more. i appreciate any help and feel free to correct me if anything i've heard or assumed is wrong. thank you

[SullivanRacing06]

lol ur off on what the skyline gearing is, $hit i got my r200 out of a 90s gts n/a rb20de skyline, the ration is a 2.90, but then again im shooting for a top speed car, then again i still have a rb26deT to get out of the hole

[White Comet]

ahh thank you, i heard form several threads as well as nico members that the skyline gearing was more then 4. mrgreeneyes has ridden in a local friends sr'ed s13 with r33 vlsd rear. he said the acceleration was insane and the gearing was chosen for acceleration.

if the skyline diff doesnt have the gear i want, what does have 4.3- 4.6 gearing?

[Didderson]

any r200 ring gear with more 'gear teeth' than the stock 4.08 one lol. good luck on the search man.

from carlist.com:This is the ratio of the gearset (usually the differential) that is farthest from the engine. A ratio of 3-54:1 means the driveshaft turns 3.54 times for every one turn of the wheels. Generally speaking, the higher the number, the better the vehicle's initial acceleration and pulling power. The lower the number, the better the vehicle's fuel economy. (See also Axle Ratio

U must be dreaming guy who said 2.9, or maybe it's custom. the skyline has this faster accelerating gearing because it doesn't need to be geared taller for boost, it has more cylinders (and sometimes displacement) that effectively spool the turbo faster without a tall ratio. Based upon this fact, my guess is the RB20det has the 4.766, RB25det has 4.687, RB26dett with 4.956.

Gear 1st 2nd 3rd 4th 5th 6th Final ratioSKYLINE=4.613-2.240-1.444-1.058-.818-.638- 4.766 (7.8-7.9)

SKYLINE=4.675-2.220-1.502-1.074-.839-.656- 4.687 7.8-7.9)

SKYLINE=4.223-2.148-1.509-1.118-.840-.629- 4.956 7.8-7.9)

source: http://www.angelfire.com/un/darklord/ratios.html

last edit i swear LOL.

Modified by Didderson at 9:46 PM 12/4/2008
Modified by Didderson at 10:04 PM 12/4/2008

[Ghast]

Hey cool, we just started learning about all this in school.

Drive gears and Driven gears.

Lower the drive gear the more torque but you will sacrifice horsepower (top speed)

Then the higher the drive gear the more horsepower but you will sacrifice torque (moving power)

Its funny that yawl would talk about it.

I am still learning though. I had no idea this stuff was inside the differential but i guess it makes sense. I thought it was all in the transmission.

One Love,

Ghasty

[hbpignosePA]

wouldnt a lower gear better for an N/A build, i mean your not going to be as quick off the line without the turbo, since you dont get teh boost once the RPMS get up to that range...

i think a stock gear or slightly higher would be best for turbo apps, but thats just my understanding of it maybe im wrong ( i was planning on gearing mine for N/A since thats what i plan on keeping

[White Comet]

my mind is fried after working 12 hours, do you mean lower as in shorter gearing or lower as in numerical (ie- 3.51, etc) i need examples

[hbpignosePA]

yea..... if you have a higher gear (numerical value) it takes longer to accelerate but you loose some top end power

lower gears would be better for N/A since you need the extra power at the start seeing as your not going to see boost...

or wait

maybe lower is better for turbo since boost will make up for lack of torque

damn drinking and tryin to think about this is tough haha

[White Comet]

a higher gear (numerical value) such as a 4.687 will accelerate faster than the stock 4.08 or the q45 3.51. i want the better acceleration but i dont want any bad side effects.

from messing around with a gear ratio speed calculator, i've found that with the stock 4.08 final drive you can do 80 mph in 5th at 2960 rpms. with a 4.867 final drive, to do 80 in 5th you need to be at 3430 rpms. so the difference is actually less then 500 rpms.

i am however wondering about this as well

or wait

maybe lower is better for turbo since boost will make up for lack of torque

[hbpignosePA]

well dont you go through the gears quicker with a higher gearing? ie in 5th to go 75 mph you will be at a higher RPM... thats the offset, sure your faster through each gear, but you sacrifice that top end due to the RPMs increasing...

if your boost kicks in around 3k, wouldnt that be enough to get the car goin? if your N/A you would want the higher gearing to help you get off the line

maybe not if i change mine ill use the s15 final drive which iirc is 4.11

[Ghast]

Drive Gear >> oO<< Driven Gear.More torque(moving power) less horsepower(top speed)more common in 1st and 2nd gear.

In this particular set up which would be somewhere around first or second gear the drive gear is smaller then the driven gear. Which means it takes more rotations of the Drive to spin the driven. So this would be like a 3.0:1 ( 3.0= rotations of the drive gear and 1= the rotations of the driven gear) So you would see that as like, takes the drive gear 3 rotations to turn the driven gear one time.

Drive Gear>> OO << Driven gearTorque and Horsepower are about the same.Usually around 3rd and 4th Gear

In this second setup the Drive gear and the driven gear are about the same so to make it easy for me to explain i am going to say it is a 1:1 ratio. So it takes one rotation of the drive gear to move the driven gear a full rotation.

Drive Gear>> Oo <<Driven GearLess torque(moving power) and More Horsepower(top speed)Usually starts to look like this in 5th and 6th The cruising gears.

In this setup the Drive gear is larger then the driven gear so this set up would be somewhere around .77:1 or even .50:1 in some 6 speeds people have them as low as .25:1 so it is practically the opposite of our first setup for example with a .25:1 set up our drive gear would rotate 1 full revolution and cause the driven to rotate 4 full revolutions thus giving more top speed and less torque.

Now people go with many different setups when it comes to adding naturally aspirated and variations of forced induction into the equation also the different types of driving styles. drift, drag, auto x and circuit hell even highway for a lot of the people we see on you tube and crap.

Hope this helps out. I had a little time to spare before i go to the club!

One Love,

Ghasty

[Ghast]

Now that is in MT but i am sure it has its similarities when being compared to differentials and LSD's

One Love,

Ghasty

[White Comet]

while i do appreciate your help, i think that example only applies to transmissions, for the most part

[Ghast]

I have to do a lot of homework today so if i come across it in my review i would be more then happy to post all the information!

One Love,

Ghasty

[carkook]

The numbers you are stating like 4.3 and 4.8 is simply the driven gear teeth(ring gear) divided by the drive gear teeth(main drive pinion).

The people say that having a lower rear end(smaller gear ratio like under 4) is going to be better for turbo, is somewhat un true. No matter what the situtation is if you have a more aggressive rear end you are going to be faster off the line n/a or turbo.

Personally I like the stock setup, its very aggresive yet you can still drive on the freeway. So going with a differential that might be more aggresive like a 4.8 is going to leave you GREAT off the line but really struggling top end. My guess is that just trying to cruise at 75 youll be over 4k rpm's.

[carkook]

from messing around with a gear ratio speed calculator, i've found that with the stock 4.08 final drive you can do 80 mph in 5th at 2960 rpms. with a 4.867 final drive, to do 80 in 5th you need to be at 3430 rpms. so the difference is actually less then 500 rpms.

i am however wondering about this as well

I dont think thats accurate, doing 80 on the freeway in my car im pretty sure my rpm's are above 3k. When doing this kind of thing you also have to consider the gear ratio coming from the Transmission and the final drive ratio(differential) to get your final output speed. The ka transmission has very agressive gear ratios also, cinsidering you can cruise in 4th gear going 35mph.

The way most 5spd trannys work. 1st gear is gear reduction(small gear driveing a large gear making alot of torque slow top speed) 2nd is gear reduction 3rd gear reduction 4th direct drive(no gearing its like the crankshaft driveing the driveshaft 1:1 ratio from the transmission but then of coarse you have a gear reduction at the final drive aka differential) 5th gear is overdrive(Large gear driving a small gear and raito less then 1:1)

Then the Final gear reduction at the differential.