What differential are you useing and why , the gear ratios ?

[pauliedrft]

See ive been looking for my answer and cant seem to find it so im asking everyone to post there diffs, gear ratio's and why they use them .. Im thinking about doing a q45 diff in my 240 cause i hate not having a use for 1st , at all with my ka24de ,now im running 17 inch rims, 205/ 40 /17 tires also . I feel once i do the sr20 swap having more horse power is going to make this problem worse . So going to said 3.69 gears would benefit from said power . What is your opinion on this and what are you running .. Thanks i feel this could be very interesting .

[blacksrjdm]

Search some there are already a few threads like this, that really arent that old.

[Lev_96_240sx]

Well look at it this way, with the stock 4.08 gears and a 26 inch tire (255/40R18 I'll use mine as an example) 1st gear will top out at 34mph. With 3.69 gear, all else being the same, 1st gear will top out at 39mph. In other words you will still not have any use for 1st gear. The final drive doesn't have as much of an effect on the low gears as the high gears. For example the difference between a 4.08 final drive and a 3.69 final drive in 1st gear at 6200 rpm is 4 mph, in 3rd gear it's a 9mph difference and in 5th gear it's a 16mph difference. (Speeds calculated using http://www.apexgarage.com/tech/gear_ratios.shtml)

In the end it's whatever you want to put into your car, but know that just because the final drive is higher will not make 1st gear any more useful. Hope that helps

[C3Sierra_S2000]

Nice link According to that I can go 197 in 5th gear with my Q45 rear and my LS V8. I might need a bigger rear wing LOL.

Oh and to answer the original question I use the oder 3.54 gear Q45 rear end because even with my LS1 1st and 2nd were pretty much useless unless you needed to put down a smoke screen.
Modified by C3Sierra_S2000 at 1:24 AM 12/2/2008

[ag240]

i have a j30 in mine, stock KAde. it has a 3.916 ratio, so it's a bit taller than stock. On the freeway, i have to be at 2800 rpm to go 65 mph. I feel a small loss of torque, but a locking diff is better than an open.

[Lev_96_240sx]

Nice link According to that I can go 196 in 4th gear with my Q45 rear and my LS V8. I might need a bigger rear wing LOL.

Oh and to answer the original question I use the oder 3.54 gear Q45 rear end because even with my LS1 1st and 2nd were pretty much useless unless you needed to put down a smoke screen.

I think you got your gears in the wrong order or something. I did the calculation and with an LS1/T56 combo with the 3.54 Q45 final drive you would redline 4th at 142 mph (6500rpm) and have a theoretical top speed of 284 mph. All of these using a 26 inch tire, i.e. 255/40R18.

Just to see if it is correct or not, I also did a gear ratio check on the Ferrari Enzo which has a claimed top speed of 217 mph, and after entering all the numbers I came up with a top speed of 218 mph which is close enough to assure me that the top speed per gear calculation of this particular website is in fact accurate.

[Dattebayo]

My S12 has a 3.69 in it stock, and it's a VG30E motor. The S12 and Z31 VG's had the same trans gears as an S13 in them too. My first gear MPH ends somewhere about 27, lol. But it does get the car moving off the line quick.

[SketchyRollin564]

i have a j30 in mine, stock KAde. it has a 3.916 ratio, so it's a bit taller than stock. On the freeway, i have to be at 2800 rpm to go 65 mph. I feel a small loss of torque, but a locking diff is better than an open.

Same thing here. As far as highway speeds, the rpms only drop 500, but its still nice to be able to go 5 or 10 mph faster without revving too high

On a n/a KA, the stock gear ratios (open diff, or 240sx vlsd) are way better, since the engine doesnt have a lot of power, but if your ka-t, you will probably like the j30 gear ratio better, and you will get more use of first gear

Right now i get more traction off the line, as both wheels get power, less wheelspin, better handling, better gas milage, and its actually nicer for DD, and i dont have to shift from 1st to 2nd so early, and i still have enough power going to the wheels to mess around and do burnouts if i want

All in all, if you dont want a j30 diff cause of the ratios, it is still WAY worth it.

The other thing you can do is swap the guts of the j30 diff into your open diff housing, and youl have a vlsd, but you will keep the stock gear ratio

[pauliedrft]

See i did search and read 7 different threads and all the posts in then and i found my answer from this here see i can drive my 240 with a na ka24de in fourth at 25 mph if i can do that now then im definitely going to hate having more power at this gear ratio . i appreciate your time and i think i will be going with the q45 diff plus it should be a little stouter seeing how it was made for a 4.5 litter Thank you for your time and replies maybe this can help someone else who cant figure out what they want to use ...

[Bumnah]

i've got an sr20det, with a 180sx rear diff. the gearing is 4.36 in the rear diff. the gearing is spot on.

[Dattebayo]

it should be a little stouter seeing how it was made for a 4.5 litter Thank you for your time and replies maybe this can help someone else who cant figure out what they want to use ...

That's precisely why you don't want a Q45 diffy... The SR20 has different torque characteristics from a V8. Your acceleration is going to be veeeerrrry slow with a 3.69 ratio in the rear with an SR20DET.

[carkook]

Same thing here. As far as highway speeds, the rpms only drop 500, but its still nice to be able to go 5 or 10 mph faster without revving too high

On a n/a KA, the stock gear ratios (open diff, or 240sx vlsd) are way better, since the engine doesnt have a lot of power, but if your ka-t, you will probably like the j30 gear ratio better, and you will get more use of first gear

Right now i get more traction off the line, as both wheels get power, less wheelspin, better handling, better gas milage, and its actually nicer for DD, and i dont have to shift from 1st to 2nd so early, and i still have enough power going to the wheels to mess around and do burnouts if i want

All in all, if you dont want a j30 diff cause of the ratios, it is still WAY worth it.

The other thing you can do is swap the guts of the j30 diff into your open diff housing, and youl have a vlsd, but you will keep the stock gear ratio

Will the j30 diff. pinion gears diff. pinion shaft and side gears fit right into the 240sx diff. case? Is that all you need?

[Lev_96_240sx]

The J30 diff will bolt right up to the S-chassis subframe. If you ask me, that's much easier than swapping the internals

[carkook]

The J30 diff will bolt right up to the S-chassis subframe. If you ask me, that's much easier than swapping the internals

Yeah but I think I want to stay with the stock Final Drive ratio.

[SketchyRollin564]

Will the j30 diff. pinion gears diff. pinion shaft and side gears fit right into the 240sx diff. case? Is that all you need?

http://www.ka24development.com/vlsd.html

all the info you need is on that link

[carkook]

http://www.ka24development.com/vlsd.html

all the info you need is on that link

Thanks, I guess the final dive ratio really isnt that much different so the easiest thing to do is just mount the whole thing in there.

[C3Sierra_S2000]

I think you got your gears in the wrong order or something. I did the calculation and with an LS1/T56 combo with the 3.54 Q45 final drive you would redline 4th at 142 mph (6500rpm) and have a theoretical top speed of 284 mph. All of these using a 26 inch tire, i.e. 255/40R18.

That was a typo on my part. I meant 5th gear. They have a horsepower calculator to determine how much power you would need to reach a given speed based on frontal area, coefficient of drag, and weight. According to that I will have more than enough with my new motor to theoretically reach 200mph. I don't plan on doing it by any means as it would be incredibly unsafe but its neat to know that it is theoretically possible.

[S13Teddy]

Make sure to get a few bottles of the quick dry stuff.

[500hpSilvia]

month old thread but hey here is my input if you guys want it, i have a s13 with a built sr20det (520hp) z32 trannz and a Q45 3.69 rear end, 1st and 2nd are pointless spinn all over the place but 3rd lol car dies! till boost kicks in again but still takes a long time for the gear to wind up.(3rd tops out at 135mph 8200rpm) so what we will be doing soon is try to get a set of gears for this diff. i highly recommend this diff for cars with high power due to the 30 spline axels and input shafts..