Taller rearend, anyone experimented?

[240z4u]

I do a lot of highway driving (3/4 of my trip to work) and would like to get the RPMs down. Turning 3k on the way to work sucks. Has anyone else tried changing to a taller rear. I currently have a J30 diff (3.96) but would like to try something in the mid/high 3s instead.

I figure first gear sucks anyway, I don't see full boost so why not. I am just trying to eek a few mpg out of this thing and make it a bit easier to drive.

Evan

[gawdzilla]

that's really strange. i have the stock final drive (i believe 4.08) so it should be shorter than what you have if you really have a 3.96 FD. I feel like my my final drive is too TALL and needs to be shortened. How fast are you going when you hit 3k rpm in 5th?

I think 3k in 5th gear I am pretty close to 80mph... (don't quote me on that, have not checked in a while). I calculated my theoretical top speed a long time ago and it was over 200 mph revving to 8k.

[mello88]

Better gas mileage? What next, you're gonna get all comfortable on the way to work and want the exhaust quieter and the ride softer and the interior squishier hahaha

Just messing with you, good luck swapping diffs around, that's always a lot of fun.

[Darius]

"The 90-96 Q45 had a 3.54 final gear, and the 97-01 had a 3.69."

Here's a link to the install guide:zerothread?id=267924

[Carl H]

q45 final drive = pain in the *** to install.gotta use the q diff, one of the half shafts, the q hubs and a z32 tt axle.

[DriftingisLame]

I believe z32 NA's have 3.73's or something close.

This is strange to me, because I have such a lack of torque in my rb20 that I'm considering going from a HICAS 4.08 VLSD to a Nismo 4.63. I do nothing but city driving and am trying to be more competative in autocross. Damn top end motors.

[Vkoslak]

z32 NA is same final drive as s13/s14

[HxC_Nismo]

z32 NA is same final drive as s13/s14

+1 i currently run a z32 na diff in my s14 and its shorter then my j30 diff wich actually has 3.92 ratio. i dont see 3k in 5th until im doing about 75mph and i have 4.08 ratio with the z32 na diff now.

[DriftingisLame]

I must be thinking of a twin turbo, my bad

[Vkoslak]

Twin Turbo is a 3.69 (or close to). However, it is a r230.

I've heard that the 350z uses an r200 diff with tall gears. However I think people putting vq motors in their 240sx are using the q45 lsd.

[Bluefire]

I'm running an S15 diff which has a 3.7 and to be honest I hate it. The Rb25 trans already has tall gear ratios. Couple that with a tall final drive and you get some seriously sluggish acceleration. I think i'm gonna put back the stock final drive or maybe even find a gtst final drive (a little shorter). Although it was kinda nice being able to drive on the freeways in 4th gear...

-Bluefire

[BoostFab]

i will be doing the q45 diff swap. it's better for highway, and stronger too.

[Darius]

I checked yesterday and with the j30 diff at 3000rpm I was at 67 mph. That is including the 4 percent gauge reading difference. But I dont know the correction for the 18s either so it might be around 70..

[240z4u]

I do a LOT of highway driving. Honestly, more highway than city anymore. I can pull away hard in 5th gear without trouble.

I was just curious, if I could find a diff that would not be a total ***** to swap it would be worth trying. Cheap thrills! lol.

I am not sure if I will follow through or not. I am turning 3k at 70mph or so. Not terrible. After some research, seems to me that using the z31 turbo trans has given me a slightly different set of ratios vs. the z32 trannies. I have a z32 trans lying on the floor, maybe getting off my *** and putting in that trans will make me happier.

Thanks for the replies.

Evan

BTW, I did swap for more comfortable seats and set my exhaust up not to drone! HAHA.

[rb25drag]

Sorry to get off topic here, I noticed in your signature you got Meth injection? How good does it work? and how did you go about in setting it up?

[240z4u]

I have an alky-control meth injection kit. I put it on about 6 months ago. Its a progressive system that uses a map sensor. Honestly, I have used it once but I had other problems with my setup. I have not tuned the meth yet and am not using it. The reality is that dialing in the meth is what you do last, and I am just not there yet.

Tuning? Its pretty easy. Turn on the controller to whichever setting you want 1-10, and make a WOT pull. Remove fuel accordingly.

I have to say, it does smell totally badass at WOT with methanol.

Evan

[rb25drag]

What kit did you buy? I have not seen any with a controller. Also Does it come with a map sensor? What is the purpose of that? I would think with a wideband it would be easy tuned.

[240z4u]

http://www.alkycontrol.com

Its a universal kit basically, but the guy who I got it from picked out the parts.

The methanol is PROGRESSIVE, you have to use a map sensor so it knows how much methanol to inject. It is somewhat basic but easy to tune.

Evan

[gawdzilla]

http://www.alkycontrol.com

Its a universal kit basically, but the guy who I got it from picked out the parts.

The methanol is PROGRESSIVE, you have to use a map sensor so it knows how much methanol to inject. It is somewhat basic but easy to tune.

Evan

are you tuned to take advantage of the methanol? i thought about doing this too but it doesn't work too well for circuit driving. guess its possible to have 2 maps and switch them around when i do or don't have meth. what safety precautions do you have on it?

[240z4u]

Sure, you can run two tunes that are swappable.

No precautions here, I have lights on my dash to let me know whats going on with the meth. Low fuel, and there is a light that toggles between two colors to show you when the pump is primed up and working (pressure in the lines).

I am not going crazy with this stuff, I have a buddy who runs 20%+ of his fuel map as methanol. Makes a ton of power, but plows through meth like its going out of style. He has the same kit as me. He has been running it for 3+ years now without a hiccup.

I am not sure how much methanol I will end up using, but I won't get too greedy with it.

Evan

BTW, there are kits that offer solenoid setups to automatically drop your boost to a safe level based on line pressures etc...