Preferred diff ratio?

[rhs]

Is there an optimal or preferred diff ratio? I have a G285 diff (4.30 LSD) sitting in my garage, but am hesitating to put it in. I have a G284 (4.30 open) right now in the car. Feels like I'm driving a Honda at times with lots of noise and little speed.

Also, other than getting a used diff, is there an easy way to change the ratio with aftermarket parts?

I got a 1JZ with single turbo if that helps.

 

[Nick M]

It depends on the trans and the engine as to which diff ratio I prefer. The stock 3.73 in mine is good enough, but would prefer closer to 3.5.

 

[SideWinderGX]

The only way to change the rear end ratio is to swap out your ring and pinion for a different ratio ring and pinion.

FWIW the 3.54 gear ratio fits our diffs (you'll have to grind the end of the pinion down .100" though because the LSD case interferes with it): http://www.justdifferentials.com/T8-354-NG-p/t8-354-ng.htm

 

[gsxr141]

I was thinking a lower ratio would help with the short first gear.

 

[emericaskater285]

I have both a 3.90 and a 3.73, have also owned the 4.10 or 4.30 whatever the hell was in the n/a cars. My favorite is the 3.73 as it loads the engine up better imo. It is also deep enough to get out of the hole well. I can tell a major difference going from the 3.90 to the 3.73. id like to swap a 3.73 in the car that has the 3.90 right now.

 

[rhs]

Thanks, guys. There happened to be a 3.73 LSD (G305) on eBay that I just snagged. I'm easily persuaded...

The 3.54 thing looks interesting, but after skimming the thread on rebuilding the diff, I wasn't feeling up to that task.

 

[black89t]

it really depends on what you want to do with the car. ive run both the 3.90 and 3.73 in my car and i like the 3.90 better. reason being when at autox i like to be able to bog 2nd and the 3.90 helps there keeps me from having to put it in 1st then go back to 2nd loosing time. also at drags with the 255/50/16 mt i run 4th is still good for i think 135 so its not so short you have to hit 5th. for a 1jz car id think it be the better choice cause they make less torque. pretty sure the ttr came with a 4.10. sorta too late though i guess lol. if you mainly like just cursing and roll racing id say the 3.73 is better cause low hw rpm and makes gears longer with stock tire height.

 

[rhs]

it really depends on what you want to do with the car. ive run both the 3.90 and 3.73 in my car and i like the 3.90 better. reason being when at autox i like to be able to bog 2nd and the 3.90 helps there keeps me from having to put it in 1st then go back to 2nd loosing time. also at drags with the 255/50/16 mt i run 4th is still good for i think 135 so its not so short you have to hit 5th. for a 1jz car id think it be the better choice cause they make less torque. pretty sure the ttr came with a 4.10. sorta too late though i guess lol. if you mainly like just cursing and roll racing id say the 3.73 is better cause low hw rpm and makes gears longer with stock tire height.

It's just a weekend car, so cruising around the city is all the driving it sees. Being on the highway in 5th at 4k kinda sucks.

 

[Nick M]

My favorite is the 3.73 as it loads the engine up better imo.

It isn't an opinion. The taller gear is a heavier load and why the car does not accelerate as well, even with the heavier load. That little bit of more boost does not make up for it. This is why drag cars do not have tall gears to load the motor. Think it through before you put a taller gear in a car with limited torque.

 

[emericaskater285]

It isn't an opinion. The taller gear is a heavier load and why the car does not accelerate as well, even with the heavier load. That little bit of more boost does not make up for it. This is why drag cars do not have tall gears to load the motor. Think it through before you put a taller gear in a car with limited torque.

I also like to be able to use 1st gear. go ahead and argue about opinions. I will bet you anything my time slip will tell you that in my application the 3.73 gear is the better gear of the two. Want to gamble on that? I have both, and will be willing to swap em out at the track in the spring, if you want to put money on it.

 

[emericaskater285]

It isn't an opinion. The taller gear is a heavier load and why the car does not accelerate as well, even with the heavier load. That little bit of more boost does not make up for it. This is why drag cars do not have tall gears to load the motor. Think it through before you put a taller gear in a car with limited torque.

I will also add, the gear that works best will depend on your application, turbo size, how the power comes in, where it drops off at, and most of all what you are using the car for, etc. My power is mostly up top btw...

This doesn't mean its the perfect gear for everyone. and opinion is valid in this topic.

 

[TurboStreetCar]

The only way to change the rear end ratio is to swap out your ring and pinion for a different ratio ring and pinion.

FWIW the 3.54 gear ratio fits our diffs (you'll have to grind the end of the pinion down .100" though because the LSD case interferes with it): http://www.justdifferentials.com/T8-354-NG-p/t8-354-ng.htm

Please, PLEASE! let me know how you verified that those gears fit our cars. Im thinking of ordering them now!

 

[SideWinderGX]

I bought them and installed them haha. You won't be able to set pinion depth without taking off .100" off the end of the pinion if you have an LSD so that'd be the first thing I'd do, other than that its a straight forward install. I think I had .075" taken off to just barely make it fit, .100" would get rid of a bit more excess material and dead weight so if I were to do it again I'd do that.

Going from my 3.9 to the 3.55 I needed new carrier shims, the old ones weren't even close. I used almost all the pinion shims that came in the rebuild kit from Weir.

 

[TurboStreetCar]

AH! Gotcha! Good to know! Was thinking it was a "my friend told me this guy on the forums said he knew someone" Type thing.

Im in a serious predicament at the moment. My rear is not happy and i need to decide what im going to do about it. Its either a Cobra 8.8 IRS setup or a solid axle.

 

[SideWinderGX]

Gotcha, not a problem lol. I have the receipt and a few pictures of the install still on my phone, it fits and works great. No noise after about a thousand miles. Cruising with the TC locked up on the highway is awesome, rpms are at 2300 at 70 mph.

 

[TurboStreetCar]

They made noise in the first 1000 miles?

 

[SideWinderGX]

No, I was just saying I had no issues with mine. The instructions say to drive easy and at different speeds for the first 500 miles to break the gears in...afterwards do a fluid change and you're good to go. If you don't break them in right (like all gears) they'll whine and you'll need to replace them again. I looked at a few different companies' break in instructions and they're all pretty much the same.

That was a long 500 miles though lol.

 

[TurboStreetCar]

How did you go about clearancing the pinion? Do you have pics of this?

 

[SideWinderGX]

That's the end of the pinion that will be machined down. The number on the bottom, 2.466", is the checking distance (distance from the face of the pinion to the ring center line) for optimal contact, give or take a few thousands. The problem is, the LSD case is 5" in diameter, meaning the checking distance cannot be smaller than 2.500" otherwise it won't fit. So at minimum, .034" needs to be taken off. In all honestly, there is still a lot of extra material overhanging the ring gear, so you could take anywhere up to .250" off and you'll be fine. After you grind the pinion down you'll have enough room to do the install/reinstall to check for pattern contact and move it around as necessary.

My cousin knew a guy who does differentials and he ground it down for free, I think I had him take .100" off. From what Nitro and that diff guy said, it's uncommon to do but every once in a while you come across one that needs to be clearanced, so its not unheard of.

I don't have any after pics of the pinion though.

 

[TurboStreetCar]

Ah so you set the pinion depth first to get the shim beneath the inner pinion bearing set, then removed it and ground it down?

What did he use to remove the material? I'd imagine it would need to be something relatively precise that wouldn't disturb the heat treatment of the gear?