Gear ratios

[Dream240]

Okay I'm planning a auto/manual swap soon, I remember it was said here by someone that the gear ratios for the manual tranny are much better than the auto, and that's the main reason for the lack of power in the auto. But I was wondering are the differentials the same? Should I look into getting a VSD as opposed to the standard LSD, will it make that much of a difference in launches?

Someone mentioned to me that I will need to get the differential re-geared to fit the new tranny set up. Never heard of this...any info would be great.

[Steeles]

All R200 rear ends that came in the 240sx are the same 4.08 R&P. you dont have to change anything with it. if you go LSD from a J30 or Z32 then there will be a different R&P in there i forgot what they are off hand Search FA and here its well documented.

Try searching under Differentials. theres threads on them that cover it thouroghly

[sykikchimp]

it's VLSD.. and it is simply a type of LSD. Look through motorsports for info on LSD's. Good info there.

As far as gearing goes, it doesn't matter, so don't worry about it.

The auto's have bigger gears so acceleration is slower. They do it so RPM's are lower when cruising. Less noise, saves gas, etc..

[Dream240]

Originally posted by sykikchimp
it's VLSD.. and it is simply a type of LSD. Look through motorsports for info on LSD's. Good info there.

As far as gearing goes, it doesn't matter, so don't worry about it.

The auto's have bigger gears so acceleration is slower. They do it so RPM's are lower when cruising. Less noise, saves gas, etc..

The offset in overall top speed, noise, gas mileage in the manual trannies is the 5th gear as opposed to the auto's 4 gear w/overdrive right?

Also thanks for the links I'll check them out.

[sykikchimp]

&nbsp&nbsp&nbspAuto &nbsp&nbsp&nbsp Manual
1 &nbsp2.75&nbsp&nbsp&nbsp&nbsp 3.321
2 &nbsp1.545&nbsp&nbsp&nbsp 1.902
3 &nbsp1.000 &nbsp&nbsp 1.308
4 &nbsp.694 &nbsp&nbsp&nbsp 1.000
5 &nbsp- &nbsp&nbsp&nbsp &nbsp&nbsp&nbsp&nbsp .759

different gear ratios from socal240sx.org

as you can see, 4th gear IS overdrive, and ALL gear ratios are different in their respective gears.

[Dream240]

Thanks for the info.

While we're on the subject of gear ratios, has anyone ever rebuilt a tranny and changed the gear ratios, if so, what were they? Also does anyone have any suggestions for what ratios are good for 200 hp, 250 hp, and 300hp?

I'm planning a turbo kit in the next year, and I want to know if the same gears used for the stock set up will be just as effective with 250 and 300 hp engine upgrades.

If there's a link to previous posts about this topic let me know.

Sorry can't search right now, supposed to be working!!!!

[sykikchimp]

I believe the only companies that make uprated gear sets for the 240 are OS Giken, and possibly a dog ear tranny from Quaife..

Like I said before.. There is no reason to worry about the stock gearset. It works fine for anything you want to do, and it's good to well over 400hp.

If you feel like you need to change anything, getting different ring and pinion gears is the better option. They make 4 or 5 different sizes of ring gear ranging from ~3.7 to 4.9... Some guys like taller rear ends on turbo cars to help with wheel spin, while some guys running 400+hp use 4.9 gears.. just driver preference.

[Dream240]

Thanks sykikchimp, that helps alot.

[IvanS13]

Originally posted by Steeles
All R200 rear ends that came in the 240sx are the same 4.08 R&P. you dont have to change anything with it.

I have a 1990 Fastback Automatic, which was later swapped with a 5-speed SR. Would my gearing be the same, considering I still have an automatic rear end? Just need confirmation, much thanks. Seems like the SR gears are somewhat long for my tastes...

[cdlong]

Originally posted by IvanS13
considering I still have an automatic rear end? Just need confirmation, much thanks. Seems like the SR gears are somewhat long for my tastes...

you don't have an automatic rear end, you have the same rear end that everyone else has (save VLSD vs. open) the gearing is the same across the board.

unless they swapped the JDM diff too, i think they are the same but i'm not sure. if anything the ratios are shorter, in the trans and the diff.

[sykikchimp]

The gearing of the transmission has nothing to do with the rear-end. However the rear-end does affect the entire system gearing. If you feel like your gearing is a little long, maybe a 4.3 rear ring/pinion gear set would help you out. Nissan Motorsports used to sell them. I believe CA18 cars used to have 4.3 gears as well. S15's Spec-R's have 3.7 gears.

Stock is 4.083 bigger number equals: shorter gears, less time in each gear, quicker accelration, and higer rpms at any given speed in a given gear. So instead of 3000rpm at 60 in 5th, it would be 3500rpm at 60 in 5th (numbers made up for the sake of example).

[IvanS13]

Originally posted by sykikchimp
The gearing of the transmission has nothing to do with the rear-end. However the rear-end does affect the entire system gearing. If you feel like your gearing is a little long, maybe a 4.3 rear ring/pinion gear set would help you out. Nissan Motorsports used to sell them. I believe CA18 cars used to have 4.3 gears as well. S15's Spec-R's have 3.7 gears.

Great, thanks for the information. Is there anything higher than a 4.3 rear ring/pinion gear set? Anyone have direct experience with these products or know someone who could give their input/reviews?

P.S.: I am trying to build the car for mainly all grip: togue and occasional circuit, so I am looking for something really short.

Once again, thanks!

[Var]

The 240 is geared way short enough already. I wish i had taller gears like the 300zx. The car tops out at less than 130 if you could redline 5th. That's way too high of gearing IMO. The only reason for it is cause the motor is gutless. With a 100 horses extra im almost certain you'd despise those gears.

On a side-note. Does anyone know what the gearing is on the silvia/180sx? I'd like to know the tranny gears as well as final drive. Thanks

[sykikchimp]

All I do is grip on race tracks, and the occasional auto-x.. I'd like a touch shorter gears for the track, but rearly only b/c I run the stock KA. I make up for it by running a bit shorter tire. a 4.3 gear is about as high as I personally would go on a car that I daily drove. The higher RPM's get rearly annoying. Remember I said earlier they make from (I believe) 4.9 - 3.7 gears.

Of course it rearly depends on the type of driving you like. If you like auto-x a rear short gear like a 4.9 would be nice, but on a long track, you need the legs for the straightaways that a taller gear will give.

If I had about 100 extra hp I would be perfectly ok with the current gearing, but it really depends on the track you run on.

Also, the stock gearing doesn't run out of revs at 130. It's more like 155. We are drag limited around 125-130 if you can get the stock speed and rev limiter cut. JWT claims you can do 130 with just their ecu, and no other mods.

[LanceS13]

Actually, with a tire that is about 25" tall, the car is gear limited at close to 170 with the 4.08 rear end.

[Var]

Originally posted by LanceS13
Actually, with a tire that is about 25" tall, the car is gear limited at close to 170 with the 4.08 rear end.

I think that's impossible. I rev pretty close to redline going about 105 or 110...i have a single cam so my redline is 6K. There is no way it's possible to hit 155, much less 170..unless you add 2 more gears on the transmission. Maybe you can do 155 with 300zx final drive gears.

[rufrydrsc2]

In my auto I can top 140 before I start to get drag limited. I've hit 143 once racing someone, but never over that. I would love to make my 1,2,& 3rd short gears to help take off, and my OD a really tall gear so it would make my highway driving more enjoyable. Since I can run it out of OD up to almost 110 I don't think it would affect a hwy run that much as most are over by then anyway. Is this doable?

[sykikchimp]

I'v seen Lance's calc's before.. I was guessing from one of his previous posts.. thats what the "~" is ~ = approx.

I'm sure he can post it..

[cdlong]

here's a good link i found top speed calculator my car tops out (gear limited of course) at 160, an auto should be able to hit 175. of course drag or ammount of balls takes over well before that.

[Var]

Ok maybe the auto has that capability on a dohc with a 7K redline..anyone else have a SOHC 5-speed that can verify that 5th gear is close to redline @ about 110mph?


well the top speed calculator says i can do 132mph @redline. I guess that sounds about right.

it says the dohc 5-speed can do about 155 @redline

it says the sohc auto can do about 145 @redline

and the dohc auto can do about 170 @redline

tire sizes are 205-50-15.

[cdlong]

if you use smaller tires than what the car was designed for, the speedo will be off. those numbers are actual speeds, which should be lower than the speed registered on the speedo (which is high anyway). your speedo assumes you have bigger tires that roll more with every rotation so it assumes you are going faster. if you went back to the stock size you could almost hit 140.

btw, i have no idea if you already knew any of that or not, i just thought i'd mention it.

[LanceS13]

Tires do have alot to do with it. Your tires are only a little over 23" tall, so your top speed will be lower.
A 225/50/16 tire is just under 25" tall. One rotation of that tire will cover 78.5" or 0.0012396 miles.
The driveshaft turns 4.083 times per one rotation of the tire, or .0012396 miles; so you travel 0.0003036 miles per rotation of the driveshaft.
In 5th, the engine rotates 0.759 times per rotation of the drive shaft, or .0003036 miles; so you travel 0.0004 miles per rotation of the engine.
At redline, the engine is rotating 7000 times per minute, or 420000 times per hour.
So 0.0004 miles/rotation times 420000 rotations/hour equals
168 miles/hour

With 23.1" tires at 6000 rpm in 5th, I calculate 133mph using the same calculation.

Another factor that can't really be calculated is the tires radial deflection at those speeds. The tire will actually become taller, allowing you an extra 2-5 mph that won't show up on the speedo.

[sykikchimp]

Originally posted by LanceS13
Another factor that can't really be calculated is the tires radial deflection at those speeds. The tire will actually become taller, allowing you an extra 2-5 mph that won't show up on the speedo.

Just an interesting side note, but I remember reading about porshe guys going faster than the "Theoretical top speed" on the GT2 on the autobahn, and they determined that it was radial deflection that allowed for this. I think they were doing in the neighborhood of 205mph (supposed top speed of 196) but it's been a while, and I can't find the article.