What is the rear end gear ratio of an 89 240?

[lbrowne]

I'm just wondering what kind of gear ratio nissan puts in a 5speed 240sx, 89 preferrably.

I can't find the specs anywhere. I'm guessing in 3.xx range somewhere?

I wonder if anyone has swapped to a different set. I know going from 3.42 to 4.10 in my TA will make it seem like a whole different car. (a mod currently waiting to be installed:) )

[Nismo_Freak]

4.08 im pretty sure... Also keep in mind that your TA had a posi unit stock and had alot more torque. If it had an LS1 the quicker ratio allowed you to reach its powerband faster. As for the 240 it is a different animal. The rear suspension is a multilink vs. the solid axel type in the TA (which aides in 60's but has less handling ability). Moving to say a 4.30 rear end in the 240 would make it even slower in my mind. You whould need to shift even quicker and the car would want to remain in the upper RPMs where the KA does not like to pull. The volumetric efficiency on the KA lies around the 3000-5000 mark (peak torque @ 4400 stock). To see what I mean try looking at the power band on the 240 tested by import tuner. Go to importtuner.com, then tech, then find the 240.

[lbrowne]

hey thanks for the reply. i know all too well about the IRS vs the solid axle, thats factor number 1 why supras can have an insane amount of horsepower yet only pull a 1/4 minimally faster than one thats got alot less power, yet the trap speeds are really high.

tons of power with IRS usually means trouble hooking up

[Nismo_Freak]

Yes... however keep in mind Skylines have IRS as well... but they have this wierd thing called AWD.

[C-Kwik]

4.08 im pretty sure... Also keep in mind that your TA had a posi unit stock and had alot more torque. If it had an LS1 the quicker ratio allowed you to reach its powerband faster. As for the 240 it is a different animal. The rear suspension is a multilink vs. the solid axel type in the TA (which aides in 60's but has less handling ability). Moving to say a 4.30 rear end in the 240 would make it even slower in my mind. You whould need to shift even quicker and the car would want to remain in the upper RPMs where the KA does not like to pull. The volumetric efficiency on the KA lies around the 3000-5000 mark (peak torque @ 4400 stock). To see what I mean try looking at the power band on the 240 tested by import tuner. Go to importtuner.com, then tech, then find the 240.

Changing the rear gear does not change the powerband. Nor does it change what RPM's each gear puts you in. What it does is put more torque to the ground. The compromise is that you will be driving at a higher RPM's for the same speeds. You'll probably end up with a reduction in gas mileage. But it will allow you to accelerate somewhat quicker. Particularly in 1st and second. If you are on a rolling start though, say 60+, you won't have much of an advantage over the next guy. Keep in mind, your potential top speed will drop as well, but it may actually increase your drag limited top speed slightly depending on where in the powerband it puts you as you near top speed. Frankly, I'm contemplating going to a taller rear gear to offset the heavy wheelspin I get in 1st and sometimes second. I'll see after I swap tires though. My current rear tires got cooked at the last track event.

[Nismo_Freak]

Changing the rear gear does not change the powerband. Nor does it change what RPM's each gear puts you in. What it does is put more torque to the ground. The compromise is that you will be driving at a higher RPM's for the same speeds. You'll probably end up with a reduction in gas mileage. But it will allow you to accelerate somewhat quicker. Particularly in 1st and second. If you are on a rolling start though, say 60+, you won't have much of an advantage over the next guy. Keep in mind, your potential top speed will drop as well, but it may actually increase your drag limited top speed slightly depending on where in the powerband it puts you as you near top speed. Frankly, I'm contemplating going to a taller rear gear to offset the heavy wheelspin I get in 1st and sometimes second. I'll see after I swap tires though. My current rear tires got cooked at the last track event.

It does change the RPMs the next gear puts you in... think about it.

If you go from 1st 3.00 ratio to 2nd 1.50 ratio and then you go through the 4.08 rear end you will be at factory RPM. But if you jump to a 4.30 you will be at a higher RPM in 2nd. This is because the next gear is now a total ratio of 5.80 instead of 5.58. This gives you a quicker acceleration but less top end speed.

The gear ratio works fine on the 240 at placing it in the power band when shifting. We all know the KA has no top end so why would you want to waste more midrange torque by going to a 4.30 or whatever gear you want to put in the car.

[C-Kwik]

It does change the RPMs the next gear puts you in... think about it.

If you go from 1st 3.00 ratio to 2nd 1.50 ratio and then you go through the 4.08 rear end you will be at factory RPM. But if you jump to a 4.30 you will be at a higher RPM in 2nd. This is because the next gear is now a total ratio of 5.80 instead of 5.58. This gives you a quicker acceleration but less top end speed.

The gear ratio works fine on the 240 at placing it in the power band when shifting. We all know the KA has no top end so why would you want to waste more midrange torque by going to a 4.30 or whatever gear you want to put in the car.

The gear spacing is controlled only by the transmission. So using you example, if you have a 1st gear ratio of 3.00, and shift at 6000, the next gear of 1.50 will put you at 3000 RPM. This will not change no matter what rear end gear ratio you use. The overall ratio will change, but the gear spacing will not. The rear end gear does not know what gear you arein. It only cares what the driveshaft speed is. The driveshaft speed is controlled by the transmission. If you change the ratios within the transmission, the gear spacing will change.

[Aries]

incorrect.the rear gear does affect the torque put to the ground, and at what RPM, however, the rear gearing also affects the shift rate (how quickly shift points are reached) and the shift drop in (the new RPM level reached immediately after a shift).

Having personally gone through the 3.18, and 4.08 gear ratios offered from Nissan, as well as a 3.81 from Houston Ring and Pinion, I can tell you from experience that the rear gearing/final drive ratio has a lot to do with the RPM drop in.

Granted, the transmission gears do have a lot more of an affect on this, but the question was asked about weather or not the rear gear effects it.

[C-Kwik]

incorrect.the rear gear does affect the torque put to the ground, and at what RPM, however, the rear gearing also affects the shift rate (how quickly shift points are reached) and the shift drop in (the new RPM level reached immediately after a shift).

Having personally gone through the 3.18, and 4.08 gear ratios offered from Nissan, as well as a 3.81 from Houston Ring and Pinion, I can tell you from experience that the rear gearing/final drive ratio has a lot to do with the RPM drop in.

Granted, the transmission gears do have a lot more of an affect on this, but the question was asked about weather or not the rear gear effects it.

No matter what your rear gear ratio is if you are using the same transmission, every shift you make at a certain RPM in a certain gear will always drop you a certain RPM in the next gear. Changing the rear gear has a similar effect as changing the tire diameter as far as gearing is concerned. All the rear gear does is multiply the transmission output speed and torque. But it does not change the gear spacing in the transmission. And By that I am not referring to the speed of the car. I am talking about RPM. Nismo Freak originally stated that you would drop out of the Powerband. But if the gear spacing does not change, it will NOT be different from one rear end gear to another. The engine will have more leverage over the drive wheels, but at the same RPM's as before, but at a slower wheel speed. I never said it would not increase torque. How quickly shifts are reached wasn't even part of the discussion. But is a direct result of increasing torque with a shorter gear. But that's another discussion.

Keep in mind the rear gear and the transmission are two different components. Using Nismo Freak's examples of gear ratios, 3.00:1 gear ratio would net a driveshaft speed of 2000 RPM. Working backwards, 2000 RPM Driveshaft speed will be 3000 Engine RPM's at a gear ration of 1.50:1. So the transmission will ALWAYS have the same output speed for a given Engine RPM and gear. The rear gear will ONLY see the input from the driveshaft.

Lets make this a little more interesting. Lets add in a rear diff with a 2.00:1 gearing. The above gears will net 6.00:1 and 3.00:1 respectively. Calculate the wheelspeed of 6.00:1 at 6000 RPM and you get 1000 RPM. Work backwards in the 3.00:1 gear and it works out to 3000 Engine RPM.

Now lets change the rear gear to a 3.00:1 gearing. This makes for a 9.00:1 and 4.50:1. At 6000 RPM, the 9.00:1 gearing puts out a wheelspeed of 666.67 RPM. Again, work backwards through the 4.50:1 gearing and you get 3000 RPM.

As you can see the RPM's have not changed one bit.

The powerband on a motor typically does not change for any given gearing. If you have a powerband from 3000 RPM to 6000 RPM, it will always be that. The only exception to this would be a turbo where taller gears tend to put more load and build boost at a different rate. But that's another discussion entirely.

I rest my case your honor.

[Nismo_Freak]

So your saying that if I use a 2.00 rear end vs. a 5.00 rear end ... when I shift into 2nd from 1st I will be at the same RPM and speed with both rear ends with the same gear ratios. If that where the case then you would benefit not only from improved acceleration but a higher top speed with the 5.00 gear since it will apply more torque in the final overdrive gear and hence accelerate the car to a faster speed.

About the powerband... of course the powerband is not effected. If you read my post CORRECTLY you will notice that I stated that a quicker ratio ... a 4.30 for example would not benefit a KA driven vehicle since the powerband for the KA lies in the midrange. I posted the link of the powerband so he knows what kind of powerband the KA has, to illustrate my point of why he sound keep the stock gears. LS1s however have exceptional top end and benefit from the move up in gear ratios.

[drifter]

No no no! You're all wrong...the rear end ratio is about 6.7 inches per square foot, plus how much psi is in your tires, minus the length of your shift knob. That's the right answer. And as for powerband, get the members of the band to work out at a local gym and make them POWERFUL. Yes, I suggest benchpressing...it also make your car faster. Thank you, this thread is now closed.

[Daunttless]

In an extremely simplied form, not using gear ratios for simplicity, what I believe C-Kwik is trying to say is that changing the gearing does not change your power band. Your engine still makes power in the same place. He's saying that your shift points will not change due to a rear end gearing. He's saying this because you'll still shift at say 5500 RPMs, you'll just be going a different speed when you do it versus another rear end gearing. I'm sorry if that's oversimplified...

[C-Kwik]

So your saying that if I use a 2.00 rear end vs. a 5.00 rear end ... when I shift into 2nd from 1st I will be at the same RPM and speed with both rear ends with the same gear ratios. If that where the case then you would benefit not only from improved acceleration but a higher top speed with the 5.00 gear since it will apply more torque in the final overdrive gear and hence accelerate the car to a faster speed.

About the powerband... of course the powerband is not effected. If you read my post CORRECTLY you will notice that I stated that a quicker ratio ... a 4.30 for example would not benefit a KA driven vehicle since the powerband for the KA lies in the midrange. I posted the link of the powerband so he knows what kind of powerband the KA has, to illustrate my point of why he sound keep the stock gears. LS1s however have exceptional top end and benefit from the move up in gear ratios.

Read my first post in this thread. I never said it wouldn't affect the speed. In fact, I said quite the contrary.

As far as the powerband, how exactly does changing the rear gear affect the powerband? The rear end does not care where the powerband is. If you want to only use just the midrange, shift early. But quite frankly, assuming you have traction and you use the same shift point in each gear(Engine RPM), you will accelerate quicker from a standstill to any speed or distance. I am taking out the time it takes to shift for this example though.

It all comes down to how much torque makes it to the ground. The more torque you can put down, the faster the car should be.

Furthermore, you're theory about staying in the midrange is quite flawed. I mapped out the dyno chart with the 240sx transmission gearing and shifting at 6000 in every gear gives you the most torque at almost all times. It may actually benefit you to rev even higher, but without the figures from over 6000 RPM, I can't tell for sure.

Here's my analysis (Keep in mind some of the numbers are estimated from the graph but should be close enough to prove my point):

Gear__Ratio_E RPM___E Torque___D RPM__D Torque

1____3.321__6000____108______1806___3582____1.902__3436____135______1806___256____________6000____108_____3154____2053____1.308__4126____142______3154___185____________6000____108_____4587____1414____1.000__4587____141______4587___141____________6000____108_____6000____1085____0.759__4554____140______6000___106

E = EngineD = Driveshaft

(Okay, that's as good as it gets)

This chart (sorry I can't make it prettier) depicts the change in torque at each shift. Between 1st and second, you see a huge drop in torque at the driveshaft. Over 100 lb-ft. Multiply that by a 4.083 gear and that's a 400 lb-ft difference. Between 2nd and 3rd, its about 20 lb-ft. That's still about a 80 lb-ft difference through a 4.083 rear gear. The shift from 3rd to 4th is very good at 6000 RPM. The Shift to 5th isn't too bad either. The first 2 gears could benefit from going past 6000 RPM to some extent. On this KA, you'll may actually hit redline before you see an optimal shiftpoint in 1st. Point being that shifting earlier would make you miss out on some of the torque available through multiplication. The rear gear would then just take the torque and RPM's from the Driveshaft and alter those. But the rear gear can not change the torque measured at the driveshaft.

[Nismo_Freak]

Try ... 6450 in 1st, 6300 in 2nd, and 6100 in every other gear for maximum torque distribution the whole run. Running it higher than that will slow you down... I have the slips to prove it.

[C-Kwik]

Aww Crap...it didn't come out right. hehe. You're numbers sound about right. But the Import tuner dyno chart was topped off at 6000. But then every motor will be a little different. Especially as you mod it.

[Nismo_Freak]

Yes... as you mod it you should creep a little more towards the redline since mods like intake, exhaust increase the motors volumetric efficiencies at certain RPMs and thus make more airflow and torque. Since HP is related to torque... it subsequentially goes up as well. However ... there are cases where you can lose peak HP but gain peak torque.

[C-Kwik]

But typically, it is better to gain HP than torque. Particularly when it's at the higher revs. You can make much better use of the leverage provided by the lower gears. And for a Given amount of torque, the higher it is on the powerband, the more HP the motor makes.

[syka24et]

?uestion If the car is turbocharged with a 7000rpm redline making about 400hp and 400lbs, with the boost coming in at like 4000rpm what ratio would you recomend for max 1/4 mile times???

[Nismo_Freak]

Stock ratios... watch your RPMs when you shift you'll notice they fall right into the sweet spot.

[Nismo_Freak]

But typically, it is better to gain HP than torque. Particularly when it's at the higher revs. You can make much better use of the leverage provided by the lower gears. And for a Given amount of torque, the higher it is on the powerband, the more HP the motor makes.

You normally gain hp higher up as its a function of torque @ RPM / constant. However in a drag it is always better to have HP/Torque in your higher RPM ranges as you said.