Are SR transmission gears any longer than KA?

[SketchyRollin564]

Im wanting to swap my transmission since my synchro's are going, and grinding all the time unless i feel it into gear. Im thinking about picking up a KA trans. Sounds like a good idea, but i cant stand the high RPM in 5th gear cruising. I also feel like the rest of the gears are too short. I could also do SR trans instead, which would have lower miles, and possibly have taller gears. Im trying to figure out if the gears on both transmissions are any different.


From what ive always read online, the gears are exactly the same, except the KA transmission has a tiny bit of a taller 5th gear for economy (which still sucks balls). However, real life experiences prove this wrong.

I currently have an SR20 with a KA transmission. I cruise at 65mph in 5th gear at a little over 3k. My friends that have SR's with the SR transmission can cruise at 65mph doing about 2.7k. They can do about 75mph at 3k, which for me is over 3.5k. Keep in mind we all had the 4.08 final drive from the diff.

Two weeks ago i swapped a j30 vlsd with the 3.91 final drive which should have made me cruise a little closer to what they cruise at, but i still cruise at a MUCH higher RPM than them. Put it this way, my 5th gear is closer to their 4th than it is to their 5th.
My 3rd gear tops at around 80ish, while their 3rd is around 93 mph. My top of 4th gear is 100...
They can also reach a little over 60mph in 2nd gear. I have to shift into 3rd and go a little before i hit 60.


If you go on google and try to look this up, you will find mixed info, but almost everywhere will say that the 5th gear on the KA transmission is taller, and all the other gears are exactly the same. I find this hard to believe given the above info about my friends cruising RPMs

(edit 5/30/12: im starting to wonder if my tach is reading higher than it should)

Heres a quote from one forum

KA is a bit taller IIRC. You should be turning less RPMs with 5th gear given the same speed. Since 5th is an OD gear anyways, you don't really lose anything.

The KA and the SR MTs are basically identical. The only difference in the gear ratios is OD; the SR is 0.838, the KA is 0.759.

Heres a quote from another forum

5th gear ratio in SR20DET 5 speeds is 0.760.
5th gear in all CA18 5 speeds is 0.838
5th gear in SR20DE 5 speed is apparently 0.838 (I can't personally confirm this one though, never pulled an SR20DE box apart)
6th gear ratio in S15 is 0.76

This one basically says that the N/A SR transmission is like the KA transmission, but the sr20det transmission is taller (which seems to be true)

OK, Changing transmissions in cars with different power levels is a good way to knock off 1/4mi times. For you guys that wanna go fast. But know this, the transmission with more torque in it will decrease your gas mileage, since you will be at a higher RPM in the taller gears.

below statement is just an example:
here's the scenario:
Nissan has the SR20DE and DET.
Now, so the DE can Hang with the DET, it has gearing that will allow it to keep up with the more powerful engine. Gears are the great equalizer for power variances.

So now, say you throw the DE transmission in the DET, you will drop seconds on your 1/4 mile time. but your gas mileage drops since your Revs will be higher in the higher gears. but hey, you'll get where you're going quicker! This is basically one of the formula that car makers go by. change a couple of teeth in the transmission instead of giving the car more power, and it can hang with the more powerful variants/cars.

This a picture from FR sport comparing the gear ratios of a KA/SR 5spd transmission vs a Z32 trans. Which states that 5th gear on BOTH SR and KA would be 0.759



For those who dont understand gear ratios, simply put: the higher the number, the shorter the gear, the lower the number, the taller the gear.

Also just for reference, heres the final drive ratios of the different differentials
240sx = 4.083636
NA z32 = 4.083636
J30 = 3.91666
180SX = 4.36:1 (this for CA18 equipped cars, not positive about SR20)



I made this thread to find the info out for myself, from people who have actually had experience with both transmissions, as opposed to just repeating what they've read on the internet. That being said, has anyone actually had both transmissions and would be able to confirm that the gears are different or the same? Also if you could answer a few questions

-Which transmission do you have (s13 sr, s14 sr, sr20de, sr20det, ka, etc.)
-what RPM do you cruise 65mph at in 5th?
-Can you reach 60mph in 2nd gear?
-What speed does top of 3rd gear put you at?
-Is the SR transmission any stronger than the KA transmission? (ive heard some say stronger, some say weaker)

thanks. Hopefully this also helps people out in the future who cant find the accurate information they are looking for.

[Hijacker]

I have the gear ratio info in the RWD SR FAQ. All gear ratios are listed in the service manuals as well.

But to answer the question, the SR-DET and KA-DE are the same except for fifth gear. SRs are a bit shorter in fifth to keep the motor revved a few hundred RPM higher at highway speeds

[asoomal]

Don't forget tire sizes, that too has an effect on top speed.

Slightly larger tire height will be much more noticeable at higher speeds.

[SketchyRollin564]

I have the gear ratio info in the RWD SR FAQ. All gear ratios are listed in the service manuals as well.

But to answer the question, the SR-DET and KA-DE are the same except for fifth gear. SRs are a bit shorter in fifth to keep the motor revved a few hundred RPM higher at highway speeds

If this is true, then why do me (ka trans) and my two friends with SR transmissions cruise in 5th gear at the same RPM at completley different speeds? The fact that he can do 75ish at 3k and im not even doing 60mph yet at 3k, does not support that "fact"

and they have the same 4.08 final drive diff

in other words their gear ratios are AWESOME for gas milage and cruising, where mine suck balls. If i do 3k on the highway, people are passing me left and right. They flow with traffic and pass people at 3k.

Don't forget tire sizes, that too has an effect on top speed.

Slightly larger tire height will be much more noticeable at higher speeds.

The three of us all have 215-225/45/17's

[Hijacker]

I have the gear ratio info in the RWD SR FAQ. All gear ratios are listed in the service manuals as well.

But to answer the question, the SR-DET and KA-DE are the same except for fifth gear. SRs are a bit shorter in fifth to keep the motor revved a few hundred RPM higher at highway speeds

If this is true, then why do me (ka trans) and my two friends with SR transmissions cruise in 5th gear at the same RPM at completley different speeds? The fact that he can do 75ish at 3k and im not even doing 60mph yet at 3k, does not support that "fact"

and they have the same 4.08 final drive diff

in other words their gear ratios are AWESOME for gas milage and cruising, where mine suck balls. If i do 3k on the highway, people are passing me left and right. They flow with traffic and pass people at 3k.

SR transmissions are geared in fifth to force you to have a higher RPM at highway speeds. This is for turbo response. Let's run the math. You can double check my results if you like. http://www.wallaceracing.com/gear-speed.php

For tires at 24.6" (which are 215/45 R17s btw) in diameter and running a final drive of 4.08 like you stated.

A KA 5th gear of 0.759 will cruise at ~71 MPH @ 3000 RPM

An SR 5th gear of 0.838 will cruise at ~64 MPH @ 3000 RPM

Put in the information for the SR set up and take a look at the chart. To make 70 MPH, you would need to do ~3250 RPM.

I've driven SRs with KA gearboxes. Ones I personally swapped. I can say that the math provided backs up my earlier statement. As for your experience, I don't know what to tell you except that something else is factoring in. Improperly reading speedos? Tire height differences between worn/new and 215/45 and 225/45 (those differences should be negligible). I know when I'm cruising on the interstate, I'm doing close to 3500 RPM around 75 MPH or so.

[AZ89two4Tsx]

I'm almost dead on 3K rpm at 65 with my SR/SR trans. Oem vlsd. Tire size is 275/45/17

[SketchyRollin564]

SR transmissions are geared in fifth to force you to have a higher RPM at highway speeds. This is for turbo response. Let's run the math. You can double check my results if you like. http://www.wallaceracing.com/gear-speed.php

For tires at 24.6" (which are 215/45 R17s btw) in diameter and running a final drive of 4.08 like you stated.

A KA 5th gear of 0.759 will cruise at ~71 MPH @ 3000 RPM

An SR 5th gear of 0.838 will cruise at ~64 MPH @ 3000 RPM

Put in the information for the SR set up and take a look at the chart. To make 70 MPH, you would need to do ~3250 RPM.

I've driven SRs with KA gearboxes. Ones I personally swapped. I can say that the math provided backs up my earlier statement. As for your experience, I don't know what to tell you except that something else is factoring in. Improperly reading speedos? Tire height differences between worn/new and 215/45 and 225/45 (those differences should be negligible). I know when I'm cruising on the interstate, I'm doing close to 3500 RPM around 75 MPH or so.

My speedo worked a while ago, but right now its not plugged in to the speed sensor because the clip is messed up and i need to connect a new one. However when i did the speed test after the j30 install, i got the numbers from GPS, which should be more accurate than a speedo if anything

when i get a new clip soldered or twisted on to the wires, ill update this with numbers from my speedo and see what they say.

In the mean time, nobody has had both transmissions and can state their experience?

[IanS]

I now have an SR trans in the rally car after having a KA trans. I noticed no difference in gearing between the 2 except 5th gear, which is now slightly shorter.

Its still way too long, cant wait to drive the car with the 4.60 rear end.

IIRC the service manuals list the gear ratios.

[SketchyRollin564]

Im wondering if i have a KA transmission from a nissan hardbody and has shorter gears than the one from a 240 KA trans. With all the info everyone is chiming in, with a taller final drive rear end, and a "supposidly" taller 5th gear transmission, there's no reason i should be doing higher RPM than my friends at the same speed. Especially since one of them with the SR transmission and 4.083 rear end has 215/45/17 and i have 225/45/17

[IanS]

Im wondering if i have a KA transmission from a nissan hardbody and has shorter gears than the one from a 240 KA trans. With all the info everyone is chiming in, with a taller final drive rear end, and a "supposidly" taller 5th gear transmission, there's no reason i should be doing higher RPM than my friends at the same speed. Especially since one of them with the SR transmission and 4.083 rear end has 215/45/17 and i have 225/45/17

Its possible. Supposidly its a bolt in affair save for modding the starter bolt holes a bit. And the hardbody trans' do have shorter gears.

I have played with the idea of swapping the boxes between the race car and truck, but my truck has 3rd gear pop out, and its slow enough as it is. Any longer gears, and it might not go at all.

[Hijacker]

Looking at the service manual for the 93 Hardbody and the 96 D21, both gearboxes for the 2WD KA have the exact same gear ratios as an SR, including 5th (0.838).

Even if you left the J30's ring gear in the diff, it's not a substantial difference of final drive to account for that much of a discrepancy. 3.916 versus a 4.08 is only a 2 MPH difference at 3k RPMs.

The tire height difference between your 225 and his 215 is only .3" That's not a whole lot to change the speed at identical RPMs TBH.

[SketchyRollin564]

Looking at the service manual for the 93 Hardbody and the 96 D21, both gearboxes for the 2WD KA have the exact same gear ratios as an SR, including 5th (0.838).

Even if you left the J30's ring gear in the diff, it's not a substantial difference of final drive to account for that much of a discrepancy. 3.916 versus a 4.08 is only a 2 MPH difference at 3k RPMs.

The tire height difference between your 225 and his 215 is only .3" That's not a whole lot to change the speed at identical RPMs TBH.

So with that being said, why would my car have much shorter gear ratios then my friends who have the "shorter" SR transmission and shorter final drive?

somethings not right...

im still wondering if the sr20de trans is shorter than the KA in 5th, but the SR20DET trans has totally different ratios... cause like i said, 3k for them is like 70mph, where for me its 60mph. Reguardless of their speedo reading being accurate compared to my GPS reading, 3k in their car crusing still FEELS for sure like we are travelling faster than in my car

[bladetech8]

I'd thought I'd chime in about comparing your in-car speedometer to the velocity reading of your GPS.. All of the speedometers in S13's slightly read higher than what your actually going (safety reasons?).. When cruising at 65 MPH in a bone stock S13, my GPS read that I was going 62-63 MPH.. At 70 MPH, the GPS read 65-66 MPH.. I've also verified with against those wonderful "Your Speed" local law enforcement speed indicators.. Sooooooo the speedometer is not the most accurate in the world.. If you're going to do this test with your S13 and your buddies, get GPS readings in all 3 cars to avoid any speedometer tolerances built-in from the factory.. Better yet, use the same GPS device as well. Then come back to us with these results.


GPS Velocity Readings: (Tire size differences are negligible)

65MPH = x RPM (car 1) [SR Motor / KA Trans / 4.08 Final Drive]
65MPH = x RPM (car 2) [SR Motor / SR Trans / 4.08 Final Drive]
65MPH = x RPM (car 3) [SR Motor / SR Trans / 4.08 Final Drive]

70MPH = x RPM (car 1) [SR Motor / KA Trans / 4.08 Final Drive]
70MPH = x RPM (car 2) [SR Motor / SR Trans / 4.08 Final Drive]
70MPH = x RPM (car 3) [SR Motor / SR Trans / 4.08 Final Drive]

[SketchyRollin564]

I'd thought I'd chime in about comparing your in-car speedometer to the velocity reading of your GPS.. All of the speedometers in S13's slightly read higher than what your actually going (safety reasons?).. When cruising at 65 MPH in a bone stock S13, my GPS read that I was going 62-63 MPH.. At 70 MPH, the GPS read 65-66 MPH.. I've also verified with against those wonderful "Your Speed" local law enforcement speed indicators.. Sooooooo the speedometer is not the most accurate in the world.. If you're going to do this test with your S13 and your buddies, get GPS readings in all 3 cars to avoid any speedometer tolerances built-in from the factory.. Better yet, use the same GPS device as well. Then come back to us with these results.


GPS Velocity Readings: (Tire size differences are negligible)

65MPH = x RPM (car 1) [SR Motor / KA Trans / 4.08 Final Drive]
65MPH = x RPM (car 2) [SR Motor / SR Trans / 4.08 Final Drive]
65MPH = x RPM (car 3) [SR Motor / SR Trans / 4.08 Final Drive]

70MPH = x RPM (car 1) [SR Motor / KA Trans / 4.08 Final Drive]
70MPH = x RPM (car 2) [SR Motor / SR Trans / 4.08 Final Drive]
70MPH = x RPM (car 3) [SR Motor / SR Trans / 4.08 Final Drive]

interesting, thanks for posting that. Only thing is i now have the 3.9 final drive (KA transmission), but i still have shorter gears than them, just by being in the car and "guestimating" how fast im going. I first noticed this cruising in the first friends car (s13) his speedo wasnt working, and we were cruising on the highway at 3k. I thought "wow, we are going a hell of a lot faster at 3k than in my car". We get to his house and i get in my car and head back home on the highway at 3k, and im thinking "holy crap, this is a lot slower in my car". Keep in mind my speedo wasnt working either.

Im still convinced that sr20det transmissions have longer gears than ka and n/a SR, because of those two cars, but nobody has yet to verify this on here. I also drove next to my friends s13 who has a stock KA, but hes on 15's. His speedo wasnt working either (its an epedemic around here), but were next to eachother comparing RPM in 4th and 5th gear and we were both the same. That being said, i definatley have a KA transmission, and not some random mystery transmission with shorter gears than the KA/SR/RB20 trans.

[rsmithdrift]

I have a KA with a KA transmission and stock 4.08 rear end. and stock tire sizes (205/60/15) and I can tell you that I cruise (GPS confirmed) at 72mph at 3k rpm. My 300zx z31 which had the EXACT same transmission and rear end and slightly bigger tires (215/60/15) would cruise at 75 at 3k rpm.

[240mikesx]

I have noticed that my ka did ride a little high in 4th and 5th gear cruising speeds. But my 3rd gear was closer to topping at 90, and I could kick the governor in the car in during 4th gear.

[SketchyRollin564]

I have noticed that my ka did ride a little high in 4th and 5th gear cruising speeds. But my 3rd gear was closer to topping at 90, and I could kick the governor in the car in during 4th gear.

thats wierd...

i dont remember the top of the gears from my s14 (stock ka), but i do remember i would hit the governor (120mph) past 4th, and a little bit well into 5th gear. I also remembmer in 3rd gear, both of the needles (speedo and tach) would move with eachother, and be the same at the same angle as eachother. In my s13 its not like that

and rsmithdrift, interesting point. I still have to look into it, i need to go to the junk yard to get a new j30, and im gonna grab the clip for the speed sensor. Ill come back and update this when i have more information

[SketchyRollin564]

bringing this back from the dead because im curious to see if anyone has any new information about this, or is having the same issues i am. Im starting to wonder if its possible my tachometer reads a bit higher than what it actually should?

i got my speedo working again and its pretty much accurate according to GPS and the radars on the side of the road that tell you how fast you are going. Seems to be about 2mph off, probably changes gradually as you increase speed.

according to those methods: on my tach, 5th gear at 2k = 40mph, 2.5k = 50mph, 3k = 60 (pretty much exact)
according to my speedometer: 2k = just under 40 (39ish), 2.5k = just under 50 (48/49ish), 3k = just under 60 (3.1k = 59mph)

riding in my friends s14 (sr20 and Sr trans), according to his speedo, 2.5k in 5th gear was 60mph... about 500rpm lower than in my car. He said hes gone through those radars and his speedometer is correct. Felt like 60mph too so ill give it the benefit of the doubt


So if both of our speedos read pretty much accurately, it should mean that the gears are different, no?

Another thing i noticed, i was cruising next to my friends s13 with a KA, both of us had 225/45/17's. At the exact same speed next to eachother in 5th gear, we were shouting out to eachother our rpms. He was at 2k exactly, and i was at 2200rpm.

last example, my friend has an s13 also with an SR (s14 SR trans). We were flooring it next to eachother in 2nd and 3rd gear, and just into 4th. I noticed we would be shifting at the exact same time, right next to eachother. He said he was shifting around 6.7k, while i was shifting at what my tach read from what i remember around 7.2k... we were right next to eachother at shifts and the RPMS seemed to sound exactly the same...

so if the gear ratios arent any different, than one of the tach's has to be off, and i would guess its mine considering its off compared to every other 240 out there it seems. Im beginning to wonder if its possible that my tachometer reads high, and gets more off the higher the RPM gets? I dont know of any way to test this, and i wasnt able to find much information on this online.

anyone have any ideas?

[asoomal]

If you have Nissan Datascan, or equivalent, use that to check RPM.

If not, use a timing light and check the RPM display on the timing light and compare it to your tach.

[SketchyRollin564]

I dont have either of those. My friend has a turbo timer thats supposed to read RPM. I wonder if hooking that up to my ECU wire that goes to the tach would read the correct rpm, or read the same rpm showing on the tach.

A little over a year ago one of my friends hooked up his lap top to my ecu, and the laptop read a little lower than what the tach read. So i know my tach is off to some extent, and im starting to believe thats all the problem has been this whole time


Side note: my car doesnt hit a rev limiter at 7.4k-7.6k like SR's are supposed to. Ive always thought my car had no rev limiter, because ive seen it free rev (not under load) past 8k before more than once when missing a shift from my crap transmission.

Now that im thinking about it, it would make sense if my car didnt hit the limiter at "7.6K" on my tach, if thats actually only 6.5-7k or around there. I would have to go well past 8 to hit it, if my tach is actually off by that much as the RPM's get higher

[bladetech8]

OP, thanks again for all your investigative work into this matter.. I think we can conclude your findings to be correct. And to further back up what you have established, I have a little more conclusive information regarding the differences in SR vs KA 5th gear ratio/speed difference.

With the same wheel/tire sizes:

My SOHC KA 240SX (S13) with SR20DET Transmission (Swapped over to KA bell housing obviously):
65MPH is achived at ~2700RPM

My DOHC KA S13 240SX (S13) with KA24E/DE Transmission:
65MPH is achieved at ~3100 RPM


So this concludes for certain that there is definitely a difference in OD gear ratios between the KA24E/DE and SR20DET transmissions. They are definitely not identical like some sources seem to indicate.