Tranny gear ratios... S13 DE vs DET

[McCoy]

I was using the gear speed calculator that Cody mentioned on Zilvia and thought something seemed off on the calculations. I was using the gear ratios mentioned in the US S13 FSM at first. What was odd is that at 3K rpm in 5th gear I am seeing 63mph (verified by GPS) and this didn't jive with the calculator. So I did a little digging and found out that the S13 SR20DE tranny gear ratios are different... dope! And from further discussion they match up with the S14 DET I guess.

I ran speed calculation for the 4.08, 4.36, and 4.63 rear ends I was looking at, 4.36 and 4.63, and ended up with a 4.63. The 255/40/17 tire size is pretty common for most HPDE guys including myself so choose that for the calculator.



I have a DET tranny in the garage, so have the option to switch to this tranny at a later date if I feel like it, if I need more top speed. With the reconfiguration of our local track it won't have any long straights anymore so I might be ok with this setup as is.

Anyways, thought it was interesting and wanted to share my findings. Any input or questions are welcome.

**UPDATED the graph***

[tonto]

For approx #'s i think using the typical revs/mile for a X/Y R Z tire is fine.

when i was gearbox shopping i made a spreadsheet to calculate the top speed in 1st and 2nd using the revs/mile for the tires i was thinking about using. here is example of top speed for street tire (rt615) and the kumho. for autox thats a fairly big difference.


gear rt615
1 47.4
2 74.78
3 104.53
4 128.78
5 169.67

gear v710
1 49.27
2 77.73
3 108.65
4 133.86
5 176.36

wow u must just bust down straights to need more than 150-160 top speed. i need more powah!

[McCoy]

Since I was looking at the different diff R&P's I went this route on the graph and stuck with one tire size.

wow u must just bust down straights to need more than 150-160 top speed. i need more powah!

150 is easy to hit on the local track, but I usually stop at about 140 for several reasons. Actually, I'm going to the 4.63 rear end, so my top speed will be around 147mph at redline. I typically never run my car out to redline, so I'd probably never see 147 in 5th gear...

I wanted the lower R&P because the RPM's (3rd gear) were dipping to low in several turns and was keeping me out of boost on corner exit. I tried 2nd gear and though it felt better I usually ended up slower overall so was looking for a fix.

[tonto]

ah... now that you mention it, i'm worried about my super long gearing (3rd) also for one particular local track. i've been thinking longer gearing is better for a turbo but now i see you going back the other way.

i'm curious, how fast were the problem turns and what rpm/boost were you at?

i'm thinking for mine, below 50 and i'll be forced to shift above 50 and i'll suffer through

rpm 3rd gear
1500 21.73
2000 28.97
2500 36.22
3000 43.46
3500 50.7
4000 57.95
4500 65.19
5000 72.43
5500 79.68
6000 86.92
6500 94.16
7000 101.41
7500 108.65

[KA240SX808]

The Euro CA18DET's also share the same Ratio's as the S13 SR20DE. Where did those S13 SR20DET ratios come from?

[McCoy]

ah... now that you mention it, i'm worried about my super long gearing (3rd) also for one particular local track. i've been thinking longer gearing is better for a turbo but now i see you going back the other way.

I typically don't find myself at the top of 3rd, going into 4th being an issue as it's typically coming out of a turn or on somewhere on a small straight. It's these not so fast 3rd gear turns that I find issues.

i'm curious, how fast were the problem turns and what rpm/boost were you at?

Better to show you with data... The first box (looking from left) coming off the front straight, 4th gear doesn't work if I want to pick up any speed and 3rd is not really possible either. The 2nd box is the 1/2 pike, beautiful camber in the two turns, but with 3rd gear I pick up no speed WOT and 2nd gear is pretty hard to hit as it's at the top of 2nd if I do it. The last one is the 2nd to last turn before the straight and 3rd bogs the whole way till I hit the front straight... I get eaten up in all three of these spots pretty bad.

[McCoy]

The Euro CA18DET's also share the same Ratio's as the S13 SR20DE. Where did those S13 SR20DET ratios come from?

Same place I found the info on the S13 DE... so I figured it was right.

[KA240SX808]

May I ask where you found that? Cause those S13 SR20DET gears you have listed right there are the gear ratios found in the 300ZX which has a completely different box. I was always under the impression that the SR gear ratios were identical to the KA's with the exception of the .838 S14 5th Gear.

[greenman100]

Yeah those S13SR ratios are wrong.

Correct: (non-europe)
FS5W71C

1 :: 3.321
2 :: 1.902
3 :: 1.308
4 :: 1.000
5 :: 0.838
R :: 3.382 (240SX)

The europe trans had a little further spacing, with a 3.592 1st and .821 5th.

FSM:
http://www.megaupload.com/?d=5Z2DB2JI

[KA240SX808]

Wait where did you get those? The FSM states:

Euro:
1st = 3.592
2nd= 2.057
3rd = 1.361
4th = 1.000 (Direct Drive)
5th = 0.821 (Over Drive)

JDM/Non-Euro:
1st = 3.321
2nd= 1.902
3rd = 1.308
4th = 1.000 (Direct Drive)
5th = 0.838 (Over Drive)


Those first 2 ratios you posted (3.214 & 1.925) are from the 300ZX Trans (and the like) The FS5W71C doesn't come with those ratios. unless it's an an FSM to prove it I've never seen those ratios.

Sorry if I'm sounding like an ass but I don't want wrong information to be going around an ppl wasting there money and not getting what the bought. I'm also trying to verify those N/A SR Trans ratios as I wanted to get my hands on a Euro CA trans but it'll be much easier and cheaper to get an N/A SR Trans if they share the same ratios.

[tonto]

The 2nd box is the 1/2 pike, beautiful camber in the two turns, but with 3rd gear I pick up no speed WOT and 2nd gear is pretty hard to hit as it's at the top of 2nd if I do it. The last one is the 2nd to last turn before the straight and 3rd bogs the whole way till I hit the front straight... I get eaten up in all three of these spots pretty bad.

props on the datalog. very cool. i want (maybe next year). i see what your saying - whenever you need to accelerate from 50 your hosed. if you go with the short geared final drive, what is your ground speed from 4k-redline in 3rd?
sounds maybe just about right but your going to suffer through a few more trips into 4th than before.

[greenman100]

Wait where did you get those? The FSM states:

My bad! edited.

[McCoy]

May I ask where you found that? Cause those S13 SR20DET gears you have listed right there are the gear ratios found in the 300ZX which has a completely different box. I was always under the impression that the SR gear ratios were identical to the KA's with the exception of the .838 S14 5th Gear.

From here... http://en.wikipedia.org/wiki/Nissan_180SX.

I just ran down stairs and looked at the whiteboard and see that my GPS was showing me I was doing 63mph @ 3K rpm in 5th gear... and not 67 like I was remembering while at work today. So it's quite possible my 5th gear is a .838, sorry about the false hope there.

[McCoy]

Wait where did you get those? The FSM states:

Euro:
1st = 3.592
2nd= 2.057
3rd = 1.361
4th = 1.000 (Direct Drive)
5th = 0.821 (Over Drive)

JDM/Non-Euro:
1st = 3.321
2nd= 1.902
3rd = 1.308
4th = 1.000 (Direct Drive)
5th = 0.838 (Over Drive)

Is this for the S13 SR20DE or both the DE and DET?

Sorry if I'm sounding like an ass but I don't want wrong information to be going around an ppl wasting there money and not getting what the bought. I'm also trying to verify those N/A SR Trans ratios as I wanted to get my hands on a Euro CA trans but it'll be much easier and cheaper to get an N/A SR Trans if they share the same ratios.

Not an ass, I prefer the truth over myth... I was just digging around this morning and got off on the wrong path due to a memory error

[KA240SX808]

Thats talking about the CA18DET's. They use the same FS5W71C Trans with a diff bell housing.

The Wikipedia page shows the regular 3.321 gear ratios. Also the final drives listed are also wrong.

Here's some information I have that I have gathered through some months of research.

http://www.240sxforums.com/forums/ni...ff-ratios.html