so confused about tranny's

[drmattyg]

i have recently been looking at

http://www.geocities.com/zgarage2001/ratios.gif

trying to decide which ratio I should change my 3.36's to in my 240z. I have a 280a 5speed tranny right now. I am confused, because the website says that I should have longer gears than the 4 speed, meaning that I should be able to hit a higher speed in each gear. My buddy with an l24 and stock 4 speed can hit a cool 60+ in second. I can only hit around 48 - 49 in second. I definately have an r180 and I am almost sure its 3.36. It makes no sense to me why this is the way it is. Any advice? Am I misreading? I have a 3.90 r200 in my garage that is super clean. How does this match up to the early 5 speed? thanks

[antipodalboy]

taller gears do allow you to reach higher speeds, provided the engine can provide enough power to turn the tires. If you're trying to get to a mph that lies too high in the power band you'll need another gear to get there. But as speed doubles, drag increases by a factor of 4 (?), and that's why we don't go flying down the interstate at 400mph @200 rpm; engines arent's powerful enough. Your buddy might have more power than you, or his gear ratios might be better matched to his engines' powerband, allowing him to reach 60 in second, while you only reach 48. Generally, using a 5 speed allows you to run a higher (numerically) gear ratio in the rear end; providing a nice comprimise between acelleration and top speed. HTH

[drmattyg]

I am still confused. We have the same rear end, and he has an l24, I have an l28. Technically, the speed should be the same at the same rpm, as long as we have the same tranny. I have a 5 speed, he has a 4. I thought that a 5 speed made for longer gears, not shorter. Am I wrong? thanks

[antipodalboy]

This should help straighten things out. Your buddy is running a four speed, which usually means that he will have higher (numerically lower) gearing than a five speed, provided that final drive ratios are the same. He can get to 60 because his higher gears allow the engine to remain in the powerband that far into the mph range. You're running a lower (numerically higher) gear ratio in the same gear. That's why he can get there while your engine is all wound out and at 48 mhp you have to shift (assuming that you are both at the same rpm, or I'm wrong). This allows you to have better acelleration than him, by focusing your engine's power. HTH

[texasz]

Ok, now I know that I will get many opinions on this but lets try and stick with the facts and proven set up.

1) Best combination for street/highway driving?

2) Best combination for autox?

3) Best combination for quarter mile?

4) Best combination for top end speed?

By combination I mean tranny and rear end. Personally I plan on running an L28 with a F54 block on carbs. If there are any special concerns between an L24 and an L28 engine please share but otherwise the questions pertain specifically to the tranny and diff.

[drmattyg]

i found a really great chart that pretty much clears up any question. Also, it enlightened me as to another factor that I was not considering...whel size and tire diameter. I figured out that my speedometer is off pretty hardcore too. anyways, the chart is here: http://www.geocities.com/MotorCity/Boulevard/6117/datsuntransmittionratios.html

this chart should help answer what combonation is best for what application as well.

my opinion:

street: late 5 speed with 3.54 or 3.90's for a little more flare

autox: early 5 speed with 4.11 r160 LSD out of suburu

quarter mile:early 5 speed(the better you shift, the higher the ratio in back)

topend:Late 5 speed with 3.36 r180

just my opinion

[texasz]

Wow, that seems to be a pretty good understanding considering that you were the one who was confused in the beginning. I'll have to keep this info handy as I will have to make decisions on what to put in my Z...once I find one that is.

[Dreco]

I had a 280a five speed with 3.9 rear end once and it was almost the same as having a 4 speed with a 3.36 rear end( the 5th gear felt like 4th in the 4speed). The fifth gear in that 5 speed is a little too short for a 3.9 rear end. You only drop about 400 rpms shifting from 4th to 5th. But you do get a harder pull from the shorter 1st and 2nd gear. I think the best combo (what i have now) is the '280b' 5speed with a 3.9 rear end. I believe it has a taller 1st and 2nd ( putting them closer to third so as to not drop too much in rpms) with a taller 5th gear. Plus I've heard it is an all around stonger tranny. Here is a transmission calculator that I used. www.geocities.com/z_design_studio/

[texasz]

I have been to these sites and would like to know where a '76 5 speed fits in; is it the same as the '77-'79 or is it different? Could not find it on these sites...

[Royce]

Okay, first there is no best setup!!! Everything is a compromise! All hill clims, race tracks, autocrosses, street corners and stop lights are a little different. What works "best" at one may not work at another. Even different wind, elevation, weather, incline/decline will make one combination a little better or worse. This is why pro racers will change there trans, diff, and maybe tire combination at just about every track. Don't forget that tire size can make a difference when comparing gear ratios!

drmattyg,

Assuming everything was kept stock. There are basically two different 4-spds available in US 240Zs. The "B" type 4-spd, used '72 and up, is very similar to the "B" type early 280Z 5-psd. But then the "A" type early 4-spd has lower 1st & 2nd gears than the above. So you first have to make sure you are comparing the right transmissions. Next, do both of you have the same size tires? Maybe your tach is not correct? Another thing is that maybe your speedo gear or speedometer is not working properly. One thing you can almost be certain of, there are a few rare exceptions, is that 4th gear will be 1:1 in most all Z gearboxes. Also, are you really sure that both cars have stock diff ratios!?

I would start by running both cars at a given RPM in 4th gear. I like using the following web site for comparing different Z drive line combos, maybe it will help you. http://www.geocities.com/z_design_studio/

texasz,

Everything I have read/heard over the years says there was no 5-spd available in the US in '76 280Z's. But if there was I am sure it is the same one you would find listed as '77 280Z - '79 280ZX.

Last thing, I prefer the 3.9 or even 4.11 diff with a '81 - '83 280ZX non-Turbo trans because in my opinion it gives the best gear spacing and most options for the widest variety of different driving situations.

Comments, questions, and correction are welcomed! Have fun!