tranny and diff

[HxC240z]

I was looking at buying an R200 and later down the line a 5 speed. I was playing with the transmission calculator http://www.geocities.com/z_design_studio/transmission.html

and noticed that you lose top end speed with the high gear ratios (something you all probably knew, but I stated anyway) and well I was wondering what the best transmission to diff combo to you guys if I don't want lose too much top end, but gain acceleration or whats your personal favorite combo?? Also would I notice a difference from a 3.364 gear ratio R200 to a 3.364 gear ratio R180?

[hd240z]

Your choice of the "best" transmissions and diff will depend on how you plan to use your car - daily driver or competition driver. Here is another site with info on transmissions and rear end data in the technical articles section. http://zhome.com/

The 83ZX 5 speed combined with a 3.90 diff will give you about the same ratios as the stock 4 speed and 3.32 diff, but with a overdrive for the highway. That's the combination that is quite popular and I feel works well for my car which is primarily a pleasure driver any more. I ran the original 4 speed with the 3.90 diff for a few years when I was doing some auto-crossing and that was great for acceleration but not good on the highway, which is why I ended up putting in the 5 speed.

The difference between the R180 and R200 with the same ratio will be minimal. Unless you modify your engine or really abuse your driveline, the 180 will be plenty strong and it weighs about 20 pounds less than a 200.

[e_racer1999]

^agreed.

for best DD ratios, go with something that was stock in a car; i.e. sdwap in an R200 and a 5 speed from the same car. if you want more accel, go with a higher numerical ratio, and vice versa.

my combo is 280Z 5-speed with a 3.7 r200. i'm eventually going to go with a 3.9 when i find it

[red_dog007]

My 240z is going to be a weekend car, or special week day occasion car. I want it mostly strong in acceleration. I don't care too much about top end speed, as that is rarely going to be used anywhere. I like the windy roads, and rather have the acceleration to pull out of the turns hard.

So, using my stock 4-speed and diff are about as good as I would get for acceleration compared to other diff and tranny combinations?

I was planning on having a stage where I get a new tranny, and diff, and coat the entire bottom with protective paint, but if the current application is great for what I want to do, then that will save me quiet a bit of money. Plus keep the car lighter too.

[e_racer1999]

if you want a good "around town" and weekend warrior combo, i would recommend a later 5-speed and a 3.9

or you could pop a 3.7 in there with the 4-speed. you'll lose a bit of top end, but getting there will be thrills to the gills!

[red_dog007]

The 3.7 is still R200 correct? So it is going to weigh roughly the same as the 3.9 R200 and require the same modifications?

Would the extra weight and money be worth it all, or would it just be a minor increase?

Is the 3.7 hard to find? I have been looking for the 3.9 and I have only found a handful and I have been keeping my eye out for them for a while.

[e_racer1999]

the 3.7 is VERY easy to find. i think i even have a spare....

[red_dog007]

Wanna sell it by chance?

[e_racer1999]

as soon as i figure out the ratio in the diff that's in my car, you bet!

[jmortensen]

The 4 speeds have the widest gear ratios of the Z transmissions, and have tall gears to enable the cars to cruise comfortably at freeway speeds. This means a big rpm drop between shifts, which is not desirable. What you want is the rpm drop to be smaller so that it doesn't drop you out of the engine's powerband when you hit the next gear. The early five speed has a little bit closer ratios than the 4 speeds, but is also relatively widely spaced when compared to the ZX 5 speeds. So still a relatively large rpm drop between gears. The ZX 5 speeds, particularly the 1980 model, have the closest ratios of any of the Z transmissions. They also came with the lowest rear end gears. This is the best combination for twisty road driving with a normally aspirated Z. The ZXT came with the T5, and it's ratios are very similar to the original 4 speed with the addition of the overdrive 5th gear. This is a particularly bad combination for acceleration with an NA engine, but it is much better suited to a turbocharged engine.

All of the parameters like how much rpm drop is preferable and speeds at shift points can be determined with a dyno sheet and a spreadsheet that shows the gear spreads like this one: http://www.geocities.com/z_design_studio/

Basically in the ideal situation you want to be running over the top of the hp curve, shifting, and then hitting the next gear as close to the top of the hp curve again as you can. By driving over the top of the hp curve in each gear you're maximizing the hp to the ground. If shifting to the next gear drops you down the hp curve too far, you end up accelerating through a longer portion of the rpm range where the engine is not making maximum power, and that takes longer, which basically means you're going slower.

[240ZX]

I've got a ZX 5spd and R200 in my 1970. Originally I had it geared at 3.90 with an open carrier.....eventually I install a 4.10 gear with LSD. With the 4.10 and the ZX tranny, I can cruise on the freeway at 2850 rpm and that equates to approximately 65 to 70 mph. I love this combination for the twist back roads as well as the freeway. By the way....the LSD is a big plus-up for exiting corners.

Tom

[Carl Beck]

I was looking at buying an R200 and later down the line a 5 speed. I was playing with the transmission calculator http://www.geocities.com/z_design_studio/transmission.html

and noticed that you lose top end speed with the high gear ratios (something you all probably knew, but I stated anyway)

You do not necessarily lose top speed when you install a lower ratio rear gear with the 5spd.

The stock L24 has 150HP and it will only pull that 3.36 rear gear to certain RPM points, which is well below it's redline.

The amount of available HP is what limits the stock 240-Z to around 120 mph in the first place.

If you look at the calculator you reference - you will see that "IF" the stock L24 could pull the car to its redline in 4th gear - it would be going 175 MPH! - - of course it can not. The stock L24 can pull the 240Z to about 120 to 125 mph in 4th gear - which means it turning about 5600RPM...

By installing a lower ratio rear gear with an overdrive 5th, it makes it possible for the engine to pull it to a higher RPM range with the same hp.

Put a 3.9 rear gear in and the stock L24 will pull that to about 6689 RPM at 120..

In 71 - Car & Driver found that putting a 5spd. (with a 0.85 overdrive) in with a 4.44 rear gear (an overall gear ratio of 3.774) allowed the L24 to pull up to it's red line in 5th - adding 15 mph to it's top speed.

So no - you do not necessarily lose top end with a lower over-all gear ratio...

FWIW,

Carl B.