Just Curious

[bonniec75209]

I hope this doesn't sound dumb (I'm just a girl, I don't know much about cars) but if I replaced the 4-speed transmission in my 240 with a 5-speed, would it still be fast on take-off? As it is I LOVE it, I take off and leave everybody like they are standing still. It has a lot of power (takes off easy from standstill in 2nd) and my ex-husband said that it had too much power and needed a 5-speed. (I think he was just mad because I always beat him and his 944 porsche in a quarter-mile.) I really don't want to change it, I am just curious as to what difference it would make because he was always wanting to put a 5-speed in it. I am going to start work on it after Christmas and get alot of things done, but that won't be one of them unless you all tell me that it is the thing to do. I really appriciate you guys letting me pick your brains, please let me know what you think.

Bonnie

[2ManyZs]

The 5 speeds that are available to fit in the 240 from the later 280's and 280ZX's have nearly the same gearing in the lower gears. They only offer the overdrive for cruising on the interstates. However, with the overdrive you can then change to a lower gear(higher numerically, stock is 3.36 and you could go to a 4.11 with no trouble) in the rear differential which will give you even better acceleration in the lower gears, and with the overdrive, the car will be able to cruise at a decent (read lower or closer to the stock) RPM on the interstates.

The main benefits of a 5 speed only show up after you change the rear diff ratio.

There are no dumb questions, but you might get an answer that doesn't make much sense sometimes......

You can see the gear ratios in the tech articles, as you can see the gear ratios didn't change much between the 4 speeds and 5 speeds, or at least not enough to make a very noticeable difference in say, 1st through 3rd gears.

Actually, your ex was a bit off the mark with his answer, as with a 5 speed and the overdrive, it would have made the car have a higher top speed.....if you could hold it to the floor long enough that is....The main reason it was a bit quicker than his 944 is simple, the 240 weighs a quite a bit less with very little HP difference.

[bonniec75209]

Hi 2many,

So basically the 5th gear is just for cruising? As far as I know the transmission is good, but supposing that when I take it in, the mechanic says that (among many other things), the transmission will have to be replaced in the near future, would you replace it with the origional 4-speed or a 5-speed? You seem very knowlegable and I would really value your opinion. Thanks, Bonnie

[2ManyZs]

I guess it all boils down to what you want and how much you want to spend. The 5 speed will cost nearly the same if you buy one from a scrap yard as a 4 speed would. It might be a bit more expensive to re-build the original than buying a good used transmission as the new parts are going to be a bit pricey, of course it all depends on what the transmission in your car really needs to begin with.

The rear diff with a lower gear will cost as much if not more than a used 5 speed. If you want quicker acceleration, and still have a decent cruising RPM, you could find a decent R-180 differential with a 3.90 or 4.11 and use a 5 speed from a 280ZX (79-83) and have the best of both worlds, quicker acceleration and decent cruising gear for on the highway in 5th gear.

If money is the biggest object, there's nothing wrong with just re-building or finding a good used 4 speed and leaving it as it is.

Not really an answer I know, but the final answer is one only you can answer......

[GunnerRob]

Hi Bonnie,

I recently had a rebuilt '81 5 speed installed in my 280z. My original 4 speed, after seeing 255,000 miles, literally ground to a halt.

I selected this 5 speed for the taller 5th gear for much better freeway speed gas mileage without sacrificing much in acceleration from a stop. But then, I'm more of a high speed in the twisties person than a dragster.

I checked out a really good web site that has a transmission calculator for all combinations of transmissions, differentials, tire sizes, etc. It appears that the '77-'79 factory 5 speed is as close as you can come to your original 4 speed in 1st thru 4th gears, with a 5th gear that will drop your rpm's at 75 mph in 4th from 3400 to 2960. The difference in 1st gear at 6000 is 37 mph now to 40 mph with the above mentioned 5 speed. These numbers are with 195/70-14 tires. The 5 speed with a 4.11 differential, as mentioned by 2ManyZs, will get you 32 mph in 1st gear at 6000 rpm and 3600 rpm at 75 mph in 5th gear.

Here's the web site link if you'd like to look at some other number comparisons:

http://www.geocities.com/z_design_studio/

BTW, here in So. Cal., it cost me $700 for the transmission and installation.

Have fun!

Rob

[Royce]

Bonnie,

What year is your 240Z and what size tires do you have on it?

[bonniec75209]

Sorry for the late response Royce, the year is 72 and the wheels are the origional that came on the car, I think 14 inch maybe. I will get all the tire specs and let you know.

[Mudge]

My 240Z with an early 5 speed, stock rear, N42 head, no header but worked exaust runs a 15.8 and feels pretty good at takeoff...

[Royce]

Thanks for the info Bonnie! I asked for those things because it would save me from putting together an even longer post!

With a '72 240Z a 5-speed would be a direct bolt-in replacement. The only thing to worry about is the throw-out bearing collar. The trick is to use the collar that matches the clutch type in your car. So if you swap trans without installing a new clutch than use your old throw-out bearing collar.

For the US market there were two 5-speed transmissions offered in non-Turbo cars, the early 5-spd in '77 280Z - '79 280ZX and the later 5-spd in '80 - '83 280ZX. Really there were three but I am not going there now. The "early" type would not change your 1st - 4th gears much and 5th would drop your freeway revs around 500 RPM. Not a big difference but if you do a lot of freeway driving or if you change to smaller profile tires it can save you some $$$ on gas. The later style 5-spd may make your car a little slower off the line because it has a slightly numerically higher gear but the gears are closer 2-4 and 5th will drop your highway revs closer to 1000RPM.

It is best to look at trans, diff, and tire height together when making changes in this area. This is why I asked what size tires you have. If you go from stock 175R14 tires to 195/55R14 is similar to changing your diff from a stock 3.36 ratio to 3.7. Either may make your car a little quicker off the line but will cause your revs to be higher when you cruise down the freeway.

I hope it makes sense! Questions are welcome!

Happy Holidays!