gearbox options for highway low rpm cruise in 5th

[alcyon]

Hi there, I am Gen X er who is almost 40, and only recently have managed to sort myself out career wise and financially. I hail from Malaysia. All this while, since 1997 when i got my lisence i drove a 1991 Proton saga , a FWD malaysian made family sedan, which is a copy of a 1980s mitsubishi lancer fiore. It comes with a 1.3 4G13 engine with 72hp. This car has gone through hell and back with me, i neglected it during its early years, and overhauled it in late 2004 and started taking really good care of it. I also started learning about the systems on this car and how to maintain them. I really learnt a lot over these yeaqrs, from some one who is afraid to open any bolt, to now being very confident.
Now since i am finacially more sorted, I want to get the car of my dreams, the AE85/86. Recently a good buy has turned up on a modified AE85 over here, and i want to purchase it.
However after a lot of research, something about the AE86 bothers me, the gear ratio.

The proton saga is a cheap low powered sedan, hence it has a final ratio of 4.32, and a 5th gear ratio of 0.777. With 175/70R13 tyres which it was designed for, i get 3500rpm in 5th gear at 110kmh.
at 120kmh, its 4000rpm. I always thoughtsince the AE86 was 1600cc and had 128hp, toyota would have given a lower ratio final gear that would let the car cruise economically at say less than 3000rpm at 110kmh. This opinion was further reinforced when i played the NFS2 game, and it does look like it revs lower than the proton saga at the same speed. But upon further reading on forums, i found that it revs just as high as the lowly proton saga!
I want a stylish highway cruiser that revs noticably lower than the proton saga, so i can use less fuel as well as reduce the engine rpm to lower wear and tear.
So my question is , what options do i have to reduce the rpms from stock specs in 5th gear? If there are options, what exactly must i purchase and do ?
Your input is very much appreciated.

[Big T]

Custom 5th gear cog or change final drive. Alternatively, fit another gearbox.


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[alcyon]

Thats true..and i do know that..what i meant was do you have links to where i can buy those. Also what options do i have for different gearboxes.are they a direct fit ?
If i were to get a 4.1 or 3.9gear
.do i re use the same axle housing ?
I would like more detailed information. That would help a lot.

[jondee86]

There are no direct fit "drop-in" gearboxes for the AE86. There are gearboxes
that can be adapted with some modifications. However, the T-Series Toyota
differential had a number of different ratios, all of which require only the change
of the crownwheel and pinion within the differential housing.

Almost all AE86 with the factory fitted 1600 4AGE engine were delivered with a
4.3:1 ratio differential. Other Toyota variants (Corona, Carina etc) had the same
T-Series with alternative ratios... 4.1:1, 3.9:1 and 3.7:1 being the most common.
You should be able to find these ratios without much trouble, as they are often
removed by people wanting to go to lower ratio for rally and race applications.

You could also consider moving to a wheel/tire combination with a larger rolling
radius, if the car is still running on 13" wheels

Cheers... jondee86

[alcyon]

There are no direct fit "drop-in" gearboxes for the AE86. There are gearboxes
that can be adapted with some modifications. However, the T-Series Toyota
differential had a number of different ratios, all of which require only the change
of the crownwheel and pinion within the differential housing.

Almost all AE86 with the factory fitted 1600 4AGE engine were delivered with a
4.3:1 ratio differential. Other Toyota variants (Corona, Carina etc) had the same
T-Series with alternative ratios... 4.1:1, 3.9:1 and 3.7:1 being the most common.
You should be able to find these ratios without much trouble, as they are often
removed by people wanting to go to lower ratio for rally and race applications.

You could also consider moving to a wheel/tire combination with a larger rolling
radius, if the car is still running on 13" wheels

Cheers... jondee86

Perfect..that exactly what i wanted. The ae85 i plan to buy has the 4age engine with t50 gb and 4.3 lsd. With 14" tyres.all i have to do now is find the 3.7 or 3.9 gears. Anyone has an idea what rpm would the engine be at 110kmh with 3.7 or 3.9 gears ?

[Deuce Cam]

MFactory and Revolver both make a special gear cog that replaces 5th gear in the t50 transmission and thus will reduce cruising rpm a bit in 5th gear.

Gearing up the final drive in the rear end (switching to 3.7 / 3.9 ratio) will make the pickup more sluggish and reduce acceleration. A 4age isn't exactly zippy with the stock gearing when accelerating up to speed.

[oldeskewltoy]

http://store.uslegendcars.com/site/prod ... C181F96C9F - 3.9
http://store.uslegendcars.com/site/prod ... C181F96C9F - 4.1
http://store.uslegendcars.com/site/prod ... C181F96C9F - 3.4

$459.00 for everything new gears, new bearings pre set inside a used housing... YOU MUST TELL them to NOT WELD the gears. These units are built for Legend Race cars, they use the Toyota center section, because they are almost always used in these small race cars, the gears get welded... So... just make sure they know @ the time you order to NOT WELD the gears

[jondee86]

Gearing up the final drive in the rear end (switching to 3.7 / 3.9 ratio) will
make the pickup more sluggish and reduce acceleration.

This apparent "sluggishness" is really only noticeable in first gear when
comparing two similar cars, one with a 4.3 and another with a 3.9 for example.
With the 3.9 the car feels more like a car with a 4.3 taking off in second gear.
The higher ratio differential has the effect of giving the car a "wide ratio"
gearbox (whereas lower ratios like a 4.8 have a "close ratio" effect). First will
feel like second, second will feel like third and so on.

The 3.9 ratio was actually used with the 4AGE in some early Toyotas, and from
what I have heard, while not exactly sporty, the performance was acceptable for
a road car of the era. Add that to the fact that first gear is quite low in the T50
and I don't see 3.9 being a problem. And definitely not if the engine has a few
power adding modifications. I will be looking at either a 4.1 or 3.9 for my car
when my next round of engine modifications sees the light of day

Cheers... jondee86

[alcyon]

Thanks a bunch jondee86. Next question..i assume that the speedometer reading is taken from the output shaft of the t50..i think...so with a 3.9 axle..will the reading be lower than the actual speed ? Also lets say i swap gears with a member here..my 4.3 for a 3.9..will the other lsd internals fit right in ?

[jondee86]

Yes, the speedo is driven off the gearbox output shaft. There is a steel gear
on the shaft (box needs to come out to change it) and a nylon gear on the speedo
cable drive. There are several combinations that are used to correct the speedo
drive ratio to match the differential ratio. The nylon gear is easy to change.
Here is some information...


http://forums.club4ag.com/zerothread?id=9626

If you browse this transmission re-build writeup, you will see how it works.
I don't have the details of what parts you would need to get the speedo reading
correctly for a 3.9 ratio diff, but a little research should get you there

The LSD is located inside the crownwheel carrier, and does not interface with
crownwheel, which bolts on the outside of the carrier. The LSD itself does not
need to be dismantled, but the carrier will have to come out to allow the gears
to be changed over. Then the setup procedure will be as per the factory manual.
This is work best performed by a specialist who has the proper tools for setting
backlash and bearing preload. These are the parts that are changed...



Just be aware that when installing a set of used gears it may not be possible to
set them up exactly as they were in the vehicle they were removed from. This
can/might result in some noise. Depending on the condition of your existing
gears, it may be quieter or louder

Cheers... jondee86