Taller top gear makes a real difference (10%)

[Multiades]

Originally Posted by 1337

I haven't touched the Protege for a month, since I left it at college while I went home for break. Anyway, I did a little more research on what 5th gears I could put in my Protege.

To covert from engine/model (eg. '00 Protege 1.6L) year info to a Mazdaspeak powertrain (eg. ZM-DE), these articles are useful:
Mazda Z engine - Wikipedia, the free encyclopedia
Mazda B engine - Wikipedia, the free encyclopedia

In Mazdaspeak, my engine is the ZM-DE engine,

Then look at Protege FAQ's article on transmissions...
Protegé FAQ - Transmission Info

According to Protege FAQ, my ZM-DE has an F25M-R transmission. This particular F25M-R has a .775 5th gear and a final drive of 3.850.

There are two American market Proteges with an F25M-R transmission and taller 5th gears:

'92-'94 Protege with B8-ME (1.8L 16V SOHC engine)
5th gear: .731 Final drive: 3.619

'92-'94 MX-3 with B6-E (1.6L 16V SOHC engine)
5th gear: .731 Final drive: 4.05

I think the easiest thing to do would be to find a '92-'94 1.8L SOHC Protege and to swap the 5th gear into my Protege. I don't remember the exact number, but I think my Protege does 3000 rpm at 65mph. The new 5th gear would be 3000*(.731/.775) = 2830 rpm.

Now, I'm debating...is it worth my time to do a gear swap, just to lower my engine speed by 170 rpm?

I assume you're the one who posted over on Pansypatrol.com in response to my article?

The Pansy Patrol » The Gas Mileage Mod

The time involved is not too much, I guess the question would be how much would the gear cost, and for your time is there possibly another gear available that would give a bigger improvement?

-Chris

[1337]

Big Dave--

My parents have a '99 F-350 diesel, which we use for a winter beater and for plowing. It's a 4x4/automatic model, which is the worst configuration for fuel economy. It has a 3.73 final drive. To swap in a 3.08 final drive like yours, would I need to change the ring/pinion gear in the differentials, or is it a transmission modification?

Multiades--

Yup, that was me on PansyPatrol.com post. I have located a few '92-'94 Protege F25M-R transmissions on car-part.com. Unfortunately, I can't seem to find *just the gear*, and all the junkyards want to sell the transmission as a whole. Do you have any recommendations on where to find just the 5th gear set? Will I also need the 5th gear synchro from the donor transmission?

[Big Dave]

You can't do 3.08 in a 4x4. The numerically lowest ratio R&P set available for the front axle is 3.55. I haven't been able to find anyone who will custom hob hypoid gears. That is how sad our industrial base has become.

3.08s are only available for the rear axle.

A Gear Vendor or US Gear overdrive unit would give you a 2.98 ratio, but they are very salty and will tend to destroy automatic transmissions.

[Multiades]

Originally Posted by 1337

Big Dave--

My parents have a '99 F-350 diesel, which we use for a winter beater and for plowing. It's a 4x4/automatic model, which is the worst configuration for fuel economy. It has a 3.73 final drive. To swap in a 3.08 final drive like yours, would I need to change the ring/pinion gear in the differentials, or is it a transmission modification?

Multiades--

Yup, that was me on PansyPatrol.com post. I have located a few '92-'94 Protege F25M-R transmissions on car-part.com. Unfortunately, I can't seem to find *just the gear*, and all the junkyards want to sell the transmission as a whole. Do you have any recommendations on where to find just the 5th gear set? Will I also need the 5th gear synchro from the donor transmission?

Yeah, I seriously doubt anybody is going to sell you just the gear. Junkyards don't work that way. I had to buy the whole trans for $100, which even so was cheaper than buying a gear new from Ford/Mazda.

I didn't use the syncro from the spare trans because it was 100% compatible with the old syncro and I knew that the one I had been using worked.

Obviously things will be a little different for you with the F25M-R trans, but I'm sure interchangeability will be similar as in my case.

-Chris

[Volones]

1337,

Try finding the transmission from a late 80's Protege with the 3.4:1 final drive (the table on Protege transmissions should show it). You can swap the clutch housing from your current transmission to that one, and it should (I'm 95% sure anyway) bolt right up to your engine. You can then swap the 5th gear if you wish.

For a 170rpm difference at highway speeds, I wouldn't go through the trouble of swapping the 5th gear. Unless a .68:1 5th gear from a 626 (I'm pretty sure that's the one anyway) would fit, I'd go for the full transmission swap for the longer final drive.

Vol
That's what I'll be doing when I get the time & money together.

[NeilBlanchard]

Welcome to EM!

Has anybody done a final drive (or a full tranny) swap on a Toyota Echo/Spectrum/xA/xB (1st gen)?

[Daox]

I gotta imagine it either uses the C15x or C5x series transmission. If you have the C15x, you share transmissions with the Tercel/Paseo. If you have the C5x you share transmissions with the Corolla/Matrix/MR2/Celica. Check the name plate on it and find out?

[tjts1]

I'm about to swap a 5 speed manual into my automatic mercedes 190e 2.3 as soon as I'm done with magesquirt conversion (Kjet mechanical injection to full wide band control). From the factory automatics had a 2.85 differential while manuals had a 3.27. Keeping the 2.85 diff with a 5 speed manual is going to give me some stupid tall gearing.
Fatboy Raceworks » Graphical Transmission Gear Ratio Calculator
I'm not even sure I'm going to be able to use 5th gear below 60mph. We'll see. Also planning to ditch the PS, smooth out the airflow under the car and move the passenger side mirror to the inside. With some minor modifications Mercedes archived CD of .29 in 1984 from the stock .32. I think I can beat that.

[cfg83]

tjts1 -

That's a cool calculator. I'm gonna reference that from now on.

CarloSW2

[azgearhead]

I found a real tall final ratio for my 2000 Metro, 3.28 vs 4.39. The difference in engine speed is 500 RPM at 55mph. The mpg is up 10% but is hard to drive above 55mph and maintain mpg. This ratio will allow me to realize real gains from planned weight reductions and aero-mods. This ratio is referenced on a 94 swift in Europe. I cannot find any other reference to it but am lucky that I found it.