Taller top gear makes a real difference (10%)
 

I have a fun little project for my first post:

My daily driver of choice isn't quite as economical as some of the cars I see here, but it's hardly a gas guzzler. I drive a 1994 Mazda Protege LX with the DOHC 1.8L 125hp engine. Unlike it's SOHC counterpart, the gearbox has much shorter gear ratios that make driving a frustratingly high-rpm experience at normal highway speeds. After some research, I discovered that a taller gear was available from a Ford Probe (this platform shares many parts with several other cars).

Some pictures:

http://www.pansypatrol.com/people/ch...reverse_tm.jpg


http://www.pansypatrol.com/people/ch...stalled_tm.jpg

Check out the full article I wrote about doing the mod.

I've seen a 10% improvement in highway mileage (which varies significantly with my driving style on a given tank). Since the change in gear ratio is also about 10%, this seems pretty reasonable to me.

-Chris

Hello Chris,

Is that the final drive you changed out? [Edit: I should have read the link first...] I would love to take the final drive from a Yaris and put it in my xA...it would be about a 15% improvement! (3.72 vs 4.312)

That is just his 5th gear set. The final drive ratio is the gear reduction that takes place at the differential. So, you'd have to swap in a new differential into the xA. Also, lower RPMs don't directly translate to better FE. It is all dependant on the engine design.

Nice swap! That's definitely nothing to scoff at.

See this thread for some info I had collected when I was considering doing the same thing.

I do agree with SVOboy though, very nice job.

Nice!

Pardon a stupid question, but did putting in a taller gear mess up the accuracy of your speedometer and odometer?

i feel you on the protege. I believe i'm somewhere north of 3500 RPM at 70mph in 5th. Very cool to hear you're getting significant results.

In some cases. In other cases, including Hondas like mine, the speed sensor is downstream of the transmission, so it runs at wheel speed, regardless of engine speed.

I just wish my turbododges had overdrive.... 3 speed autos FTL!

Great idea and excellent write up. I drive a 1991 bmw 318i that came equipped from the factory with a 4.11 LSD differential which runs about 3300rpm at 70mph.
http://farm1.static.flickr.com/231/5...dc947c06_o.jpg
Not only was the high RPMs on the highway annoying but first gear was virtually useless for a daily driver. I had to shift to second almost immediately after starting from a light. I found myself using 4th and 5th gear on city streets more often than I was using 3rd. Eventually I replaced the differential with an open 3.64 which made a world of difference. Fuel economy improved by about 10% in all driving situations and the cabin is a much quieter place to be.
http://farm1.static.flickr.com/190/5...13535d9f_o.jpg
On the E30 BMW offered virtually any diff ratios between 2.79 to 4.44 while they kept the gear box ratios the same.

Sweet swap

barring a spedo being off wouldn't the simplest gearing change be a tire size swap... I was looking at old beetle tires.. 165/80-15's same tire patch size as my stock 165/70 13's but 15% taller..

For the speedo i was going to run a GPS.. most likely far more accurate than my 10 year old spedo.. lol

to calculate mileage just correct the miles by the tire size difference.

Best part is its easily put back to stock and only about 220 bucks to try a different gearing ratio with a new set of tires..

GPS is accurate, but likley less accurate than your speedo. the best you can hope for is 3m accuracy w/o dgps. my gps is 1-3mph faster than any of my vehicles speedos, inc. my '04 tacoma

Multiades -

Welcome to EM! That's a great mod. I've done the same type of 5th gear swap on my Saturn, but I haven't published mine. I agree that it's a big boost. I basically "live" in 5th gear probably 90+% of the time. I'll publish mine soonish. Thanks for reminding me.

CarloSW2

I think my neon has the same transmission, does yours lock the converter? For pulse and gliding I think our 3rd is a benefit as it locks from 40mph. Most autos are hunting around slipping until 60mph with any kind of acceleration. For highspeed highway cruising I agree, although I've got a few tanks at 6.5L/100km averaging 110km/h with 130 at times.
I would trade the auto for a manual in a heart beat though.
Ian

Yea the neons have pretty much the same trans.

The shadow has lockup, the spirit unfortunately does not. They didnt have strong enough lockup clutches and such back then to take the turbo motors power.

Wow, thanks for all the replies guys! I monitored the thread for a while then forgot about it. Glad to see it was educational for so many people.

I noticed this thread on the front page of the site:

http://ecomodder.com/forum/showthrea... swap-2779.htm

That's a pretty big ratio change. 21% is amazing -- I wish they made such a thing for my car!

Right now I'm driving a miata which gets pretty bad gas mileage for its size. I suspect this is largely due to the engine being poorly optimized in the low range (intake manifold design and cams), so peak BSFC is at higher RPM and is a lower value there because of higher friction. The car really can't get out of its own way below 3000rpm despite being a couple hundred pounds lighter than the Protege LX and having the same engine.

It is possible to change the final drive ratio, but much taller ones are hard to find and making the speedometer read correctly again may not be possible.


BTW: It turns out the automatic protege had a taller top gear (4th).

-Chris

P.S. Speedo is not affected with changes to individual gear ratios. Final drive changes CAN affect the speedo, but in FWD cars generally do not.

Taller top gears in automatics are really very common. That is one reason why some of the new automatics actually get better highway mileage than the manuals. The reasoning behind not putting in taller 5th gear sets I believe is only to accomidate the lazy consumers who don't wish to downshift to pass. Pretty sad when you think about it. That change alone could net every manual transmission car another 5% at least on the highway without ANY increase in price in the vehicle.

So true. It's cool from an aftermarket standpoint, but such a waste.

And some of that is to prevent lugging and need for downshifts at speeds above 55mph, because everything is designed for a theoretical driver that isn't the norm.

I've been poking around some Protege/Escort/Probe forums, and cannot find a definitive answer on this: What manual transmission is used on the '99-00 Protege LX 1.6?

I'd like to do a 5th gear swap on my Protege, but I'm not sure what transmission I have, so I don't know what transmission would work as a 5th gear donor.

The lowest speed limits outside of parking lots here is 40km/h.... that also happens to be the speed at which I shift into my top gear. I wish it was economical to make a swap, or better yet a new FD with DOUBLE the ratio.

Surprised at that, the old Shadow turbo 91 that the family used to own was a 4sp. Sadly I actually got better milage with the 90 Acclaim 3.0L v-6 that I regularly got 35 mpg and peaked at 41mpg with it.
Do a little digging, finding the old Getrag 5sp manual is not hard for them, a good trans, just the install will take a bit to run everything right. Or do a little digging into other transmissions, you just may find something interesting.:thumbup:

MazdaMatt-

Yeah, I do the same thing. I regularly drive at 30-35mph around town in 5th gear. I really want to install a taller 5th gear.

Does anyone have information about '99-00 Protege 1.6 transmission compatibility?

thanks god for modern fuel injection systems, you could never do that with an old carburated engine... it would buck and pop if you lugged it like that, from not enough vacuum signal.

In the last 2 months, I started to do about the same with my 3 cylinder metro, which has a factory shift advisory light in the dash, I shift about 5mph before the light comes on. Get this, I am in 2nd gear at 20ft from a standing stop, I'm in 4th gear at 30mph, shifting into top gear, 5th, at 40mph. My documented FE got better by about 2mpg driving this way <I burn about 18 gallons/wk, it's easy to see trends> I am sure if I did more in town driving I'd see a larger difference. I do wonder if I am contaminating my oil faster, though

When I drive around town, I usually just shift 1-2-3-5, and sometimes just 2-3-5. When I make a turn from a stop, I am in second by mid-turn, and I'm in third a couple seconds after that.

The protege is really fun to drive around town and it's comfortable on the highway, but its gearing is just atrocious. ~3k at 65mph is such a waste of fuel. *REALLY wants 5th gear swap.*

I wonder if an I4 Probe/626 5th gear would fit in my tranny. If I get a free minute, I'll call search car-part.com for 626 transmissions, call the junkyards, and ask if they know the compatibility with my Protege transmission.

1337 -

I've been googling, but I can't find a thing. I suspect that a Japanese forum would have more information. But then you would need Japanese fonts and the ability to read Japanese.

CarloSW2

1337, you have a Mazda F5M, or F25M transmission in your protege. The difference is the F5M came with the SOHC engine and the F25M came with the DOHC engine. I believe you can swap the 5th gear from a Mazda 626, but that may be the G-series tranny instead of the F-series. I have the F25M in my MX-3, and plan on swapping in the transmission from a 1.5L SOHC Protege when I can afford to. The individual gears are the same, but the final drive is 3.4:1 instead of 4.1:1

I'll try to find the link I have for the Protege transmission info in a few minutes.

Cheers,
Vol

Edit//
Here's a link regarding swapping 5th gear in a Mazda F-series transmission
http://www.mx-3.com/phpBB3/viewtopic.php?f=24&t=65457
Hopefully, you won't need to be a member, and even though this isn't your car, the transmissions are the same for this procedure.
Best of luck!

Here's the link I was looking for...
http://www.protegefaq.net/transmission.html
Lots of great info here. Anything with an 'M' is a manual, anything with an 'A' is an automatic (in case you get easily confused like I do). Have fun!

wow, 15% gearing change in the FD...

I suppose that I'd be dealing with a totally different engine and tranny family with my 2.0L 2k2 pro5, eh?

MazdaMatt,
I'm not sure, but if you have a G-series you should be able to swap parts with a 626. The F-series swaps parts with a Ford Escort. Beyond that I really don't know, you're car is far too new and powerful for me. :)

Haha... sorry if my shiny new sports car is out of your expertise...I just read that article... interesting... very easy... only question is, what does he mean by "unstake the bolts"? Are they bolts with a pin through them or something?

Did he swap in a different ratio in that article or just replace a worn out gear?

Mazda Familia - Wikipedia, the free encyclopedia

OH MY GOD! My car has a deisel option somewhere else in the world! Hm, i wonder what the gearing is like on THAT guy :)

It leads me to believe that there is either a shear pin, or key or some such that holds the gear retaining nuts in place. I think he just replaced 5th with the same gear, but the procedure would be the same whether or not the ratio was changed.

BTW, I refreshed my memory and the F5M is the earlier of the F-series transmissions, while the F25M is the latter version. According to the second link, it doesn't seem to depend on the engine being SOHC, or DOHC. Also the A26M-R is a manual even though there is an 'A' in the name.

The A26M-R might just work in your Protege5 MazdaMatt, IIRC the MS-Protege was a '03 model year, so that would be good for you. I'd sure love to shoehorn that critter into my MX-3 though! :)

Oh yeah, i forgot to mention that I have a 2.0 L FS-DE DOHC I4. Funny how just 2 years ago I was considering changing to the FS-DET (turbo), and now i'm considering making the gears taller... my how things change.

Volones,

Thanks for the help. I'm pretty sure I have the F25M, because the 1.6L is DOHC. (Unless someone knows of an SOHC version of the 1.6... if you trust Wikipedia, there is only a DOHC 1.6 Mazda Familia - Wikipedia, the free encyclopedia )

Protege FAQ gives a table of the Protege models that come with the F25M, but does anyone know what other cars (probe? escort?) also use F25M or at least the same gear design as the F25M?

Sidenote: Less than a year before I bought my Protege, the previous owner had the transmission replaced at a shop (the owner paid $2500 for a new clutch and trans on a $3000 car). Is there a chance the shop could have installed a non-F25M transmission?

Yes, the '92-'93 model years Mazda MX-3RS came with a SOHC B6 engine. Check out this wiki page about the Mazda B-series engines...
Mazda B engine - Wikipedia, the free encyclopedia

Yes, the previous article explains which cars used which engine, so that should help.

Yes again. It is common for people in the MX-3 community to swap their F-series transmission for a G-series one when they add a turbo. The F-series has trouble when the engine can produce over ~200ft/lbs torque and has a tendency to shred gears, especially 3rd and crack cases. The G-series has a more robust case and stronger gearset, so that's why they use them. Evidently it's a pretty straight forward swap too.

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?

A taller gear did wonders for my truck. Replacing 3.73s with 3.08s gained me 3 MPH on a 20 MPG truck. Now I go down the road turning 1700 RPM @ 70 MPH.

Gotta watch taller gears if your vehicle is an automatic. Less flow through the cooler will lead to spectacular (parts and ATF scattered down the road) automatic transmission failures. If you have a manual, you are golden.

The next set of tires I put on my '88 Escort are going to be over sized, probably going from a 185-70-13 to a 185-75-14 which will be an increase of 7.5%. I should get some noticeable increase in FE and don't have to get my hands greasy.

A lot of guys in the pickup truck community have tried larger diameter tires and the empirical result is always the same: Larger diameter tires result in lower MPG.

Wheel and tires are "flywheels" that have to be accelerated everytime you pull away from a stop. The energy stored can be tapped to a limited extent by a skilled hypermiler, but mostly gets wasted.

Forget the tires and get taller gears.