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!