How to hypermile a VX/CX Civic transmission?
 

Tips?

I just completed the install of a 1993 Civic CX transmission in my 1998 Civic DX. Way tall gearing. Speedo registers 25 mph when I hit 2000 RPMs in 2cd gear. I'm in third up to 40mph/2000rpms... the tranny seems to be turning about 2000 rpms at maybe 58 mph. I have 14" DX wheels on, so I'm actually a little taller than a VX/CX would have been with its 13" wheels.

P&G is still going to give you the very best results. However, driving normal (constant speed) will now net you better mileage. Once MetroMPG did all the stuff to his Firefly he stopped P&Ging cause the difference was so little and it wasn't worth the extra work to do P&G. I believe he only does it now for competition. So, you need to test what constant speed will give you vs P&G. If the difference is small enough, just start driving normal, and coasting with your engine off when you don't need any power (down hills, to red lights/stop signs, etc).

The VX/CX transmission turns 2000rpm at 100kph (62mph) in 5th gear in a VX/CX with stock 13" wheels. You hypermile this transmission as you would any other manual transmission. Except when climbing a hill, shift up before rpms reach 1500-2000, and freewheel coast as much as possible given your driving conditions.

Wow. I start experimenting today for real, but it had not occurred to me that P&G might no longer be as useful. Very interesting.

Sounds like you need to move everything down a gear. Where you formerly used 4th, use 3rd now. (2000 rpm @ 40 mph is where my 4th gear was). Where you used to use 5th, now use 4th. And the new 5th is all bonus!

I expect P&G will still be useful. I do 4th gear pulses regularly, so it's not just about coping with a short top gear. It's about alternately using optimal BSFC and free coasting. What it should give you is better highway speed options whether cruising or p&g'ing. Sounds nice.

When I swapped to the Fit, I went backwards in this area. (Honda went backwards, that is :rolleyes:) Now I'm at 2800 rpm @ 60 mph.

That's what I just experienced getting to work. Was really neat, and strange.

I suspect you'll be correct, but the spacing between 2cd and 3rd is really awkward. If I shift from 2 to 3 at 2000 rpms, I come in at 1300 in third. Yuk. So I got up to 2300 or so in 2cd and get 1500+ in third.

Sorry to hear that. The Fit is a nice little car. Having done the transmission swap now, I think a person with the right fabrication skills could possible figure out how to mate a taller (older, I guess) tranny to the Fit engine. Just spit balling...

Gotta go... at work... class soon...

Not much else you can do there. Would be even better to have a 6 speed so 2 and 3 are closer as well as a tall top gear.

Calibrating distance
 

I just got an odometer reading of roughly 11.280 (almost 11.3) miles on a thirteen mile homeward commute route, as measured using ridewithgps.com, which takes elevation changes into account. What is that, a 14% under count? I can't believe it. I don't believe it. I am running 14" wheels, but this is too much of a difference. So I'll track it again tomorrow, and probably the day after, across both legs of my commute.

The VSS reports data that the instruments use to represent both miles and miles per hour, and I am running the CX VSS that came with the tranny. Maybe the VSS gear is a different size?

[EDIT: I DISCOVERED A MAPPING ERROR THAT EXAGGERATED THE DISTANCE OF THE ROUTE. THE ROUTE IN 12 MILES, NOT 13, AND SO THE DIFFERENCE IS IN THE AREA OF 5%, NOT 14!]

6k RPM on the VX tranny is something like 120 MPH in 3rd gear! The tall overdrive gives you a much better highway cruising gear. The lean burn VX engine would pull from 30 MPH at 1000 RPM, at least in mine it would, even with the AC on.

rregards
Mech

Gearing is tall! So I am continuing to experiment with its tallness. Fifth gear has me in the 2100-2200 range at 65 mph. I used to cross 2000 at about 50 mph with the DX coupe's stock transmission.

Hill climbing "experiment": I put the instant mpg gauge back onto my main display on the ultra gauge. I can slide into 5th gear at 45-50 mph, down around 1600 rpms and accelerate easily, so sometimes I climb long and steep hills in that gear where the speeds are 45 or 50 and cars are everywhere on two lanes. I can go up to 79% load and stay at 30 or 31 mpg (climbing a hill at high load!); my old DX tranny could only do 23 or 25 mpg up this same hill in fifth gear. My goal climbing this hill is only to maintain speed for a few seconds until I can position better or find out if a light ahead will be green, stale, or red.

The '93 CX tranny is making it easier for me to drive at speed limit more often without dipping below my daily goals of 60mpg. Warmer weather is also a factor, but I don't really don't think it's the whole story because right now my average speed has probably increased significantly while my MPG is also going up.

On my old 1976 280 Z I had it geared to do 30-60-90-120-150 at 6 k in each gear. At first it was even taller geared with a .75 OD and a 3.54 differential. I think it went 85 MPH in 5th at 3k RPM. I switched it to a 3.90 which gave me the listed speeds in gear. 2nd gear maxed out at 60 MPH which was good for 0-60 times and the car would get close to 30 MPG at 65 MPH.

I always was an advocate of having the large step between 4th and 5th gears. That way you have the performance of a fairly close ratio 4 speed with the highway mileage of the much taller 5th gear.

Compared to that the VX gearing gave me 120 in 3rd gear compared to 120 in 4th with my old Z car.

Like Pale suggested you not have the option of using your previous P&G strategy, which should be your starting point (as close as possible) while refining your strategy using the availability of much taller highway speed gearing. Should be lots of fun and higher average speeds may actually be on of the solutions if you feel it is necessary.

regards
Mech