Transmission and Gear Swap Thoughts ('00 Ford Crown Victoria)

[24601]

Having a 4-speed automatic with a 3.55 ring and pinion have had me contemplating how to go about alternatives that would provide better fuel economy.

My first thought was to swap out the 3.55s for taller 2.73s but which would significantly lower my cruising RPM, but would also make the engine work that much harder off the line.

I'm worried it would trade better hwy mileage for potentially worse performance in the city. So, this got me to thinking about the possibility of swapping the gears in conjunction with a swap to a 5 speed manual.

I've put together a comparison of cruising speed RPMs between different setups and the total gearing ratios. (Current setup in red)



If I did a swapped to a 5-speed with 2.73s I would only lose about 8% of gearing in 1st with the differences between 2nd and 3rd being negligible. It would also further reduce cruising RPM in 5th gear.

To put in perspective, doing the 2.73 swap along would result in a 23% reduction in gearing.

Thoughts?

[dirtydave]

I would try to get the best highway mileage you can. You have a heavy car. mileage sucks in the city. make it better on the highway and just drive at highway speeds and don't stop moving. Keep it above 45 as much as possible.

[arcosine]

Id swap the rear end first.

[ksa8907]

Use as small of a tire as possible while staying in the laod range required. You will reduce the effective gearing and reduce the energy required to spin the wheels vy moving the weight closer to the axis of rotation.

Looks like 2.73's with the 5 speed would be perfect.

[Occasionally6]

For a definitive answer, you need a BSFC map.

Don't forget that with an auto. torque converter slip alters the effective gearing (lower) where it is occurring.

[Baltothewolf]

I think a vic with manual would be awesome in the first place, but just remember, you will lose your off the like performance.

[cRiPpLe_rOoStEr]

Originally Posted by ksa8907

Looks like 2.73's with the 5 speed would be perfect.

That would be good with a wide-ratio transmission out of a truck instead of a close-ratio out of a Mustang.

[24601]

Originally Posted by Occasionally6

For a definitive answer, you need a BSFC map.

I've searched high and low on the web and came up empty handed.

[tyronasauras]

My 2 cents, just change the rear end gear first. Your PI v8 has plenty of power for the city for an ecomodder. Stick with a taller tire, the beast needs lots of rubber on the road.

[adam728]

As said, going manual is going to lose the torque multiplication given by the torque converter off the line and when unlocked. 2.73's and a manual will be a chore every time you get rolling from a stop, lots of clutch finesse.

Not to mention - what's the cost and time to go to a manual? I know others have done it, but seems very involved to try and save gas. I would guess it would be very difficult to pull off for less than $1000, and lots of fabrication time. I'd definitely start with a rear gear swap. While still costly, it much more easily doable. I also would take some time to think about what speed you drive, what rpm the converter can lock in 4th gear (and under what loads). It wouldn't be a great thing to go to 2.73's and then find that load/rpm means the converter stays unlocked until 65 mph or something.