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

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. :turtle:

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)

http://ecomodder.com/forum/attachmen...1&d=1411765772

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?

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.

Id swap the rear end first.

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.

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.

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

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

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

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.

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.

I haven't been able to find anything concrete in regards to converter lockup rpm, but I can tell you that it's occurring between 40-45 mph with my current setup (3.55) and civilian model Crown Vics came with 2.73s standard.

Well I guess that should pretty much answer that question!


I know there's a trillion variables, but in the world of putting bigger tires on a truck/Jeep without regearing people often run into the situation where convertor lock up doesn't happen until too high of a speed. Gearing for more rpm often helps highway mileage, as now they aren't turning power straight to heat in the converter. Not to mention helping transmission life and power/accel. There is such thing as too little gear. But if civil one's came with 2.73's than it should be perfectly doable.

Might not be too hard to find someone with a panther chassis that wants 3.55's that you could swap rear axles with.

Ironic, your looking for taller gears, and I'm looking for shorter gears in my mustang haha.

From a guy who has been down the gearing road (see my signature) and is fixing to go down it again, here are some thoughts.

The cheap and dirty way to go is to convert your CVPI to an LX drivetrain. 2.73 gears and whatever torque converter comes in LXs. LX torque converter stall speed is probably in the 1400-1600 RPM range. All the engineering is done and this is as cheap as mechanical projects come. Visit your local junk yard, find a 2.73 axle and a torque converter from an LX and swap them in.

If you are reliability bug like me, this would be a good time to rebuild your automatic. Make sure the cooler is good and the lines are clear and not kinked.

Slowing your engine down at a given road speed reduces the volume of ATF pumped from the transmission to the cooler and the transmission will tend to run hotter than your 3.55s. Heat buildup can result in spectacular (parts scattered down the road) automatic transmission failures.

All that said, you can gain 2.0 MPG by doing a manual transmission swap alone. A stick offers whole new vistas of hypermiling possibilities and maybe another 1-2 MPG can be had from improved driving without having to outfox your transmission. A stick will also allow you to reap additional benefit from any aero improvements you can make. If you enjoy rowing the stick, a manual is flat-out the most durable way to go long term. In an ecomodded car, a clutch should last a quarter million miles.

That said, a conversion to a manual is not for the faint of heart or short of resources. They don’t call this conversion a “sex change operation” for nothing.

But it can be done and has been done. Check out Crown Victoria, Grand Marquis, Marauder, and Towncar. In their forums is a very thorough discussion of five and six-speed swaps into Crown Vics. Mechanically, Crown Vics and Mustangs are almost identical, so Mustangs are a fine source of parts. A number of guys have done this and are willing to tell you the short cuts.

A TR-3650 transmission from 2001 to 2010 Mustang should work OK for a ecomodder. A more durable and flexible option would be a T-56 from a 2003-2004 Mustang Cobra. Some T-56s come with a spectacular 0.5:1 overdrive sixth gear. (Imagine driving down the road at 70 MPH and turning only 1190 RPM or 1550 RPM with 3.55 gears) Unless you have plans for a supercharged 5.4 or 6.8 (V-10) a Tremec 6060 (aka T-56 Magnum) is overkill. That transmission is built to withstand torque that would snap the crankshaft of a 4.6 V-8. Tremec 6060s are used on Corvettes and Vipers but you can get bell housings for Ford engines.

All the stock Ford torque converters are junk. Invest wisely once in a built converter, then the 2.73s will launch better than the 3.55s with Ford converter ever did. I speak from experience, I did this to my old '95 Z28 convertible. Ended up with a B&M 2400 that let me leave twin black stripes at will, even with 2.73:1 gears and suitably wide tires for cornering, but because these converters lock up 1:1, no impact to highway mileage.

It sounds to me as another reason to use a wide-ratio transmission instead of a close-ratio.

It's actually a NPI motor. Mustangs got the PI in 99, and the Panthers received it in 01.

I have 2.73s in my Grand Marquis and love it. I don't need off the line acceleration, because I already know it's a slow boat. You want to keep it slow for the mileage.
I've been cranking out 24 mpg combined in my 03 Town Car. That;s pretty f'n awesome, considering it weighes 4500 lbs. (PI motor, Steeda underdrives, and 3.08 RAR)
I'm eventually going to throw in a 5 speed manual. Probably in a year or two.

I'd do rear gears first. Don't forget to cahnge out your VSS so the speedometer reads correct.

# of teeth Color Part Number Stock RAR (ref. only)
16 Blue D0AZ-17271-A 2.73
17 Green C7SZ-17271-A 2.73, 3.08
18 Gray C7SZ-17271-C
19 Tan C7VY-17271-A 3.08
20 Orange C8SZ-17271-B 3.27, 3.55
21 Purple D0OZ-17271-B 3.27



-ryan s.

Losing the torque converter is plenty offset by the heavy flywheel the clutch requires.
Multiplying first gear in the trans times the axle ratio is your launch ratio. For the V8 Mustangs and V8 Camaros, from the sixties through 2000+, the majority of drivers of such cars feel a launch ratio of 9:1-10:1 is the sweet range for a manual, but with an automatic, more like 10:1-11:1, which seems contrary to the idea of having the torque converter. But a stock GM V8 torque converter multiplies the torque by roughly 1.6:1 when the car isn't moving. Your Ford is likely between 1.4:1-1.8:1, unless you buy a race converter. Those can approach 2.5:1. Even so, once you begin moving, the multiplication drops to effectively nothing.
Most stock V8 GM converters slip roughly 400 RPM at WOT, so when the engine is spinning 5800, the trans input shaft is spinning 5400. So there's still a little multiplication, but on the chassis dyno it shows up as lost efficiency, mostly from having to pump the ATF at pressure, manuals don't have that problem.
ICEs convert heat to rotation, torque converters and ATF pumps do the exact opposite. Lost efficiency.
With a manual, you want to gear it for at least 600 RPM in first gear at 5 MPH. Any less RPM at 5 MPH will feel wrong in normal driving. 9:1 gearing gets you close with tires around 26" diameter. Typical for ponycars, your tires should be taller, so you'll need slightly more gear.
A Ford 4.6L V8 is perfectly capable of 1600 RPM at 65 MPH, any less RPM than that is your own experiments, not Ford production offerings.