2.73 with an 4rw70 trans?

R

Rpdboss

Registered User
would there be any gas saving to put a 5spd 2.73 pumpkin in my 97 v6 bird vs the 3.28 posi one I got from Dave D years ago? thinking it should perk my mpg to around 30+ since I do alot of constant speed driving.. This bird is a bit lighter than most with only the most basic features. no abs, dual manual seats, skinny aluminum spare, no low coolant sensor, basic manual dash, no stock sub, no bling!
 
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Rpdboss said:
would there be any gas saving to put a 5spd 2.73 pumpkin in my 97 v6 bird vs the 3.28 posi one I got from Dave D years ago? thinking it should perk my mpg to around 30+ since I do alot of constant speed driving.. This bird is a bit lighter than most with only the most basic features. no abs, dual manual seats, skinny aluminum spare, no low coolant sensor, basic manual dash, no stock sub, no bling!
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The 2.73 is an 8.8 differential while the v6 bird has a 7.5 inch. If you are swapping out the entire pumpkin you should be ok but I would be certain the splines on the axles on the v6 are the same as the 8.8. How many rpm does your v6 turn now cruising on the highway? You should just be sure the rpm's wouldn't be so low that the v6 would start lugging.
 
Rpdboss said:
would there be any gas saving to put a 5spd 2.73 pumpkin in my 97 v6 bird vs the 3.28 posi one I got from Dave D years ago? thinking it should perk my mpg to around 30+ since I do alot of constant speed driving.. This bird is a bit lighter than most with only the most basic features. no abs, dual manual seats, skinny aluminum spare, no low coolant sensor, basic manual dash, no stock sub, no bling!
Click to expand...

If you do, be prepared to take a running start up a hill.

The V6 can use a bit of extra torque to get the car motivated anyway.

Also, you may want to datalog - if you drop the speed, you reduce the actual horsepower the motor is generating, so you MAY end up using MORE gas. Or may not, hard to tell without some idea what your current injector duty cycle is at cruise.

RwP
 
yes whole pumpkin swap, hmm didnt think the splines would be different. At lower speeds i would turn overdrive off and use the correct speedo gear too. usually my driving speeds are 60+ on rolling hills, so engine rpm should be sufficent. I believe 2k gets me 68mph
 
Splines for the axle half shafts are the same for all Tbirds, V8 or V6.

Any change to the mechanical advantage ( gear ratio ) is a give and take .. you gain torque and lose speed with numerically higher gears, with lower ratio you gain speed and lose torque. So overall you would most likely gain on the gas mileage since the engine will be running lower RPM's at the same wheel speed. IE: It only takes 2.73 turns of the driveshaft to turn the wheel 1 revolution versus 3.27 turns of the driveshaft = higher RPM.


- Dan
 
thats 16% less engine rpm. so in a perfect world i would net 16% better fuel mileage... hey, also the car was lowered too..:rolleyes: broken springs that got cleaned up and matched. Rears lowered by hand and careful eye with a torch;) should help a bit
 
at best u may get a 3-4 mpg increase

depends on your cruising speed

u may benefit more from a tune, bias the hegos lean and dump some timing in her

keep them tires pumped and drive like a normal person

post your results
 
New 02's would be nice since they only cost $10 each, but there is 4 of them, ah the benefit of ebay. as fo timing i have a ovaled out crank sensor that i can get a few degrees from :rolleyes:
 
My 94 convertible stang with the na 3.8 had 2.73 in the rear. I got 30mpg one time going to florida. I was drafting trucks alot at 70mph. I made it from northern VA to orlando on 2 tanks 15.4 gallon tank. Wasn't all that bad on accel.
 
what year is this LX? Can't you adjust timing by turning the distributor? I wasn't aware that the N/A V6 had a crank sensor.
 
With a 4R70 and 2.73s I don't think it would be too bad. 1st gear would be the exact same final drive ratio as with an AOD and 3.27s, so the acceleration would be on par with an 89-93 3.8NA bird.
 
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