3.55 Vs. 3.73 Slip
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Originally Posted by pmason718
What does it mean? and is there a big diff in the two? I have a 07 FX2 screw which I love but I notice on my window sticker that it says 3.55 limited slip diff. Being that he truck is a 2WD is this something that I should be concerned about? Even though its too late, lol.
If you have a 3.55, your driveshaft is going to rotate 3.55 times per 1 tire rotation. If you have a 4.10 gear ratio, your driveshaft will rotate 4.10 times per 1 tire rotation. The thing is that it will take roughly the same amount of time for the driveshaft to rotate 3.55 times as it will to rotate 4.10 times because the engine is at a higher RPM generating more HP and torque, so the result is the tires get spinning faster and the truck moves faster.
The higher the gear ratio number the faster the truck will be and it will be able to tow more, but the RPMS will be higher at all speeds so you will get worse fuel economy... also the top speed of the vehicle will be reduced.
Hope this helps you out.
Originally Posted by General Motors
When there are 30 teeth on the ring gear and 10 teeth on the pinion, you have a ratio of 3:1. In this situation, when the ring gear (and axles and wheels) turns one revolution, the pinion (drive shaft) will turn 3 times. If the ring gear had 40 teeth, the ratio would be 4:1.
Higher numbered rear axle ratios require a higher engine speed for a given road speed. More engine speed means more horsepower being developed.
These gears, like transmission gears, also multiply torque for added pulling power. So, if you want more performance, choose a higher numbered rear axle ratio. Unfortunately there is a downside to this – if we have more power strokes, the engine will also have more intake strokes – more fuel drawn into the engine that raises fuel consumption especially when lightly loaded. Modern automatics with overdrive tend to reduce this negative.
Higher numbered rear axle ratios require a higher engine speed for a given road speed. More engine speed means more horsepower being developed.
These gears, like transmission gears, also multiply torque for added pulling power. So, if you want more performance, choose a higher numbered rear axle ratio. Unfortunately there is a downside to this – if we have more power strokes, the engine will also have more intake strokes – more fuel drawn into the engine that raises fuel consumption especially when lightly loaded. Modern automatics with overdrive tend to reduce this negative.
Last edited by baja150; Aug 6, 2007 at 04:09 PM.
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Also, Ford is pretty conservative with their gear ratios. One of the main reasons is because such a large % of Ford's total sales come from trucks and they have to maintain an overall vehicle line fuel economy standard or they'll be penalized by the government.
Dodge and Nissan on the other hand don't have as large of a market share in trucks, so they can be a little more liberal with their gear ratios. Dodge offers a 3.92:1 in their Hemi 5.7L Ram and Nissan does some strange gearing, but they offer a final drive gear equivelant of 4.10:1 in the V8 Titan. That's a big contributor to why people say the Ram's and Titan's are a lot more "snappier". It's also the reason why the F-150's generally outrun a Ram or Titan in the long run.
I personally would like to see the F-150 offered in a 3.55, 3.73, and 4.10.... well I'd love to see 4.56 too, but that's a dream.
Dodge and Nissan on the other hand don't have as large of a market share in trucks, so they can be a little more liberal with their gear ratios. Dodge offers a 3.92:1 in their Hemi 5.7L Ram and Nissan does some strange gearing, but they offer a final drive gear equivelant of 4.10:1 in the V8 Titan. That's a big contributor to why people say the Ram's and Titan's are a lot more "snappier". It's also the reason why the F-150's generally outrun a Ram or Titan in the long run.
I personally would like to see the F-150 offered in a 3.55, 3.73, and 4.10.... well I'd love to see 4.56 too, but that's a dream.