GlassTop09
Senior Member
Got a good point here..........especially w\ these modern computer controlled cars due to how the PCM's go about calc'ing load% (TQ).My experienced advice/comment,
Keep in mind that in the many gear swap threads there are also many different year/model/engine applications that likely differ from your exact application and your results will vary.
I personally went to 3.73 from 2.73 in my 2013 V6 auto expected MORE SOTP feel than I achieved.
With this gear swap I didn't expect the gear whine and DS (or split bearing?) hum in top gear cruising speed that I now have.
I have since been told a couple interesting things by a Mustang mechanic and previous employee of a local service department. One of the highest number of valid returns and redo's were from gear swap customers.
Another item he shared, which I'm not sure how true it is, was that even with a perfectly installed set it is a "roll of the dice" for 3.73 gears in particular on the amount of whine you'll experience.
Lastly he and others I've spoke with on the subject tell me that Ford now outsources their gear manufacturing to Motive. Funny the shop I used required I purchase FRPP and now I learn that they're all made by Motive?..
Anyways theres my input FWIW.
Typically the trans gear ratios data in the tune, along w\ the rear gear ratio & wheel revs\mile (includes the tire radius which is what the PCM needs for load% calc's) the PCM uses in TQ Management to calc the mechanical TQ available to the ground (and to the engine as well) in each gear to then know how much actual engine load% (TQ or twisting force) to achieve to match the desired load% (TQ) as calc'd from a given APP angle% position (accelerator pedal) in each trans gear selected (being used) to move the GVWR (gross vehicle weight) at a given rotational speed so w\ an actual rear gear ratio change to a shorter gear ratio the PCM can actually "mask" some of the expected acceleration result from a gear change w\o doing some TQ Management tuning to "unmask" it all. This is due to the PCM calc'ing less engine TQ needed to achieve the same desired load% at the same rotational speed so the acceleration can be somewhat subdued (read non-linear here) from what has been "felt" thru the prior rear gear ratio used. This will show up more at the lower end (1st & 2nd gear mostly) than at the higher end (3rd gear on) due to the higher mechanical TQ available in these lower trans gear ratios to the PCM thus engine.
That trans gear ratios\rear gear ratio\tire revs\mi data in the PCM tune does more than control a cruise control or a speedometer............also controls actual engine TQ output according to actual input need which can be different from what is calc'd from the desired APP angle%....properties of a drive by wire throttle control system.
Putting this out here for informational purposes.