IS there any advantage to 3.73 gear upgrade

Discussion in 'Mustang Chit Chat' started by Monkeyporn, Apr 12, 2021.

  1. GlassTop09

    GlassTop09 Member

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    Got a good point here..........especially w\ these modern computer controlled cars due to how the PCM's go about calc'ing load% (TQ).
    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.
     
  2. Norm Peterson

    Norm Peterson corner barstool sitter

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    Wouldn't that mostly just require the driver to step a little deeper into the throttle in order to get the desired part-throttle acceleration? IOW, if 50% pedal used to get you 50% throttle but now gets you only 40%, wouldn't giving something like 60% pedal get you back the 50% throttle?

    I would hope that WOT at the pedal would still get you to 100% throttle.


    Norm
     
  3. GlassTop09

    GlassTop09 Member

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    From a general POV, yes that is all 1 has to do....if all other operating variables are the same as well outside of the rear gear ratio change. But this cannot always be....this is why the throttle feel w\ these ETC systems will never quite mimic a direct linked manual throttle system. These Spanish Oaks PCM (and the newer Copperhead PCM as well), due to the advent of VCT along w\ MBT spark timing mapping that Torque Management will use (the 2 main items that have a direct effect on the engine's TQ output by controlling the engine's dynamic cylinder pressure...VCT by retarding cam timing upon demand which reduces static cylinder pressure during compression stroke & retarding spark timing upon demand which also further lowers total cylinder pressure during power stroke) along w\ the ETC throttle settings (electronic feedback control so signal proportional gain, derivative gain, integral gain...these determine how the PCM throttle will react in kind to the APP response input but there are more than these to consider as well.....) along w\ any emissions programming to perform in the background (this will also involve the VCT & MBT spark timing tables....most notably EGR\combustion chamber temp....for NOx output control.....a big TQ killer that most don't realize & what makes engine cooling capacity so critical...even for a tuned NA engine) will have a say in how the PCM will apply the necessary engine load%(TQ) output that is desired from APP position load% calc's.....none of this is linear in operation as all this is being controlled dynamically in the PCM when in CL operation separate from the APP so you'll very seldom have the exact same scenario occur back to back simply due to ever changing operational variables. The signal ramp rate of the APP is also taken into account as well....this tells the PCM how fast\slow to actuate the TB response in kind as well. The quicker you ramp the APP signal will get you as close to a linear throttle response as you're gonna get....as long as the other variables allow.

    Even when you depress the APP fully, unless the tune is readjusted, the PCM will only open the TB to a max of 82% TBA (this is done to ensure that the closed PCV system will still operate as designed). This is a fact of Ford's ETC operation that is very overlooked (all laid out plainly in the FWM under ETC Theory & Operation) so when you think you got 100% full open throttle....if this section of the tune hasn't been touched....you ain't got 100% open TBA...only 82%. Anything above this ETC TBA will set off a MIL & put the engine in limp mode....unless the tune is readjusted to compensate.

    The Ford Racing tune you alluded to has the ETC controls specifically set up by Ford to give as crisp & as linear an engine load% output response feel to the APP position load% (my guess is that it has pedal follower enabled in the tune then the mapping adjusted to respond in kind to the APP position load% calc w\ the emissions stuff disabled) for drivers who demand that type of feel but when using an OEM stock tune file as the base file the tuner will have to redo this part of the tune to tighten this up as the OEM tune wasn't set up w\ us enthusiasts in mind (and older folks that cut their teeth back in the olden days of non-computer driven engines when everything operated in a linear fashion due to all controls being essentially mechanical) & manuals are the worst as all this was initially set up to make driving a stick as easy on a beginner as feasible by intentionally making the throttle response thus engine TQ output softer to assist in retaining vehicle control. They were selling these to the masses.....not just for us..........

    The 04 Stangs were the last that had a mechanical, linear type of throttle feel. From 05 on we're DBW & non-linear by design.

    So in the end, we have 2 choices w\ these vehicles......
    1.) Get w\ a tuner & get all this dialed in as best can be done according to your tastes. This is where you want to get w\ someone who has been tuning Ford specifically & for a number of years to take advantage of their knowledge gained to speed up the process. Lito is a good source for this but there are others out there as well. Lito will most definately be desirable since his tuning is done remotely which will be taking in all aspects of your actual driving habits w\ the APP modulation thru the datalogs.............OR,
    2.) Learn to think as how the PCM operates...get a feel of how the PCM responds to varying APP position load% inputs\ramp rates to differing operating variables then gain some intuition as to how to manipulate the APP to get the desired engine load% output when you want it........

    Sorry for the length but hope this helps.
     
    MrBhp and Norm Peterson like this.
  4. Juice

    Juice forum member

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    Just want to add that while 82* max may seem like there maybe some power if you could open the blade more, it only has a total of 90* maximum possible movement. And idle is not zero degrees. If for example idle was 5*, max throttle would be 87*. How much difference in flow that 3* are? Not much.
     
  5. Norm Peterson

    Norm Peterson corner barstool sitter

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    Much appreciated, though there's a lot there that I'm going to have to re-read before I'll be fully grasping it.

    Your description of the FRPP tune confirms in much better detail than I had available to me back in 2008 why that tune was most likely the best approach to a re-tune for me. At the time, I was still autocrossing (hadn't yet got into HPDE), and yes I'm old enough to remember tinkering with mechanical linkages for dual-quad carburetor setups.

    As for EFI, I once reworked the throttle operation on an aftermarket EFI system (Accel/DFI) to slow down initial tip-in response (drivability reasons) and did some remapping of the fueling and ignition tables. But that sounds like really primitive stuff compared to what's going on inside EFI these days

    Thanks.


    Norm
     
  6. Juice

    Juice forum member

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    Yup, these "new gen" drive by wire pcms are really complex. This is why some tuners struggle w/drivability. WOT is easy to tune.
     
  7. Norm Peterson

    Norm Peterson corner barstool sitter

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    For sure.

    That's all that the guy at the local Accel/DFI 'EMIC' shop wanted to do for me, basically telling me that anything more than tuning for a WOT blast up through the rpm range was going to be on me.


    Norm
     
  8. MrAwesome987

    MrAwesome987 forum member

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    That's exactly what happened when I first got my supercharged tune by a local dyno tuner. It worked great for WOT, but drivability was absolutely pathetic. I would never go back to that guy, or recommend him to anyone else.
     
  9. Juice

    Juice forum member

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    Dont forget, tuning for drivability/idle on highly modified combos is time consuming. Just adding a tune required CAI throws things out of whack. Time is money. Im sure most tuners could get it right. But there is that profit thingy....
    And sometimes you will have to deal with minor startup issues, if all else is good, Im willing to accept a little compromise.
     
  10. MrAwesome987

    MrAwesome987 forum member

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    I paid the guy I think ~$600 and I was around 2 hours. I get you have to make money, but at least be transparent about the process. The car ran absolutely terrible when cold too. It would run dead rich for multiple minutes after startup, literally couldn't pull out of a parking lot like that. Lito had it worlds better in the base tune file he sent...

    The tuner I used first claimed he had tuned similar setups before too.
     
  11. Juice

    Juice forum member

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    ^^ Part of the reason I ended up buying the PRP software.
    That, and not many tumers want to deal with swaps. My buddy actually brought in a 'coyote expert' for my dyno session. My idle developed a surge after about a half tank of fuel as the PCM 'learned'. Part throttle was ok, but half throttle acceleration was horrible, and then as you gave it more throttle, power would come on like a 2stroke hitting the power band. Some expert tuner huh? lmao
     
    MrAwesome987 likes this.
  12. Rich

    Rich Member

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    I took out the 3.31's in my 07 and put in FRPP 4.10's, Eaton True Trac, DSS Aluminum 1-piece DS and Lito tuned it for 93 and really brought the 5R to life. Damn, what a difference in acceleration! Mines a daily and I on the freeway I turn 2800rpm at 80mph. Sounds great and never downshifts to pass unless I floor it. Best $2k you can spend in order to turn a stocker into a great accelerating ride. I don't need 7,000HP, I'm fine with my 325 or so. The accleration is what I wanted. I wouldn't waste my time with 3.73, you'll end up regretting that you didn't put the 4.10's in there to begin with. The rpm difference between the two at any given speed is negligable (100-400 approx)
     
    Redrebel13 likes this.
  13. Laga

    Laga Member

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    That sounds exactly like the tune that Brenspeed sent me when I purchased the Detroit Rockers cam from them.
     
  14. Bad Horsie

    Bad Horsie Member

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    I went from 3:55 to 3:73. i was pleased with the change. i dont drag race but do go to the road course a few times a year. noticeable improvement at the track. jussssst start to run out out of 4th gear on some long straights but it was time to brake anyway
     
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