What is the best Rear end ratio for Fuel economy?

Transmissions and Rear Ends

  1. M_Body_Coupe

    M_Body_Coupe Well-Known Member

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    HA!!! No way, couldn't disagree more and I will tell you this: I will take a vacum gauge over a foot pretending it's a sophisticated TPS anyday!!!
     
  2. 69-

    69- Well-Known Member

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    Very interesting read.

    What would you use as on-board adjustable timing control?
    That's some thing I was thinking about as well, how could I adjust timing "online"...
     
  3. R.W.Dale

    R.W.Dale Well-Known Member

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    I would not do onboard adjustable I would upgrade to a MAP based timing control

    The CB Black box is probably the least invasive system to retrofit to an older car
     
  4. MiradaMegacab

    MiradaMegacab Well-Known Member

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    rear axle turbine forabodiesonly - Google Search
    EB37C26E-B15D-4E96-BCAB-74D327DB10E1.png
    Add this turbine to the rear axle and you won’t have to worry about merging on the freeway entrance ramp.
    Couple that with a Latham Axial Flow SuperCharger and “Once this baby hits 88MPH, you’re gonna see some serious shit!” LOL
     
  5. AJ/FormS

    AJ/FormS Well-Known Member

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    and that is why you will never get past 25 mpgs with a carburated/ distributor 318LA, never mind over 30 with a 335 hp 367LA.
    See, you are just like my wife. You got an opinion, but you never ask the next most obvious question.
    which
    in this case is,
    How do I keep my foot steady?
    See; I didn't give that information on purpose, so guys like you could embarrass yourself. Well done.
     
  6. AJ/FormS

    AJ/FormS Well-Known Member

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    I have an old Jacobs unit with a range of 15 degrees. If I set the dial to midway, and then set the timing to whatever, then the dial can add or subtract 7.5 degrees either way from where it is set...... while driving.
    Jacob's is no longer in business but I think I saw a similar stand-alone unit offered from MSD. 8680

    msd-8680_ml.jpg

    Looks like that can do the job.
    You can also use it to help determine your
    Power-Timing,
    Idle-Timing and
    Stall-Timing. All of which should be done BEFORE you get to
    Cruise-Timing,
    but is not mandatory on a vehicle intended for cruising only.

    After you get it installed, do this; make yourself a $0.50 throttle-stop from an old coat hanger and adjust so it will get you about 60/65 mph. Exact number not important. Install a vacuum gauge readable from your seat. Then drive. Record your EXACT vacuum reading. Then dial-back 3 degrees and wait. When the roadspeed stabilizes, record your vacuum reading. Then add 6 degrees, and wait. When the roadspeed stabilizes, record your vacuum. Now do the math from the starting point, to whichever timing recorded the highest roadspeed. See what I mean? The vacuum did not change or was almost too small to register, yet the roadspeed may have changed 5 or more percent, at the exact same throttle opening.
    So lets say you did NOT have the dialback, and you baselined the vacuum reading at 62 mph. Then you stopped the car, added 3 degrees of Idle-Timing, and again ran the car up to 62 mph. What would your vacuum gauge tell you? Answer; nothing. The graduations are too small to accurately read and compare. And are easily lost with tiniest changes in grade, wind, barometric pressure, etc and are not repeatable on another day or direction. It is, IMO, a complete waste of time, to try and use a vacuum gauge for trying to tune for fuel-economy, at ONE particular roadspeed.
    To be fair, you can use it to tell you how hard the engine is working at 80mph, versus at 65, but again, now the rpm has also risen 23%, so now the RPM alone is triggering a change in fuel-consumption, and the timing has changed, and the throttle blades are further up the transfers, maybe on the mains, so really, what is the vacuum gauge telling you? Answer; the only thing it can possibly tell you is that the throttles are open further at 80 than at 65; and com'on, you already knew that. It's like the seat belt buzzer telling you that your seatbelt is not latched; I mean tell me something I don't know......., I've been putting it on for over 50 years, ... I doneedno steenking reminder.
    Once you start using that dial-back, you will wonder how you ever managed without it.
    Assuming this is pre-LeanBurn'
    I can guarantee you that the first thing you will do after about the second run, is you will be pulling off the VA and sawing off the stops, to increase it's capacity. And you won't stop until the Cruise-Timing gets to be about 44 or more degrees at 2000rpm.
    BTW; on a DD, this is why your other timings need to be worked out first, because if you do it afterwards, your ideal sub-2800 (or so) timing may put you into or too close to detonation with an over-modified V-can.

    Here is something that looks like my Opto-timer; dial-back and dial rev-limiter. Comes with a built-in amp for the Chrysler magnetic pick-up. I use the rev limiter for an adjustable "cruise-control", by running the car up to 65mph, then setting the rev limiter to where it pukes the ignition, then slowing down to 62mph/100kph, the speed limit in most of Manitoba.
    At other times it is set to 7300 or so, in case I miss a shift.
    images?q=tbn:ANd9GcRInmYIwwUO3JnYmAHHtj2rFC5Ti2Dun9q0PQ&usqp=CAU.jpg
    And YES, I did get my 335hp 11/1 367 4-speed/overdrive up to 32 mpgUS.
    I know it was AT LEAST 335 hp cuz it went 106 in the Quarter at 3650 pounds, shifting the 223* cam at 7000 or more.
    I know it was 11/1 cuz I built it to be that.
    I know it was 32 mpg cuz I measured out a tankful of jerry cans in the trunk. then filled the tank, and ran til it puked, measuring the distance on the previously -calibrated odometer.
    But I admit, my secret weapon was the overdrive gearing; namely 65=1600 rpm/ 85=2100
    Butum, with 2.2s and lock-up, yur gonna be able to go about 65=1900...... not very far away, plus my engine is 4.04 x3.58 versus your 3.91 x3.315
    My timing at 2100? Over 50 degrees....
     
    Last edited: Mar 19, 2021
    69- likes this.
  7. Lightning II

    Lightning II Well-Known Member

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    yikes.
     
  8. ChryslerCruiser

    ChryslerCruiser Well-Known Member

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    That is amazing, and a testament to thinking out side the box!

    I'm wondering if one can build/create a version of adjustable timing advance for cruise situations where one takes installs a vac advance can with lots of travel. For every day driving, put some type of restrictor/ bleed on the line so it does not get full vacuum. Then for interstate driving, close off the bleed, and it sees full vacuum, and thus gives more advance at light throttle cruise..
     
  9. AJ/FormS

    AJ/FormS Well-Known Member

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    You could but there are easier ways.
    For a warm to hot streeter, with an automatic;
    Most guys think they have to run 20/25 degrees of idle timing. but that is nonsense. I mean you can, but if it messes up all your other timing points, then there is no advantage to doing so..

    The First time your engine cares about ignition timing is when setting up the idle, and the transfer-slot sync will spit out the timing all by itself.
    If you have an auto trans; then the next time that the engine cares about timing is at Stall-rpm/WOT.
    And the third time is at WOT, some time after 3200rpm or so. So you work out those points and work on connecting the dots as best as you can.
    When you get it right, it will look something like;
    12 to 18 degrees of Idle timing
    about 28 degrees at 2800, and
    36(iron heads), at 3600, maybe a lil sooner.
    Now you are safe to floor it....... but the ONLY TIME your ignition timing is right, is at WOT. For all other times, it is the Vcan that is responsible to try and get it right. To that end, the V-can is adjustable in three ways. On the sarm is marked a number that tells how much advance the can is capable of bringing in, rated in distributor degrees which you double to be read on the balancer. So if you see a 9 on the arm, that means it has the potential to bring in up to 18 crank degrees. If you eyeball that arm, you will see where the stops are, up by the can, and you can cut those down, and when you do, you may find that the absolute max your can is capable of with the diaphragm mechanically bottomed-out inside the housing might be 24*. That is parameter #1
    The second adjustment is by spring preload on the diaphragm, which slows down the application advance and speeds up the dropping out of it.
    The third adjustment I have found is that if you continue cranking up the preload, past the point of max vacuum required to pull it in, then it will reduce the amount of advance from it's rating on the arm to some lesser number.
    So with those possible adjustments, you can better tune the unit to your engine's needs.
    But let me be clear;
    it is HIGHLY unlikely that you can fully satisfy ALL your engine's needs , with these timing systems. The best you can do is get close, and bias your controls for maybe two parameters.
    Now, here's the thing;
    Everybody wants the Power-Timing to be dead-nuts on. But to what end? How often will you be at 3600 rpm and WOT? compared to say idling away from a stop? What's more important?
    And how often will you hit the gas hard from a stop, that the stall rpm is instantly reached? This is the time you want your Timing to be pretty darn close, cuz your combo will be doing a lot of that. But if you have 3.23 gears say, then you won't get to say 3600rpm until over 30 mph. So your timing in this zone is very important! If you have to sacrifice timing somewhere let it be above or below this zone. I mean that makes sense to a streeter. How much power will you lose at 3600rpm , if the timing is short? I'll tell you; not enough to notice by seat-of-the-pants. At peak power, 2 or 3 degrees might be 7hp at WOT for a 360. If your combo roasts the tires without those 7 hp, why do you even care?
    I'm not saying that you have to accept 2 or 3 degrees short of perfect Power-Timing at 3600rpm.
    What I am saying is that if you have to make a choice, for me it's a no-brainer to just delay the Power-Timing all-in until the engine can deal with it.
    So then, once the PowerTiming is known and the Stall-Timing has been worked out, now you can work on the Cruise-Timing, and the best and fastest way to do that is with a dash-mounted, dial-back, timing-retard box.
    Now;
    For a drag-racer, he might bias his combo for Power-Timing at WOT.
    For fuel-economy, you might bias the Cruise-Timing at a particular Cruise-rpm
    For a streeter, he might bias for from stall to 3600 to 4000.
    For a grocery-getter, he might bias for idle to 2800
    When I say bias, I simply mean concentrate on getting that right, at the expense of something else if need be.

    When you do this in the right order, the Vcan tuning is fairly straight-forward, when you use the dial-back.. I wouldn't dream of doing it any other way; it takes way too long.

    Butum if you have a manual trans, the tune is a fair bit different.
    The biggest cam I have tuned for was a 292/292/108, and
    I can only speak to the SBM. I have little to no experience with BBs.
     
  10. M_Body_Coupe

    M_Body_Coupe Well-Known Member

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    Wow, all of a sudden this took on a real erie kind of a personal twist...but I'm game.

    So, buckle up because I'm going to take you on a bumpy ride, and you will need your wife's shoulder to cry on afterwards! lol

    I skip the quasi digital, but really stil analog way of hacking this and cut through the chase to the good stuff, drumroll please: Innovate LM-1, LMA-3AuxBox and/or LMA-2 RPM Controller.

    You see, what this allows me to do is to start the tune with wide-band O2, basics really, but with the AuxBox setup I now have 5 additional channels of data capture..."ohhh...ahhh..." (as he picks up his jaw from the floor) that's right, one of them is a TPS sensor, the other one is the vacum signal. Just for kicks I played around around with the thermocouple to see the exhaust temps, as well as pulled a few G-force measurements.

    So now picture this: I hook all this up, set myself a decent trip "agenda", hit the road, I have my laptop in the pass seat so that anything I'm recording (or not) I also see in real-time. However, plenty of data means that it's best to digest after I wrap up the session and head back home to d/l it all have some fun learning what's going on.

    No embarrasment there my friend..NONE!
     
  11. ChryslerCruiser

    ChryslerCruiser Well-Known Member

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    Great perspective(the whole thing, not just the quoted above) and one I have never heard before.

    I follow what you are saying AJ, other than this: I don't fully understand how does one get the transfer slot to communicate when it is happiest?

    The rest makes sense, and I ought to know enough to hang myself up somewhere, but it will be fun in the exploration.
     
  12. AJ/FormS

    AJ/FormS Well-Known Member

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    The Vcan is only active at Part-Throttle. The signal line is set up so that idle AND low rpm, it is dead. In neutral, somewhere around 1500rpm, the port will begin generating a signal. By say 1800/2000 she is generating enough signal to fully activate most cans that I have seen. Most street cams will generate max vacuum between 1800 to 2200, maybe 2400max, still in neutral.
    You can find many and diverse controls for the Vacuum-Advance system, in Emission catalogs. from simple temperature controls to electrical solenoids to amplifiers.

    My Dad bought a brand spanking new 72 Nova/307/auto, loaded with timing controls. There was one device that controlled how hot the engine needed to be before the VA was available. Another said the trans had to be in high gear, and another for when the engine got too hot. And there was one that transferred the ported spark to full-time vacuum I forget why. And IIRC the whole thing was tied into the A/C system as well. The whole thing worked pretty good when it was new. But as it got older, poor Dad was tearing his hair out trying to keep up with thatchit.

    So there are a multitude of various and diverse devices to play with.
     
  13. Duke5A

    Duke5A Well-Known Member

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  14. AJ/FormS

    AJ/FormS Well-Known Member

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    that's easy;
    take the carb off, flip it upside down, and with the throttle on curb idle, adjust the Transfer slot exposure to;
    on a lo-po engine about square.
    On a warmed up engine; a lil taller than wide, just enough to see it.
    On a 292cammed hot streeter a lil taller than wide, easy to spot maybe 20% taller.
    Close the secondaries up tight but not sticking.
    Reinstall it and set the mixture screws to in the center of their operating range. After this DO NOT TOUCH the speed screw. Start it up, warm it up, and set the timing to achieve whatever target rpm you want from;
    550 on the lo-po to 750/800 on the hi-po engines.
    If the engine seems to run overly rough, she MAY be wanting some extra air. Figure out how much and give it to her thru the primaries.
    Now; the purpose of this exercise is ;
    to not have a tip-in sag,
    to not stall going from Neutral to in-gear, and
    to not bang into gear.
    that's all.
    This is your starting point.
    the closer to perfect your balance of; transfer fuel, to mixture screw fuel, to bypass air is; the smother the engine will run and the slower you will be able to make it idle in gear, without encountering a tip-in hesitation..
    So in the quest for smoothness, you didle-around with the mixture screws first. If you find that the engine idles better with the mixture screws in the rich position, add a lil transfer fuel with the curb-idle screw, then put the mixture screws back in the center, and restore the idlespeed with timing.
    If the engine speed is too slow, unless you add a lot of timing; just add some bypass air and start over.
    As for bypass air, during the tuning, I Tee into the PCV line and install a metal tube with a series of holes in it and the end crimped shut. Then I cover all the holes except one or two and try it. Adding more or larger holes as may be required. When I'm finished, I calculate the area of the holes, divide by two, and find the corresponding drill bit; then drill one hole in each primary blade, that size, in the front half somewhere between the idle discharge port and the transfer-slot. Badaboom.
    If you screw up and drill too-big holes don't panic. chamfer both sides of the holes , warm up the blades and drop a solder slug into them. When it cools, I file them flat a lil, move over, and try again with smaller holes. The symptom of too big a hole is too high an idlespeed with very little timing, and you'll probably see the return of the tip-in sag.
    I've never had a properly installed solder ball drop out, and if it did so what; It will be liquid long before the piston gets to it. And if it isn't so what, it's just solder.
    I target an Idle-Timing of 12 to 18 degrees, the bigger the cam, the more timing it will want. All my three cams in the same 367 cuber, have liked 14/16 degrees. And all have idled down to 550 in first gear (manual trans) with enough power to pull the 68 Barracuda on hard,flat,level ground.
    But wait; this thread was started on another topic, and this has been talked about in other threads. If you need to know more PM me.
     
    Last edited: Mar 21, 2021
  15. ChryslerCruiser

    ChryslerCruiser Well-Known Member

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    Got it! Thanks AJ. Makes perfect sense now. This is gonna be fun..