Gear swaps.....should I put the 3.73's back in?

Discussion in 'Transmission & Driveline Topics' started by Millwright, May 15, 2019.

  1. badazz81z28

    badazz81z28 Veteran Member

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    The speed limit wasn’t 75 back in the day lol. Remember when “55” was orange on the dash?

    I guess you can’t miss what you never had...overdrive is great!
     
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  2. 76z28

    76z28 Veteran Member

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    The two reasons engines last so long today... Fuel injection and over drive.
     
  3. big gear head

    big gear head Veteran Member

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    The speed limit in the '60s and early '70s was 70 MPH. If you look at a some of the speedometers in cars that were built back then you will see that there is a red line or red numbers starting at 70 MPH.
     
  4. Gary S

    Gary S Administrator Lifetime Gold Member

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    Back in the early 70s, the speed limit here was 75 just like today. And, a few miles west of here in Montana, there was no speed limit at all in the daytime. My SS Camaro isn't geared as deep as the Z28s so it doesn't rev as high on the highway, but even with the 3.31 gears, I could run it at 4000 rpms all day long through Montana. It doesn't have the high performance engine like the Z28, but for some reason, that mild engine has a sweet spot at 4000 rpms where it smooths out and quiets down. It loves to cruise at that speed.
    Yes, the engines wore out faster at the higher rpms, but many of those engines are still functional today and running great without repairs. The higher rpms weren't that bad for them.
     
  5. K1ng0011

    K1ng0011 Veteran Member

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  6. jeff swisher

    jeff swisher Veteran Member

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    Math for you.
    336 is a given to make the math work out.
    336 X gear ratio X MPH, divided by tire diameter = RPM.

    You want more low end TQ.
    Is the distributor set up with a quick curve or is it set at 10 BTDC and full timing not in until 4500rpm?

    I want all my timing in on most of my SBC and BBC engines in by 2200rpm..If I cruise at lower rpm than that I want it all in before cruise rpm.
    I also like 18-24 initial timing of course depends on engine and the tolerance it has to timing.

    Timing is a big player in low end TQ .
    As are a set of long tube headers.
     
  7. Fbird

    Fbird Veteran Member Lifetime Gold Member

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    for every carb adjustment then is an equal and opposite distributor adjustment...;)
    Just saying that it takes BOTH to really make a difference.

    10% gear change is ALMOST un-noticable. Yes it makes things different...but really hardly worth the effort. I agree with the M21 being a larger problem than the rear gear for "fun" meter.
     
  8. jeff swisher

    jeff swisher Veteran Member

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    My 57 chevy is a heavy pig and I had 3.70 gears in it then swapped to 3.00 gears.
    9" Ford makes it easier.
    If it hooked out of the hole with sticky tires it felt a bit down on power. yes I could light them up if i wanted to.
    But that is not a quick way down the track.
    I swapped in my 4.56 gears and sticky tires and tested it.. yea still felt like I needed more hole shot.
    It did not come on in power until 3500rpm or more.
    I have an automatic TH350 with 2.52 first gear and the converter was stalling to 2500.

    Max TQ on that 350" came in at 4750 rpm.
    I knew I could not hole shot my buddies supercharged mustang like it was.
    even with 4.56 gears..I swapped in a 4500 stall Coan converter.
    That fixed it!

    Poor little 4 speed when it hooks up solid the RPM is way low and it can feel gutless.
    Well not really gutless more like eeehhh wish I had more kind of thing.

    Gears will help but will not be the end all.

    Lets do the math above for grins.
    28" tall tire at 60 MPH with 345 gear is about 2480 rpm.
    25" tire would put you at about 2780.
    373 gear and 28" tire would be about 2680

    Have any shorter tires you can swap onto it to just take it for a spin and see how it feels.
    Maybe the front tires are shorter and will fit the rear.

    Just for a little testing you know
     
  9. ZRODDER

    ZRODDER Member

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    My experience is a 74 Z with a T-400 trans and 390s. Drove it 950 miles non-stop while rushing home on leave and then 950 back to base again several times at or above highway speeds. In 85 I drove it to Uhma, AZ from Oklahoma City and pulled my 77 Z my brother gave me back home with the 74 Z using a tow-bar and bumper hitch:) after he popped the engine.

    As for the 77 Z. It had 373s with a turbo 350 and after dropping the 74 Z 10:1 350 engine in it, it lacked the low-end performance the 74 had with the 390s. Later I stabbed a T-400 in it with no noticeable changes.

    Following that I dropped a muscled up 425HP 427 in it with a TCI T-400 and 456s in the rear. Now we are talking to tall a gear. Should have stuck a placard on the panel that said not for Highway use:bowtie:.

    Today some 35 years later I'm going super stupid with the 77 Z and putting together a 496, T-400, with 430s. Yep, it is going to be a :lush:, but after I get it out of my system, I'm thinking of an LS with overdrive and autocross fun.

    What ever you go with, it will be yours and you will enjoy the ride.
     

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