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Rear-end gear ratio recommendations for my 79' Camaro?

Discussion in 'Transmission & Driveline Topics' started by 1979SportCoupe, Feb 21, 2021.

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  1. Feb 21, 2021 #1
    1979SportCoupe

    1979SportCoupe New Member

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    Hey all,

    I have a bone-stock 1979 Camaro Sportcoupe with a 305, a th350, and a staggeringly tall 2.40 rear end ratio….. I’m in the process of building up a pretty healthy but streetable 350 that I can run on pump gas, and not too aggressive of a cam, probably around 350 hp, and I’m not sure what to do for a rear-end. I heard in ‘79 the Z28’s with auto’s got the 3.42, the 4 speed cars got the 3.73, but I am not sure if these would be too short of gearing for my build. I have had my eye on the 3.08 posi as well. I would appreciate any advise/expertise!
     
  2. Feb 21, 2021 #2
    Gary S

    Gary S Administrator Lifetime Gold Member

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    Everybody has different preferences probably because they use their cars differently. For all around street use, I would go with either the 3.42 or 3.08. The 3.73 and deeper are unpleasant on the highway at higher speeds.
     
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  3. Feb 21, 2021 #3
    81Z28LS

    81Z28LS Member

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    If If you don't do a lot of extended highway driving at higher speeds, go with the 342. If a lot of 70 mile per hour highway runs are in your future, 308 would probably be better. Look at some of the rpm calculators out there that factory in gear ratio and tire size. Look at the RPM at whatever speed you think you'll be driving. As an example, 373 would put you at about 3000 rpm at 60 miles per hour depending on tire size.
     
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  4. Feb 21, 2021 #4
    Dueling73s

    Dueling73s Veteran Member

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    I know it might not be in your budget, but while you have the engine out, if there is any way to swing it, it sure would be nice to get rid of the TH350 and get a trans with an overdrive. Then you can get more aggressive with the gearing. It just makes cruising so much more enjoyable and was one of the best changes I ever made.
     
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  5. Feb 21, 2021 #5
    Zspoiler

    Zspoiler Veteran Member

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    I have 1979 Z-28 that was originally a 350/Turbo 350 /3:42 gear car. Of which I have converted over the years to a 377 cubic supercharged small block /Super T-10 4 speed car .And when I rebuilt my original 8.5 10 bolt .I could put any gear ratio I wanted. And I have driven an original 1979 Z-28 4 speed and it was too steep a gear for what I was going to use the car for. So I kept the 3:42 gears but bought Chevrolet gears since they are quieter than aftermarket ones. And the normal rpm is around 25-2600 rpm depending on tire size.I got in the 20 -4 mpg on the freeway at 60 mph. I have turned over the speedometer over 5 times .( I had a lot of trips from Seattle to Camp Pendlton California .) So I have lot of experience .with the car . Even my 1981 El Camino SS 290 350 /Turbo 350 has 3:42 gears .And is my daily driver.Good luck to you on what ever gears you use,
     

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  6. Feb 21, 2021 #6
    Dueling73s

    Dueling73s Veteran Member

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    Z spoilers experience is sure good if staying with TH350. I think there is one other option for the 10 Bolts that the OP hasn't listed and that is 3.23, I believe I have seen that ratio available. I had a 12 bolt with a 3.31 combined with a non overdrive Richmond 5 speed and that was a decent all around combination.
     
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  7. Feb 21, 2021 #7
    Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    Take into consideration the cam and torque converter too.

    Assuming you want a better performance off the line... A higher stall TC will also help. (23-2500 RPM)
    Your new engine/cam probably won't play real well with the factory torque converter as they are around 1700 stall.

    3.42 is a decent gear set for general driving.
    You can keep the same gears if you swap to an OD transmission down the road but if you are planning an OD transmission swap in the future the 3.73 would be a great gear set.

    I'm running 3.42 gears with a 200-4R (70 MPH = 2000 RPM) but 3.73 probably would have been a better choice for performance and mileage wouldn't suffer much either.

    My son is running the same transmission with 4.10 gears. Off the line launch is great but 1st gear is done very quickly.
     
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  8. Feb 21, 2021 #8
    CorkyE

    CorkyE Veteran Member Lifetime Gold Member

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    Agree with the 3.42 ratio - 3 speed automatic. Chevy engineers worked that out for a reason. With an OD transmission, 3.73 is a good ratio. That's what I have behind a 700-R4.
     
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  9. Feb 21, 2021 #9
    big gear head

    big gear head Veteran Member

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  10. Feb 23, 2021 #10
    jksvet

    jksvet Veteran Member

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    I put the 3.23 in my 79 4 speed Z. No problem getting the correct transmission gear either to keep speedo accurate. Works great for me. 3.73 was pretty brutal at highway speeds.
     
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