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    Results 1 to 10 of 10
    1. #1
      Join Date
      Jun 2009
      Location
      Bangor, Northern Ireland
      Posts
      43

      Rear gears - 3.25 or 3.40 gears to replace 3.73's. '69 Camaro with Ford 9"

      Hi guys

      My Dad's pro touring 383 '69 Camaro is waiting for its SBC 427 to be installed. We're discussing trans/rear gear ratios for it.

      My 383 '69 Vette has a TKO600RR (2.87 1st .82 fifth), 3.55 gears. It's lovely to drive, but we will change gears to 3.36 where it will be perfect.

      The Camaro has a TKO600 (2.87 1st .64 fifth), 3.73 gears. It's horrible, 1st is borderline pointless, 2-4 are over in a flash, then you're into 5th where the car dies on its ass.

      The .64 trans is not a good ratio for cammed cars, people use the 3.73 rear end ratio as a compromise so that you can get into fifth at a reasonable speed, but at the expense of 1-4 being too close. This creates a car that is never in the right gear IHMO.

      ....so we've decided to lower the rear gears to make the most out of 1-4, were not fussed about 5th, the only time we'll use it is on the motorway at 70+, so if we can't use fifth below that speed then that's fine. It's worth it to get a good 1-4 spread which is 98% of driving.

      Here's the engine -

      https://www.tristarengines.com/perfo...cylinder-heads

      So my question is, which rear gears? (Ford 9"). Both cars are driven hard.

      A - 3.25's, my choice

      B - 3.40's, my Dad's choice

      Any advice appreciated

      Cheers!

    2. #2
      Join Date
      Mar 2020
      Posts
      199
      To be clear, I'm assuming you mean driving at part throttle. This, I can understand as you have a very deep first gear & the jump between 4th & 5th is huge.
      Your trans (.64 5th) is mainly meant to be used as a 4 speed performance trans that will drop the rpm on the highway.
      I would not anticipate a shift to 5th under power as it drops the RPM too far.

      The .82 5th has a good spread that allows you to use 5th as another gear while driving.

      The ideal rear gear depends on the ability to lug the engine due to cam etc.
      I currently am running a T-56 Magnum with a .63 6th & 4.10's. I can drive it about anywhere in 6th over 35mph... but I have another gear (which happens to be a .81) between 4th (same 1:1 as your 4th) & my 6th gear.

      I also think the 5 speeds have too wide of a spread 1st thru 4th.

      You never stated your tire height so it is tough to recommend a rear gear, but I never think about less than a 3.55 or 3.73 in a performance car... unless it is strictly for highway or top speed runs.

    3. #3
      Join Date
      Jan 2014
      Location
      Portsmouth NH
      Posts
      247
      Country Flag: United States
      Hi aaroncorvette,

      If you have not found the app that Tremec has for your phone you should take a look at it. It will help you quickly look at all the combinations you could do.
      https://www.tremec.com/menu/tremec-toolbox-app/
      Cheers, Steve
      1969 Camaro (Small Tyre Restomod/mild Protour) 245/40/18 F, 275/35/18 R, stock frame, full Ridetech suspension, LS engine, T56 Mag, Wilwood Brakes. A driver car.

    4. #4
      Join Date
      Aug 2004
      Location
      Ontario, Canada
      Posts
      2,313
      Country Flag: Canada
      Here's another calculator for you.

      https://weddleindustries.com/gear-calculator

      I have spent waaaaaaaay too much time on it.

      Ken
      If there is a hard way to do something, I'll find it!
      My other car is a Vega.

    5. #5
      Join Date
      Jun 2009
      Location
      Bangor, Northern Ireland
      Posts
      43
      Quote Originally Posted by Lonnies Performance View Post
      To be clear, I'm assuming you mean driving at part throttle. This, I can understand as you have a very deep first gear & the jump between 4th & 5th is huge.
      Your trans (.64 5th) is mainly meant to be used as a 4 speed performance trans that will drop the rpm on the highway.
      I would not anticipate a shift to 5th under power as it drops the RPM too far.

      The .82 5th has a good spread that allows you to use 5th as another gear while driving.

      The ideal rear gear depends on the ability to lug the engine due to cam etc.
      I currently am running a T-56 Magnum with a .63 6th & 4.10's. I can drive it about anywhere in 6th over 35mph... but I have another gear (which happens to be a .81) between 4th (same 1:1 as your 4th) & my 6th gear.

      I also think the 5 speeds have too wide of a spread 1st thru 4th.

      You never stated your tire height so it is tough to recommend a rear gear, but I never think about less than a 3.55 or 3.73 in a performance car... unless it is strictly for highway or top speed runs.
      Hi, thanks for the reply. The tyres are 285/40/17 (25.7" diameter) on both cars. From driving the Vette i've learned that to accelerate hard and have nice long gears, 3.36 rear gears would be perfect (currently 3.55). I think with my small tyres on both cars that a lower numerical gear works well. This is from 5 years of driving the vette. Vette has a 383

      The Camaro has the same 1-4 gears as the vette, but the .64 5th, it will have a SBC 427 so will be a bit more trackable low down. The diff is boxed up and ready to go to Hauser Racing for a gear change.

      My Dad's main concern is that he'll lose acceleration from going from 3.73 to 3.25 or 3.40's. My argument is that the car will be much improved as 1-4 will be longer and more useful and that the 427 will accelerate hard with either rear end ratio.

      He's stuck in the old school mindset of 3.70's-3.90's for acceleration whereas i'm trying to show him the rear tyres are smaller than stock and we now have a Tremec with a 2.87 first which both helps acceleration and doesn't need those high gears. It's basically a battle of perception than reality.

    6. #6
      Join Date
      Jun 2009
      Location
      Bangor, Northern Ireland
      Posts
      43
      Thanks guys

      That's brill, forgot about the app. thanks!

    7. #7
      Join Date
      Oct 2004
      Posts
      2,544
      Country Flag: United States
      Quote Originally Posted by aaroncorvette View Post
      Hi, thanks for the reply. The tyres are 285/40/17 (25.7" diameter) on both cars.

      He's stuck in the old school mindset of 3.70's-3.90's for acceleration whereas i'm trying to show him the rear tyres are smaller than stock and we now have a Tremec with a 2.87 first which both helps acceleration and doesn't need those high gears. It's basically a battle of perception than reality.
      Curious what 285 tires you're running. Most are 26.2-26.3" (which is right at stock diameter), whereas the 275s run 25.7" (tad shorter). Either case, only a 2% difference, so that would be pretty negligible compared to gears. And 2.87 is a decent 1st, but I wouldn't consider it very steep. At least 10:1 (first gear x rear gear) is a good combination for getting out of the hole (assuming ~26" tall tires). So 3.55s-3.73s would be perfect.
      Red Forman: "The Mustang's front end is problematic; get yourself a Firebird."

    8. #8
      Join Date
      Mar 2020
      Posts
      199
      Quote Originally Posted by aaroncorvette View Post

      My Dad's main concern is that he'll lose acceleration from going from 3.73 to 3.25 or 3.40's. My argument is that the car will be much improved as 1-4 will be longer and more useful and that the 427 will accelerate hard with either rear end ratio.

      He's stuck in the old school mindset of 3.70's-3.90's for acceleration whereas i'm trying to show him the rear tyres are smaller than stock and we now have a Tremec with a 2.87 first which both helps acceleration and doesn't need those high gears. It's basically a battle of perception than reality.

      I'm not sure I follow your reasoning. With less gear, you will not accelerate as well... more gear = more torque = harder acceleration, but less road speed for a given RPM.
      Your dad is correct.

      With less gear you will shift less frequently & have more time in each gear. It's all in what you want though. I have 3.54's in my Firebird (with a 25.7" tire) & wished I went with 3.73's. I had 3.42's in my Camaro with a 383 & it was very drive-able, but the cam was a 220/230 so it had good low end... and I built it for a supercharged application so it did not need a lot of gear.

      If you have an appropriate cam (for low end torque, not a lumpy aggressive one), the long stroke of a 427 SBC should have the ability to make low end, but your cam is pretty aggressive (241/247 @ .050), making me question the low end.
      3.40's will work OK driving around, but 5th gear will be even worse & less useful than it is now.

    9. #9
      Join Date
      Jun 2009
      Location
      Bangor, Northern Ireland
      Posts
      43
      Quote Originally Posted by 68Formula View Post
      Curious what 285 tires you're running. Most are 26.2-26.3" (which is right at stock diameter), whereas the 275s run 25.7" (tad shorter). Either case, only a 2% difference, so that would be pretty negligible compared to gears. And 2.87 is a decent 1st, but I wouldn't consider it very steep. At least 10:1 (first gear x rear gear) is a good combination for getting out of the hole (assuming ~26" tall tires). So 3.55s-3.73s would be perfect.
      Hi

      The vette tyres are 285/40/17 Bridgestones, I have not measured them in the flesh, just put it into a tree calc. 26" apparently.

      The Camaro actually has 275/40/17 Falkens, these are what are 25.7", again with a calculator.

      Currently the vette is 2.87 first gear, 3.55 rear gears. this is 10.1 first gear ratio, I find makes 1st gear a little 'short'. I know a change to 3.36 gears which will happen over winter will give me the perfect length of gears. this will be an overall ratio of 9.6.

      I've been driving this car hard for 5 years and this is my experience. I get consistent 4.5 second to 60 times with the 383. It will fry the tyres at will and will fry them leaving in 2nd gear. a change to 3.73's would not make the gear accelerate any faster in the real world. It would make it slower because each gear would be shorter and I'll be unloading/loading the car more often. Again my real world experience. No calculator will tell me how the car lugs in 5th or how nice it is to have longer gears.

      The Camaro has 2.87 fist and 3.73 gears. this is an overall 1st gear ratio of 10.7 to 1. It is much more difficult to accelerate than the vette due to 1st being borderline pointless and the other gears being too squished up. I never know which gear to be in going around roundabouts. The gearing ruins the car. I'm forever. loading/unloading the car which = a slower car.
      It's this real world driving that made me realise a 10 to 1 1st gear should be an absolute maximum for a manual 5-7 litre Car. something around 8.5-10 is the area to aim for with 10 being a peaky small block and 8.5 being stroker big block.

      Therefore the vette will get a 9.6 first gear and the Camaro with get either a 9.7 (3.40 rear gears), or 9.3 (3.25 rear gears), the. I'm sure the 427 can handle the 9.3 first gear just fine. I'd just like to hear from people who have a big block with a Tremec or similar with gears around 3.25-3.40.

    10. #10
      Join Date
      Jul 2008
      Posts
      453
      Country Flag: United States
      Hopefully this calc will help you out.



      I have found this to be the best gearing calculator you could ever use. Visually shows you difference in gear changes, tire sizes, etc. I use it a lot and recommend it more than I care to admit. Helped me figure out shift points when I installed my T56, showed me where / when I could downshift.

      https://www.blocklayer.com/rpm-gear.aspx

      There's ads all around it, but once you use it, you'll never try anything else. The compare function is awesome on it.

      Write up on how to use it I did on another forum: https://www.chevelles.com/threads/gr...#post-11450264
      *Jeff*
      Project Salty - 1964 4 door Malibu, beaten, neglected, red headed foster child
      Cammed LQ4 / T56 Swap Project Thread <-click to read! 😁






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