highway rpm too high.

Discussion in 'Transmission & Driveline Topics' started by Robert J Licher, Aug 7, 2019.

  1. Robert J Licher

    Robert J Licher New Member

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    Hello I have a 71 RS with a 454 and 410 gears I'm looking for a trans that can cruise on the highway. I have a M21 muncie now and it's just not getting it. I live in Lake Havasu and I don't take it out of town, it needs another gear. Don't know what the gears are in the trans but 4th gear is about 50 just cruising, how ever to bump it up to 70 or 80 the motor would be to high of an RPM. I was looking into 6 speeds, but from what I've seen it looks like a big dollar nightmare! Plus I wouldn't be able to use my skatershield! I had an uncle that raced at irwindale and he had a clutch come thru the floor and almost cut his right foot off, After seeing the car and how easy it cut thru the floor, I want to keep my skatershield I want to know more!
     
    Last edited by a moderator: Aug 7, 2019
  2. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

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    You can get a 5 speed and keep your current bell. Look at tko 5 speeds. you will need to dial it in. Vendors like bowler or hurst drivelines can help you.

    You say you don't leave town, so maybe dropping a pile of cash on a trans isn't the best move. Have you considered different rear gears? My experience with BBC is they generally don't need that much gear on the street.

    Btw you can get scatter shields for a t56.
     
  3. Coadster32

    Coadster32 Veteran Member Lifetime Gold Member

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    I'm thinking that your car is a tire shredder as it is with 4:10's. I agree with Bonzo, 454's normally produce a lot of low end torque, and you don't leave town with the car. New gears could be a cost effective alternative for you. 3:55 seems like it would be really nice, but you will give up some on the low side, (you might have enough to spare). I understand about the highway dilemma. I run 3:90's out back with TH400. I don't drive it too fast on the highway, but that wasn't the intent of my car in the first place. You need to compromise. If you want the best of both worlds, you'll be shelling out big cash. Gear vendors units cost a good amount of money, and need some massaging to make happen. At that cost, a new tranny might be more desirable. It's a fight we all fight. Good luck on your direction.
     
  4. mech393

    mech393 Veteran Member

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    I have a 71 SS I pulled the original 402 out and put a 454 in it, it has the original 3:42 gears with a Muncie m20 trans and it it runs fine in town and on the highway.
     
  5. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

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    I think 3.42 is the numerically highest id go. I might even go a step below that
     
  6. G72Zed

    G72Zed Veteran Member

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    If your in the market for a trans, and want ease of conversion and fitment, look at the Richmond SS 5spd. You will be able to use most of all your M21 parts and gain the .77 OD of 5th. You will be a little "over-geared" in first, but more than livable with what you gain in 5th.

    Or, like others have said,cheaper option might be a gear change to a 3:42 or perhaps you can find a set of 3:31's, assuming it's a 12 bolt.
     
  7. grzewnicki

    grzewnicki Veteran Member Lifetime Gold Member

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    4.10 out back with a TKO first gear is a little extreme, first gear will be gone and over with before you know it. The TKO 600 has a better first gear for that low of a rear end ratio. The install isn't that bad and I have a Lakewood scattershield in mine with the TKO 500, bolts right up.
     
  8. G72Zed

    G72Zed Veteran Member

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    That's why I mentioned the Richmond SS 5spd, it has a 2.89 first gear, almost the exact same as the TKO600's 2.87, and may be an easier fit looking at the details.

    Final OD gearing with the 4.10 would be 2.62 with the TKO600 (.64) and 3.16 with the Richmond (.77).

    Guess the OP needs to see what RPM's/cruise speed is needed/wanted to be in the sweet spot.
     
  9. 1980RS

    1980RS Veteran Member

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    T-56 took care of my high RPM on the highway. Takes some work to put it in but the results were worth it. 1600RPM at 70mph with a 3.55 gear and 28" tires
     
  10. G72Zed

    G72Zed Veteran Member

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    Cool, looks like a .53 OD in 6th to give you that result.

    Is that Fuel injection? if not, you must be on just the Idle and transition circuits, unless annular and they come in early with good signal.

    I've had customers go the "too low" of a gear, or the 6spd only to find out they get better mileage with more RPM and using 5th in a 6 spd. But every engine/carb-tune is different. Good tune to get this at 1,600 if carbed.
     

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