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Big Block with OD

Discussion in '1965-1970 Shelby Mustang GT350 & GT500' started by firestanggt, Oct 6, 2007.

  1. Oct 6, 2007 #1
    firestanggt

    firestanggt Well-Known Member

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    I'm looking into the tremec 5 speed kit from Keisler. I'd like to hear feedback from anyone who has run one behind a an FE. I'm trying to decide on a good rear gear and OD ratio combo. The car originally had 3.89's and I'd love to leave them in it but I think thats just going to be too much gear for it.

    I'm not planning on doing a ton of highway driving but I would like to be able to take a highway trip if I decide to.

    What is the best cruising RPM range for a 428 on the highway?

    I've been using 2100 rpm in my calculations but I'd like to hear from anyone who has had some highway time with a bigblock. I'm aiming for around 70mph cruising speed.
     
    firestanggt, Oct 6, 2007
    firestanggt, Oct 6, 2007
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  2. Oct 7, 2007 #2
    John76

    John76 Well-Known Member

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    We have been running 3.73's with a FE/tremec TKO600 5 speed. Runs good at high speeds...2800 to 3k at 70 mph. They have calculation charts for tremecs on the internet. You put in rear gear, tranny and tire size and it gives you speed and RPM.
    Tremec takes a bit to get used to. I find it tight compared to a top loader. But the short throw is very cool. And always put it into 1st before you go into reverse.
     
    John76, Oct 7, 2007
    John76, Oct 7, 2007
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  3. Oct 7, 2007 #3
    tesgt350

    tesgt350 Well-Known Member

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    would it lower the Hi-Speed RPM's if you went to 17" Wheels & Tires? A buddy of mine hasa 2004 5 Speed Mach 1 with a few mods and 4:10 gears. At 65 MPH, he turns just 1800 RPM's. Just a thought.
    David.
     
    tesgt350, Oct 7, 2007
    tesgt350, Oct 7, 2007
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  4. Oct 7, 2007 #4
    firestanggt

    firestanggt Well-Known Member

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    Actually thats exactly what I'm doing

    I picked up a set of 01 GT wheels, or Bullet wheels, whatever you want to call them. I wanted 17's, I like the torque thrust D style, and I'm tired of chrome wheels so these were the perfect choice, and quiet inexpensive as well.

    According to Keisler's calculator, I'd be looking at about 2300 at 70mph with 3.89 and 245/45/17 and the .64 OD. That seems like a decent highway RPM to me. Any thoughts?

    My other concern was that the .64 OD is kind of a big jump from a 1:1 4th
    John, are running the .64 OD or the .82?
     
    firestanggt, Oct 7, 2007
    firestanggt, Oct 7, 2007
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  5. Oct 8, 2007 #5
    John76

    John76 Well-Known Member

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    I have to take a look but i remember the tranny to be .64 OD. It really isn't that big a difference from .82 to .64 when you compare the RPM's at different speeds. I would rather take a shorter gear for the OD...it makes for faster top speeds. The car also runs a 17" wheels...
     
    John76, Oct 8, 2007
    John76, Oct 8, 2007
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  6. Oct 8, 2007 #6
    67GT500#2100

    67GT500#2100 Shelby Forums Pit Crew

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    My brother has a big block 68 Mustang GT fastback with a Keisler 5 speed. He has a 3.90 rear end and says he is just under 2000 rpms at 60 mph in 5th gear. He is not sure about 70mph but did say it cruises nice and is not working to hard. His has the .64 5th gear.
     
    67GT500#2100, Oct 8, 2007
    67GT500#2100, Oct 8, 2007
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