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Thread: Ratios and Sweet Spots

  1. 25th September 2015, 03:45 PM #1
    flagg's Avatar
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    Ratios and Sweet Spots

    Hi All,

    About to make an order for an Ashcroft's R380. The HD Bearings are a no brainer but I'm not sure on the 5th gear ratio.

    With my 1.222 transfer and 255/85 tires I have 2320 RPM at 110 kmh (std ratios) and 2206 at 110kmh with the high ratio 5th. (on the ashcroft's ratio calc site)

    I'm leaning towards the high ratio (especially as I have the reduced transfer..) and 2200 should still be well within the sweet spot for the 4BD1?

    Am i wrong?

    Cheers,
    Dec
    Hercules: 1986 110 Isuzu 3.9 (4BD1-T)
    Brutus: 1969 109 ExMil 2a FFT (loved and lost)
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  2. 25th September 2015, 05:22 PM #2
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    flagg
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    also just confirming I need the V8 input shaft ?
    Hercules: 1986 110 Isuzu 3.9 (4BD1-T)
    Brutus: 1969 109 ExMil 2a FFT (loved and lost)
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  3. 27th September 2015, 11:07 AM #3
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    Dervish
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    Mine has a 1:1 transfer case and pulls like a train at 110km/h (around 2000rpm), so yes I'd say you'll be fine at 2200. It depends on your turbo though, and I noted on your thread that you said that with the 1:1 TC it was only getting going at 120km/h (which would've corresponded to ~2200rpm).

    I don't know how you got your r380 behind the 4BD1, but whatever r380 you had previously is what you need now. I believe most have used the diesel box.
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  4. 29th September 2015, 09:05 PM #4
    Adrian18 Guest
    300tdi pinion input shaft



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  5. 29th September 2015, 09:09 PM #5
    Adrian18 Guest
    I use 255 85 16 and these are my no.and are correct with my tacho

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  6. 21st November 2015, 04:55 PM #6
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    Vern
    Vern is offline OldBushie
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    Well just changed my transcase from a 1.003 to a 1.222 with the Isuzu 5speed. And upgraded the inter cooler.
    Can't wait to change it back to the 1.003.
    However egt's have dropped heaps with the new water to air, time to remove the fuel s few completely
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  7. 21st November 2015, 09:34 PM #7
    Adrian18 Guest
    Ha ha told ya so😀😀😆😆

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  8. 21st November 2015, 09:37 PM #8
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    Vern
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    I had to be sure
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  9. 22nd November 2015, 05:15 AM #9
    Adrian18 Guest
    .ive swap a couple of times now ...wish someone would make a 1:1.1 ratio

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  10. 22nd November 2015, 07:30 AM #10
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    Could try a 1.192, but probably not worth it. Will stick the 1.003 back in and tune it better.
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