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Thread: Series IIA "Bitsa" Dormie

  1. #11
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    Quote Originally Posted by greenmeanie View Post
    The 292 is a torque mill with the peak way down the RPM range compared to a V8. As such you want to gear it for somewhere between 2200-2400rpm at 65mph.

    exactly:
    1966 GM truck repair manual,power ratings: 292 inline 6 has 170 hp at 4000 rpm and 275 fbs of torque at 1600 rpm.283 V-8,175 hp at 4000 rpm,275 ft lbs of torque at 2400 rpm. Your gearing philosophy has to consider that difference. Highway performance expectations are different too so period gearing (On GM/Chevy P/Us may or may not work- OTOH With an overdrive it probably will.

    [edit] Most of you know this but it is probably worth mentioning for those less accustomed to Land Rovers. In a LR high range ratio is something of a underdrive*- so comparison with other trucks ring and pinion ratios should take that into account. A 199Range Rover with 3.54 diffs also has a 1.22 High Range ratio and is like driving around with 4.3 diffs in an American car. A Series Land Rover with 4.7 diffs has a 1.15 high range ratio so they are like 5.4 diffs in a US vehicle.

    * Some people like Teriann, Greenmeanie, and Mercedes Jim have the Ashcroft High Ratio Transfer Case (HRTC) that does the exact opposite- it is effectively an overdrive. http://www.ashcroft-transmissions.co...-case-kit.html
    1965 SIIa 88",1975 Ex-MOD 109/Ambulance, 1989 RRC, blah, blah, blah...

    Land Rover UK Forums

  2. #12

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    still brainstorming….Nope hasn't been in CT…..Webasto/espar was my initial thought for heat as well….

  3. #13
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    If you go with an SM465 4 speed then you should use the 3.54 coiler diff in front and re-gear your Sals to 3.54. Off road performance will still be improved versus stock. That transmission has such a ridiculously low first gear that it more than makes up for the ratio change from 4.7 to 3.54.

    SM465 1st is 6.56 to 1
    Series 1st is 3 to 1
    '55 SI 86

  4. #14
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    Quote Originally Posted by meatblanket View Post
    If you go with an SM465 4 speed then you should use the 3.54 coiler diff in front and re-gear your Sals to 3.54. Off road performance will still be improved versus stock. That transmission has such a ridiculously low first gear that it more than makes up for the ratio change from 4.7 to 3.54.
    SM465 1st is 6.56 to 1
    Series 1st is 3 to 1
    I have always been a fan of Data so here goes

    You end up with that really huge gap between first & second gears in high range making it a 3 speed gearbox on the street. But otherwise this looks to be an attractive combination.

    Off road in low range:

    Overall gear ratio at the axle = gear selected in gearbox X selected transfercase ratio X ring and pinion ratio

    SIII: first = 3.68:1, second = 2.22:1, stock transfercase = 2.35:1, stock R&P 4.7:1

    low range ratio at axle: 40.65:1 first low, 24.52:1 second low


    SM465: first 6.55:1, second 3.58:1, stock transfercase = 2.35:1 low, 1,15:1 high range, coiler R&P = 3.54:1

    Low range first = 54.49:1, low range second = 29.78:1

    For the kind of off road driving I do I consider 55:1 to be a near ideal low first. When you convoy with other series vehicles a lot of the time you are in low second. The 29.78 ratio may be close enough if you have good low end torque to handle your lower RPMs but you need to be careful about outrunning stock Series rigs on the trail.



    1:1 high range fourth

    Stock SIII gear ratios:
    high range fourth = 5.41:1 which with 32 in. dia. tyres gives you 3692 RPM at 65 mph.


    Stock transfercase with 3.54 R&P:
    high range fourth = 4.07:1 which with 32 in. dia. tyres gives you 2778 RPM at 65 mph.

    Ashcroft high range transfercase with 4.7:1 R&P
    high range fourth = 4.01:1 which with 32 in. dia. tyres gives you 2737 RPM at 65 mph.

    The overall ratios of the two combinations are similar and both would work well. The only real difference is that with a NP435 you have a 4 speed gearbox on the street and with the SM465 with its granny gear you have a 3 speed gearbox on the street.

  5. #15
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    Quote Originally Posted by TeriAnn View Post
    I have always been a fan of Data so here goes

    You end up with that really huge gap between first & second gears in high range making it a 3 speed gearbox on the street.

    The overall ratios of the two combinations are similar and both would work well. The only real difference is that with a NP435 you have a 4 speed gearbox on the street and with the SM465 with its granny gear you have a 3 speed gearbox on the street.
    If you find a close ratio NP435 that is true, most I've run across are wide ratio. (I suppose you could use a close ratio T19 toowhich is more common) Those wide ratiotransmissions were designed largely when work trucks were 2wd or even 4wd with a 1:1 transfer case so the first gear was meant to be something of a low range in and of itself. Sometimes you'll even see them marked L-1-2-3 instead of 1-2-3-4. A vast majority of vehicles back then had 3 speed transmissions so using the truck 4 speeds as a 3 speed around town generally wasn't seen as a problem- nowadays it seems odd and to some- annoying.
    1965 SIIa 88",1975 Ex-MOD 109/Ambulance, 1989 RRC, blah, blah, blah...

    Land Rover UK Forums

  6. #16
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    Quote Originally Posted by TeriAnn View Post
    I have always been a fan of Data so here goes



    Ashcroft high range transfercase with 4.7:1 R&P
    high range fourth = 4.01:1 which with 32 in. dia. tyres gives you 2737 RPM at 65 mph.
    Way to much rpm for a 292 and even a 250 if he is still thinking Chevy 6.

  7. #17
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    Quote Originally Posted by greenmeanie View Post
    Way to much rpm for a 292 and even a 250 if he is still thinking Chevy 6.
    I wonder if a Roverdrive/roamer drive could survive with the torque?

    (t18/series T case/roverdrive/3.54)

    Gear Speed (MPH)
    10 20 30 40 50 60 70 80

    Fourth 426 853 1280 1707 2134 2561 2988 3415
    Fourth OD 307 614 922 1229 1537 1844 2151 2459

    http://www.solemnwarning.net/transmission/?
    1965 SIIa 88",1975 Ex-MOD 109/Ambulance, 1989 RRC, blah, blah, blah...

    Land Rover UK Forums

  8. #18
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    Quote Originally Posted by yorker View Post
    If you find a close ratio NP435 that is true, most I've run across are wide ratio.
    Most all Ford NP435s have a granny first and most of the Chevy NP435s are close ratio. Gears on the later NP435s are interchangable.

    I'm running a NP435 with Ford case and Chevy close ration gears inside. It mans a Chevy clutch disc and a Ford pressure plate but it works just fine. With the Ashcroft high ration transfercase & 4.7:1 R&P it gives me real close to 55:1 low first, a low second close to a stock Series low second (which make traveling with others easier) and decent highway gearing.

  9. #19

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    Yeeesh....I thought my Dormie was dormant....turns out I have been also.....I still have the dormie. boughtb a van a few years ago and chased snow for a couple of monthes the first Winter we had the van. LOVED it.....I need to think about selling the dormie.....Rob Norwich, VT

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