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Thread: 3:54 or 3:7?

  1. #1
    Formerly known as Koalia Reverend's Avatar
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    Default 3:54 or 3:7?

    Im swapping a "new" tranny (-77 5speed) and im thinking of changin the differential too. Which one is better ?
    -72 240Z "Goldie"

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    Registered User d240zx2's Avatar
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    Are you gonna cruise or track the car?
    First & Third owner of HLS30-00721
    B. 01/70 D. 03/12

    New owner of HLS30-15653
    B. 12/70 D.

    Frank in Houston, Texas

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    Registered User cbuczesk's Avatar
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    Better for what???

    Chuck
    East Coast Z Nationals held at the Carlisle Import & Kit Nationals - May 16-18, 2014 Carlisle, PA
    www.carlisleevents.com/events/import
    1969 240Z #390
    1971 Fairlady Z
    1971 240Z parts car
    1972 240Z ITS race car
    1972 240Z turbo
    1974 260Z turbo
    1975 280Z my first car
    1978 620 King Cab

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    Crumudgeon
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    There's a 4.5% difference in gearing between the two. I bet that if the tach was covered you wouldn't be able to tell which gear was installed.

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    Registered User olzed's Avatar
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    I have a 3.54 with five speed. It makes for quite a lazy cruisin' ride, but still has enough go for me. I seldom use fifth gear. Fourth at 100 km/60 mph is 3000 rpm.which is in good zone for passing. Down shift to third and it goes really well.
    Fifth at 100km/60 mph is around 2600 rpm.

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    Registered User Travel'n Man's Avatar
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    I'm doing a 5 speed swap as well (82-280zx) and moving to the 3.9 diff - I like more spirited driving. I will put the 4 speed and my 3.5 diff in storage like the other stuff I have been collecting (or should I say "swapping"). Just for record my 4 speed with the 3.5 diff is very spirited!
    Life's a journey; enjoy the ride!

    Mitchell
    L28 - N42 Block w/Flat tops - N42 Rebello Head & Cam - Triple 40 PHH Mikuni's - Headers - Recaro Seats -
    R180 3.9 Diff - Close Ratio 5 Speed - Toyota Vented Brake Upgrade w/ Porterfield High Performance Pads & Shoes

    1972 Datsun 240z
    HLS30-75040


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    I suspect I have the 3.54.

    In my car, what I find is for coming OUT of a corner, 3rd gear is too high. If I downshift to second coming INTO the corner, I have to rev it too high to match rpm's, and my 200k mile synchros just aren't up to the task. So what I've BEEN doing is stomping on the brake AND the gas and leaving it in 3rd. But my RPM's are too low to pull away quickly.

    I SUSPECT I'd like the 3.7 or even a 3.9 simply because of where 2nd and 3rd would end up, range-wise. (Higher RPM's in 3rd at the same speed)

    I find for passing, I really have to go down to third. Fourth just doesn't give me the accelration to get the job quick enough, not up here at 6000' altitude, with appx. 15% power loss. With the 3.7 I might be able to "only" go down to 4th.

    So do you want a quiet, comfy cruiser, or a hells-bells cornering and passing machine.

    I probably have it all backwards, but you get the gist of what I'd prefer the gearing to be. A few hours going back and forth between two cars, one equipped with each ratio, and you'd instantly know which you'd prefer.
    Last edited by Wade Nelson; 09-10-2012 at 04:17 PM.

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    Registered User Walter Moore's Avatar
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    Quote Originally Posted by Koalia View Post
    Im swapping a "new" tranny (-77 5speed) and im thinking of changin the differential too. Which one is better ?
    What do you have now? The 3.36 was standard equipment in North America, but I believe the 3.9 was stock in Europe. Did your car come to you from the U.S. or Canada, or was it originally sold in Europe? If it has a 3.9 now, I can not imagine dropping down to a numerically lower ratio unless you have a lot of high speed long distance crusing to do. Most people here want to find a 3.9 when they drop in a 5 speed.
    '71 240Z, Because any fool can drive fast in a straight line.

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    The early 4 speed, the later 4 speed and early 5 speed, and the later 5 speed all have different 1st gear ratios. This will affect the quickness from a stop. Something to consider. You can see how the 240Z got away with a 3.36 final ratio.

    3.592 240Z 4 speed
    3.321 280Z 4 speed to 79 5 speed
    3.062 80-83 5 speed

    Looks like the factory tried to stick around 12:1 for first gear overall ratio, in general. The 260Z and 79 ZX are oddballs.

    240Z - 3.36 x 3.592 = 12.06 (if this is what they had, the FSM says 3.9, still confused on that. Looking at the numbers it looks like they just got 3.36 and 3.9 swapped in the FSM since the 5 speed has a 2.906 1 st gear)
    280Z - 3.54 x 3.321 = 11.76
    80-83 ZX - 3.9 x 3.062 = 11.94
    Last edited by Zed Head; 09-10-2012 at 07:55 PM.

  10. #10
    Formerly known as Koalia Reverend's Avatar
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    My z is California import, so it has 3:36. I dont do tracks, only cruising + occasional bimmer harrassing in traffic lights. I've been offered 3:54 and 4:11, that would be quite the hasty differential i suppose.
    -72 240Z "Goldie"

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    In a stock 4 speed moving to a 3.54 would be a noticeable difference with acceleration - the only challenge is with 60mph your taching in the 3K mark. If you don't do much interstate driving is not too big of a deal -
    Life's a journey; enjoy the ride!

    Mitchell
    L28 - N42 Block w/Flat tops - N42 Rebello Head & Cam - Triple 40 PHH Mikuni's - Headers - Recaro Seats -
    R180 3.9 Diff - Close Ratio 5 Speed - Toyota Vented Brake Upgrade w/ Porterfield High Performance Pads & Shoes

    1972 Datsun 240z
    HLS30-75040


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    Registered User cbuczesk's Avatar
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    It sounds like a 3.54 is the way to go.

    Chuck
    East Coast Z Nationals held at the Carlisle Import & Kit Nationals - May 16-18, 2014 Carlisle, PA
    www.carlisleevents.com/events/import
    1969 240Z #390
    1971 Fairlady Z
    1971 240Z parts car
    1972 240Z ITS race car
    1972 240Z turbo
    1974 260Z turbo
    1975 280Z my first car
    1978 620 King Cab

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    Registered User cbuczesk's Avatar
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    It sounds like a 3.54 is the way to go.

    Chuck
    East Coast Z Nationals held at the Carlisle Import & Kit Nationals - May 16-18, 2014 Carlisle, PA
    www.carlisleevents.com/events/import
    1969 240Z #390
    1971 Fairlady Z
    1971 240Z parts car
    1972 240Z ITS race car
    1972 240Z turbo
    1974 260Z turbo
    1975 280Z my first car
    1978 620 King Cab

  14. #14
    Formerly known as Koalia Reverend's Avatar
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    What kind of results do you have had with 3:9 + 5 speed?
    -72 240Z "Goldie"

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    Registered User olzed's Avatar
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    [QUOTE=Koalia;409673]What kind of results do you have had with 3:9 + 5 speed?[/QUOTE

    For Motorway driving with a five speed and 3.9 you would want to be in fifth I would think.
    Personally I prefer to stay in fourth as its direct drive through the trans. so I chose a 3.54
    Less wear on moving parts through the trans.

    I would go for the 3.54, but depends a lot on your traffic conditions and style of driving. If you liked the 3.3 then the 3.5 is little different.

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    Back in about 1973 when I wanted to go with a 5-speed in our 6/70 Z, there were only two options:
    (1) to swap in a 5-speed out of an SRL311 2-liter roadster, or (2) bite the bullet and spend the
    money on the HD Competition Dept unit. I bring this up only because the internal gearing of the
    transmission itself is going to affect your final drive ratio. Since I was doing a lot of highway
    driving at the time, I wanted to go for fuel economy by keeping the 3.36 differential. The final
    drive ratio had been 1:1 with the 4-speed, so I figured the 0.864 5th gear would give me a nice
    overdrive.

    The problem that evolved was that with a high ratio (low numerically) differential, I basically had
    to ride the clutch just to get the car in motion. So much for economics: clutches were more
    expensive than gas at the time. So I went ahead and got a 3.90 Comp Dept limited slip.
    Multiplying the 0.864 times the 3.90 differential ratio brought me right back to a 3.36 final drive
    ratio, so after considerable expense, I was right back to where I had started.

    Except that I now had 5 gears to choose from to better suit the driving conditions of the moment.
    And for a guy like me who has always enjoyed shifting his own gears, the additional gear gave me,
    in effect, 25% more enjoyment.

    All Z Best,......................................Kathy & Rick
    1969 Z.CAR (#00013 10/69) since 8/30/76
    1969 ITSA.Z (#00171 11/69) since 8/24/73 28K mi
    1970 (#01905 2/70) since 1/24/11
    1970 (#06289 6/70) original owner
    1971 (#19851 1/71) sold
    1975 280Z (#01343 1/75) mint original
    1971 PL-510 2dr (our 160Z) since 12/31/75
    1969 1600 Rdstr (another 160-Z) since 10/3/10

  17. #17
    Formerly known as Koalia Reverend's Avatar
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    Thanks for all the input!
    -72 240Z "Goldie"

  18. #18
    Registered User madkaw's Avatar
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    Go as low az you want, you'll have an OD for the highway and still get decent MPG. it might make 1st gear a little more useless, but these engines are capable of rpms, so why not use them.
    3.54 's with my t-5 in OD was about ridiculous unless you wanted to cruise at 85 or more. Also, with anything other than stock exhaust that has any drone at 2200-2500rpm - you will be in the drone zone at cruise.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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