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Ls1 sedan diff gearing ratio

Discussion in 'VT - VX Holden Commodore (1997 - 2002)' started by matqld, Aug 23, 2011.

  1. matqld

    matqld New Member

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    Hey all, Got vt/vx sedan, fresh rebuilt ls1, (fresh strong auto and shift kitted) ramjet otr, mafless tune, cam 224-228 112lsa, 918 springs, comp rods, 1:8 yt r/r, chain, oil pump ect, hand port heads (mild-mod) not cnc, catback, pacemaker Headers n ballistic cats (coming now) ,,,, i want to change my diff gearing from standard, was thinking might be cheapest option to look for maybe a diff out of 6sp man ute from a wreckers or something?
    I have done this on small budget... i realise may not be best setup to suit all liking.. goin for retune once headers n cats on.
    When i do 100-110kph the car seems to really be at a sorta flat spot in revs, (just under 2000 rpm) this is when im cruising along, its like a flat spot just before the cam comes into operating range but like all cars it seems to have its "sweet spot" when it comes to revs and speed on the hwy like a happy cruisin speed lol, and when i do say 120-125 its seems much happier ;p crispier throttle response ect, the rpm's are a little over 2000rpm when im doing that speed rather then just under 2000rpm.

    I want do be doing those revs that i do now when i do 120-125 kph but with different diff gearing to reduce my speed down to say around 100-110kph.

    So really what im asking if anyone knows is what diff ratio am i after ?

    Like a factory man ute lsd? or factory sedan manual lsd? atm i have the "factory auto diff". thinks its 3:46 or something lol i dont have a clue.

    Im not after a drag ratio lol, Its my everyday driver hehe,, just a small difference in ratio to what i have now so the car cruises at a better revs for me, i think fuel would prob be better off as its cruising with less effort at that speed or wouldnt be much different.. although i realise the principal of usin higher ratios reduces your overall top speed which would/could result in more fuel use lol, but im not after 4:11's lol


    Also is changing the diff ratio something that requires a tune touch up for performance reasons? (apart from speed recalibration)
    As headers and cats will be goin on soon and getting tune tweaked but wondering if i should hold out for diff gears or just put new diff ratio
    down the track... could a tech2 be used to recalibrate speed?
    If there is a whole thread already on this sorry had no time to search through the jargon.
    Thanks in advance anyone who offers advice/opinion/help ect thanks very much....
     
  2. MrSirWantalot

    MrSirWantalot New Member

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    I changed my diff from a 3.07.1 to a 3.46.1 & it took the revs upto 2300 approx from 1800, but because I do alot of hwy driving I asked the tech that tuned my car to give me less revs in top gear (auto) witch he did & @ 100kph it sits on 2000. Ideally if I didnt do as much hwy driving I would of went & got a 3.7.1 diff out of a manual HSV. A 3.46 is good for standing starts & towing witch I dont think you will be doing with ur mods...unless you wanna pull the trailer apart :). I think the speed recal is all you should need to do!
     
  3. TI3VOM

    TI3VOM Active Member

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    How did the guy that tuned your car do that? That's not possible to do!
     
  4. MrSirWantalot

    MrSirWantalot New Member

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    oh yes it is...I think its all to do with the torque convertor.....you know when u get to top gear & the last drop in rev is to do with the convertor...well mine is a very noticable drop in rpm
     
  5. goose202

    goose202 New Member

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    No, it's not. The torque converter locks up at about 80km/h with the standard tune, making it a 1:1 link between the crank and the trans input shaft. The only thing your tuner can change in software is when that lockup happens, and shift points. When it's not locked up, you will be doing more revs at the same speed since there's slippage. Maybe that's the higher revs you saw.

    If the car was doing 1800rpm at 100km/h before with a 3.07:1 diff then it will be doing 2028rpm now at the same speed with a 3.46:1 diff.
    3.7:1 diff would get you 2169rpm at the same speed.
     
  6. MrSirWantalot

    MrSirWantalot New Member

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    Its a good thing you own my car & not me....otherwise I would'nt be able to give my opinon. Btw i didnt say how he did it speciffically ....but i know he ask me if i wanted it like that & he did it. So therefor Im guessing it is possible!
     
  7. goose202

    goose202 New Member

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    I'm glad you're happy with your tuner and your car.
    But the fact is if you went from 1800rpm to about 2000rpm with the 3.07 to 3.46 diff change, then that's just what it should have been, and that's what the OP should expect in the same situation. It's not possible to go back to the tuner and ask for less revs than that with no mechanical changes.
     
  8. MrSirWantalot

    MrSirWantalot New Member

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    I went from around 1800 (3.07) to 2300 with the (3.46) diff in, if thats not right well...... i cant explain....... So at 2300 @100 kph The tech asked me if i would like less revs in top gear witch I said yes witch once he done brang the revs down to 2000 at 100kph (or 2023 to be exact) . Anyway we have drifted off away from the question matqld asked....& in my opinion Id use a 3.7 out of a man hsv. :). Btw this was all done whilst he was plugged into the ecu, & yes he did change trans pressure, for harder changes i suspect!?
     
  9. Jesterarts

    Jesterarts Your freedom ends where mine begins

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    OMG this forum is so full of fail today.

    I thought I had heard it all and then I came across this chestnut. Tuning the car to rev lower in a certain gear. Brilliant.

    I'm going to have to pop down to my tuner and get him to dial out a few few's at 100kmph to same some fuel.

    To the OP, not sure what ratio you should run. I'd say the highest you would want to run in an auto would be 3.73 and still retain sensible fuel economy.

    Most people will probably agree that 3.73 is plenty for an auto while the 6speeds work well with 3.91's.

    A tech2 SHOULD be able to recalibrate the speedo to account for the new diff ratio but in the past I had an issue with holden calibrating a 3.73 diff when I put it on my old VX S.

    Though I think this will be more to do with the fact they couldn't simply look up the pulse count in a book and would have had to work it out.

    This is a none issue since any tuner can adjust this value so not to worry about.
     
  10. MrSirWantalot

    MrSirWantalot New Member

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    Dont beleive i said i tuned the car to rev lower keyboard warrior. But i guess you just needed to be there to understand what i mean...or maybe you could of told the tech how to do his job. In My opinoin i already said i would go a 3.7....so nothing new there.
     
  11. TI3VOM

    TI3VOM Active Member

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    This is the last thing I may post about this particular topic you brought up, your tuner cannot tune your car to lower the RPM of your engine after a mechanical change has been done. The particular change that you did (changing diff gears) makes your rear wheels turn 3.46 times to every 1 rotation of the engine as opposed to 3.07:1, what this does is change what speed you need to rev the engine at to maintain the same speed as previously, in other words you need to rev your engine more!
    This cannot be changed by a tune.
     
    Craig Lewis likes this.
  12. MrSirWantalot

    MrSirWantalot New Member

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    ffs mate look & read what i wrote...like seriously you sound like a broken record. Where did i state that i tuned the car to speciffically to lower the revs? like mate read it before you comment!. Just for the ppl who are a little slow. I got diff changed, I got a mafless tune, while i got a mafless tune the tech recalibrated the speedo to suit, wound up the pressure for the gear changes (harder if im not mistaken) whilst doing that he did whatever he did to lower the revs by 300 in top gear cruising. Now i dont know how to explain it better than that Im not a mechanic as i guess you must be. If ur close enough for me to show u what i mean id be more than happy to prove it. And thank you for the leason in the math of diff gears, but nothing new there either. Does anyone else want to go around in circles & say i said something i didnt??
     
  13. Jesterarts

    Jesterarts Your freedom ends where mine begins

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    To refresh your memory, here is where you said it:

    and here:

    To achieve a reduction of rpm like that you need to swap the diff out. A reduction of 300rpm is quite substantial. If I was to change from the 4.11's I currently have to 3.73's I would only see a rpm decrease around the 200 mark. So if we used that as a baseline, in order to achieve a 300rpm reduction in top gear would require you to go form 3.46 to 3.08.

    Maybe the tech just swapped your diff back? :p
     
  14. MrSirWantalot

    MrSirWantalot New Member

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    Nah, just read my last post...surely that cleared it up!.....anyway....its getting old & plus ur too far away to prove what im trying/tried to say/mean.
     
  15. DLFHUB666

    DLFHUB666 GIT 'EERRR DONE!!!

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    I think this fella needs to change his name to SIRFAILSALOT as every post that i have seen from him is 'winning' that is sarcasm if you didnt know. An to the OP 3.73 would be ideal.
     
  16. MrSirWantalot

    MrSirWantalot New Member

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    sorry, what am i winning? And to think all i did was try to give my opinion.

    "Do not argue with an IDIOT.
    He will just drag you down to his level an beat you with experience".


    Ok i wont argue
     
  17. matqld

    matqld New Member

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    hehe thanks guys........ im looking around for 3.73, these are standard from a vx hsv manual right?
    I see diff gears (just the pinion and crownwheel) for 599 on ebay new.
    But im looking for a complete 2nd hand diff at this stage from a hsv,
    Not sure if im right but,
    vx 6speed man = 3.46 vx hsv 6peed man = 3.73
    So im after 2nd hand hsv 6speed man diff.
    So what sort money would i expect to pay for this?

    this way ill have an lsd diff.

    thanks again guys...........

    Hey guys atm my diff is just standard auto 3.07 i think and its not lsd i dont think. i say this because once i held 1 wheel still while turning tailshaft and the free wheel turned. has the "use the high performance oil tag" but thats it.
    Sound right? standard executive vx ls1 non lsd? was the lsd diff a factory option in this situation?
     
  18. MrSirWantalot

    MrSirWantalot New Member

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    Dare I say it :boxing: but yes I had the same diff, was a 3.07 non lsd with that tag as factory standard, LSD was an option only ( I think ). Although mine is a berlina, the LSD was an option only & not standard. Probibly best to ring a diff speacilist & tell him what you want & he'll tell you what the best diff ratio is for ur situation. I rang up a year or so ago & the price I was given for a 3.73 was $750...but i didnt shop around too much! & went for the 3.46 lsd out of a manual maloo ute witch cost me $500 :banstick:
     
  19. Munz

    Munz Right Foot Action

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    if your car was v8 from factory its got an lsd, your diff is probably getting a bit on in age and wear and needs to be reshimmed to get that LSD feeling like it should

    3.73 or 3.91 should be your choice
     
  20. MrSirWantalot

    MrSirWantalot New Member

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    Not exactly true. Mine is a v8 vx berlina & it had a 3.07 non lsd, all it had on the tag was high performance & yes it was the original diff according to VIN number. But anyway mat is better off ringing a diff speacilist, that way you should'nt get the bum steer.
     
    Last edited: Aug 27, 2011

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