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Author Topic: 4.2 dif  (Read 3025 times)

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feeutfo

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4.2 dif
« on: 19 July 2010, 11:27:42 »

Been talking to 2woody about gearing and lsd's etc. I'm not convinced I need an LSD tbh but if going to the trouble of swapping or building one I was thinking of adding it. But  in the absence of any cheep tuning for the 3.2 I wondered about fitting a lower geared dif for a bit more acceleration. This obviously will mean higher revs meaning more fuel and noise.

Woody went through some figures to suss what I wanted and he suggested fitting a 4.2 from a 2.5 or 2.6 for now just to see how the gearing goes.

Anyone with experience or thoughts on this? Seems it can make a difference of 400 revs at 70 mph. Or there abouts.

Ta
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Kevin Wood

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Re: 4.2 dif
« Reply #1 on: 19 July 2010, 11:53:51 »

Would be worthwhile if acceleration is the be all, IMHO, especially as the auto gearbox is geared a bit tall at the low end to get away from the lights fast and the top end of the speed envelope is not really open to sensible exploration in this country.

It's a relatively small change in gearing in the overall scheme of things, though, so I wouldn't expect a "night and day" improvement. You'd be better of fitting a driver involvement pack if that's what you're after.

Some of the ratio change will just be winning back what you've lost going to big wheels, of course. ;)

LSD? Not convinced either, TBH. A 3.2 auto breaks traction so rarely in "normal" fast road driving on dry surfaces (yes, I know it can be provoked, but..) that it wouldn't add a lot, other than making it a bit more prone to the back coming round in the wet. Not that I've driven an Omega with an LSD extensively - it's just that the back end of mine stays firmly planted when I'm pressing-on smoothly. The only thing it might improve is when the inside wheel is unloaded almost entirely - i.e. emerging from T junctions when the inside wheel is prone to spin.

Economy? I reckon the 3.2 is geared a little high for UK cruising speeds anyway. Engine will still be doing the same work shifting the car - just at slightly higher RPM, which may or may not be a more efficient speed. You will see a reduction in economy at high motorway cruising speeds, but you'll probably win it back at A road mimble speeds where these days it's hard work keeping the autobox in 4th.

Kevin
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Marks DTM Calib

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Re: 4.2 dif
« Reply #2 on: 19 July 2010, 12:18:02 »

You may find the fact that the torque convertor locks out at a slightly lower speed beneficial to general fuel economy
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serek

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Re: 4.2 dif
« Reply #3 on: 19 July 2010, 14:37:04 »

got 4.22 on mine. you can see differents on your speedo when you push your foot down
better start from 0-60.
still lock up at 45mph
but after fit manual box 1st gear is just waste time

got spare 4.22 diff here if you need

Kevin Wood

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Re: 4.2 dif
« Reply #4 on: 19 July 2010, 15:17:02 »

Quote
got 4.22 on mine. you can see differents on your speedo when you push your foot down
better start from 0-60.
still lock up at 45mph
but after fit manual box 1st gear is just waste time

got spare 4.22 diff here if you need

My Westfield is like that with a 3.6 diff. ;D
A box with a longer 1st is required to fix it properly though.

Just recalled that Robsey had a 2.6 (auto IIRC) that was upgraded to a 3.2 and it initially had a 4.22 in IIRC. Might be worth asking for his opinions.

Kevin
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tunnie

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Re: 4.2 dif
« Reply #5 on: 19 July 2010, 15:20:42 »

what ratio is plod? Noticed the pickup on those was much more noticeable in the 0-60 dash
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serek

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Re: 4.2 dif
« Reply #6 on: 19 July 2010, 17:16:21 »

Quote
Quote
got 4.22 on mine. you can see differents on your speedo when you push your foot down
better start from 0-60.
still lock up at 45mph
but after fit manual box 1st gear is just waste time

got spare 4.22 diff here if you need

My Westfield is like that with a 3.6 diff. ;D
A box with a longer 1st is required to fix it properly though.

Just recalled that Robsey had a 2.6 (auto IIRC) that was upgraded to a 3.2 and it initially had a 4.22 in IIRC. Might be worth asking for his opinions.

Kevin
that where coming from one of my 4.22. did ask him before and hi say was go like f~*** k from traffic lights :y

Kevin Wood

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Re: 4.2 dif
« Reply #7 on: 19 July 2010, 20:06:21 »

Quote
that where coming from one of my 4.22. did ask him before and hi say was go like f~*** k from traffic lights :y

Sounds like the desired outcome. :y

Kevin
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Marks DTM Calib

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Re: 4.2 dif
« Reply #8 on: 19 July 2010, 20:27:03 »

Quote
what ratio is plod? Noticed the pickup on those was much more noticeable in the 0-60 dash

pretty sure its 3.9....hence why they are quicker off the mark
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feeutfo

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Re: 4.2 dif
« Reply #9 on: 19 July 2010, 23:17:50 »

Quote
Quote
what ratio is plod? Noticed the pickup on those was much more noticeable in the 0-60 dash

pretty sure its 3.9....hence why they are quicker off the mark

ahem   *cof * cof*
http://www.omegaowners.com/forum/YaBB.pl?num=1163895469
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05omegav6

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Re: 4.2 dif
« Reply #10 on: 20 July 2010, 00:43:38 »

think mine is 3.7 lsd, poss 3.9 :-/. manual box believed to have same ratios as 3.0mv6. only breakes traction on wet cobbles and rough concrete :). daren't turn tc off though, not good for passenger comfort, esp on fri/sat nights :D. 0-60 is about 7.5 secs ;) not sure what the engine is producing though. hope to find out once cambelt is done at next service. :)
« Last Edit: 20 July 2010, 00:44:37 by 05omegav6 »
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Kevin Wood

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Re: 4.2 dif
« Reply #11 on: 20 July 2010, 10:15:41 »

Quote
Quote
Quote
what ratio is plod? Noticed the pickup on those was much more noticeable in the 0-60 dash

pretty sure its 3.9....hence why they are quicker off the mark

ahem   *cof * cof*
http://www.omegaowners.com/forum/YaBB.pl?num=1163895469

Depends if it's auto or manual. Auto 3.0/3.2s have the 3.9 diff anyway but a manual retail will probably have a 3.7 so an LSD, if 3.9, will be lower geared.

Kevin
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Marks DTM Calib

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Re: 4.2 dif
« Reply #12 on: 20 July 2010, 11:30:40 »

Quote
Quote
Quote
what ratio is plod? Noticed the pickup on those was much more noticeable in the 0-60 dash

pretty sure its 3.9....hence why they are quicker off the mark

ahem   *cof * cof*
http://www.omegaowners.com/forum/YaBB.pl?num=1163895469

Sorry, was referring to LSD diffs as opposed to standard ones.

The one on my old explod auto was certainly a 3.9  :y
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zirk

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Re: 4.2 dif
« Reply #13 on: 20 July 2010, 12:12:56 »

Sorry to Hijack, but have a question, been trying to work out whether my Ex Met 2000 Project FL is 3.9 or 4.2 (Auto), any pointers on what the revs would be per MPH ?, assuming box locked up, standard 15" wheels.

Chris.
« Last Edit: 20 July 2010, 12:14:13 by zirk »
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Kevin Wood

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Re: 4.2 dif
« Reply #14 on: 20 July 2010, 13:10:45 »

Quote
Sorry to Hijack, but have a question, been trying to work out whether my Ex Met 2000 Project FL is 3.9 or 4.2 (Auto), any pointers on what the revs would be per MPH ?, assuming box locked up, standard 15" wheels.

Chris.


It's in the link Chris posted above. About 24 MPH/1000RPM with the 4.22 and 26MPH with the 3.90.

Don't forget that the speedo might not be accurate and tyre revs per mile will be a factor.

Kevin
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