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[mkaminski100]

My first question is: All Omegas 2.0 and 2.2 autobox owners - Can you please tell me how many revs do you have when driving 60MPH?  

I have an Omega 2.0, auto. I found that when driving 60MPG, revs are about 2000. Few days ago I had a chance to drive 2.2 saloon, auto. When driving this one at 60MPH, revs were about 2300-2400. When driving the same way, gears in 2.2 are also changing on lower speed (45 instead of 50). My 2.0 is doing 23-25 on the run (short trips, many roundabouts etc) while 2.2 on the same road is doing almost 30.
I found it very odd, as 300-400 revs more is quite a lot. Gearbox is the same so even if it’s a different engine or gearbox controls, ratio has to be the same.  Every autobox AR25 (I would say AR35 as well) has the same ratio and it’s only rear axle which is changing ration for different engines and gearboxes.
I was told that my 2.0 Omega was custom made for some rich MP as a “gift” and is almost in ELITE spec. Is it possible that there is a rear axle from a different engine or for manual gearbox? It would explain why my Omega drives like wouldn’t have enough torque and consumption when driving  70MPH is the same as driving 100MPH (on German “Autobahn”).
Can you please tell me where can I find my rear axle number plate and how can I find for which engine/gearbox it is?

[Tafty]

It maybe that the software versions for the autoboxes are different. Have you had yours updated? Don't believe VX would put a different axle on very similar engines.

[mkaminski100]

Yes, both in rev 9. Gearbox controls are different, but the ratio is the same. Above some speed (usually it’s 50) TC is blocked so transmission is straight (no slip – like manual) so there is no way that the ratio could be different. Speed and revs have to be the same when driving same car at speed above 50MPH (locked TC).
As I said – this cur was custom made, and from I was told it should have V6 engine but first owner told Vx that he wants 4 pot. There is a way that the axle is from V6 or it was replaced later (by second owner)
I don’t have an access to EPC right now so could you advice how to find axle number plate and to find if it’s the right one?

[TheBoy]

Did they put an LSD on it?

[mkaminski100]

Low Slip Diff? I don’t know, but don’t think so. How I can check if I have one?

[Kevin Wood]

My V6 does a shade over 2000 RPM at 60, IIRC. That does seem very tall gearing for a 2.0 so maybe it has had the diff swapped.

Kevin

[mkaminski100]

http://www.opel-infos.de/ ->Achsantriebe -> Hinterachse -> Differentiale
All sort of mixtures of diffs and engines.
Mine should be 3.900, but as you can see, 4.222 so this might be explanation. Why GM decided to go for such a low ratio (4.222 is much lower comparing to 3.700)

[Kevin Wood]

There you go, then.  

3.9 to 4.2 takes your 2000 RPM up to 2165
3.7 to 4.2 takes it up to 2282.

Maybe they lowered the ratio on the 2.2 to increase performance.

Remember also that dashboard gauges aren't the most accurate instruments in the world, and you've got the uncertainty of both the tacho and the speedo in your observations.

Kevin

[mkaminski100]

I’ve also found this in internet:
According to Haynes, up to 1988 model year;
The 2Ltr manual & auto both had a 3.90 unit.
The 2.5Ltr manual had 3.70, the 2.5 auto had 3.90 unit.
The 3Ltr manual & auto both had a 3.70

After 1998 model year:
The 2Ltr manual & auto both had a 3.90 unit.
The 2.5Ltr manual had 3.90, the 2.5 auto had 4.22 unit.
The 3Ltr manual had a 3.70, the auto had a 3.90

I was wondering,
(1) if anyone knew why they changed the ratios for the 2.5 ltr in 1998?
(2) If I put on the 3.90 unit of the later model, instead of the 3.70 that I am supposed to, would my mpg improve noticeably?


Why the hell did Vx put 4.222 for 2.5 auto and 3.900 for 2.0 auto and manual. This doesn’t make sense…

[Entwood]

The final drive (Differential) is not the only thing to consider, you MUST consider the gearbox ratio's as well... it is possible that the gearbox has a lower ratio to match a higher final drive ratio, in order to keep the "power band" of the engine in a certain range, for either performance or economy, or both .... lower gears short, top gear long , to give some performance when stirring the stick but economy on a long run ....

Each element cannot be cosidered on its own .. it is a part of the total drive system

[mkaminski100]

I agree that this is important in manual boxes, but every AR25 automatic gearbox (I would say AR35 as well as spares are interchangeable with AR25) has the same ratio. Ratio is locked when TC is locked so there can be no differences in any versions.

[Marks DTM Calib]

Beware as the AR25 and 35 do have slightly different ratios.

To complete the picture, the diff ratios for the 2.2 are as follows:

Auto 4.22
Manual 3.9

[Kevin Wood]

I was wondering,
(1) if anyone knew why they changed the ratios for the 2.5 ltr in 1998?
(2) If I put on the 3.90 unit of the later model, instead of the 3.70 that I am supposed to, would my mpg improve noticeably?

I would imagine ratios were tweaked to change the economy / performance balance due to "market pressures". Also depends on market. A 3.90 diff on a 2.0 auto might have been OK in Germany, where the requirement is to wind up to 3 figure speeds and cruise. In the UK this would result in the engine being off the bottom of the torque band at cruising speed, necessitating a downchange every time you accelerate.

It could also have been due to fitted wheels getting larger. Remember wheel circumference is an important part of the equation.

Why the hell did Vx put 4.222 for 2.5 auto and 3.900 for 2.0 auto and manual. This doesn’t make sense…

It looks like they brought in the 4.222 diff in '98.

Also, where does the 4 pot redline? Where doe the torque peak? Could this be lower than the V6 so, even though it's the lower powered engine, it needs taller gearing?

The final drive (Differential) is not the only thing to consider, you MUST consider the gearbox ratio's as well...

Very true. I believe there's a slight difference between the AR35 and AR25 auto boxes however, I think it's only the middle 2 ratios.

Kevin

[mkaminski100]

I found this
      AR25       AR35
1      2.40       2.40
2      1.48       1.48
3      1.00       1.00
4      0.72       0.72
R      1.92       1.92

It looks like ratios in AR25 and AR35 are the same. Clutches for 25 and 35 are the same. I think that the only difference is a number of clutches in overrun.
Manual gearbox has different ratio than auto so I only look at diffs for automatic boxes

P.S. Wheels are the same and standard - 225/55 R16 in both

BTW - Quote - According to Haynes
So it looks like these diffs were on UK market