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[Diamond Black Geezer]

I got thinking, as a purely inquisitive paper exercise, what would happen to the respective 0-60, top speeds etc of various Omegas given different differentials?

Not sure if anyone has already done some work on this before, as my mathematical skills are shaky at best, so hence I ask.

Please show your working for extra marks

[Kevin Wood]

Here you go... http://www.omegaowners.com/forum/index.php?topic=90497.0

As to their affect on 0-60 times and top speed - it's probably going to be pretty marginal overall, since that's basically dependant on power-to-weight ratio for acceleration and power-to-drag ratio for top speed assuming the gear ratios are at least able to keep the engine "on the boil".

It will have an impact on in-gear acceleration. A shorter diff will give better acceleration in a given gear, but you'll also run out of revs earlier and have to change to the next gear.

For top speed, the best gearing will give maximum speed at the engine speed at which the power peaks. That might not be ideal for cruising. You can see that for example, the setup on the 3.2 (auto box with 3.9 diff, power peaking at 6000 RPM) gives 6000 RPM and 155 MPH in top gear against a top speed of 149, so not far from ideal.

Anyone who has tried it will know that acceleration is very slow once it's in that top gear, so you might want to consider sacrificing top speed for better acceleration. A 4.22 diff would give you 145 MPH at 6000 rpm, but probably better acceleration up at the top end. A cruise at 80 MPH would now give you 3400 RPM rather than just over 3000 rpm, so you might have worse cruise fuel consumption, noise, etc. You win some, you lose some.

EDIT: Hypothetically speaking, of course.

[Diamond Black Geezer]

Much appreciated, that answers plenty of questions, and saves a lot of maths (which I'm bound to get wrong  )

[zirk]

The Link in Kevins post shows that Charts, there not all entirely accurate, probably because it doesn't take into account of the different Gearbox Ratio's across the Gearbox Model range, but is good enough for comparisons.

If were talking, in real life, 3.0 / 3.2's Ive done comparisons (mainly on Plod's and MV6's) 3.0 Manual with a Auto Diff (3.9) for increased 0-60, 3.2 Auto with a Manual Diff (3.7) for increased economy and am about to try a 3.2 Manual with Diesel Diff (3.45) also for increased economy.

the Manual with with a 3.9 did give a slight improved acceleration, 1st was a tad short, but became quite annoying at 70mph in top on a cruise (was purring away at 3000 rpm) so you felt you kept needed to change up a gear, so guessing a 4.2 would be out of the question for normal day to day driving.

Auto with a 3.7, remember looking for improved economy here, didn't seem to make bugger all difference in both 0-60 or economy in everyday driving, probably due to the Autobox Torque making up the differences in Diff Ratio,  , possibly a tad better on mpg on a 77mph cruise if driven carefully but nothing to shout about or make it worth while in my book.

And the 3.2 Manual with a Diesel Diff (3.45), have yet to do this one and mainly geared to one of my 3.2 LPG Manuals for improved cruising, I reckon with the extra gears to play with on the Manual box you shouldn't see too much of a loss on the 0-60 over the Auto, but hoping to see an improved mpg in 5th over 50 mph or on a Motorway cruise (We shall see).

As for maxed out Power and Top Speed differences. no idea, well not on a UK internet anyway.   

[Kevin Wood]

What you have to remember with economy, is that fuel is consumed primarily to generate power, and the power required to push an Omega along a motorway at your chosen speed is constant. If you change the gearing, you have the same engine producing the same power. The RPM will have changed marginally, but any improvements or otherwise depend on whether the engine is more efficient than at the previous speed. If the speed is not excessive, and somewhere in the middle of the torque spread of the engine, the difference will be negligible.

[Diamond Black Geezer]

The Link in Kevins post shows that Charts, there not all entirely accurate, probably because it doesn't take into account of the different Gearbox Ratio's across the Gearbox Model range, but is good enough for comparisons.

If were talking, in real life, 3.0 / 3.2's Ive done comparisons (mainly on Plod's and MV6's) 3.0 Manual with a Auto Diff (3.9) for increased 0-60, 3.2 Auto with a Manual Diff (3.7) for increased economy and am about to try a 3.2 Manual with Diesel Diff (3.45) also for increased economy.

the Manual with with a 3.9 did give a slight improved acceleration, 1st was a tad short, but became quite annoying at 70mph in top on a cruise (was purring away at 3000 rpm) so you felt you kept needed to change up a gear, so guessing a 4.2 would be out of the question for normal day to day driving.

Auto with a 3.7, remember looking for improved economy here, didn't seem to make bugger all difference in both 0-60 or economy in everyday driving, probably due to the Autobox Torque making up the differences in Diff Ratio,  , possibly a tad better on mpg on a 77mph cruise if driven carefully but nothing to shout about or make it worth while in my book.

And the 3.2 Manual with a Diesel Diff (3.45), have yet to do this one and mainly geared to one of my 3.2 LPG Manuals for improved cruising, I reckon with the extra gears to play with on the Manual box you shouldn't see too much of a loss on the 0-60 over the Auto, but hoping to see an improved mpg in 5th over 50 mph or on a Motorway cruise (We shall see).

As for maxed out Power and Top Speed differences. no idea, well not on a UK internet anyway.

That's what I'm on as present, as per factory, so interesting to note your findings. The combo that intrigued me was the diesel diff, which should be the 'punchiest' - but at expense of higher engine speeds at motorway driving, of course. Hmm.. the plot thickens... 

[Kevin Wood]

That's what I'm on as present, as per factory, so interesting to note your findings. The combo that intrigued me was the

diesel diff, which should be the 'punchiest'

- but at expense of higher engine speeds at motorway driving, of course. Hmm.. the plot thickens... 

Other way round. Diesel diffs give a taller ratio - so lower engine speed for a given road speed due to the fact that diesels have a lower rev limit than petrol engines. If you want punchy you need to try a 3.9 or 4.22.

In fact, I find it odd that you have a 3.7. I thought they were only fitted to manual V6s?

[zirk]

The Link in Kevins post shows that Charts, there not all entirely accurate, probably because it doesn't take into account of the different Gearbox Ratio's across the Gearbox Model range, but is good enough for comparisons.

If were talking, in real life, 3.0 / 3.2's Ive done comparisons (mainly on Plod's and MV6's) 3.0 Manual with a Auto Diff (3.9) for increased 0-60, 3.2 Auto with a Manual Diff (3.7) for increased economy and am about to try a 3.2 Manual with Diesel Diff (3.45) also for increased economy.

the Manual with with a 3.9 did give a slight improved acceleration, 1st was a tad short, but became quite annoying at 70mph in top on a cruise (was purring away at 3000 rpm) so you felt you kept needed to change up a gear, so guessing a 4.2 would be out of the question for normal day to day driving.

Auto with a 3.7, remember looking for improved economy here, didn't seem to make bugger all difference in both 0-60 or economy in everyday driving, probably due to the Autobox Torque making up the differences in Diff Ratio,  , possibly a tad better on mpg on a 77mph cruise if driven carefully but nothing to shout about or make it worth while in my book.

And the 3.2 Manual with a Diesel Diff (3.45), have yet to do this one and mainly geared to one of my 3.2 LPG Manuals for improved cruising, I reckon with the extra gears to play with on the Manual box you shouldn't see too much of a loss on the 0-60 over the Auto, but hoping to see an improved mpg in 5th over 50 mph or on a Motorway cruise (We shall see).

As for maxed out Power and Top Speed differences. no idea, well not on a UK internet anyway.

That's what I'm on as present, as per factory, so interesting to note your findings. The combo that intrigued me was the diesel diff, which should be the 'punchiest' - but at expense of higher engine speeds at motorway driving, of course. Hmm.. the plot thickens... 

Not sure what mean by punchiest, if you mean quicker off the mark, then no, other way round. The lower the Diff Ratio figure then the lower the RPM in all gears over standard Ratio, potentially a higher top speed (if your power to wieght gets you there). The higher the Diff Ratio figure then the higher your RPM over standard meaning your probably run out of Rev's / Power at top speed over standard.

Fairly sure, your V6 Auto will be a 3.9, but being a 96,?.

[Diamond Black Geezer]

Might have been a misprint in the brochure.. or me simply mis-reading it and skipping a line Will confirm when I get home 

Thanks for the info, it's all being greatfully added to the old grey matter