Working out acceleration?

Princey

Princey

Princey

Soldato
Joined
26 Apr 2003
Posts
5,746
Location
West Midlands
Currently my Monaro has a 3.45:1 diff which is good for a 0-60 sprint of around 5.0s. If I where to change my diff to a different ratio would I see much of an increase in acceleration or do you think the difference would be minimal?

3.45:1 Engine speed @ 70 mph: 1647 rpm

3.7:1 Engine speed @ 70 mph: 1761 rpm

3.9:1 Engine speed @ 70 mph: 1857 rpm

4.1:1 Engine speed @ 70 mph: 1944 rpm
 
At what speed in which gear would you like better acceleration?

You aren't magically going to make your car faster, but you can improve performance at given speeds in given gears.
 
I think you'll get around 18% more torque going from 3.45 to 4.1, and you will get an increase in in gear acceleration, however you will need to change gear more often as you accelerate so timing may not differ all that much.

Also, if you increase the torque in the output shafts of the diff, and therefore the turning moment of the wheel, you may find you get more slip and therefore less acceleration.
 
You'll get more torque at the wheels for each gear as shoes says, but that is at lower speeds so you'll be out of one gear earlier than before and into the next giving lower torque at the wheels for a while - i.e. at a speed you would have been at the end of third before, you'll now be at the start of fourth. So it all pretty much cancels out to making no real difference to acceleration times through the gears at all. That shouldn't be surprising really - you've not increased your car's power so it's not magically going to be faster. You're 0-60 sprint must be largely traction limited, so probably that won't change much either.

From your figures, though, you seem geared to around 200 even with a 4.1 diff :o. So the car seems really tall-geared. If you swapped your 3.45 to a 4.1 the car would just feel more alive cos of that extra torque in the gears than what you're used to and the fact you'll be changing gears earlier and more often when pressing on, even though real acceleration times are not very different at all, so probably worth doing. Of course you'll have even worse cruising economy, but you don't care much about that if you have a monaro :)
 
There are hundreds of identical threads to this on the swathes of Monaro and Holden forums that populate the net, yet you come to OcUK with another opportunity yet again to spout the line 'my Monaro'

You also give the exact figures for what the difference will be but still ask anyway.
Just go read some forums about your car, it's all there for you.
 
tigerstyle said:
There are hundreds of identical threads to this on the swathes of Monaro and Holden forums that populate the net, yet you come to OcUK with another opportunity yet again to spout the line 'my Monaro'

You also give the exact figures for what the difference will be but still ask anyway.
Just go read some forums about your car, it's all there for you.
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Mr Grumpy.

90% of the questions asked on this forum can be found else where on the net. I ask here because I want to and because I have friends here? Problem?

Also yes I start my thread with 'My Monaro' because we'll it is my car and it's also a Monaro. Heh. I also have more than one car.
 
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Princey said:
Ok. :)
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Not that I don't love the pics of it in the relevant threads and all, t'is a fine motor vehicle!

Just with the shall I get it vinyl wrapped, shall I supercharge it, shall I turbocharge it, shall I change the diff etc etc, good god man just enjoy the beast! ;)


/ahhh cute, you edited your post!
 
tigerstyle said:
Not that I don't love the pics of it in the relevant threads and all, t'is a fine motor vehicle!

Just with the shall I get it vinyl wrapped, shall I supercharge it, shall I turbocharge it, shall I change the diff etc etc, good god man just enjoy the beast! ;)


/ahhh cute, you edited your post!
Click to expand...

Hi, I would like to post a motoring related question but I thought I would run it through you first. Would it be okay if I asked about buying a used vehicle for £6-£8k? I don't want to upset you because I've posted about buying cars with money before.
 
Lots of TVR owners do or want to do this. The TVR Speed6 engine is over geared for UK roads IMO (probably great for the track). Nearly 80mph in 2nd and 110 in 3rd.

To answer your question, I hear a lower diff makes a big difference. Not 0-60 as you'll be limited by traction *, but obviously it will lower all the gears so not only will you be nearer peak power at any given speed, the lower gearing gives more leverage for better acceleration (think riding a bicycle).

* A guy who put an LS7 engine in his Sagaris changed the diff from 3.54 to 3.1 (I think) as he just got too much wheel spin. Even then he was starting in 2nd gear at Santa Pod to try to control the wheelspin!
 
There used to be a very basic piece of freeware called cartest that let you change a number of details for various testing etc, wasn't perfect but gave a reasonable idea.
 
Janesy B said:
Hi, I would like to post a motoring related question but I thought I would run it through you first. Would it be okay if I asked about buying a used vehicle for £6-£8k? I don't want to upset you because I've posted about buying cars with money before.
Click to expand...

:D
 
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