Gear ratio's

[Northnoble]

Has anyone ever changed any of their gear ratio's?

My gearbox is coming out for a refurb in a couple of weeks and I am tempted (if possible) to lengthen 5th and 6th.

Current feeling about the gearbox.....

1st, waste of time
2nd, excellent for acceleration
3rd, excellent for acceleration
4th, excellent for acceleration
5th, would prefer slightly longer gearing (but still use a lot on track)
6th......would prefer more of an overdrive for longer motorway sections.

Thoughts......?

[Bungle009]

If you change the final drive from 5.06 to something like 4.2, you will lengthen all the ratios by about 15%.

[phil4]

[quote="Bungle009"]
If you change the final drive from 5.06 to something like 4.2, you will lengthen all the ratios by about 15%.
[/quote]

So that has me thinking, could it bring 1st into play, essentially making it what 2nd is now, thus leaving room for 6th as that overdrive mentioned.

[Bungle009]

Existing ratios for atom 3 & 3.5 are :-

1st  3.266
2nd  2.130
3rd  1.517
4th  1.147
5th  0.921
6th  0.738

FDR  5.062

In my opinion the atom (particularly supercharged) is crying out for a taller set of ratios.  These are for a 1300kg civic type R, not a 600 kg Atom. 

[Bungle009]

Even with  4.2 FDR, first would still be ridiculously short, but at least cruising revs in 6th would drop from 4000 rpm at 80 to < 3500 RPM.

5th would be similar to the existing 6th with 6th being like a close ratio 7th.

[Bungle009]

Some scenarios if it helps


Final Drive 5.06      4.2      3.8

Mph/1000

1st            4            5          6
2nd          7            8          9
3rd            9          11        12
4th          12          15        16
5th          15          18        20
6th          19          23        25

[phil4]

So my thinking was that the thing you'd want to be careful of with just playing with the final drive is denting the acceleration.  I'm sure it's mainly power + lightness, but figure the gear ratios play their part.

I suspect the only way would be to try and replace 2 with 1, almost in a direct replacement way, that then leaves 6 where a 7 would be and everyone's happy, and we all have to start learning to use 1st again.

[8407jeff]

The car can certainly handle a taller FD--especially with a supercharger.  The drivetrain was designed to haul around a 3200 pound car.  Not, the 1500 pound Atom. 

[Bungle009]

I think as Jeff has posted a 300/310 could take a 4.1 final drive, whereas a 245 would probably be better suited to a 4.3 final drive.  In either case a shorter final drive (longer gearing overall) would improve the car significantly.

No impact to acceleration.  (Thanks Jeff)
1st becomes more useable
sixth becomes a more relaxed/cruising ratio, (but still with more acceleration than most cars can dream of)
Less frantic grabbing of really short gears in the middle of overtakes....
Presumably better economy on the way to and from trackdays

[fieldl]

I run the Quaife Sequential with the following ratios: 2.417  1.611  1.263  1.000  0.852
With a 4.750 FD

First is very low and most of my driving is done in 2/3/4 with fifth barely used either.
Wouldn't want it on the road it's a bit hair trigger and it still could do with the other ratios dropping a bit.

[Bungle009]

Hi Fieldl.  Do you mind me asking how much the quaife upgrade set you back.  PM me if you prefer.  I understand there is a lot of configurability WRT ratios, although for reasons which my brain doesnt understand, you cannot compare FD ratios with the Quaife sequential to the standard manual box.

[fieldl]

PM sent

[AtomMadStew]

It's a very nice & easy gearbox to work on - I've overhauled a fair few.

Stew

[Bungle009]

As you've worked on few atomstew, how long would it take to get the box out and change the final drive ratio.  I assume we are talking engine out ?

[AtomMadStew]

On the type R I could have one out and stripped in 45 mins no bother. I believe in the atom it's an engine out job.

If I remember right the FDR is closest to the bell housing end and would require all gears/synchro's removing using propper tools and a hydraulic press as some of the assembly is interference fit.


Stew