Gear Ratios

[gmunro]

Hi guys,

Due to significant damage to the lay shaft in my 4.2 Series 1 all-syncro gear box, the engineering firm who rebuilt the gearbox for me changed all the gear cogs etc resulting in new ratios ( they told me they couldn't get original or near original close ratio gears ). The gear ratios are as follows -

Original Ratio New Ratio

1st 2.68 3.04

2nd 1.74 1.97

3rd 1.27 1.44

4th 1 1

What difference will I notice with these new ratios?

My diff is still standard with a 3.07 ratio. Should I consider changing this in view of the new gear ratis?

Help and advice would be most gratefully received.

Yours aye,

George

[gmunro]

Hi guys,

I have posted this again as the ratios were not laid out clearly and the formatting I input was not carried forward when I posted originally. Hope this is a bit clearer!

Due to significant damage to the lay shaft in my 4.2 Series 1 all-syncro gear box, the engineering firm who rebuilt the gearbox for me changed all the gear cogs etc resulting in new ratios ( they told me they couldn't get original or near original close ratio gears ). The gear ratios are as follows -

Original Ratio/New Ratio

1st 2.68/3.04

2nd 1.74/1.97

3rd 1.27/1.44

4th 1/1

What difference will I notice with these new ratios?

My diff is still standard with a 3.07 ratio. Should I consider changing this in view of the new gear ratis?

Help and advice would be most gratefully received.

Yours aye,

George

[Mich7920]

Hi,

Your gearbox is shorter than the original for the 1,2 and 3rd gears and between 3 and 4 the hole is bigger.
As the XK has a lot of power, it couldn't be a problem for the 3/4.
Perhaps you'll must get more rpm on 3rd gear before taking the 4th to prevent this hole.

For an idea:
Original box / 3000rpm / 185VR50
1 : 46 km/h
2 : 71 km/h
3 : 98 km/h
4 : 124 km/h

Your box / 3000 rpm / 185VR15
1 : 41 km/h
2 : 63 km/h
3 : 86 km/h
4 : 124 km/h

Mich

[malcolm]

Wouldn't change the diff. Top gear is still 1:1, so you'll have the same mph/revs for cruising in fourth. Shame the changes lower down give you less mph/revs; the torque on these motors is such that the taller gears suit better in my view.
Won't make too much difference though Might get slightly more acceleration in lower gears? The jump when you go to fourth will be handled by the torque. Thing to do I guess is drive it and see what it's like!

[christopher storey]

Your old gearbox was the most desirable one, an EJ series with the close ratios. The ratios you now have sound like a set compiled from cogs for a mark 2, ( and probably a 2.4 at that ) and the ratios are far wider than is desirable. I have examples both of an EJ box and of a series 2 with a KJS box. Even that does not have 2nd and 3rd ratios as low as your new ones, but it makes 2nd much too low for overtaking purposes, with an effective usable maximum with 3.07 final drive of about 55 mph or not much more . Before installing these ratios I should make a renewed effort to find a closer ratio gearset

For information, the ratios on the later box in the E ( KE/KJS series ) were 1.00 ; 1.389 ; 1.905 ; 2.933

[gmunro]

Gents,

Many thanks for your replies. I'm not overly techy and some of the info went a little over my head I'm afraid ! The new ratios have already been fitted to my gearbox but I still have the original gears. The damaged part was the layshaft. Can I use any of the original cogs with the new layshaft or do they have to be fitted as sets? I have a feeling that the new cogs were suitable for a Healey or something similar.

Perhaps I should add that my car is not a "show" car. Rather, it is a driver (albeit in great condition!) and I want to drive and enjoy. I intend touring both within the UK and the continent and what I am looking for is a car that drives well, moves through the gears well and you know the rest.

Not being knowledgeable about gear ratios and the effects, I am turning to this forum for your most valuable advice and from the response so far, I realise that there is a vast amount of knowledge out there and I am really grateful.

More advice please??

Yours aye,

George

[mgcjag]

Hi George...what was the engineering Co that done the work for you asked to do.......a face to face chat with them would be advisable.......especially with the knowledge on ratios you pick here........if they are a decent firm im sure they will work with you to get the results you want....

[gmunro]

The firm was Hardy Engineering. I'll make some enquiries with them to see what they suggest. Thanks for the advice.

[graemea]

Your intermediates are still slightly taller than a standard 3.54 axle car.

Not the end of the world.

Cheers

Graeme

[Hugo]

To my mind, the leap from 1.44:1 in third to 1:1 in 4th sounds uncomfortable. Sure, she will handle it, but I feel that if it were my car it would be a constant source of irritation to me. The gaps between gears normally get smaller as you go up - yours are getting bigger!
That guy in Florida - Paul wossisname isn't it? He has some very useful stuff on his website about ratios, but I can't remember the name of it I'm afraid! :(