[Stuey]

Ok, a bit of background first:

For those that don't know, my car is a 1997 SV420 Vitara manual, originally fitted with 215/65/16 wheels and 4.6:1 (? from memory) diff ratios. I've since swapped out these diff gears for 5.125:1 ratio. I'm unsure of the SV420 gearbox outputs (but I would like to know if anyone has that info).

The car has recently undergone an engine transplant and been fitted with a H27A motor paired with a manual gearbox from a SV620. Diff ratios are still 5.125:1 but wheels are now 255/70/16. Once again I don't know the output ratios of the SV620 manual box (and would like to know).

The problem is...... My car has found a ridiculous appetite for petrol and Suzistore have questioned my diff ratios as my vehicle now sits on 3000rpm at 100km an hour and they believe this may be the cause given they feel it is revving too high. My speedo reads true in the vehicle when compared to a GPS (within 1-2%). They are suggesting swapping back to SV620 diffs which I assume are also 4.6:1 but I'm worried this will throw out my speedo and low range.

Long story short, can someone provide me with the output ratios of the gearboxes in question and do a few sums for me (as I'm not too sure what calculations are needed) to determine the best/required setup given my current wheel size etc.

Any help appreciated.
Cheers
Stuey.

[tanshi]

just ran your specs through my calc and the gears look like they are same as all vits
1st 3.652
2nd 1.947
3rd 1.423
4th 1.000
5th 0.864
reverse 3.466

if you drop to 4.6 diffs you will come down to 2700 in 5th at 100. makes you lowrange 30:1 though

[atari4x4]

haven't got a lazy o2 sensor, checked the error codes?

could the economy issue be due to you using the extra power you've now got on tap, how many litres per 100kms are you getting?

[Stuey]

atari4x4 wrote:

haven't got a lazy o2 sensor, checked the error codes?

could the economy issue be due to you using the extra power you've now got on tap, how many litres per 100kms are you getting?

18-20L/100km. Ive tried driving like an old man but made no difference.

Had an O2 code flash up once whilst driving on a cold night but not happened since.

I just want some numerical facts to take back to Suzistore to back up the fact I feel it isn't the diffs being the problem. If I can prove the gearing is ok, then it's on to the next possible solution.

[Stuey]

tanshi wrote:

just ran your specs through my calc and the gears look like they are same as all vits
1st 3.652
2nd 1.947
3rd 1.423
4th 1.000
5th 0.864
reverse 3.466

if you drop to 4.6 diffs you will come down to 2700 in 5th at 100. makes you lowrange 30:1 though

Thanks Tanshi.

Can you tell me what my low range is at the moment?

And what would my engine be revving at in original config with 4.6 diffs on the original 215 tyres at 100?

I'd like to know what a stock SV620 sits on in 5th at 100 for comparisons sake.

[tanshi]

by the looks of it 30:1 is about standard for a vit

by my specs standard engine and gearing on 215/75 15s will be reving 3013 at 100 in 5th

as far as i know there would be no difference between the sv420 and sv620 as the diff gears are the same.

[Stuey]

Guess is comes purely down to actual proof then that the SV620 box has the same output ratios as the SV420. Had a look in my Haynes manual but found no reference. Nor in the owners book.

Where are you referencing your numbers Tanshi?

[tanshi]

you dont need any more proof.

you say your doing 3000 at 100kms an hour right now right?

.864 over drive in 5th
1:1 high range in the transfer
5.1 diffs
tyres with a diameter of 763.4 mm

these sums give you just over 3000 at 100 ks

thus these sums work out to be the same as what your getting in real life numbers so the gearing is correct

[tanshi]

i can also tell you that my GV3 with the H27 motor in it is doing around 2800 give or take at 100 in 5th

[Stuey]

Thank you and thank you. Appreciate the input fellas.