Gear Ratios

Morning Gents,

firstly apologies if this topic has cropped up before, my searching skills are inept and i could not find a clear reference to it.

unashamedly, my Jimny is road biased, although its off road abilities are most useful when taking engines onto the rallyfield, that is the most it does barring the bad weather we can get in Ferryhill (high up relative to the land around it and notorious for disproportionate weather).

a lot of the time this involves a run up the motorway for the wife, and 3000+ rpm at 60mph is too high, I'd like to get the revs down in the future when the warranty expires, so is there suitable components available to alter the transfer box ratios for high box or even the final drive?

I don't really want to fit taller tyres, as it really doesn't need the extra height, we're happy with it in that respect.

so this is just a curiosity or request for information at this stage.
cheers,
Paul.

I've read somewhere that it's possible to make a hybrid box using the 5th gear from a vitara just to make highway cruising more confortable, but you should look at it as a way of increasing top speed and not as a way of lowering the rpm, as the jimny is pretty gutless bellow 2800rpm. Heck, an m13a only really pulls after 4k

Decklandpt wrote: I've read somewhere that it's possible to make a hybrid box using the 5th gear from a vitara just to make highway cruising more confortable, but you should look at it as a way of increasing top speed and not as a way of lowering the rpm, as the jimny is pretty gutless bellow 2800rpm. Heck, an m13a only really pulls after 4k

Thanks Deckland,

to be honest, i'm not looking for increased top speed, or the ability to pull, as 60 is a cruising speed, and if i want to overtake i'll drop a cog or two for power, but the Jimny doesnt need power all the time, and I think it is producing wasteful power on motorways. its the latest VVTI 1.3 in the Jimny (2015) and its mid range is healthy enough, I do agree that if you let the redvs build up it can really pull, but i don't need that all the time.

Paul.

I think you'd be surprised how much a slightly taller gear will mess things up, both power and economy! 3000rpm really isn't that bad is it? I find transmission and road noise drowns out the engine at those speeds.

I think I'm right in saying the newer automatics have longer diff ratios than the manuals, so that might be worth looking into.

I mean no disrespect when I say this but you sound as bad as my dad, he insists on chugging about in the jimny with as little rpm as possible "because it is economical ". It is not good for the engine and certainly not good for the mpg. When i took over the day to day running of the jimny it would barely rev past 3000 it was that choked up with soot and it was a good day if it got 30 to a gallon. It needs to rev and for a modern small capacity petrol engine 3000 rpm is nothing. Now it revs cleanly to the red line and regularly gets over 40 mpg. Also, making it work at motorway speed at some low rpm will be impossible because it simply doesn't have the right torque curve to do that. It's a square engine, by that I mean the power and torque are about equal unlike a diesel which is rectangular meaning that the torque is disproportionately higher than the power and is developed lower in the rev range, a jimny just can't cope with high speed low rpm. Accept it as it was designed and use it accordingly and it will be a faithful companion that will surprise you with its ability to do almost anything.

thanks 11/60 its a very fair appraisal,

it may surprise you then that I am a design and development engineer in the automotive sector, and prior to that designed engines for a prominent engine manufacturer. I currently manage an engine test/development dynamometer.

when we're talking of dropping revs down, i'm talking 250-500rpm max at 60mph.

its not an exact comparison, but two vitaras i owned, the 16v had straight through fifth, in that fifth was 3000rpm at 60, whereas the 8v one was 2500 at 60, and the cruising performance of the 8v was much more refined, and it did not struggle anywhere, the 16v was obviously quicker, but it had quite a lot more hp.

anyway, thank you for the constructive advice.

Paul.