Floppy

I've been looking around on the US forum and know that some people on here have used the KIA diff with some success but know that this is better for faster acceleration but am I right to understand you lose a fair bit of top end?

They are talking about a 4.30 and a 4.44 from an MX5 is an option and it doesnt whine like the 4.57

Can someone confirm this for me as well as give me any ideas what sort of MX5 they are off? If its not too much money I may give it a go as I have a spare diff laying around.

Also, if there are any advantages or disadvantages of each then that would be good to know too...I'd like the car to have some extra pace but also don't want it sitting on cam at 80-90mph.

TIA

Ultra_Nexus

Believe it or not, the MX5 internals are the same as the S2000. I have been looking at MX5 running gear for my next project, but the best gear I have seen is a 4.1 from the 1.8.

lovegroova

Floppy, have a read of this before you decide to do it,it makes very interesting reading:

https://www.s2ki.com/...st__p__22393092

eSeM

Only 2 of the results in the table linked to can be used to make a direct comparison, the 30-60 and the 30-120 where the gear changes are the same and in both cases the lower gears give better acceleration.

Choosing other speed differentials you will get different results and if the gear changes are the same the lower gears will be quicker.

lovegroova

The gear changes are not the same, which is a truth and is very relevant to the discussion.

You are quite correct to emphasise that different final drives will improve your acceleration for some parameters and worsen it for others (which is very clear from the data).
I've just been looking on the site where these were derived, and there is a new graphing facility which shows speed, distance, acceleration and gap over time - well worth a look before forking out a lot of money.

Acceleration from 20mph



And distance covered from 20mph:

eSeM

Same can be said for the standard ratio .... it is simple physics, the lower gear will be quicker overall.


I would have thought the most important 'real world' acceleration would be something like 40 - 60 when you need to overtake, I rarely go into positive boost other than when I am overtaking.

zzkamikazezz

When I switched to 4.44 gears it was certainly a noticeable improvement due to the extra torque at the wheels, it was about the same as when I had my car flashpro'd and gained a good bit of midrange with the lower vtec. 8% is what is gained I think with a 4.44.

Cruising at 4600rpm @ 80 can get a bit annoying, I wish we had a 7th gear! 4.77 are meant to be more transformational, but for cruising it would become tiresome for me and I would be worried about having to change gears through corners on track days more often.

Theses may help:


https://www.s2ki.com/s2000/topic/100...#entry22351153

I know those graphs can show that not much is gained, but I found a 4.44 has really added to the drivability, especially when paired with a remap.

lovegroova

You need to change gear in normal driving, so it's negated, as clearly shown.


Good point. 40-60 is quicker with a stock FD as you can do it all in 2nd with no gear change

eSeM

A 4.44 final drive will be quicker than stock from 40-60

A lower final drive is good for b road blasts and tracks .... but it is shit if you do a lot of motorway driving.

lovegroova

And a 4.57?

That's not true regarding tracks as it varies from corner to corner and circuit to circuit (see kamikaze's comments about shifting mid-corner). For some corners a longer FD will be quicker than a shorter once and vice versa.

As you say, it's simple physics...

But for Floppy, if you are going drag racing, then definitely get a shorter FD.

Otherwise, do some research (hopefully the discussion above helps) and don't assume that a shorter FD will give you "better acceleration". It does in some scenarios, but not in others.

Your car will certainly feel faster with a shorter FD because the revs rise more quickly, so your body fools you into thinking that there is a big difference in acceleration, and that may well be a reason to go for it as the car feels more tractable, so is more fun.

As Steven says, it's a lot less fun on the motorway (and at the pumps), so consider that too.

Good luck