4.363 Vs 4.375 Ratios.

[R32 TT]

Hi guys,

Just looking to lower ratios in my 32 GTR from 4.1 down to the 4.4 region. Mostly I see reference to the 4.375 ratios out of GTS4's. However I've managed to get hold of a 4.363 unit for front (and would need to find a matching rear). Obviously the ratios are more or less exactly the same, but they get there slightly differently:

4.363 = 48:11

4.375 = 35:8

I am just wondering if anyone has had any experience if one is weaker than the other - or if there is any reason you would use on in favour of the other?

cheers!

[GTSBoy]

Where did you get a 4.363 for the front? What vehicle is it from?

FWIW, the 4.363 is the standard R32 GTSt diff, so it's strong enough. It's not as though the CW&P teeth are the weak spot in any of these diffs anyway.

[R32 TT]

I think its come out of a R34 GT-four. I purchased it complete with the 4WD sump etc.. (so same at GTR 4WD sump etc). Just my concern being it came out of a NA car - more teeth on CW&P so perhaps weaker? Or perhaps more efficient and less heat.... but good to know that typically they don't break - so I assume I should be ok with it.

(mind you I just busted a chain in a fully rebuilt transfer case - and you don't hear of that often either)

[KiwiRS4T]

4.363 are to be found in R33 and R34 GTS-4 25DE and also Stagea awd 25DE (not very common in Australia - most are DET).

[XKLABA]

Correct, more teeth = weaker, I had this very discussion with Terry@Award when considering using the GTR drive line for offroad racing use

If I'm correct you make a cubic fark load of power and torque, why the change to lower ratios ?

It is something I personally am dead set against for cars making big power unless for dyno queen or auto backed drag queen

[GTSBoy]

It is something I personally am dead set against for cars making big power unless for dyno queen or auto backed drag queen

Well, as a general aim/goal that people have to just go lower ratios because it "accelerates faster", I tend to agree. Good old Corky Bell used to go on about fitting taller diff gears when adding a turbo so as to take advantage of the torque and also to make it spool by loading it up. But in the larger scheme of things, assuming you are trying to be as professional about (say) drag racing as you can be, then there might be reasons to do it, auto or manual. If your rev limit and power production behaviour have you crossing the line at the wrong point in one gear (say you must sneak a gear change in just before the line and don't gain any benefit from having to do it), you might well benefit from a shorter overall ratio and possibly go faster.

[XKLABA]

Don't get me wrong I know all the theory behind it I have also seen first hand the practical side of going both ways for motorsport use with the BSM team and that is why I am dead set against it

I was just wondering why Matt was considering it for his own particular reasons cause IIRC he has a 3.0 which means he will have more torque then one could ever need ( not to be mistaking with want ) and for anything but dyno or auto backed drags the fighting for traction and inefficient use of said torque makes it not worth IMO, which is why I asked the question

[R32 TT]

Interesting your feedback on the BSM team there Mick and yes I can see why sometimes longer legs and less gear changes can help - so I'll have a think. Do you reckon that car is quite 'tuned' to a specific track? Or did that work across the board at all circuits it goes to?

Over here in Perth we don't have tracks with very long straights like say PI, and so rarely would I have a place to hit more than 230-240km/hr (back straight of Barbagallo). Even with 4.3 I can easily make that speed.

I'm not really into drags, so it doesn't bother me if I needed a gear change to 5th on the 400m.. The best part of the drags is the left hander at the end... And in any case on the drag strip you are never out of the power band.

So for Drags and any larger flowing circuit, you rarely come down below 4000rpm anywhere and the power is just always there..

But over here, aside from Barbagallo circuit, there are other Tarmac Rally Sprints at various venues which might see 200km/hr tops in some parts - but have tight chicanes and hairpins as well - sometimes taking me down to 2500-2700rpm in 2nd but not quite wanting 1st gear either. EVO's rip out of these short corners and you can see it in the way they are geared. This is the main reason I am looking at it, to try and get some slow corner exit speed when up against EVO's and supercharged Lotus' etc..

I figure anything that improves in-gear accel is a good thing and as a bonus I figure its got to be easier on the gearbox and 3rd.. giving it mechanical advantage and less stress.

Just really gathering parts at the moment - so I'll have a think before I jump. But didn't want to go to all the effort with 4.363 and then get told "ahhhh mate - you should have gone 4.375!!" (you can hear it can't you...)

[warps]

As you say, the 2 ratios are almost dead spot on (in fact, different tyre pressures, or tyre wear will probably have as big an impact on gearing as that small change in ratios.

In theory, low numbers on pinions (anything less than about 9) means that the tooth profile is less than ideal, and you get less efficient meshing of the pinion and gear. This leads to more noise and heat, and possibly more wear. However, as stated by others, the larger number of teeth means you have narrower tooth pitch (assuming that the CW&P's both take up the same amount of space). This means the teeth are weaker by default (about 30% lower tooth pitch).

For strength, you'll be better off with the 4.375. For efficiency, the 4.363 may actually be better.

[tricstar]

Those dam evos on the tight rally sprints and state sprint circuits.

Sequential with short ratios should help that Matt.

[R32 TT]

Haha - I just can't bring myself to go a sequential Rich - there is just something about driving a clutch pedal and H Pattern which feels like driving..

I know sequential will be faster - but it takes something away.. maybe one day I'll change my mind.

pesky EVO's - will never catch the front runners, but might pick a few off..