Gear ratios

sambo · #1 (**permalink**) 11-26-2013, 04:42 PM

I'm doing a bit of a thought exercise here, interested in your opinions.

Working through the gears in my Cobra, the L98/T56 combo with 3.692 final ratio is kind of "busy". Thinking ahead to a proper tune and maybe a cam, I'm going to be swapping gears even faster. I've had a look at alternate gearbox ratios and there's a version of the T56/TR6060 with taller gearing (also comes in a Magnum version with many improvements - shift quality being a big one).

I found a calculator and entered all the specs for my current setup on the left (below) and the alternate gearing on the right.

The top of second gear at 95 is spot on, so it seems accurate. Looking at the right hand side, I'd get a bit more out of the first three gears.

Other than the 0-100 dash needing only one gear change, am I really going to benefit from taller gears? I know that highway cruising rpm will increase a bit.

Thoughts?

vatdevil · #2 (**permalink**) 11-26-2013, 06:09 PM

Tough to offer opinion without knowing motor build and intended usage. In general, the 6 speed trans are intended for use with shorter final drive ratios than your current 3.69.

sambo · #3 (**permalink**) 11-26-2013, 07:24 PM

Hi vatdevil. It's a Holden spec (Australian) 6.0L L98 which is very similar to the LS2. Intended usage is 95% street duties with 2-3 circuit track outings per year. Maybe in a heavier car the shorter final drive would work, but it would be ridiculous in the little Cobra. I'd go a taller final ratio if they were easy to come by or an easy swap - mine uses the helical LSD from the Nissan R34 Skyline / 200SX.

stiffy · #4 (**permalink**) 11-26-2013, 11:22 PM

Sambo,

As you know my set up is similar to yours, having a cam/tune does

Nothing to alleviate the busyness of the final drive.

I changed my diff from 3.9 to 3.5 as I thought the 3.9 was too busy,

I should have left it alone ( people have been telling that for ever

) the 6

Speed is useless on the highway and the 3.9 would have been better on the

track.

The actual redline is closer to 7000rpm so take that into consideration also.

Stiffy

Gav · #5 (**permalink**) 11-27-2013, 12:21 AM

IMHO, I reckon your 3.7's would be spot on.
I had 3.9's and they are too short.
I have 3.45's now and they are a little too tall.
3.7's would be just right...

Modena · #6 (**permalink**) 11-27-2013, 02:11 AM

Thinking less about the specific car and more about the diff/tranny combination, I agree with Gav. SS Commodore with this combo uses 3.45 and is a little long, HSV's are 3.7 and are just right. HSV dropped the GTS from what used to be 3.9 to now also be 3.7

With 3.9 in the Cobra you won't get traction.

What do you mean "busy"? Do you mean you're shifting gears to much? With L98 power in a 1100kg car you shouldn't be!

Tenrocca · #7 (**permalink**) 11-27-2013, 03:21 AM

Don't like changing gears? Put in an auto and a beaded seat cover. I find my l76\t56\3.45 about right. 110 on the freeway just idles along nicely in 6th, but a lot have said its too tall. Might just have fluked a good tune for that ratio.

sambo · #8 (**permalink**) 11-27-2013, 04:33 AM

I'll put it another way. On a track doing speeds between 60-200km/h. The car is light enough and the engine makes enough torque that slightly taller/longer ratios wouldn't slow it down. Taller ratios mean you spend longer in each gear, power is more usable. Less shifting.

I'm not touching the final ratio, it's a torsen centre and seems to do what it's designed for. I'm thinking about a tougher, much more refined gearbox that is available with the std Commodore ratios as well as the taller ratios in the screenshot above. It may also provide a better location for the shifter - waiting to hear back from Mal Wood on that one.

Rog246 · #9 (**permalink**) 11-27-2013, 04:46 AM

Sambo, as an aside what oil are you using in your g/box?
All the blokes on the Aus ford forum (with few exceptions) swear by Mainlube in their 'boxes. It apparently smooths gear changes out incredibly and cures rollover noise in the 1st motion shaft (imput shaft) that the boxes are prone to.
I'm certainly going to use it in mine.
Rog

gjkrv8 · #10 (**permalink**) 11-27-2013, 04:51 AM

Sambo, I have the T56 and 3.45 and I would recommend working with what you have already. 3.7 would be a little punchier, but the 3.45 is ok enough. cheers gregg

LJ47 · #11 (**permalink**) 11-27-2013, 02:33 PM

Leave it alone when you get more power you are going to be more busy anyway. If you want to be lazy get an auto like Gav

byroncobra · #12 (**permalink**) 11-27-2013, 02:56 PM

Thanks for this discussion, it's something that I've been meaning to address with my car, same T56 box but with (so i've been told) the Nissan 4.3:1 diff.

I don't mind the busy box on the road really but my main issue is on the track as a shift to 5th is needed half way down the straight to stop the rev limiter bouncing on redline. I've enough to do screaming into turn 1 without getting that shifter across the gate to 4th and as I've done, grabbing 6th instead....makes for a whole lot of footwork without engine braking

Anyway, having discussed going to a 3.something diff with a few guys, something that was mentioned was a loss of low to mid range torque with my Trickflow topend engine mods.

Thoughts?

The consensus seems to be a 3.7:1 may be the best compromise.

Any suggestions on where's the best place to source Nissan diffs?

Cheers

LJ47 · #13 (**permalink**) 11-27-2013, 03:44 PM

Greg the T56 should centre to the gates 3rd and 4th easily try slowing the shift down and use the palm of your hand instead of chocking the stick to locate centre (keep it clean boys trying to help) regarding final drive in my option if its fine on the road leave it. Instead practice shifting regarding turn 1 I presume its Winton or Wakefield do a short shift to 5th and give yourself more time if you ask around using more than 2 gears at Wakefield or Winton is still ok.

byroncobra · #14 (**permalink**) 11-27-2013, 07:46 PM

Thanks for the advice LJ, you're right about trying to slow things down a little I spose....practice.....practice. The shifter relocation kit is a bit stiff too, so feel is an issue.

Quote:

regarding turn 1 I presume its Winton or Wakefield do a short shift to 5th and give yourself more time i

Both Wakefield and QR give me grief, are you saying shift earlier into 5th on the straight

Quote:

if you ask around using more than 2 gears at Wakefield or Winton is still ok

seems most only use 3rd and 4th but with 5speed boxes I think

stiffy · #15 (**permalink**) 11-27-2013, 08:15 PM

Byroncobra,

My T56 has been mofified by Aussie Mike (relocated shifter

and stronger shift kit ) and I use DEXIII auto tranny fluid.

The T56 seem to be a more notchy box (compared to a T3550)

JL47 is correct the slower you shift the better they are...........

STIFFY

Gav · #16 (**permalink**) 11-27-2013, 08:21 PM

Do you spit on your palm first too Stiff?

stiffy · #17 (**permalink**) 11-27-2013, 09:43 PM

Gav,

I said Notchy Box..............

STIFFY

Gav · #18 (**permalink**) 11-27-2013, 09:52 PM

You could spit on that too

stiffy · #19 (**permalink**) 11-27-2013, 09:59 PM

yes you can,

or do a Rocky and spit somewhere else

LJ47 · #20 (**permalink**) 11-27-2013, 10:19 PM

Greg
Yes change gear into 5th down the straight their is nothing wrong with a short shift if it sets up the next corner and makes it easier for you. After all we are all hobbyists not professional drivers. When I was at QR earlier this year I tried 2nd through to 4th with 4th bouncing on the limiter. Helpfully next year with the new motor and a little more power could be the same might even have to grab 5th down the straight and do a down shift into 1. What I am trying to point out is sometimes its better doing what works for you.