Ok. A bit of background information.

I have just had a T56 installed and Nizpro stage 2 kit bringing the power up to an easy 338rwkw (thanks Simon!). The first time I drove a T56 was behind a mk.2 XR8 ute and I was a little dissapointed however it seems to feel much nicer in my XR6, why, I don't know, maybe luck of the draw.

Anyway, the car goes like a cruise missile especially over 3000rpm however there in lies the problem. My rev limiter is set a 6800rpm which means I am pulling 91km/h at the end of first (if I really ring it out) as I still have the mk 1 3.45 diff ratio.

My question is has anyone with a higher rev limiter changed their diff ratio to a 4.11 and what have been your experiences? Also, how much did it cost and where from?

Alternatively, are there any mk.2's getting about with big power and a raised limiter and what are your thoughts on the gearing (as mk.2 has 3.73 diff ratio)?

By my calculations a 4.11 should see about 2103rpm in 6th at 100km/h, which isn't too bad considering 5th in a T5 is about 2045rpm. At 120km/h it would be about 2454rpm.

Changing up at 6400rpm with a T56 and 4.11 diff ratio would yield similar effect to changing up at 5800 with a T5 and 3.45.

T5 (3.45) T56 (4.11)

5800 6400

1 70 72

2 106 107

3 154 147

4 207 191

5 283 239

6 304

Obviously considering only the first few changes for comparison sake.

By the way I have had no issues with traction control and the edit and can highly recommend Nizpro to anyone considering a similar path.

Cheers,

Chris

Chris,

Great choice on the Nizpro kit. I think the Stage 2 kit with Edit is easily the best on the market.

The diff you’re referring to is a 4.10.

I’ve had the T5 plus 2 different T56’s (with different ratios), also 3.46, 3.73 & now 4.10 diffs.

I assume you’re running the Ford T56

I think Ford actually have a good set of ratios with the current T56 & 3.73, although I’d change 6th from .62 to .56, given the extra lower torque.

My Mal Wood prepared T56 runs the same ratios as the Ford T56.

Personally I think the 4.10, that I have now is too low (especially with a 5800 rev limit), a 3.89 (that does not exist) would be far better.

Part of the reason for my move from 3.73 to 4.10 was to protect the gearbox, and assuming I was going to run a brass button clutch, to make it easier to get off the mark in first in traffic, and preparing for a lift of the rev limit from 5800 to 7500 revs.

I haven’t driven the car with the 4.10 and 7500 rev limit, and I’m sure it’d be far better than with the 5800 rev limit.

My experience was that I got sick of changing gears so often with the 4.10, especially in traffic, and that the car would have had ample torque to carry the 3.73 diff. We were actually surprised when Ford released the T56 with a 2.66 first and 3.73 diff, the result being a slightly overall taller result than the T5 with 3.46 diff. We expected a 2.97 ratio first in the T56.

The other problem is 6th for me should really be a cruising/overdrive gear. I just find that the 4.10 with the .62 ratio 6th is nowhere near tall enough. It would work easily with a .5 ratio, although a .56 6th with 4.10 would be more preferable. With my first T56 I was running a .62 6th with a 3.46 diff, and cruising at 120kph was a sweet 2200 revs (it did it so easy, 160kph was just 3000 revs). With your Nizpro stage 2 you’ll find you make ample torque at 2000 revs for cruising.

By comparison, for me now it’s a way too high 2640 revs at 120kph. A 3.73 would give 2400 revs at 120kph, far more preferable.

Note these figures are based on my tyres, and I have a spreadsheet for rev to speed (and vice versa) for a gear/diff selection to calculate any required combination.

I only wish I was in Melbourne now to check out how the 4.10 diff works with extra revs and power. I’d suggest you talk to Simon about it, as he’s driven all these combinations. I’m likely to try the 3.73 again, and keep the 4.10 as a spare.

Brian

Chris,

with Cobra stage 2, what internals are strengthened ?

6800 rev limit seems high to me on stock internals

Brian's post answers your question, I would also suggest 3.73 as the best option.

Changing gear while ringing its neck is fun but short lived ... take it easy and enjoy the extra power

Chris,

Great choice on the Nizpro kit. I think the Stage 2 kit with Edit is easily the best on the market.

The diff you’re referring to is a 4.10.

I’ve had the T5 plus 2 different T56’s (with different ratios), also 3.46, 3.73 & now 4.10 diffs.

I assume you’re running the Ford T56

I think Ford actually have a good set of ratios with the current T56 & 3.73, although I’d change 6th from .62 to .56, given the extra lower torque.

My Mal Wood prepared T56 runs the same ratios as the Ford T56.

Personally I think the 4.10, that I have now is too low (especially with a 5800 rev limit), a 3.89 (that does not exist) would be far better.

Part of the reason for my move from 3.73 to 4.10 was to protect the gearbox, and assuming I was going to run a brass button clutch, to make it easier to get off the mark in first in traffic, and preparing for a lift of the rev limit from 5800 to 7500 revs.

I haven’t driven the car with the 4.10 and 7500 rev limit, and I’m sure it’d be far better than with the 5800 rev limit.

My experience was that I got sick of changing gears so often with the 4.10, especially in traffic, and that the car would have had ample torque to carry the 3.73 diff. We were actually surprised when Ford released the T56 with a 2.66 first and 3.73 diff, the result being a slightly overall taller result than the T5 with 3.46 diff. We expected a 2.97 ratio first in the T56.

The other problem is 6th for me should really be a cruising/overdrive gear. I just find that the 4.10 with the .62 ratio 6th is nowhere near tall enough. It would work easily with a .5 ratio, although a .56 6th with 4.10 would be more preferable. With my first T56 I was running a .62 6th with a 3.46 diff, and cruising at 120kph was a sweet 2200 revs (it did it so easy, 160kph was just 3000 revs). With your Nizpro stage 2 you’ll find you make ample torque at 2000 revs for cruising.

By comparison, for me now it’s a way too high 2640 revs at 120kph. A 3.73 would give 2400 revs at 120kph, far more preferable.

Note these figures are based on my tyres, and I have a spreadsheet for rev to speed (and vice versa) for a gear/diff selection to calculate any required combination.

I only wish I was in Melbourne now to check out how the 4.10 diff works with extra revs and power. I’d suggest you talk to Simon about it, as he’s driven all these combinations. I’m likely to try the 3.73 again, and keep the 4.10 as a spare.

Brian

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Thanks for the detailed response Brian and I certainly agree regarding the Nizpro kit. The car has plenty of power and feels great up top however I find first is so tall (91km/h) and by the time I can enjoy 2nd or 3rd I'm lookin at jail time lol.

I wish Ford used the first gear from the XR8 (2.97) as this would result in approx 81km/h @6800rpm as opposed to 91km/h. I too have set up a spreadsheet to help me decide. I have concluded the following (on 18" rims):

6th gear @120km/h

(3.45) (3.73) (4.1)

2118rpm 2290 2517

4th gear @ 80km/h

(3.45) (3.73) (4.1)

2241 2423 2664

3rd gear @ 60km/h

(3.45) (3.73) (4.1)

2185 2363 2597

alternatively 6400rpm in 1st:

(3.45) (3.73) (4.1)

85km/h 79km/h 72km/h

This difference is there however like you say, it may get anoying changing gears so often...then again, changing up at 6400rpm would result in similar speeds then changing up at 5800rpm with the T5 3.45 combo.

Any more thoughts or oppinions would be greatly appreciated.

Cobra, the only internals I have changed to date are valve springs and in the interests of durability my car was pulled back from 350rwkw to 338rwkw @ 15psi peak.

Cheers,

Chris

Chris,

As you know I have the exact combo you currently have (Nizpro Stage II, Ford T56 and OEM 3.45 diff). I do alot of highway kms, but also alot of around town stuff. I also do "hill and mountain work" and can say that with the Stage II there is so much low end torque you don't need to change the ratio up to 3.7 or 4.11. The 3.45 makes the car so easy to drive in either a lazy way, but cause the gearbox ratios are well spaced, there is no problem when you want to go to a racer style of driving. Unless you want to do so for a particular application, ie circuit racing or drags, then for best flexiblity across a majority of driving styles stick with the 3.4.5 ratio.

I was considering a 3.7 ratio, but I'm not going to bother. Now I'm going with a new engine (Stage 3+), and an appropriate boost in rwkW and torque, the diff ratio is even less important.

Cheers

Robin.

Thanks for the response xlnt6. I like your style re chasing more power however a rebuild is out of the question for me at the moment. I will keep considering my options at this stage.

Cheers,

Chris

I might be talking to myself here, but I think somewhere between a 3.73 and 4.1 would fill the gap beautifully. Does such a ratio exist that is suitable for the T? Say, 3.91?

Chris.

I might be talking to myself here, but I think somewhere between a 3.73 and 4.1 would fill the gap beautifully. Does such a ratio exist that is suitable for the T? Say, 3.91?

Chris.

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Unfortunately not.

Anyone care to consider why the ratios that are "such horrible crap" in an SS commodore, are now "so beautifully spaced", with a blue oval on the front? (2.66, 1.78, 1.3, 1.0@ 3.46 diff?)

Anyone care to consider why the ratios that are "such horrible crap" in an SS commodore, are now "so beautifully spaced", with a blue oval on the front? (2.66, 1.78, 1.3, 1.0@ 3.46 diff?)

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Who said they were beautifully spaced? I am in fact commenting that I think first is too tall hence why I am considering diff options.

Chris.