T56 + 4.1 Diff = Quicker 1/4 Time?

[GreenXR6T]

I've got a T56 in a BA 1 with a 3.45 ratio diff and have ran a 12.5 @ 119mph.

Would a 4.1 ratio give me a quicker 1/4 mile time without any more mods?

I'm told I would need another gear change which would slow things down a little.

Would a 2nd gear launch be out of the question?

Is it worth going to the trouble of changing it over?

Rob

[senna_T]

Hey Rob, I'd probably just go to a 3.73 like the BA2's. If you go to 4.11's 1st gear will be short as hell and you would struggle to get power down. Plus the highway cruise would be up around 3000rpm IMO.

When are you gonna head up for a run next, I might be able to lend you some sticky tyres instead of those 19's!

[bcl]

I have had the 3.45, 3.73 and 4.10 diffs over the past 4 years.

As a guide, at 6000rpm you will obtain the following speeds in 4th gear:

3.45 diff 130mph

3.73 diff 120mph

4.10 diff 116mph

So you will max out of 4th gear before the end of the ¼, although I’d guess you’d do a better time, but more likely on better tyres.

2nd gear launch would put major stress on drivetrain, as something has to give, as the 1st gear ratio is 49% lower than 2nd. (2.22 / 1.78).

4.10 diff feels much better on the street, although fuel usage will probably go up, and highway economy will suffer. You will get wheelspin quicker!

Brian

[ETM]

dont forget the diameter of the tyre you are using when looking at ratio changes, you could use a 4.1 ratio diff and use a taller tyre to find a middle ground.

use a calculator like this to work out what suits you best

[GreenXR6T]

Hey Rob, I'd probably just go to a 3.73 like the BA2's. If you go to 4.11's 1st gear will be short as hell and you would struggle to get power down. Plus the highway cruise would be up around 3000rpm IMO.

When are you gonna head up for a run next, I might be able to lend you some sticky tyres instead of those 19's!

Ta

The reason I asked is I've got a 4.1 here waiting to go in.

I just wanted to know if it was worth the trouble.

I want to run the 19's for a few more passes, then I'll look at MT's thanks anyway Pat

I have had the 3.45, 3.73 and 4.10 diffs over the past 4 years.

As a guide, at 6000rpm you will obtain the following speeds in 4th gear:

3.45 diff 130mph

3.73 diff 120mph

4.10 diff 116mph

So you will max out of 4th gear before the end of the ¼, although I’d guess you’d do a better time, but more likely on better tyres.

2nd gear launch would put major stress on drivetrain, as something has to give, as the 1st gear ratio is 49% lower than 2nd. (2.22 / 1.78).

4.10 diff feels much better on the street, although fuel usage will probably go up, and highway economy will suffer. You will get wheelspin quicker!

Brian

That's a good guide thanks Brian

So I'd probably be looking at 5th at the end of the run then, I'm still in third atm.

Maybe a short shift to second might be worth it?

Economy etc doesn't matter too much, it's sh1thouse now anyway.

I'd like a more impressive feel on the street.

[GreenXR6T]

dont forget the diameter of the tyre you are using when looking at ratio changes, you could use a 4.1 ratio diff and use a taller tyre to find a middle ground.

use a calculator like this to work out what suits you best

Thanks Leigh, I'll do some calcs later (not my strongest subject)

That will mean slicks and a few breakages though.

I don't know if I want to go that far. Street slicks would be my limit I'd imagine.

[bcl]

Ta

The reason I asked is I've got a 4.1 here waiting to go in.

I just wanted to know if it was worth the trouble.

I want to run the 19's for a few more passes, then I'll look at MT's thanks anyway Pat

That's a good guide thanks Brian

So I'd probably be looking at 5th at the end of the run then, I'm still in third atm.

Maybe a short shift to second might be worth it?

Economy etc doesn't matter too much, it's sh1thouse now anyway.

I'd like a more impressive feel on the street.

It will feel like your torque has jumped say 15%, although in reality it hasn't.

Getting of the mark when driving in traffic will appear easier, as there won't be as much stress on the clutch.

Where you come to roundabouts, you will find you will stay in 3rd (if that's what you were in), rather than dropping to 2nd.

You will more likely stay more in a taller gear rather than changing down.

On the other side of the coin you will have to shift quicker to the next gear, as it will come earlier, and you will be "busier" and more active with your driving style.

Note it is a big jump from 3.73 to 4.10. Logically there should have been a 3.89 ratio gear, which would be the perfect compromise, and I thing would have been the best diff ratio for the car.

Brian

[GreenXR6T]

I remember the old days when it was a cheap, easy way to better 1/4 time.

That was with a lot less HP and nowhere near a 11-12 sec pass

I might whack it in and see how it goes. Brians description of streetability is a good enough reason to try it.

It has 390rwkw but it doesn't feel like it. I've been in Franks car (TURBO4LT) which has around the same power and it's a totally different car. Mine won't break traction in third, his has no trouble at all.

He has the same diff but different T56 ratios

At worst it will only cost me a few days labour if nothing goes wrong.

[senna_T]

Keep us informed Rob, I can see us doing battle for the quickest Manual Sedan in NSW!

[bcl]

Just remember Rob that if you go a more aggressive tune AND change diff ratio you may have really trouble keeping it under control.

I have a more docile tune below 4000rpm then all hell breaks loose, so I'll only get into trouble if I do something stupid.

Better to look at your torque graph, not the power graph, if you are comparing with Franks.

Brian