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Xr8 Diff Ratios!


fordboy1981

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I worked out if you put 3.73:1 ratios in the back of a BA XR8 you would end up getting the same freeway rpm as a STOCK XR6T!!!

(this is all manuals of course!)

XR6T with standard 3.45:1

2.95 - 11.49 - 68.94km/h

1.94 - 17.48 - 104.88km/h

1.34 - 25.30 - 151.80km/h

1.00 - 33.91 - 203.46km/h

0.73 - 46.45 - 2150rpm@100km/h

XR8 with 3.73:1

3.38 - 10.27 - 61.62km/h

2.00 - 15.68 - 94.08km/h

1.32 - 23.76 - 142.56km/h

1.00 - 31.36 - 188.16km/h

0.68 - 46.12 - 2150rpm@100km/h

I reckon you could EASILY tear an XRT a new one down the quarter with these gears...also I've been quoted $450 supply and fitted c/o for these gears.....a VERY CHEAP mod indeed...

I donno about warrentee though, but I can't see it should be a problem, if anything it's putting LESS load on the drivetrain!!

think of a XR8 ute with 3.73:1, a herrod exhaust, filter, uni-chip....13 flats!!!

anyhoo, just some food for thought.

Dave.

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So now, what would happen if we put that ratio into the XRT? I rekon quicker 1/4 but probably slower 0-100 because you would have to grab 3rd before 100km/h whereas now we can stretch 2nd out to 105km/h. $450 is pretty cheap though!

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yeah but in REAL TIME!!! the 0-100 time is useless, I mean the XR8 might be quicker to 90 and quicker to 110 but slower to 100.....so you would say it quicker, yes??

this was the problem with the old EF/EL XR6 manuals, they needed 3rd to hit 100, like JUST, they would do like 98km/h@5700rpm in second....so they were a far bit quicker then they're 0-100 times suggested....

if you lined up a XR8 with 3.7s in it against a XR6T, the T wouldn't know which way it went. I mean the XR8 can JUST keep up by like half a car length with a T and that's the XR8 have 3.23s. So you're drop the ratios by 1/2 a ratio, that will make a hell of a difference......all for $450.

Dave.

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Dave, you might end up a little slower down the quarter than a standard XR8 due to having an extra gear change just before the line if you use 3.73s.

Furthermore, having the XR8 revving the same as the T at 100 kph is still not going to help you in a rolling start top gear drag from this speed, as the T simply has more torque at those revs than the Boss 260. This is a fact the V8 boys don't like but simply have to live with heheheh.

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Ok now. Well this may not be 100% accurate however.

Using the 3.73 ratio I came up with 0-60mph of 5.95, with a 1400RPM clutch dump and a 1/4 mile of 14.0. Using Ford 3.23 ratio I came up with 0-60mph in 5.47 with a 1600RPM dump and a 14.1 1/4 mile.

This was done using a program called cartest. Could be more accurate if someone knew the coefficient of drag and the % weight over the front wheels. As well as tyre width. I put 200mm (8") on the 18's.

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sounds like a neat gigger you got there....but the only reason a lower diff ratio would make a car accelrate slower then a higher one is if it causes excesive wheelspin.....or of course if the engine itself won't literally accelerate fast enough!!!! but considering even big heavy V12 Jag engines with 6500rpm redlines take less then .8 of a second from idle to redline, I don't think that's going to be a problem....

now maybe traction is the problem, maybe that's why ford put 3.23s in it instead of 3.45s like in the T......but there's one way to find out and I will be giving it a go....

I just wondering if anyone else had thought of/tried it already..

Dave.

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