Craig, Neil has a good point. If you can be arsed, drain the rear diff oil & count the teeth, find out what ratio it is & go from there. Or, you know what ratio your gearbox is (4.11), get a known 4.11 LSD diff, swap it over and try again on the dyno. I am happy to help swap the diff over if you need a hand?

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Cheers,

Simon.