I wasn't expecting this but when I moved two Sierra diffs one was obviously heavier.

Both 7" diffs but the 3.62 has small input shafts. The other is a 3.92 diff with larger input sockets but no Lobro adapters in place. So I would have guessed quite similar in weight.

3.62 diff weighed 18kg and the 3.92 diff weighed 21kg. Both emptied of oil but 3kg difference. Now if you take into account the smaller diameter driveshafts with no Lobro adapters that's got to be a good 5kgs difference just there?

May not seem significant to some but to save that sort of weight on my car elsewhere would require much thinner body work or an alloy gearbox casing. Both quite expensive options in comparison.

Trouble is though, the ratio of your diff is dependent upon which engine you're running. Simply swapping the 3.62 for a 3.92 to save 5kg will also mean sacrificing top end speed.

It is interesting to know the weight difference though........

Phil

The weight difference is probably, mostly, just in the drive flanges.

I fitted the lighter diff and lighter shafts on my car. For lightness by the way, in case that wasn't so clear...

I struggled to find the smaller shafts though, and it ended up costing me a lot in the end...

quote:

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Originally posted by Hellfire
Trouble is though, the ratio of your diff is dependent upon which engine you're running. Simply swapping the 3.62 for a 3.92 to save 5kg will also mean sacrificing top end speed.

It is interesting to know the weight difference though........

Phil

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3Kg is not a lot but i understand trying to loose weight every where you can but don't start throwing money at 3Kg if you have a heavy battery or a steel gearbox or heavy wheels.
Look at the whole picture before getting blinkered over one thing, I speak from experience.
By the way a few tins of slimfast is supposed to save that much weight in a few weeks

I know you aren't specifically referring to me - but I didn't have a heavy battery/steel gbox/heavy wheels etc.

I pretty much went all out on my car to reduce weight as much as possible. The only time I drew the line were when it didn't make financial sense to do so (for eg - I'd already spent money on upgrading to lightened sierra discs for the rear, so couldn't justify to then spending money again going to wilwoods etc)

Whilst building the first time round though, I did cut down every one of my bolts to 1.5 threads past the nut to reduce weight. I know it's totally anal, and it didn't pay off straight away until I started replacing a lot of my body panels with CF. But it all adds up and I was happy to put that sort of dedication toward my first build!

quote:

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Originally posted by snapper
3Kg is not a lot but i understand trying to loose weight every where you can but don't start throwing money at 3Kg if you have a heavy battery or a steel gearbox or heavy wheels.
Look at the whole picture before getting blinkered over one thing, I speak from experience.
By the way a few tins of slimfast is supposed to save that much weight in a few weeks

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The way I look at it that's a 20% weight saving on one component be it a fairly large one. So as already mentioned it only becomes significant when the all parts are taken in to consideration.

If I were to go on a weight saving crusade then I'd start with a BEC anyway and neither of these diffs are ideal to start with. Oh well I just wondered why people kept quoting different weights for the Sierra diffs and now I know!

quote:

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Originally posted by snapper
By the way a few tins of slimfast is supposed to save that much weight in a few weeks

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Don't focus on the one thing, as he says...

I had the 7.5" viscous Sierra in a GSXR750 BEC (diff weight probably not so far off the engine weight!), wasn't too slow.