Thanks mate. Now the L series upgrade is becoming more appealing. Could also be expecting to much out of my little mate.

It won't matter what engine you use, if the overall final drive gearing [diff ratio & tyre size] is short, then more power will make it even more obvious.

You won't get much more tyre diameter in there so diff ratio is all that's left if you're finding that top gear is still a bit low.

Even if you switch a Ute rear end in there with its H165 diff, you are still looking at 3.7 to 1 as the tallest ratio that I know of in Australia.

I know that there is a 3.54 ratio for the H150 in the USA but don't know what the six cylinder auto models had in their H165's.
I might see if I can find out.

Cool. Thats true but surely i will feel more like i am getting somewhere and not just revving its head off with say an L18 5 speed and skyline diff rather than a A14 5 speed with stock 1200 coupe diff. Would love a ute diff Just hoping to sell my turbo and bits to pay for one. Or what about the idea of a Sunny diff to match the box and motor, what ratio are they ?

I have a 200B wagon & the almost stock L20B in that thing pulls like a train. I fitted a Bluebird 5 speed & it cruises as smooth as the QE2. The diff ratio in that is 3.9 to 1, like our 1200's but I run a 215/65/14 tyre which measures 636mm in diameter.

If a stock L20B engine hauls this 1110Kg barge around without difficulty then imagine how much better it would handle a 690Kg 1200 coupe. [OK, add a bit for the heavier engine & trans]that's roughly a 400Kg weight reduction that the engine would see, & with a tyre that is almost 10% smaller in diameter giving a lower overall comparative ratio.

My bush maths tells me that a diff ratio of about 3.5 to 1 would come close to evening out the difference in overall ratio & even then, performance would be much improved since the engine still sees a 400Kg weight reduction over my 200B wagons weight.
The beauty of the L20B is its long stroke & great torque which make it able to handle tall gearing while the L18 would rev more freely & lower overall ratios would be less of a problem, however either one would barely notice the weight of a 1200.

The Sunny [B310] uses the H150 differential in 3.9 to 1 ratio in all models except the late wagon that came with the A15 engine. In these it used the H150A diff in 3.7 to 1 ratio.

A Skyline rear end would be good but it will require narrowing [$$$] & I do not know what ratios are available but if it's a Borg Warner rear end, then, from memory, ratios as high as 2.7 to 1 were made for larger cars with V8's & autos. They are also heavier & this may negatively affect ride quality.