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.

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 ?

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.

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

The 195/50/15 tyre measures a nominal 577mm in diameter. This is 3mm larger than the stock original 600x12 tyre so it's all good there.
I use 205/60/13's which measure out at 576mm.

Are you saying that the engine revs out too fast or too quickly in gears 1-2- & 3 without any real pace but it seems to come good by the time you hit 4th & 5th?

This is a common problem with our small Datsuns. Forever looking for another gear.

The gearing was originally designed around small low powered engines & when you increase the power output, particularly with the longer stroke A14 & A15 engines, the gearing seems too short, particularly in the lower gears because the engine now has the power to handle the load without any real effort at all.
Like I said, taller tyres [which you seem to already have] & higher diff ratios help out a bit & the overdrive gearbox helps in cruise mode.

Even in stock trim the A14 & A15's were used in the heavier Sunny Wagons in Australia & they moved these barges along adequately. Reduce the weight by installing one of these engines in a 1200 & you get this problem.

The option 1 five speeds that were available for the 1200's & 120Y models used a first gear that was almost equal to second gear in a regular four speed & all the ratios up to fourth gear were raised, but top gear was still 1 to 1, so while the intermediate gears were better, top gear wasn't & these boxes are not really suited to the longer stroke A14 & A15 engines.

Untill somebody comes up with a replacement gearset for the 60 series five speeds the problem you have will remain.

O.k Lets put it this way Keep in mind im not very good with words and explaining things in a forum. Also i have 15 inch TRX Rims with 195/50/15 tyres on them. My problem seems to be that i have to change gears from 1 -3 way to quickly The car just doesnt want to Wind out threw the gears until i hit say 3rd then its a bit better.

The problem is we don't know what DatsAndy's question is. Something about revving and gears.

"short" gearing is actually too low gearing not too high.
What wheels/tyres are u running? using a 14" with a high profile or a 15" with a low profile should fit ok and be acceptble rpm@kmh final drive witha 5 speed.
If u had to drive a 4 speed with 12" tyres u would know about it,
try 4000rpm@110kmh haha.

Using the words "gearing too high" & "Datsun 1200" in the same sentence is all but a contradiction.
At least in those 1200's that have the longer stroke A14 & A15 engines.

As soon as we start to get a little pep into our lightweight cars we often find that they sit on way too many revs at a very light throttle & driving everywhere at 4,000rpm & more is not my idea of motoring.

The stock Datsun H145 diff ratio is 3.9 to 1 & that's as good as it gets.
You can use the 3.7 to 1 diff from an Aussie Sunny wagon that was originally equiped with the A15 & this will help a little. These are the H150 diff & will need the 2mm spacer to make it work properly.
I also use tall tyres on my stock 1200 with auto & still find it to be short geared.
Hopefully I can get the A15 & overdrive auto installed before too long & along with the 3.7 diff, easy cruisin will be a reality.
At least there is a 3.54 to 1 ratio available [USA] if it should become necessary to go even higher.

I'm saying it depends on your gearing -- mainly:
- diff ratio
- tire height

If the gearing is too high, you won't be able to get to redline in 4th, and maybe not even in 3rd.

But with a stock A12 (or A15) with stock gearing, you can hit redline in gears 1-4.