After reading David Vizard's book on how to tune the British A-series, I'm dead set on trying a single SU on my naturally aspirated A14. It sounds like all the benefits of twin SU's without the fuss. The only problem is I'll have to make a manifold, but that's still a hell of alot cheaper than the stock twin hitachi's in the US. I just picked up six old 1 3/4" SU's for $80!

It just seems strange that this isn't more popular for the 1200.

If you want odd ball carb setups, a good frind of mines grandfather raced 1000/1200 in the day, and his favourite setup was a twin hitatachi down draft setup. He cut two standard manifolds in half and then stuck em together. Cheap as chips and as good as sideys he reckoned.

A single sidey, hmm cant imagine that you would really get the benifit of sideys. i always thought that it had more do with with having more carbs rather then the benifit of straight airflow.

I think it could run pretty well if you can make a decent manifold. I can't give you any help on a datsun a series but I had an 1 3/4" su running on a stroppy 1293 mini, it ran pretty well but i made the manifold out of to thin steel and it would get frost forming on the manifold at idle.... in summer. I ending up changing carbs before i got it running properly (smoothly etc). It did show promise though. It is worth a go i guess if you got the carb that cheap, just make sure the needle is in good condition as the needles quite often get bent if ithe carb has been pulled apart and molested with in the past.

Nick

lots of folk run single SU's on drawthrough turbo A series. so It should work okay on an NA set up.

Quote:The thickness of the steel tubing that was used to make the manifold should have no real bearing on the formation of frost, or even ice in some conditions, on the manifold. If the engine was used in high vacuum situations [like in light throttle cruise mode] the temperature inside the manifold would drop just the same.

This is why the factory twin carb manifold, as well as the later single carb manifolds were water heated. When the manifold gets so cold that frost or ice forms on it, the fuel doesn't vaporise properly, causing raw fuel to be drawn into the cylinders which washes the thin film of oil from the cylinder walls, which accelerates bore wear, & raw fuel makes its way past the rings into the sump, which dilutes the oil & can lead to other problems.

On top of that, the fuel that does not vaporise is taken from the correct fuel mix that is leaving the carb, meaning that the fuel air mix reaching the cylinders is on the lean side, causing bad running, reduced power & increased fuel consumption. [because you need to give it more 'stick' to get the power you need to just drive it]

Those clever engineers at Datsun heated the manifolds under the bottom of the twin carb inlet runners [which is where the raw fuel gathers] to ensure that the engine ran smooth, developed full rated power, & returned maximum fuel economy.

An A series Datsun engine with a single SU carb on a suitably designed manifold should, when correctly tuned, run like a top, but if you have ice forming on the runners in normal urban driving, then you will need to get some heat in there for best overall performance.

Make an alloy manifold like for a fuel injection setup, that is even runners curved to a reasonable sized plenum then at the centre of the plenum facing the sparkplug side of the engine place a single 1 3/4 or 2 inch SU if its an a15 or big bore a15.
Ive seen this setup on a racing k series (5k big bored to 1.6) and it ran like a thundering japanese clock. It looks very neat also with the induction on the other side picking up colder air but mixes very well without frosting.
The plenum is a similar design to the old 1973-76 vega cosworth manifold but with one SU instead of two. If you make the plenum out of an alloy pipe you could cut along the one side and have a removable flat plate that houses the single carb which you could remove in the future to fit a second carb on a new flat plate or use for a turbo setup.
regards, d.