Quote:
nick_m wrote:
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. Nick
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.