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Heater hose to Inlet Manifold
Monty2556 - 9/4/14 at 06:48 PM

I've got a 1600 xlfow with a 32/36 inlet manifold. Whats the purpose of sending hot water through the inlet manifold? I've seen setups with the inlet union blocked off at the manifold. I assume it's to heat up the manifold but surely the engine heat would achieve that on it's own.

coyoteboy - 9/4/14 at 07:36 PM

Often used to prevent throttle/fuel freezing at very low temps.

Run with my tin-top one disconnected for 5 years no issues.

[Edited on 9/4/14 by coyoteboy]

britishtrident - 10/4/14 at 06:25 AM

Because carbuerretors evaporate at least some of fuel that goes through them they act as refrigerators, together with the effect of changes in pressure due to the venturi effect this results in the air going through the carb dropping in temperature and in right atmospheric conditions will lead to ice formation.
Note that this does not require the ambient temperature to be below zero a part from ambient temperature relative humidity is major variable to be considered. In the damp UK climate sever carbuerrettor icing can occur at 10c ambient temperatures.

A heated manifold cost power because increasing the inlet temperature reduces the mass of air going through the engine however because the jet sizes have been calibrated with the heating effect then running with out it will result in weak mixture which will cause hesitation, misfires and result. In engine damage typically burnt exhaust valves.


More info http://en.wikipedia.org/wiki/Carburetor_icing

[Edited on 10/4/14 by britishtrident]

r1_pete - 10/4/14 at 07:26 AM

quote:
Originally posted by britishtrident
Note that this does not require the ambient temperature to be below zero a part from ambient temperature relative humidity is major variable to be considered. In the damp UK climate sever carbuerrettor icing can occur at 10c ambient temperatures.


More info http://en.wikipedia.org/wiki/Carburetor_icing

[Edited on 10/4/14 by britishtrident]


Its a similar effect as, if you lick the back of your hand and blow on it, it feels cold despite the ambient temperature.

I've run crossflows in Cortinas, Escorts etc. back in the late 70s with and without the coolant flow, and never had a problem with icing, the manifold will warm up due to being bolted to a hot lump of iron anyway, coolant flow just speeds it up a little.

DIY Si - 10/4/14 at 11:39 AM

I found that the spicier the engine, the more likely this is to happen. On my old stock 1275 minis, is was never an issue. Stage one tuned, never an issue. With my almost race engine'd mini running a 48 IDA, it would ice up regularly and would be a bit of a PITA at times as it just wouldn't run right. And due to the design of the manifold and the plumbing, heating the inlet wasn't a viable option. Despite painting the manifold black in an effort to get it to absorb as much heat as possible, I did see ice on the outside of it at times, despite it being above the exhaust.

rusty nuts - 10/4/14 at 05:57 PM

One thing to take into consideration is air locks in the cooling system . If your not using a heater it may be a good idea to run a horse from the inlet manifold to the water pump inlet.

Monty2556 - 10/4/14 at 06:17 PM

Thanks for all the advice. I've looked on Google as well and it seems that there's a wide difference of opinion. It varies from
"a heated manifold is essential" to "it doesn't matter". From what's been said on this thread I think I've got the message.

Once again, many thanks