SALAD
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| posted on 26/2/08 at 07:20 PM |
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Which Twin Carb Manifold?
I was about to ask anyway but following on from contaminated's thread, what are the benefits/dissadvantages of using an inlet manifold with or
without a water jacket?
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rusty nuts
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| posted on 26/2/08 at 07:24 PM |
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Can stop the carbs from freezing, which can cause lack of power or even stopping . Problem sorts itself out if engine is left for a few minutes until
the next time . also helps with fuel economy and emissions
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Canada EH!
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| posted on 26/2/08 at 07:26 PM |
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Which Twin Carb Manifold
Ones with heat assit in starting and cold running by heating the intake charge, resulting in less fuel consumption. with out heat colder mixture, more
tempermental, more fuel, more power.
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SALAD
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| posted on 26/2/08 at 07:28 PM |
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So why would you choose one without then........inlet temperatures, or is that irrelevant?
EDIT: ah ha, as I thought.
[Edited on 26/2/08 by SALAD]
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r1_pete
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| posted on 26/2/08 at 08:28 PM |
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Cold air is more dense, more air = more oxygen = longer lasting combustion = more power.
The main advantage of the water jacket is to prevent the incomming charge condensing in the manifold in real cold conditions. Which is also the reason
for the thermostatic inlet on some cars, which when cold draws air from round the exhaust manifold, but as it warms up it reverts to cold air.
[Edited on 26/2/08 by r1_pete]
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SALAD
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| posted on 26/2/08 at 08:52 PM |
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I guessed it would be down to inlet temperatures, cold start etc. However I didn't know about freezing carbs.
How much of a difference is there between the characteristics of a car with and without.......fuel consumption, tempramental etc? Is freezing a common
problem?
I was wondering if it was advisable to use a jacketed one or not. From the answers, personally I could live with the comparitive power decrease as the
benefits outweigh this in my opinion.
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r1_pete
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| posted on 26/2/08 at 08:58 PM |
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Unless you're driving in the depths of winter, I doubt you'd get much benefit from a heated manifold, carb icing isn't much of a
problem in cars either, most have an insulating sandwich between the carb and manifold anyway to keep heat down.
I'll be running without a heated manifold, bike carbs on boggs manifold, and dont forsee any problems.
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rusty nuts
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| posted on 27/2/08 at 06:57 PM |
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Had problems on the way to SVA with carb icing . Carb was sticking up through the bonnet at the time . Very common on VW models with carbs.
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SALAD
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| posted on 27/2/08 at 08:11 PM |
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How is it that using a heated manifold, with the resulting effects of heated inlet charge, can improve fuel consumption when the fuel has been mixed
with cold air before it reaches the manifold?
If a heated inlet manifold can't alleviate carb freeze how can it effect the amount of fuel used when it is positioned after the mixing has
taken place and the required/optimum amount of fuel has been added to a given amount of (cold/dense) air?
Am I missing something? I understand how it can prevent condensing but I don't see how fuel economy would improve.
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Schrodinger
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| posted on 27/2/08 at 09:40 PM |
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The carbs freezing cause the fuel to drop out (condense) of the mixture thereby making a weaker mixture.
Keith
Aviemore
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rusty nuts
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| posted on 27/2/08 at 10:01 PM |
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One way of looking at it is that petrol as a liquid will not burn, petrol as a vapour will . With cold manifold and ports as already stated fuel will
"drop out" which basically means the petrol condenses back into liquid which results in a weak mixture hence the need for a choke or
mixture enrichening when engine is cold. Heated manifold or warm air pick up helps to reduce the effects . Hope this makes sense.
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SALAD
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| posted on 27/2/08 at 10:13 PM |
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That does make sense thanks. Would you think it is needed on a 7 where (I'd guess) under bonnet temperatures tend to be higher than
'normal' cars?
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r1_pete
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| posted on 28/2/08 at 11:22 AM |
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Why not run a poll, 'who has a heated inlet manifold'
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David Jenkins
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| posted on 28/2/08 at 12:03 PM |
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The effect of carb heating is obvious if you've ever been in a light aircraft - the engine rpm can drop 250 - 500 rpm when you've got carb
heat on, and that's a lot of power drop when your prop is only turning at 3500 - 4000 rpm!
One of the skills for a light aircraft pilot is knowing when carb heat is required, and when you can get away without it.
Perhaps a driver control is required, to turn it on and off...
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r1_pete
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| posted on 28/2/08 at 12:48 PM |
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Too right David, problem is when you really need a hot manifold and hot air, on 1st start up, the car is clock cold, and a manifold full of cold
coolant is counter productive. By the time the car has warmed up, the engine bay would be hot enough to keep the fuel in vapour.
Light planes are generally air cooled, and up in the sky where its colder anyway, and loads of air gushing through the engine you get the problem in
extreems. I've been in one twice and pulling that carb heater knob is a real laxative, feels like the engine's going to die.
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David Jenkins
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| posted on 28/2/08 at 01:01 PM |
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There was a CAA report in the BBC news the other day - a pilot new to the plane had engine trouble as he approached the runway, and eventually crashed
in a field a few hundred yards short. They decided that he'd left his pre-heat on too long and the engine had refused to idle properly on his
approach glide.
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