10 replies to this topic

[huw_jenks]

I have finally got round to reading The Bible, by David Vizard. The chapter on cold air induction (explaining how beneficial it is to keep air cold as it enters the engine) left me wondering why all stage one kits have water heated inlet manifolds? I realise that cold starting requires warmer air but surely this is sapping power when the engine is warmed up? Are there any decent aftermarket manifold available that arn't heated? Or would a tap in the water pipe work?

[eden7842]

it mean water cooled really so the manifold is cooled, thus the fuel/ air mixture is cooler as it enters

correct me if im wrong

[newdawn1st]

Thats there to prevent carb icing in low temperatures. I've been led to believe on mild tune engines it doesn't make any real difference in performance (in a neg. way)

EDIT: and in water cooled means engine coolant passes thru it to keep it warm not to chill it. Hence water heated not cooled.

Edited by newdawn1st, 23 July 2009 - 08:47 PM.

[Ethel]

It's all relative, warmer or cooler than what is the question.

A water heated manifold is a replacement for one that was heated by being in one piece with the exhaust manifold. Heating pays off in getting the engine up to running temperature. Unlike heat conducted from the exhaust, the water in a water heated manifold will stop getting hotter when the thermostat opens and will help stabilise the induction temperature making it easier to optimise the ignition timing.

[Wil_h]

Just because it has a pipe doesn't mean you have to connect it. I've never connected on in my life, never had any problems, and the only carb icing I've had wouldn't have been solved by a slightly warmer manifold.

[huw_jenks]

Is there enough heat radiated from the exhaust manifold to heat the seperate inlet manifold when it's needed?

[Ethel]

Depends,

Obviously you have to get the engine started before it produces any heat at all so a unheated manifold won't stop it running. It will help it warm up quicker so can cut emissions & help mpg. I'd plumb it in on a year round road car.

[Cooperman]

I always by-pass the water pipes and run a hose straight across. Cold air is better than warm for best power and, ultimately, best economy. It stands to reason, the colder he mixture going in, the more potential it has to expand and create power when it burns.

[m1tch]

With carbs, hot air helps the atomisation up to a point, its why the air box is plumbed into the hot air coming off the exhaust manifold

[Cooperman]

It's hot enough at the back there without making it worse. The ideal is a cold air pipe running from the grill to the carb inlet. The only problem with that is the risk of water getting into the induction system. Remember, a lot of performance cars run cold air boxes and, on turbos, an intercooler to cool the inlet charge.

[Ethel]

But again it's relative: on a carb'ed engine, especially a siamesed A series, a hot manifold will help to vapourise the fue and keep it airborne and better distributed. A couple of degrees won't make much difference to the charge temperature once it's been squished into a hot combustion chamber. Bear in mind at wide open throttle the charge will also be denser and whip through the manifold quicker picking up less heat.

An intercooler cools the charge from way above the temperature found in a N/A manifold to comparable levels. Some coolers even have a thermostatic valve to avoid over cooling.