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Why intake manifold requires heat.

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Old 09-06-2015, 09:13 PM
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The floor of the intake (where the fuel is) needs heat to keep fuel from condensing to it. The more surface heat the better. Direct contact best. Unless the whole floor below the carb is heated, condensation will happen during warm up worst, and some after. Hot intake air, exhaust heat and radiator heat under hood eventually help.

Smaller intakes see less problem because of velocity moving the liquidized fuel at lower rpm and heat on more surface area directly below the carb where the fuel would be attracted to the colder area.

Stock intake: floor completely heated, high velocity, no issues

Dual port: some heat, medium velocity, some issues

Offy C: some heat, low velocity, issues

I am back on E85 now and let me tell you about a cold floor and condensation! The base plate of the carb and middle of the intake dripping sweat on the outside. I stick my finger under the intake it's ice cold after running for an hour and burn the tip of my finger on the ex mani. Also, I have a .020" gap between my Offy C and HD exhaust mainfold. The gap is there because being turbocharged the mani moves alot and would snap the "marriage bolts", or worse.

When I was running gas+torco(real octane booster) I was able to tune most of the issues out with lean Idle and lean IFR.(Idle-2000 rpm) A mile down the road and the coolant circulated, all was good.

Gas guys with issues can benefit from a stronger dose of heet or iso(1 bottle to 5-10 gallons of gas, all the way up to 45*F outside. We use it in all carb/gas vehicles because of the effects the cooling of a carb has on an intake floor...even V6 and v8 engines. Even tho E85 is basically alcohol ie heet or iso, it's the percentage that counts. On the v-type engines this really helps in sub zero temps before the floor can be heated sufficiently by the exhaust cross over. Will likely not be a huge benefit on an inliner without antiquate heat.

This winter I will be doing some work on my 300, in which the transmission fluid will be cooled by the intake and intake warmed by tranny fluid. This is primarily a drag vehicle, so this makes sense. (Guessing) over 700 ftlbs stalling to 5000 rpm, pulling a 3920# truck with 2.75 gears down the quarter mile makes some serious heat. This will of course be useless as far as warm up until the first pass. I usually warm it up on the trailer, unload it, shut it off and let the mani and underhood temps warm the intake...and i'm golden. Now on E85, that works for about 10 seconds and the bottom of the intake is ice cold.(perfect for power of course) The only solution to heat is rpm to move the re-liquefied fuel to the cylinders steady to prevent a falsely flooded engine. In the case of the offy C and E85, it's a 1200 rpm permanent idle.

Edit:Heet contains methanol which is what I use for meth/water injection and in other vehicles for cold weather carbs. Not sure if the iso would do the same thing as far as aiding carb heat. Also I have tried mixtures of E85 all the way down to E40. The intake wasn't as cold with E40, but much colder than gas. Even tried 1 bottle of heet added to 5 gallons of E85, didn't help. The warmest intake temps were with premium gas that contained no ethanol.

Hmmm. I wonder why oem's have a high idle during cold start up's? To move the liquidized fuel until the intake floor is warm enough. Try bumping your idle up to help, it may or may not take much.
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