OK it is said you need exhaust or water heat in you intake manifold to stop icing which causes hesitation in the acceleration. I have exhaust heat. But in the summer the manifold and carbs get so hot it boils out the fuel when I stop the car. Doesn't heating the manifold also add to the fuel boiling in the summer? Am I missing something?
I am assuming this is an inline 6?? If thats the case, you want hot intake and cool carbs. do you have insulators between the carbs and intake?
Heating the manifold was mostly done to improve cold weather drivability without waiting for 10 minutes for the engine to warm up. Most of the problem nowadays is modern gas, which is formulated for fuel injection. The problem is even worse if you buy gas in the winter and store it or keep it in the tank until summer.
This is ABSOLUTELY correct! If you have an inline, you need to insulate the carburetor. If you are running Rochester single barrel Model B's, I pretty much guarantee that the castings will be warped by the heat. You will know this by the leaks at the bowl to airhorn gasket. The manifold heat helps volatilize the fuel and is critical for good performance and fuel efficiency. Modern fuel volitility is another issue. The boiling point has been reduced. However, I have not had boil overs if the carb base is insulated from the intake.
Manifold heat is not necessary in our climate. Without it you will wait a little longer to warm up on a very cold morning. But it will run fine. Maybe on a hoodless car you might want it on the coldest of days but with the hood down and a good T stat (say 185 to 195), good dry fuel (I keep a can of heat handy in the winter and put one in the tank about once a month) you shouldn't have a problem. I always try and keep my intake as cool as possible. Hot intake just goes against every performance theory I have ever encountered. Unless you are going with one of Smokey's hot air engines in which case you are going to have to keep an even heat and right on the edge of boiling all the time.
PnB: I agree in most cases, but have always felt better with exhaust heat for contorted manifold configurations like you have on the inline engines. If the engine is enclosed and driving is strictly in the summer, I would agree that exhaust heat could be deleted without too much issue. However, there is a tendency to pool fuel on the sides of those inline intakes if they aren't kept hot. More of an issue it seems when multiples are used in moderate performance applications.
not trying to start a war here, but didnt the stocker 235's have exhaust heat to the intake controlled by a flapper and a bi-metallic spring? Corvette too/
Yes, no wars. Just professional deliberation! And yes, they used a heat riser type configurtion that moderated the heat as the engine warmed. Most of the aftermarket intakes have limited means to direct heat to the underside of the intake. If the intake is used without the heat riser assy with a stock exhaust, I foresee real problems with excess heat...unless you are in Minnesota!
You mean in the exhaust manifold right. I have nearly always knocked those out asap. 1931 Av8. I understand what you are saying all I'm saying is that I have always deleted all the manifold heat that I could. I've never really had a problem as long as I keep my fuel dry. It doesn't get cold enough here for gasoline to freeze and being cold isn't as bad as being hot, gasoline does boil at a very low temp. Never the less they did come from the factory with a heated manifold so as long as everything is factory correct it should run just fine that way. leave it in the winter and block it in the summer.
My experience with a 235. With the rochesterB and Fenton headers, it ran fine w/o intake heat. But poor mileage and gas seapage lead me to switch to a holley weber 2 barrel. Warmed up much slower, more hesitation, so built to hot water system to heat the stock intake manifold. So far so good, warms up quicker, as soon as the water gets warm. We'll see how it goes next summer.
I messed around with water heated intakes on a Chevy 261 and GMC 302.I did a lot of jetting changes and came to the conclusion a full time heated intake allows somewhat leaner part throttle mixtures. The leaner mixture gives sharper throttle response from off idle to midrange and improved fuel mileage.Not to mention no unvaporized fuel puddling in the intake.There were aluminum intakes which tend to run cool.There are some negatives about a full time heated intake;maybe a few percent loss of power at full throttle and a greater tendency for the engine to run into detonation if the compression ratio is high. I never had hot start issues......I suject you experiment with heated intakes to see if you engine benfits from it.
That counterweight and spring are there for a reason. If the flapper valve inside is stuck in the position where it blows all the exhaust up under the carb, it will put too much heat up under there. Free up the valve and see if that helps.
PnB: Agree with your analysis all the way. Inliners are odd creatures and seem to benefit from some heat. Everything else I have has the heat blocked. My '62 Vette has a WCFB that is heated right into the throttle plate on the carburetor. Nearly impossible to keep running after being stopped for a short time due to overheating of the fuel. I had to block the heat riser at the heads to help eliminate the problem. Leaving the hood cracked during these short stops helps also. It is all attributable to the unstable fuel we use today. And the higher the octane, the worse it is. Much lower boiling temperature than previously.
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