426 Hemi heat tubes

[darkhorse]

How important and what are the functions of having the heat tubes risers for the intake manifold, I dont have them on mine and was wondering if I really need them or not? do I need to be using exhaust manifolds for these to work? thanks guys ahead of time.

 

[skyman51]

How important and what are the functions of having the heat tubes risers for the intake manifold, I dont have them on mine and was wondering if I really need them or not? do I need to be using exhaust manifolds for these to work? thanks guys ahead of time.

The heat to the intake manifold and therefore the carb(s) is so the engine will warm up quicker. Without the heat the engine may run rough or stall until it gets warm. You have to keep it running. Neither the race hemi nor the max wedge have heat tubes, but everything else should to my understanding.

 

[Meep-Meep]

The neat thing about the HEMI heat tubes is they come from the exhaust pipe and are on either side of the thermostatically controlled flapper valve. When the engine is cold the flapper is closed and directs some of the exhaust gas through the manifold. I'll have to look again, but it seems to me the arrangement of the flapper is such that high exhaust gas flow when cold will not blow the valve open but rather force it closed, which is beneficial for cold engine operation. When the engine and manifold are warm and the flapper is open and should block the upstream riser port thus not allowing much (if any) exhaust flow to the intake. If I'm correct it's really the best of both worlds, unlike the conventional wedge setup, which takes the exhaust gas from the port with no good mechanism to shut it off when the engine is warm. These days with the crap gas I find myself having to block the heat riser in the head to keep the intake and carb cool enough to stop the fuel from evaporating and/or flooding the engine on a hot shut off. The flip side is poor drivability until the intake reaches proper operating temps for good fuel vaporization. Controlling and maintaining the intake manifold temp has huge effects on engine performance.