The Stovebolt Site Forums The Shop Area The HiPo Shop Dual Offenhauser manifold heat

This is not to start the fight about heat risers.

I'm installing an Offey dual manifold and Fenton exhaust on a 235.

The intake manifold heat kit is a plate with a single 1/2 inch copper tube connection to 1 header.

There is no outlet/circulation. Trying to push exhaust into a closed container is not very useful.

Further, on a stock manifold the carb is directly above the heat riser so any unatomized droplets fall on the hot spot. Here the carbs are equidistant on either side of the heat source. So half the flow from each is away from the center and half toward.

Yes I know there is a a channel cast the full length, but that assumes something is going to circulate through it.

No, I really don't want to run a hot water system.

Since the headers run directly under the full length of the manifold and actually touch in a few spots, has anyone ever documented any actual improvement by adding the exhaust heat kit?

I think that the only way you will get true circulation with an Offenhauser intake is to run coolant into either side/port in a dual-port base-plate and have the coolant run out-the-other-side/port.

When you use the exhaust header connection/connections (with either the one-port base-plate or the two-port base-plate), you do not get true circulation - you get heat transfer.

Many people believe you need some heat, somehow, to the base of the intake manifold.

That being said, I have never used the one-port exhaust-heat base-plate, but I would guess it works fine.

I merely have the fenton headers with no heat at all, and at 40° or so I do have some issues with it accelerating smoothly, which I never did with the stock system with the heat riser in the not-heat position. So I can only imagine the effect running an aluminum intake would have. However next weekend I am going to install the fenton intake, but I am going to use water. I don't see any reason you couldn't drill and tap another hole in the heat adapter plate, and use the tapped holes in both headers. That way you would actually get circulation of sorts as there is only one header with pressure at any given time, and the gas should go back and forth between headers.

OK. I have the the kit anyway, It is no big deal to drill and tap a second hole into the other chamber. I'll connect it to both headers and see what happens.

But, do the math. At 2000 rpm's there are 6000 exhaust pulses per minute. That means that an exhaust pulse has 0.01 seconds (1 one hundredth of a second) to travel through 24" of manifold chamber until the pressure reverses to the opposite direction.

That is not really circulation.

Yes, heat transfer is what you will end up with (there will be no circulation).

Yet, with two holes, maybe you will get twice as much.

No joking: I liked/used the two hole plates because I like the symmetry of the appearance of the two tubes on that side of the engine. A better appearance over no better function?

I still use the two tubes on the plate under the original intake and a Holley AA-1 two barrel carburetor. It heats up nicely and runs very smoothly. I'd bet that a one tube set up would be just effective.

I like the two pipe one on each split exhaust manifold also as stated above because the symmetry of the appearance of the two tubes looks better. With the exhaust heat method does not circulate since you can not blow air into a bottle idea you do not get circulation but you do get heat transfer as already mentioned.

I personally went with water heat instead of exhaust heat and that's my choice not saying there anything wrong with exhaust heat. I chose it because I read water heat is slower but very clean and not corrosive to aluminum manifolds and water heat utilizes the water pump to continuously supply warm water to a passage underneath the manifold.

The bottom line we are all trying to prevent the manifold from staying cold or even building up frost under some conditions.

I remember reading somewhere a long time ago about the water leaking out of plugs on the bottom of the manifolds, and the sulution was to have the plugs welded. Any thoughts or experience with this?

the reason I say that is someone had posted pictures and posed the question about how his intake got all carboned up in that chamber. When all you had was two tubes going in and none going out, This is the conclusion the group (being the stovebolt group) came up with. It may or may not be the case, I don't know for a fact. I guess you could exchange those pieces of tubing for pieces of copper rod. If it is only conduction/convection, this should work just as well. The important thing is if it actually works, regardless of the reasoning.

Circulating exhaust gas through aluminum isn't going to be a good idea. if it's possible to run a steel tube the full length of the manifold and connect that tube to both headers, it might be a better procedure, just using the aluminum tube as a carrier for the steel. The firing order impulses will move a little gas from one header to the other. Since I've never had any hands-on experience with that manifold, I might be all wet!
Jerry

Hotrod lincoln

Actually Langdon specifically mentions the external tube idea on his web site and how it won't work.

Since this manifold would have the space of the heat channel between the tube and the floor of the intake passage, the heat transfer would be poor.

If I try the 2 exhaust connections and don't like it. I can always put the plugs back into the headers and connect the tubes to the cooling system.

That could wash the carbon out, or leave enough behind to seal the core plugs so they won't leak water.

I did the water circulation on a Tattersfield intake and the owner drove the truck without problem (he said it ran like a striped ape) during that supercold snap we had around Christmas. It was a lot of work to make everything but it seems worth the effort.

Where can I find a two-port base-plate for a offenhauser dual carb manifold? I have a chevy 235 with headers. I would like to add the heat plate to my intake for my cold winters.

Thanks,

Dad and Son

coolant heat

exhaust heat - my preference

When I bought my Edelbrock intake a long time ago used it was so badly contaminated and filled with very think deposits in the exhaust chamber. Im not sure if the previous owner had a bad head gasket and was burning coolant. Took lots of time to chip it all out and get it all clean. Even gave the inside a little plastic blast to get it all out. After seeing what i removed from it i opted to go with water for heating. I got the manifold kit and thermostat spacer kit from Ton L and it bolted right up. Install looks cool also.