The Stovebolt Site Forums The Shop Area Engine Shop Carburator heat lines from tube headers ???

Well..No matter how many options are available out there some of us seem to invent a problem that there may not be an eazy solution to..Guilty as charged!

I have a vintage set of Clifford tube headers for my 235 engine in my 55 truck. My first phase upgrade is to use these headers with the stock intake if clearance isn't an issue. I'd like to heat the intake with a kit that takes exhaust heat and pipes it to the intake(from larrowe and sons-not sure who makes it) It's intended for cast headers. Do you think I could drill a hole in the tube headers and weld a female threaded section to it so that I could use the kit?

Thanks,

Keith

Keith,

I haven't done this task. The tube headers are pretty thin, but what you want to do is 'do-able'. There are things called 'weld flanges'. You can get them through McMaster-Carr in the pipe size of your choice...probably 1/4" or 3/8".

If you can't find weld flanges, you can use steel couplings instead, they just don't look as professional. Make sure whoever welds them in knows what he/she is doing...the wall on tube headers is pretty skinny, and even skinnier on used ones.

Stuart

In a word- - - -NO! You definitely don't need exhaust gas flowing through the manifold heat tube. The idea is to get hot air to the intake, not exhaust gas. It might be possible to wrap a piece of open-ended steel tubing tightly around the header tube, or possibly braze the tube to the header pipe. Attach a vacuum line to the other end, and draw hot air, not exhaust gas to the intake.

Better idea- - - -use a stock exhaust manifold that's already got a very efficient heat riser- - - -designed by engineers who knew what they were doing in the first place. Headers look cool, but they're virtually worthless except at very high RPM.
Jerry

HRL,

Didn't the stock intake manifold have accommodations for hot exhaust gas to heat it? Maybe I don't understand what is being asked in the original post.

Stuart

Well I was under the same impression Stuart..that my existing exhaust gas heats up the bottom of the intake manifold...Also Fenton cast headers have ports for running lines to a plate on the bottom of various intakes...I respect what HRL says but I don't think we're all on the same page..

Always appreciate the replies..

Keith

The stock intake manifold doesn't allow exhaust gas in, it is heated by the exhaust though. I'm pretty sure that putting tubes from the headers to the bottom of the intake will not do a thing. The stock exhaust and intake are connected of course, so heat transfer is instant. If you run the exhaust through a couple tubes for a foot, the heat will disipate, know what I mean? By the time the exhaust warms the intake, the motor will be warm. That's my theory. BTW, I had an 81 C20 that I put headers on (350)... didn't worry about a heat riser pipe. How many custom vehicles have you seen with an exhaust heat riser?

It might be possible to route exhaust gas from one section of the header to the other, using the alternating pressure pulses from each exhaust pipe. The stock heat riser arrangement uses a flapper valve in the exhaust stream to direct the hot gases either toward or away from the bottom of the intake depending on the position of the weight and spring. With the headers and the piped heat, it would not be possible to stop the flow of gas under the intake once the engine warms up, resulting in too much heat to the incoming mixture. The only time manifold heat is needed is for a few minutes during warm-up, so unless some type of cutoff valve is incorporated into your piping system, the intake will get heated all the time, not when it's actually needed. That's just one of many reasons headers don't belong on a street machine.
Jerry

Edit: My comment about not getting exhaust gas in a heater tube was a result of misreading the original question. Some automatic chokes use heated air from around the exhaust manifold to help release the choke. People have drilled into the exhaust stream for this purpose, which does severe carburetor damage almost instantly. Sorry about the misunderstanding!
Jerry

You could use water heat instead. Then you wouldn't have to drill those nice headers.

My uneducated understanding about needing a heated intake-manifold is that heat is needed at all times; and, the heat transfer through the head to the manifold (when the engine is warmed up) is not sufficient to keep gaseous fuel from condensing in the intake manifold right below the carburetor(s) (caused by latent heat of evaporation).

Many people who have used unheated intake-manifolds (including myself) have experienced acceleration hesitation, even after the engine has reached operating temperature. This hesitation has disappeared after water-heating or exhaust-gas-heating the bottom of the intake manifold.

I have used a water-heat plate with excellent results (Offenhauser dual-carb intake). I have recently installed an exhaust-heat plate that seems to work fine but I have only used it for one short trip (Fenton header to Fenton dual-carb manifold).

If I were working with a tube header, I think I would try Stuarts adapter but simple clamp the adapters to headers, and then run tubes (with threaded adapters on the intake side) to a plate on the intake manifold. If the heat transfer is sufficient to prevent acceleration hesitation, I'd then either weld the the adapter to the headers or clamp them with stainless steel clamps.

I like the idea of exhaust heat because its much faster then water heat, but in this case, even a 3/8" line won't provide enough heat till its been driven awhile.

You will need some type of heat full time or you will find a flat spot when accelerating, been there and done that! Heated intakes are not just for warming up, it also keeps the fuel vaporized. The intake hanging off the side gets a lot of cooling air from the fan, and the fuel atomizing creates a cold mist, so its no wonder they won't run! A V8 intake has a natural heat source under it, even with out the exhaust cross over.

Use a water plate and pipe hot water right off the thermostat housing. You could even make your own plate if you have a hack saw and a grinder, just use a gasket as a pattern.

Joe

Would one of you proponents of full-time exhaust heat please explain to me why GM, and every other manufacturer of inline engines I've seen goes to the trouble of installing a thermostatically-controlled deflector to route heat away from the intake after warm-up? Also, maybe one of the flyboys here can explain why aircraft engines don't get carburetor heat all the time. Those engines operate in sub-zero air temps without needing carb heat, except on takeoff and landing.
Jerry

Gosh, this is getting close to being like a political or religious argument.

Just in case one of the "fly boys" does not chime in, here's some information on carburetor icing and heat. Seems the problem is greater in carburetted aircraft engines than in fuel-injected engines.

One of the reasons that updraft carbs were commonly used in early engines was supposedly to eliminate the problem of fuel droplets forming inside the intake manifold.

Maybe the thermostatically controlled damper was placed in a standard 216/235/261 intake/exhaust manifold combination because the exhaust manifold was directly bolted to the intake manifold and the proximity of the two manifolds allows adequate heat transfer when the valve is closed. Thus, there is always heating of the intake manifold in the standard set-up?

I think the the three ton trucks had a manual heat riser valve (at least on AD trucks). Heat on all winter, heat off for summer. Vapor locking on warm winter days! Here in the great white north, intake heat is a good thing. A few minutes after I start my truck, which has intake heat, my carb starts to freeze. Now, I don't think the intake manifold would freeze up, as there just isn't the restriction and drop in pressure throughout the intake, but I do get condensation on the outside of the intake, and if it's cold enough to condense water vapor, surely there would be drops of gas condensing inside there. I also notice, that my intake heat comes back on after the truck sits at idle for a few minutes. I have also noticed, that on days when its fairly cold, like 20 farenhieght, the heat never shuts off. That's my non-scientific two cents.

216 Carb Freezing Pic

http://i221.photobucket.com/albums/dd45/HomeCrafter/IMG00014.jpg

Mr. Lang,

Thanks for the memory joggle. Also, nice picture.

The need for the thermostatically controlled damper does seem to be a matter of degrees on GMC 248, 270, and 302 engines used on larger trucks through at least 1953. The standard (through 1953) 228 GMC engines used an automatic manifold heat control, similar to the damper on Chevrolet engines. However, the larger engines had a manually-set heat control (even on the updraft manifold used on the COEs).

This allowed the owner to manually adjust the control valve from full-off to full-on, depending on the prevailing temperature of that location or the time of year.

I cannot find information about the manually-controlled heat riser valve on A-D trucks (USA and Canadian Shop Manuals) but it is described in the 47-54 USA GMC Maintenance Manual.

Tim

You're right Tim. I had read about the manual heat riser valve in the 48-50 update shop manual, and it does cover the 248 engine, and that's what I have read about, the GMC engine.

The heat valve never fully stops the flow of heat to the underside of the intake, no matter how well it works.

I had my truck out on Sunday when it was 18 degrees, even with a heated intake, the two outer carbs were stalling out.

Fuel vaporizing pulls a ton of heat out of the surrounding metal and air which is great for a race car, but terrible for everyday driving and questionable fuel quality makes it even worse. The intake needs to be hot enough to replace some of the heat loss, but not so hot it vapor locks. This is where the flapper valves comes in. Its used to heat up the undersize as fast as it can then shut down and maintain a constant temperature.

My alcohal carburator would ice over so bad on damp nights I had to add heat under it just to make to the end of the quarter mile!

Joe

The stock heat riser is an impressive piece of engineering and I sacrificed an intake to see exactly how it works. In heat on (cold engine) mode the exhaust is deflected up into the intake where it must pass over the top of the horizontal runners and then down the outbound side. Exhaust heat comes very close to the area all around the base of the carb. This leads me to believe that a Corvette exhaust manifold or split stock one are best on vehicles where immediate driveablilty is desired.

http://good-times.webshots.com/photo/2743005060023244788OCMEnj

Hey thanks everyone for your input..Loved reading it but darn it now I'm on the fence again-I came close to making a decision this time now I'm undecided...lol. I am getting comfortable with trying things in stages..There are lots of schemes out there for intakes and exhausts..I'd still like to try a stock intake..but the "hesitation thing" does sound like a given. Wouldn't mind it on warm up..but if it still does it after warmup I'd have to change it..

Keith

Just give it a try, yours may work all right and it's not that big a deal to change it. Joe

Aircraft engines with carburetors have traditionally all equipped with up draft carburetors. One reason being a downdraft carb would have to be mounted on top of the engine. In case of a stuck float or an overflow the engine would be covered with raw fuel with the possibility of an engine fire in flight. Carburetor heat is controlled by the pilot from the cockpit with a cable attached to a flapper valve in a carb heat box attached to the bottom of the carb. This box is supplied with hot air from a muff surrounding an exhaust pipe. It doe's NOT use exhaust gas. Carb heat is not normally used on takeoff because it typically lowers RPM. During runup before takeoff the carb heat control is operated to make sure it is working. The way you can tell it is working is that the tach should show an RPM drop. Depending on the particular engine the drop can be from 50 to 150 RPM. Carb heat is almost always used on landing because this is most likely when the carburetor would ice up because the engine is at idle RPM. In case of a botched approach or landing the throttle is then opened and carb heat shut off and the engine will go back to its takeoff RPM. The carb can ice at partial or full throttle also depending on the humidity.

Weeds

I got a question about this since I am considering it as well with my new Fenton intake. Has anyone out in the hot States had a problem with it getting too hot, like in traffic or highway driving? I'm in Dallas and during the summers it can get pretty hot and I don't want it dieing on me in traffic.

Also note that carb heat and manifold heat aren't really the same thing. The manifold heat is to keep any puddled fuel droplets in the intake from building up too much by flashing them back into vapor. Carb heat takes care of the frost formed around the throttle plate due to venturi temperature drop. Some cars have carb heat as well- its usually a heat stove around an exhaust manifold connected to a flapper in the air cleaner snorkel.

ApacheFiend, in your case of getting to hot, you may not need any kind of heating for the intake. Mine worked fine all summer, it wasn't till fall that it started acting up. I would go with out and see how it works. You could always water heat it with a shut valve inline. Joe

Well, just thinking, why couldn't you fix a shut off valve in an exhaust line anyway? That may be the best solution with a Texas truck anyway.

Hey, a real newbie here. I just bought a 51 coe. I was told the engine comes out of a newer car. Anyway I am missing the exhaust manifold that would mate up with the intake manifold. The previous owner made a hokey exhaust manifold that does not connect with the intake manifold. In reading these posts that sounds like a recipe for disaster. A little help and or a lead to the right updraft carb, intake and exhaust manifold. I am told my engine is a 235