Hi, this is my first post here. I'm new to inlines and I've got a '67 C10 with a 250. I'm going to rebuild the motor and I've bought the Offenhauser Intake with a Holley 390cfm Carb and Clifford headers. Do I need to heat the intake, and if so how whats the best way to do it?
Thanks.

Welcome to the Inliner's BB!

Under the "Tech Tips" link in the menu to the left is an article by Tom Langdon about manifold heat. Exhaust heat is best, but hot coolant is better than nothing. Most automotive engineering books (e.g., Smith and Morrison's Scientific Design of Exhaust and Intake Systems) also recommend the use of heat. The real purpose of the heat is to vaporize any liquid fuel droplets that get deposited on the floor of the intake manifold, not to heat the air, as many seem to believe. If hot coolant is used, one could install a heater shut-off valve in the supply hose to stop the heat addition if it is felt that heat is not needed. This would be an interesting experiment.

Thanks for the reply!

Kyull67,

I have proof that heated intakes are the way to go. In 2002, I built a Mercruiser 4-banger and used an intake that I designed and built myself. I mounted two Carter-Webber progressive two-barrels on the manifold and did NOT heat the intake. The engine ran, but wasn't fuel efficient and very cold-natured. Especially in traffic, the car was irritating to drive; it ran rough and idled irratically....even in the summer. Tom Langdon had told me, when I was building the intake, that I should use either exhaust, or engine coolant to heat it. Finally, I removed the intake and built a water tube beneath it. With no other modification, I quickly saw an improvement in mileage and it was a pleasure to drive...in traffic, or not. I would definitely recommend heat to your intake!

is it always necessary to heat the intake?
or only in cold weather conditions?

And if you use LPG?

When I installed my 292, I asked a lot of questions about it's set up. I had been living in Wisconsin and did drive when the weather was in the 40's and 50's. Tom Langdon @ Stovebolt Engineering was the individual that I was referred to as I purchased a lot of the parts from him.
After several calls to Tom, I felt fairly confident that the way he was telling me to set up my car was right for my area. He prefered the manifold heated intake for a number of reasons. The best reason was for the above mentioned "atomization" of fuel. He also suggested that with 3 Holley/Webers on an Offey intake, it would improve the idle, fuel burn and mileage. He said that if I didn't like the look or set up, it's an easy take off item. Well it worked wonderfully and I have never had a problem with idleling, low or high speed misses and the mileage was pretty good too.
After meeting Tom and talking to him, he had explained that he headed the 6 cylinder research division at General Motors for a number of years. Now who can dismiss those credentials!
Here's a close up of my Heated Intake set-up.
Make your own decisions but I would use a heated intake in any part of the country. What does it hurt?

RapRap
1940 ChoppedChevyCoupe

Another positive response for manifold heat for the Offenhauser. I also purchased my Carter/Webers from Langdon who at the time, recommended water heat. I chose to go with the exhaust gas instead.

My rationale was for ease in installation and reducing the potential for problems should my system develop a leak. With a water leak, you have the potential for engine damage if you don't catch it before the engine overheats. With the exhaust heat, there is no major effect other than a bit of noise. I have pictures in both my GM webshots albums that show the simplicity of the exhaust heat plumbing.

No "valving" is necessary as the firing of the engine creates a pressure differential which supplies the heated air to Langdons heat plate option. The heating process is instantaneous and obvious when checked with an infrared thermometer. Disconnecting the tubes left me with a rough idle condition and poor performance at WOT. Conclusion: go with heat!

Dave

Can anyone address the question of manifold heat when using 3 X sidedraft carbs (Weber dcoe)? The manifolds I've seen for these carbs have no provision for heat and I'm wondering if it's necessary given the short runners.

I'm not aware of anything short of wrapping a few copper coils around each runner and tapping into your water heat. It sounds kind of Mickey Mouse but it might work.

The weber side draft manifold ist supposed to have heat to it. It is used mostly for racing appliations. But even in the street driven Jags and other performance cars, they dont have a provision for heat. Supposedly the atomize the fuel so much better. I know Dick Bertolucci has one on his roadster and he drives it all the time with no trouble (without a vacuum advance too), so i guess it can be done.

The lack of a 90 degree turn exiting the carb helps reduce the need for manifold heat, or so I'm told.

Webers (not that farmiliar with DCOE's ) can generally be tuned more closely to the engine (supposedly why they have a rep as being 'hard' to tune, it's easier to get lost).

FWIW the hard turn inside the heads of some of our types of engines (or blocks if their flatheads) should get enough heat from the cooling system (and the exhaust ports coming out on the same side ) as it is.