Inliners International Forums General Discussion Engines Intake heat - exhaust or water?

I have a 1954 261--am going with dual Carter/Weber carbs on this newly rebuilt engine. Have gotten some conflicting advice about heating the intake manifold. May still get conflicting opinions here, but what is the general consensus? Exhaust heat or water heat? Living in the Colorado foothills--it does get brisk.

Thanks for info,
T.K.

some conflicting advice

Such as?

I take it the conflict you expect is whether to run it or not.

I expect you may see a benefit as you say it gets cold.

From everyone I've spoken with, exhaust heat comes in quicker, water heat is easier to regulate.

Wheter or not you "need" it I suspect depends on how much you intend to drive it durring the cold season, so if you would elaborate on that it would help those giving advice (ie, is this your year round driver, or do you just want the driving season to be a bit longer? ).


Either way, sounds like a neat way to go, and probably a neat ride (pickup, hotted up car perhaps ? ).

My 1953 Chev 3/4 T is a daily driver--and I will drive it this winter when snow is not too deep. The conflicting advice is that some folks are insisting that using the water heat is better--while others say that exhaust heat will be fine. Am currently running Fenton exhaust and a stock intake (with exhaust heat). I am planning to install Fenton intake with dual carbs--will the exhaust heat be sufficient in your opinion(s)? (Sorry for lack of info in original post--) T.K.

The problem is that exhaust heat may be too much, and it's highest when you don't want any.

I have been using exhaust heat from my fenton headers to aluminum dual intake for many years on my daily driver.
I am in the CA high desert and drive often across the desert freeways including mountain climbs in the middle of summer for hours and never had a problem with overheating of the engine or intake.

All you have to worry about these days is too much ethanol blend in the gas, when you park after a hot run and it wants to boil over.
But even that is not a real problem and water or exhaust wouldn't make any difference there.

I prefer exhaust heat cos it heats up my intake quicker during the freezing months up at altitude.

I ran a McGurk dual intake, similar to Road Runner's, for many years (1956-60) on a 261 with a Corvette six exhaust manifold and an operable heat riser. It warmed up and ran as smoothly as the stock one-barrel. I later replaced the McGurk manifold with a Harper "Stubby" with three 97s, which was still fairly driveable. Of course, with the Harper there is no flat "floor" for the fuel droplets to accumulate, as the droplets will run straight and down into the head where they should quickly evaporate, once the engine is warmed up.

The late model "Fenton" headers do not seem to have the real heat riser, just bypass ducts. How well do those work?

In the Tech Tips to the left Tom Langdon explains some of the physics involved with the need for manifold heat. The purpose of the heat is not so much to heat the air, but to warm up the floor of the manifold so that any fuel droplets that hit the floor will quickly evaporate and not accumulate, especially when there is a sudden drop in manifold pressure. The late model "Fenton" headers do not seem to have the real heat riser, just bypass tubes. How well do those work?

If the heat riser valve sticks in the position to force continous circulation of hot gas through the intake manifold, the air can be heated too much, reducing power at wide-open throttle and lowering the knock resistance, as I believe Panic was indicating.

I got the Fentons with 3/8 tubes and heat plate design on my 235 aluminum intake (also McGurk) and it works just as well as the heat riser.
Each exhaust pulse passes a small amount through the tubes across the intake floor chamber into the other header.
I have done the same driving with this setup and also never overheated.

Notice, I don't use carb spacers, as the cast aluminum doesn't get as hot as the original cast iron intake.

Getting the intake hot as soon as possible after cold start is definetly key, especially in the colder months.
On cold winter mornings, I place a small space heater on the ground directed at the intake for at least 30 minutes with the hood closed.
Starts easier and the carbs run smoother the first mile or so, until everything comes up to temp.

I never tried water heated intakes, but in the winter it must take a lot longer before the fuel gets vaporized properly.

When you say 'regulate', what exactly do you mean? Do you a way to keep the manifold heat less than the engine temp?

I ask because I found that I was boiling the fuel out of the carb after it was parked if the coolant temp was around 180 deg. I put in a cooler thermostat and the problem was solved, but now I don't know if I'll have enough heat when the ambient temp is around zero.

The manifold will never run as hot as the water, because the flow rate is low. Want even lower? Restrict the water, or turn it off.

well this is the perfect place to share this with everyone. i'm running fenton headers with an edmunds intake which of course eddy edmunds intended to be heated with water. the tube cast into the manifold is 5/8" OD, just right for 5/8 commpression fittings. that's exactly what used & then adapted down to 3/8" tube to the headers. works great, warms up very quickly. you can feel it on the side of the intake with your hand. the bypass tubes in the fentons DO WORK. i suspect that exhaust heat in hot weather probably probably hurts performance some. i also suspect the amount is miniscule.
Robert