239 flathead, block the heat riser passage, or no?

[rjlester]

I recently picked up a Canadian 54 Meteor with a flathead (yes, Canada got the flathead one more year than the USA). Pulled the intake yesterday to look for a vacuum leak and I discovered two pennies in the block covering the heat riser passages.

One was 1980 and the other one was 1976. Kinda cool! I had a feeling the car was last worked on in the 80s. Been parked for many years.

The flathead in my other car (also a 54 Meteor) did not have them blocked, and I've had very few vapor lock issues. Only on very hot days will it turn over a bit more to start, but I can always start it. I rarely drive it on hot days so I suspect a previous owner had issues, or maybe whoever rebuilt the engine figured it was the thing to do.

Thoughts? Leave them, or take them out? Any performance issues either way?

[Merc Cruzer]

I block mine off, with a little pieces of metal, with a 90 degree flange. That way I can take them out or put them in, by simply loosing the intake bolts and sliding them in or out. I like the penny idea, used to block off the opening, but this is just simpler.

If I remember right, you are supposed to use "wheat penny's".

For me I noticed the big reduction in the temp of air going to the carb, resulting in fewer heat related issues, on the hot days of Summer.

[38 coupe]

I've never felt the need to block the heat riser passages when driving here in Texas. I do have to adjust the float down a bit to compensate for the "modern" gasoline with alcohol in it since I'm not willing to pay $1 per gallon more for gasoline with fewer refining processes done, and want to have my car ready to drive anywhere in Texas that sells gasoline. I appreciate the heat riser on cooler mornings with tons of humidity. A foggy morning with temps between 40 and 60 F can ice up a carburetor without heat.

[Merc Cruzer]

I will freely admit, mine is a little slower to warm up on the cooler mornings. But once the sun gets higher, and driving at 8300 ft with the "modern" gas, it runs fine. But that is also why I made the tabs easier to remove, in the event anything changes.

This works for me, it may not work for everyone.

[flatjack9]

I would not block the risers.

[Merc Cruzer]

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A little additional reading on this subject:

https://www.fordbarn.com/forum/showt...ng+heat+risers

https://www.fordbarn.com/forum/showt...ng+heat+risers

https://www.fordbarn.com/forum/showt...ng+heat+risers

https://www.fordbarn.com/forum/showt...ng+heat+risers

https://www.fordbarn.com/forum/showt...ng+heat+risers

https://www.fordbarn.com/forum/showt...ng+heat+risers

https://www.fordbarn.com/forum/showt...ng+heat+risers

[cjshaker]

To get around the icing problem on older engines, I always start the car, let it run till it starts to ice and sputter, then shut it off. The heat sinks into the intake and carb and it goes away. Never had a problem after that. Yes, it takes a few extra minutes, but I'm never in that big of a hurry.

[Flathead Fever]

Some of the flathead racing manifolds don't have the passages at all. The street manifolds have them there for a reason. They were needed for everyday driving in cold weather. With that said I block them off on my hot rods. Mainly because it changes the sound of the exhaust. I'm here in SoCal where its doesn't get that cold. I like to being period correct, so I use the 1943 steel wheat pennies.

[ford38v8]

Wheats are said to be best due to ther alloy differences with the newer pennies. With opinions on both sides, there's another option to consider, that being to drill a 1/8" hole in wheat pennies. A compromise can satisfy both camps sometimes.

[Pete]

One of the percieved benefits of blocked heat risers was noisier pipes if you had Smittys. More noise equates to more hp. Many bench races were won for the measly cost of 2 pennies

[Tim Ayers]

Originally Posted by Pete

One of the percieved benefits of blocked heat risers was noisier pipes if you had Smittys. More noise equates to more hp. Many bench races were won for the measly cost of 2 pennies

This seems the best HP gainer per dollar (or cents) spent ratio one can do to a engine. LOL!

[RalphG]

I'd never heard of blocking those heat passages on a flathead before. In fact it was standard procedure when working on the engine to clean out those passages so that there was good flow of exhaust to help prevent carburetor icing. I've never seen a problem with icing on these carbs but do see it on tractors with the updraft carburetor even on a high humidity day in summer. As someone else commented already, if a carb ices up after a cold start, just let it set a few minutes and the heat of the engine will melt the ice and no more problems. I've done that on the Holley two barrel on IH truck V8s. It works.

[blucar]

Originally Posted by Pete

One of the percieved benefits of blocked heat risers was noisier pipes if you had Smittys. More noise equates to more hp. Many bench races were won for the measly cost of 2 pennies

Back in the early '50's when I was a teenager working on improving the performance of engines it was very common to block the heat risers of flathead engines and eliminate them from inline engine manifolds.
The purpose was to increase the noise, especially 'rap' on twice pipes. The down side was that the engine ran rich and cold.
Of course as 'pete' said, the myth that noise means more horse power, is just that, a myth.
Of course when I got older and smarter, got tired of having the cops on my tail for excessive noise, quite stealth became my motto.

[RalphG]

Originally Posted by rjlester

I recently picked up a Canadian 54 Meteor with a flathead (yes, Canada got the flathead one more year than the USA).

Ryan, did you get a second Meteor? The one in your videos last year was a Rideau and had the 255 Mercury engine. Not that it would make any difference on the pennies blocking the exhaust crossover.

[blucar]

I was a little off base in my earlier comment that an engine would run 'rich and cold' with the heat riser removed and/or blocked.
The combustion temp will be lowered, thereby dumping poorly vaporized fuel into the engine which would result in an engine that runs rich with only minimal lowering the engine operating temp.

[rjlester]

Yep, I got another one! This one is a glasstop, but somebody put this 239 in it decades ago and then it was parked. I got it from a friend in Saskatoon.

[RalphG]

Originally Posted by rjlester

Yep, I got another one! This one is a glasstop, but somebody put this 239 in it decades ago and then it was parked. I got it from a friend in Saskatoon.

Great! Hope to see a video of it soon.

[cjshaker]

Originally Posted by blucar

I was a little off base in my earlier comment that an engine would run 'rich and cold' with the heat riser removed and/or blocked.
The combustion temp will be lowered, thereby dumping poorly vaporized fuel into the engine which would result in an engine that runs rich with only minimal lowering the engine operating temp.

It's not about lowering the engine temperature. In every engine, keeping the incoming air/fuel charge as cool as possible means a more condensed charge in the combustion chamber, which makes more power. That is a simple fact of physics. A cooler charge does not mean the engine will be "rich" unless it is improperly tuned. All those things can be addressed within the carburetor with jetting, fuel level etc.


The only reason cold engines will run "rich" are because chokes are typically being used, usually along with throttle advancements, which open transition slots covered by the throttle blades, that will then introduce more fuel into the airstream.


The ONLY reason heat risers even exist is to combat carb icing. They are not there to make the engine run better when at operating temperature. At that point, they are a hindrance to best performance. That's why exhaust manifold heat risers (later engines) are designed to close off once operating temperature is reached. Unfortunately, they never designed an intake system that would, or could, withstand the abuse of the exhaust byproducts and heat, otherwise they would have used it as well.

[pistonbroke]

It's an old racers trick for sure and the ones I have seen were done with Mercury dimes. Cooler fuel mixture is more volume so more is better was / is the idea. Tim

[blucar]

As the seasons change the importance and/or need for a heat riser/like a thermostat in the cooling system also changes.
In a mild climate like So Cal the average engine will run just fine without a heat riser or a thermostat, However. on a cold January/February morning, both items are a must have feature on a vintage engine.
During the '70's/'80's when everyone was crazy for RV's, they found themselves with under powered engines and poor fuel mileage.. A common practice was to remove the stat and heat riser, the result being a engine that stumbled and sputtered. I solved the problem by pulling the 283 V8 out of my C20 truck, replacing it with a 350 HP 396 out of a '68 car that had been wrecked with 2.300 miles on the odometer. We used that truck/RV for 18 years with no issues.