Blocking Off Heat Risers

dullchrome

dullchrome

Senior Member
Ive heard of guys blocking off their heat risers with pennies for years. Is there any advantage or disadvantage to doing this? I am running dual exhaust on my 48 but it is stock other than that.
 
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Re: Blocking Off heat Risers

Not real good for all weather drive ability... It's to help keep intake air cool, condensed... Cold weather... Not so good, will stumble..
Karl.
 
Re: Blocking Off heat Risers

There are both advantages and disadvantages.

Pro - Your exhaust note with duals will be awesome!
Pro - Your carburetor will not boil over anymore.
Pro - Your engine will gain a vary slight raise in horsepower due to a colder intake.
Pro - You will gain bragging rights on your oldtime hotrod modification.

Con - Your exhaust note will be louder.
Con - Your carburetor will need to be choked until your engine is fully warmed up.
Con - High speed driving may tend to burn your center cylinder exhaust valves over a long period time.

If you do it, be sure to use wheatstalk pennies. The new pennies don't have the metalurgy that the old ones had, and may burn out whereas the copper pennies won't.
 
Re: Blocking Off heat Risers

The one advantage I like is the sound it gives a car with dual exhaust. The pennies block the exhaust gasses from crossing over to the other side and equalizing the pressure. An old dirt track racer told me they blocked the heat risers to get a little more power. I guess the thinking was the cooler gas would be more dense and perform better.

Too, with today's alcohol-gasoline it might help prevent the gas from boiling in the carb.

Just my thoughts...

Shadetree
 
Re: Blocking Off heat Risers

Provided you slathered all the surfaces of your intake gasket, manifold and block with grease, you can also slip copper or steel shimstock in (out) to block(unblock) the holes just by loosening & tightening the manifold bolts. Gaskets are usually resilient enough to seal OK.

Jack E/NJ
 
Re: Blocking Off heat Risers

Karl Wolf said:
Not real good for all weather drive ability... It's to help keep intake air cool, condensed... Cold weather... Not so good, will stumble..
Karl.
Click to expand...

Since I live in Southern California and we really dont have much weather change to speek of do you think it would be an issue to block them off?
 
Re: Blocking Off heat Risers

I used oil can tin back in the old days to seal heat riser holes on all manner of things including Olds engines.
 
Re: Blocking Off heat Risers

ford38v8 said:
There are both advantages and disadvantages.

Pro - Your exhaust note with duals will be awesome!
Pro - Your carburetor will not boil over anymore.
Pro - Your engine will gain a vary slight raise in horsepower due to a colder intake.
Pro - You will gain bragging rights on your oldtime hotrod modification.

Con - Your exhaust note will be louder.
Con - Your carburetor will need to be choked until your engine is fully warmed up.
Con - High speed driving may tend to burn your center cylinder exhaust valves over a long period time.

If you do it, be sure to use wheatstalk pennies. The new pennies don't have the metalurgy that the old ones had, and may burn out whereas the copper pennies won't.
Click to expand...

This may sound stupid but do you just shove the pennies into the riser ports? What holds them in place?
 
Re: Blocking Off heat Risers

The pennies need to be tapped in with a ball peen hammer. I was talking with Walt Dupont today, and he told me that he had done this with a dragster engine and had blown the pennies right out the exhaust. (He couldn't tell me if they had been the wheatstalk or not). He later just used expansion plugs to do the same thing.
 
Re: Blocking Off heat Risers

Since I live in Southern California and we really dont have much weather change to speek of do you think it would be an issue to block them off?

I see no big difference in warm up here in West Virginia, but then I never run it in the winter time.

Shadetree
 
Re: Blocking Off heat Risers

I just blocked mine a few weeks ago. I used .020 SS 1 1/8"X 1 1/2". Bent a tab up 3/8" on the 1 1/2" side to hold it when sliding in place. Punched a 1/4" hole in the center 5/8" from the other end. Loosen the intake bolts and slide them in centering on the heat riser humps. Tighten the bolts and your done. This will provide some heat and not completely block it. This along with a 1/2" vented phonolic spacer and longer studs from Bob Shewman gadgiteer@aol.com will completely solve the gas boiling in the carb. I just installed one of Bobs spacers. Before the heat riser block and the spacer the heat on the manifold where the carb mounts was 157 degrees + and the base of the carb the same. After the heat riser mod and the spacer today when it was 85 degrees out after close to 2 hours of driving the manifold away from the carb area before was 157, at the base where the carb mounts and 140 today which is a 17 degree drop. The big differance is the carb base above the spacer 107 and bowl of the carb where the fuel is stored was 115. The gas is heated in the fuel pump from the 157degrees of the intake manifold 3/4" below the fuel pump to 122 degrees and loses a little heat from the cooler gas flowing through the pump from the tank. The longer it sits at idle or slow speed the more the gas in the pump is heated. I'm rising the fuel pump next week with a 1" phonolic spacer and a longer push rod I started making today. Threaded the push rod 3/8-24 1 3/8" long, 1/2" hex steel drilled 1 1/16" deep and tapped 3/8-24. Turned the hex beyond internaly threaded area down to 3/8" OD like the push rod. Will screw a 3/8 24 jamb nut on the threaded push rod then the new hex part. and with a little locktite, adjust the push rod to the length I want and lock it in place with the jamb nut. Now I will be able to adjust the pump pressure if require. I'm pretty sure this will take care of the heat on the pump which is maybe the biggest problem. If you ever saw the gas boil in the glass bowl this is what its from. Just a few bubbles in the bowl leads to lower pump pressure that pulsates. Also you can see the pump pressure drop as the pump gets hotter. G.M.
 
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I don't mean to sound like a nincompoop :rolleyes: but where on the flat head are the heat risers located. Dose anyone have a picture so I could see what you all are talking about. This is my first flat head and am in the learning process. :confused:
 
You'd be a nincompoop if you casually nodded your head without understanding. I don't have a picture to show you, so I'll try to describe it for you with words.

The top surface of the block where the manifold bolts to has a hole exact middle on each side the same size as a penny. These holes pass directly into the center exhaust dumps of the block. The manifold has corresponding holes, with the passage from each meeting at the top of the manifold, directly under the carburetor base.

Exhaust passes from each side through the riser to the other side, in a back and forth manner, as the firing order dictates. If you know anything about how a muffler works, the effect is the same here, each exhaust pulse helps cancel out the pulse pressures of the opposite side, and consequently reduces noise as well as excess heat and backflow at the twin ports next to the exhausting ports.
 
under the intake manifold on both sides are two exhaust outlets which combined with the holes in the intake form a passage under the carb but within the manifold that allow exhaust gases to heat the intake thus heating the carb-ever notice paint seems to burn off the intake under the carb??
 
What is this and does it have anything to do with what you are talking about? It comes from some old original sales promotional literature for the Sedan Delivery. I always wondered what it was. I've not seen one on my engine but is promoted as standard equiment. Anybody know?
ExhaustValve.jpg
 
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Here's some more about it. Don't any of our engines have this any more? If not, why not? Sounds like it would solve the problem you all have been talking about and give all the pros of both options? This is from the Passenger Car Sales Handbook:
ExhaustValve20001.jpg
 
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Thanks for the explaining this to me. This is some I'm interested in because last summer on several occasions my car would start spitting and sputtering and eventually die out on me. Let it set for a while and it would start and away we would go till the next time. This some thing I'm going to try and see how it works. Like I said this is my first flat head and I need to learn the tricks of the trade.
Thanks again.
 
bige386 This is what you and all flathead owners are going to face with the new gas mixtures in temperatures above the area of 80 degrees. I explained how to partial block the heat risers above. This will give a little relief but for complete cooling of the carb Bob Shewmans 1/2" vented spacer cools the base of the carb as shown in my temperature report also above. There are also problems of the gas heating in the line and pump also in the above post. If you have a glass filter bowl on the pump and you see bubbles in the gas your getting ready for vapor lock. These vapors and heat in the pump also cause the fuel pressure to drop and the pump not provideing enough fuel. These problems start with stop and go traffic, long periods of idle and heat build up after the engine is shut down. When you stop in hot weather lift the hood right away to allow the heat to excape. Buy a laser pointed thermometer and check the temperatures on the base of the carb. the area on the carb where the fuel bowl is, the fuel line where it is clamped to the fire wall and the pump it self. When any of these get in the 120 range the problem is just starting or all ready there. G.M.
 
There are two factors at work with the heat risers on any engine...
Stock, or near stock engines love the heat risers, the fuel is properly pre-heated for complete vaporization..
Speed freaks love to block/eliminate the heat risers because the exhaust makes more noise, which givers the impression of more power.
In the real world, elimination of the heat riser will make an engine run rich.
When I was young and foolish we would block off the heat riser ports in a Ford flat-head by sliding a piece of shim stock or thin metal from a pipe tabacco can between the intake gasket and the block... When the weather cooled, or we were tired of the added noise of the pipes, we would loosen the manifold bolts, with-draw the metal and re-tighten the bolts.
The whole subject boils down to.... do you want reliability or do you want noise?
 
This isn't a question of noise. The reliability applies because if this new gas gets to hot it boils in the carb. Read my temperatures in warm weather and you will find out what I'm talking about. This isn't guess work or what I think will happen as most of the posts, these are actual temperature readings and visual veiwings of the gas boiling over the top of the carb, bubbles in the fuel bowl and pressure drops on a fuel pressure gauge. These are real facts with this new gas in warm weather and can be corrected. G.M.
 
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