Batwing-eight

Eliminating exhaust manifold heat riser on '30s-'40s vintage cars?

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Has anyone had experience, good or bad, with removing the thermostat-controlled exhaust manifold "butterfly" used in vintage cars to redirect exhaust gas to warm the intake manifold upon start-up? Obviously, there's benefit in warming the incoming fuel/air mix when the motor's cold, but it's also likely impossible to completely close-off the heating after the motor reaches operating temperature, thus increasing the chance of vapor lock and hard starting. That butterfly also places some restriction in the exhaust flow. Leave it in or remove it? Bill.

 

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Just repair it.

 

While you are in there look at how it works. If it is an inline engine, it is not a restriction when hot/open. More heat goes to the carb with the plate removed, not less, because there is nothing to deflect the exhaust away from the intake when the engine is hot.

 

If you get back into the 1920s you may find some units that provide way too much heat. From the mid 30s on, probably not.

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4 hours ago, Batwing-eight said:

Has anyone had experience, good or bad, with removing the thermostat-controlled exhaust manifold "butterfly" used in vintage cars to redirect exhaust gas to warm the intake manifold upon start-up? Obviously, there's benefit in warming the incoming fuel/air mix when the motor's cold, but it's also likely impossible to completely close-off the heating after the motor reaches operating temperature, thus increasing the chance of vapor lock and hard starting. That butterfly also places some restriction in the exhaust flow. Leave it in or remove it? Bill.

 

 

Dammned if you do, dammned if you dont.

 

It might come down to where you are living. In a cold climate it will certainly reduces the potential for throttle ice, in a hot climate it raises the potential for vaporizing; so perhaps it's the toss of a coin ?

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Up draft or down draft ?  I’ve done it to both. And the only negative is that on the updraft it takes forever to warm up an I get carb ice certain times of the year. (West coast of Canada). On the down draft I notice no difference. Fuel is much better these days and not so fussy on warm air, but as said above depends on where you live for warm uptime. 

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Can you be a little more specific please. What car ? My 28 DB 6 butterfly is controlled manually with a cable from the inside of the cab. Some are controlled by vacuum from the carburetor via a vacuum tube under the air snorkel via a rod to the butterfly inline the exhaust pipe with all types of sheet metal baffles. Some work with a thermostatic coil  spring attached to the shaft on the outside of the butter fly shaft. If you  want to drive  only in summer,  remove any type of thermostat it really does not matter. Initially the system was provided for quick warm up in cold weather . Very important during the gas crunch days.  The system was not perfect and there was always the danger of the butterfly being stuck in various  undesirable position.

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Heat risers are not just for cold weather. They exist because fuel tends to fall out of the air when the air makes a bend, The fuel then pools on the bottom of the manifold (assuming a downdraft system), and runs around, maybe re-vaporizing, maybe not. It is basically impossible to get reasonable fuel distribution with this happening.

 

EVERY carbureted or TBI car that is even remotely modern has a hotspot under the carburetor or TBI. You would have to go back nearly to the brass era to find something that doesn't. The only exceptions might be racing homologation specials (NASCAR, NHRA, etc.) that are meant to run with the throttle wide open most of the time, and some multiple carb setups that really need to be fully "warmed up" before they drive very well.

 

Sometimes the heat comes from exhaust, sometimes from coolant, but it is ALWAYS there.

 

Even over on the HAMB they seem to know this. The first rule of hot rodding is to get as much COLD air into the engine as you possibly can, (because thats how you get the most oxygen in, more fuel is easy to add) and yet, when someone tries to run an old Edmunds or similar multiple carb manifold, and cant seem to get it to work for street driving, the first bit of advice is always to add a hotspot. Some of those old manifolds even have provisions for one cast in.

 

 

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I agree with Bloo. I have a TBI on my buick.  On a self made manifold.  When the manifold was first installed she did not always run right an low throttle conditions. The are just below the throttle [ carb?] body would ice up due . When one thinks about it, at slight throttle, high vacuum, the fuel system is working almost sorta the same as AC.  Pressured liquid gas squirting into a vacuum equals cold.  I added heat to the area beneath the throttle body and icing went away.

 

  Ben

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Carburetion 101 - fuel atomization

 

There are three major enhancements for improving fuel atomization:

 

(1) Increase air velocity

(2) Add heat

(3) Increase the amount of fuel

 

Jon.

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With no pics or even a reveal of what you have it's a shot in the dark but Ford and others used hot water (coolant) to heat the carb. A heat exchange plate would not be difficult to make.

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The car is a '36 Studebaker President-8 with a joined intake and exhaust manifold and thermostatically controlled heat riser valve in the exhaust stream below. Unfortunately, years of improper tightening of the bolts between the two manifolds allowed exhaust gasses to pass the separating gasket and "eat" away some of the cast iron manifold's mating surfaces.

 

Fixing this required making  an .080" thick steel plate fitting between the two manifolds to make-up for the original metal that was lost, plus the machining necessary to obtain new, parallel manifold surfaces.  (The plate also restored the correct alignment of manifold ports along the block).

 

This new plate offered two opportunities: 1) make no cutout in the plate for heat riser directed gasses, then lock the heat riser butterfly in the "open" position. Now the intake manifold above the plate has NO exhaust gas coming near it. 2) Cut a pathway in the plate for exhaust passage and leave the original butterfly untouched. Unit would now operate as original.

 

My question dealt with the wisdom of eliminating the heat riser "system," by "'no exhaust passing through the .080" plate" and securing the heat riser butterfly so it's always "open."  Another benefit of this approach is that only one asbestos gasket is required (below the plate). No gasket is required above the plate because this area is now "dead air."

 

I'm in Washington, where temps are usually somewhat mild, so I thought this approach might be workable. Bill.

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I'm driving a 36 Pontiac around in Washington State. It has a thermostatic heat riser similar to what you describe. When I fixed it, the car started running right. YMMV.

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I think the butterfly valve in the manifold is "closed", meaning no exhaust into the intake manifold chamber, on my Dodge 8. I have had icing problems when the temp is below about 12-15oC. My solution is to start the car, idle for five or ten minutes while doing checks etc., then shut off for five or ten minutes while I fetch my jacket, camera, lunch, water, marbles, whatever. During this time the heat from the exhaust manifold and the warm engine has permeated into the base of the carb and the car will then drive away with no problem. It is not a "jump in and drive away" car in cooler weather.

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On my 62 and 63 Catalinas I welded the butterfly in the rt side manifold to the open position. In 1969 Pontiac division eliminated it altogether. the manifolds have a boss but no butterfly.

On my 455 LeMans I use a factory RA4 aluminum intake which uses a factory cast iron exhaust crossover that I discard for block off plates , a modified choke less Q jet on a 1 " phenolic spacer and  heat shield and a open element air cleaner.  It can be 17 degrees outside and I still never have a problem starting that car. All my cars with carburetors do not have chokes or are blocked in the open position except for a euro. VW beetle that has a manual choke that I don't use.

 Starting is easy. All the early Porsches start this way as they have NO chokes. Crank the engines until 60psi is reached and the engine sputters. This tells me three things. 1. I have fuel to the carb and can now manipulate the throttle without fear of damaging the accelerator pump. 2. the sputtering tells me I have ignition to the fuel. 3. My engine is oil primed. NOW I press the accelerator to the floor four times and then crank the engine. I use the throttle to do the choking and the engine comes to life and I nurse the engine to 1,000 and hold for about a minute and then I can slowly release the throttle and the engine will stabilize itself all on it's own.

Many of the cars I've owned since new like the LeMans which is coming up on it's 51th birthday in Dec. and when they were daily drivers they were perfect for the wife. The wife had a tendency to rev up and go immediately on a cold engine. With the choke and the fast idle cam disconnected or removed the cars would fall on their face so it taught her to respect a engine and let it warm up before taking it to task. She finally understood when I put it to her like this; you wouldn't want to run a 50 yard dash without warming up and stretching would you?

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