Center mount carb preheat question help

[ccowx]

Actually, OPRN is right, the pre-heat into the air cleaner is the bigger part of the solution to the issue of carb icing, due to it's being before the carb. I have been told that the factory system picking up heat at the head is adequate to around -10C, after that it needs improvement. However, there is a reason why both systems are installed at the factory. I will stand by that the intake heat will improve the icing situation somewhat, but really what you need to run the engine efficiently at all temps is both. The factory would not have had a constantly evolving and improving series of systems for this if it was not needed. They don't like spending money when they don't have too!

Much of the effort into performance is stemming from California and/or summer only cars. The art of making it run right in all normal environments that a car sold world wide is going to encounter seems to be lost. You can get away with a lot of things when you live in a dry environment and the car normally doesn't see temps below 65F. Try driving in a fog at 50F on the west coast at idle speeds with neither manifold or air cleaner heat and see how it all works. Or better, try driving in -35 and icy fog. I have done both and I will take any heat I can get!

Chris

[Fair-cooled]

Not how I understand it, and not how Porsche fixed the trouble. The problem isn't before the carb, it's from gas chilling as it becomes vapor. The bend actually becomes frosty when this condition is severe...not above the carb.
Good luck.
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‘74 Super beetle, originally from California until 5 years ago.

Seize the day...not the Engine...

[oprn]

There is a third problem that I have experiance that has not been mentioned here are far as I know. I have experienced it 3 or 4 times in my life. It happens in cool damp weather also and after driving for a while at a steady cruise speed. you go to slow down or speed up and the throttle does not respond! It's stuck!

This is a form of carb icing but it is caused by a worn throttle shaft and/or bushings. Damp air is being drawn into the carb along the throttle shaft and forming ice there. It literally freeze the throttle shaft in one position. Lift the hood and you cannot move it. The quick fix again is to shut off the engine, coast to a stop and let the carb heat soak from the manifold. Lock de-icer can work too if you have some and can reach the shaft at both ends.

This in my view is the most dangerous of these conditions! The stock Solex carbs were bad for this as they aged. The long term fix is to replacement.
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Our cars get old, we get old but driving an old VW never gets old!

[Fair-cooled]

Yes, I have read that damp air makes the situation worse, and your experience reflects this. I think if there was zero moisture in the gas a heat-riser would likely not be needed. Good point oprn.
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‘74 Super beetle, originally from California until 5 years ago.

Seize the day...not the Engine...

[oprn]

[Fair-cooled]

Irregardless of the poor dogs plight, the fact remains that the heat generated by the engine occurs below the engine tin inside the engine compartment. Of course that is why the tin is located down low...to keep the engine heat from rising into the engine compartment, which would start a process that would lead to heat soak. If the warm air below the tin was allowed up into the engine compartment, then warm air ( read low on oxygen air ) would enter the carburettor. This would lead to less power generated ( because the air has less oxygen ) but more heat ( the warm air entering the carb getting much warmer after combustion). Then the cycle would repeat, only now the air entering the carb is even warmer, so it generates less power again, but still gains more heat from the combustion. Then this happens again, and then again, each time the engine produces less power until heat soak is reached and the engine no longer gets enough oxygen for combustion and the engine stalls. And it is very hot when it stalls.
So Porsche ( and Hans Ledwinka ) block the hot air with the tin, but use heat-transfering aluminum for the heat risers, which only have to go up into the engine bay a short distance to reach the ninety degree bend in the intake manifold, which was deliberately placed low in the bay so that not too much heat from the heat riser tubes would be lost into the engine bay, but would be absorbed into the lower part of the intake manifold, which is where most of the "riser" heat is absorbed, and this keeps the fuel-air mixture from becoming cristaline, which would soon be ice if it wasn't for the heat riser tubes.
So this is a case where saving the dog necessitates swimming against the current if
Pooch is to survive. To return to the heat riser tubes briefly, we should rember that Germany has very cold winters, and for Hitlers KDF car to be affordable, air-cooling was seen as the best alternative. It was only a few years before the Beetle was designed that anti-freeze was designed to replace the water in a liquid cooled car. Before this, during winter even in the northern parts of the USA, the water had to be drained from the engine every evening or a fractured engine block would be waiting the morning after a particularly
cold night. THIS NEXT PART IS ASTOUNDING, AND I HOPE YOU BOTH WILL HUMOUR ME AND READ IT. IT ONLY TAKES ABOUT 5 MINUTES...PLEASE...

BTW- HANS LEDWINKA , a fellow Austrian like Porsche, but who was working in what was then Cheyzloslavakia for the Cheyz government to create a peoples car for that country, had done years worth of air-flow testing to enable air-cooled cars to get enough cold air in an area that is low pressure ( directly behind the car ). He patented a vast amount of new patents, and when Hitler took a ride in a Tatra with Ferdinand Porsche, he said " this is the kind of car I want you to build for the German people".
When Ledwinka found out about the Beetle, he immediately took Porsche to court for patent infringement. Porsche was ready to pay Ledwinka for these damages, but Hitler heard about it and instructed Porsche NOT to pay for the patent infringement, because
Hitler said " I will take care of this", and he did, by invading Cheyzlosavakia. This is all known and documented, so when the war was over and the NAZIs defeated, Ledwinka returned to the courts. He was awarded the equivalent of 1 million American dollars, but sadly he died before he received one red cent.
The way that automotive writters describe this TRUTH, is that Volkswagen "is very sensitive about this issue". Look this up some time if you find it interesting. It is 100 %
factual. It is well documented, and if you both are like me in that you enjoy Jay Lenos utube automobile programs, you have likely heard him refer to this event. He is not afraid to tell the
truth about this rather foul piece of automotive history. One reason that I have great respect for Mr. Leno.
I hope that if you didn't know this ( many people have absolutely no idea of the situation thar led to Germanies " Amazing recovery" post WW2 ) you find it both interesting and intreaging. I know I do.
Cheers gents,
Darren.
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‘74 Super beetle, originally from California until 5 years ago.

Seize the day...not the Engine...

[oprn]

[Fair-cooled]

You are a phunny little guy, but I've been wasting my time with you. I won't be replying to you again, but feel free to write ( type ) your hate out! I mean write your heart out. Good night.
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‘74 Super beetle, originally from California until 5 years ago.

Seize the day...not the Engine...

[Hnoroian]

Never mean for anyone to be in a tiff, especially when we talk about different experiences and situations. Everything that has been stated holds a valid truth for individuals. There are some great ideas being thrown around, and thank you for all of them.

Much of my particular problem I believe will be alleviated because of the generalized operational and personal temperature limits in my location.

So then comes to question how would one in this situation achieve warmer air to the carb?

Remembering this is a non-stock Baja (open engine compartment) tri mil exhaust, center mount IDF, etc. not ideal for perfect operation.
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Stupid people do stupid things.

[modok]

With the heater.

"but I took the heater boxes off"

hmmmm

[jberger]

Late to the party... but that Tupperware is brilliant.. I used a cookie tin on a center mount progressive Type IV years ago.. with a heat riser off the exhaust crossover. Was a game changer, until ambient temps got into the 90's.. then you needed to "pop-the-lid".. Ended up using gutted 1600 DP bug oil bath with automatic "lid-popping"! Still runs that way.. no manifold heat.. but plenty of pre-heat.

J

[Fair-cooled]

Hi Hnoroian.
Your question of how an engine ( in this case the VW air-cooled Beetle ) can create an air intake tract that is operating at an optimium temperature is a very valid one imo. Since the Beetle was to be air-cooled, Dr Porsche had to devise a way to achieve a warm intake without coolant, which is the most common method for water cooled cars, motorcycles etc.
So, since he had no thermostatically controlled water to use, he picked the most obvious source of an air-cooled cars, the exhaust heat. He simply connected an aluminum tube from one muffler up through a hole in the engine tin, over to one side of the intake manifold, through on to the other side of the manifold ( but never are the two pipes open to each other, only touching each others outer tube, and thus heat was conducted from the heat riser tube
{ the narrow tube that connects between the two mufflers } to the intake manifold tube thereby raising the intake tube to a warm temerature ( thanks to the heat taken from the mufflers ) that assured that the fuel-air mixture would stay a mixture of fumes and NOT condense and then freeze at the 90 degree bend in the intake manifold, as the mixture splits to feed both the left hand side cylinders, and also the right hand side cylinders.
So that is how the Volkswagen air-cooled flat four cylinder engine keeps the fuel-air mixture from freezing up and stalling the engine. Quite clever I think.

Cheers Hnoroian.

Darren.
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‘74 Super beetle, originally from California until 5 years ago.

Seize the day...not the Engine...

[jberger]

[oprn]

Has no one on this thread ever seen the stock air cleaner with the hose that runs down and connects to the tin elbow fitting under the right cylinder bank? Have they all hit the garbage so long ago that nobody has seen one?

Maybe our Tupperware guy has a picture, I suspect that is what he is using. Stock VW parts guys, no need to reinvent the wheel.
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Our cars get old, we get old but driving an old VW never gets old!

[ccowx]

OK, I have no interest in joining whatever p#ssing match seems to be started here, but in the interest of clarity I do need to put out a fact or two.

-First of all, what you describe, fair-cooled, is perhaps theoretically possible with the heat soak, but in practice of having driven ACVW's for roughly 20 years as daily drivers, it has never happened. If the heat in the engine bay was hot enough to cause the issue of low oxygen in the air, you would have other issues first, probably including a fire. I would estimate you would be hitting something close to 200 F degrees and the engine bays are just not that air tight to hold that. Most likely what would be the reason for the engine to stop would be the oil breaking down and the engine seizing.

-The one time I did experience a heat soak issue with my engine was when i was climbing a 2500' hill, behind a slow moving truck, in a fully loaded 4000 lb+ camper, in temps over 100F/35C. At that point, what actually happened was not an issue of lack of O2 but that the fuel pump itself heated up via heat obsorption from the block and fuel vaporized there, causing the pump to stop working. The engine itself ran fine, as intended by Porsche, but the pump stopped working, just as any liquid pump will stop at any temperature if there is a no liquid in the pump. The issue was not combustion but a mechanical failure that prevented the fuel pump from delivering fuel to the engine.

-Just for clarity, there is in every factory acvw engine I am aware of a 2" hose that picks up air at the cylinder head via an L shaped pipe and feeds it into the air cleaner and into the carb. It is thermostatically controlled either by connecting to the engine thermostat/vane assembly over the cylinder heads or with an independent thermostat. Either way, there is a factory designed system to deliver warm air to the carburetor for the purpose of preventing carb freezing.

-A note on the system of air pick up for the air cleaner. It is thermostatically controlled so that it does not function when the heads are warm enough or when the carb air temp is high enough. It is worth noting that the VW engineers constantly developed this system and eventually made it independant of the head temp. Effectively, the final 1971 and up system was an independant thermostat that would keep the air temp at a minimum of 50-60 F/15 C regardless of the outside temp.

-Also worth noting is that the carb pre-heat system is adequate to around -10C or 20 F or so. After that the pick up at the heads is not efficient enough. This might make for a slightly rougher engine or in extreme cases allow for carb icing. I suspect that in practice most situations that are cold enough to make that happen probably don't have much moisture in the air anyway, but it could be an issue. More likely is that the combination of the intake and carb pre-heat would simply not be able to keep the fuel/air mixture in suspension and you would have a rough running engine.

My personal opinions are this:

-The carb pre-heat is nice to have for carb icing and has the effect of taking some of the load off of the intake pre-heat. The warmer the air going in the less freezing issues in the carb/intake and the less intake heat needed to keep the fuel in suspension.
-The most important heat issue to address is the manifold pre-heat. This is because no matter what the outside temp and humidity the fuel air will chill due to the venturi effect and this will likely cause fuel distribution issues.
-There has been a lot of talk over the acvw world about heat being conducted through the heads and intake manifolds and that being sufficient to insure fuel vapourization. I can see this working to some extent in warmer conditions where most of these cars operate now, especially for dual carbs. I can not see that working at -40 on any set up and I absolutely can not see it happening on a factory center mount system. No way will heat move against the airflow for the 18"+ per side needed for it get anywhere near the carb or the bend in the manifold below it.

Not trying to fuel any fires(pun inintended!), but practical experience and theory both tell me that the pre-heat is needed both at the carb and the intake to insure smooth operation at much less than room temperatures. How smooth or otherwise is a function of temperature, humidity and some variation in each system. However, having operated acvw's for years in temps from 40C to -40C (110F to -40F) with and without either or both pre-heat systems, I assure you they are there for a reason.

In the OP's case, the lack of humidity and extreme temps means that it will be fine overall, but there will be some roughness at colder temps and warm up will be slower. Mileage may suffer a bit at times. Otherwise it will run fine I am sure.

Chris

PS: Fair-cooled, no one is hating on you, but on a forum like this it is fair ball to disagree with you. In this case I respectfully submit that my experience does not support your statement about heat in the engine bays and in the interest of helping the OP I feel that I need to say that. I did enjoy the historical note on the development and thanks for that.

[vamram]

Sorry if this is a dumb question that doesn't contribute much to this thread, but the topic makes this a good place to post it....I would like my stockish '74 Super to run well once I get it back n the road. Do any of you have experience w/the '74 CA dual pre-heat intake manifolds? Are these better than the single pre-heat manifolds? I was planning on using it along w/this header:

Thanks,

Víctor
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[ccowx]

Vamram,

I have seen those before and I think I might have even considered buying those headers, or a set just like them. The main reason I did not was that I needed a better intake center section for my purposes and they would not have hook ups for the dual pre-heat pipes.

I would imagine that it would add some extra heat to the system and help in serious cold. California added it to improve fuel atomization and therefore combustion efficiency. It would also help in extreme cold I am sure, how much or how neccessary it is are probably functions of your overall system. Probably an insulating wrap would serve a similar purpose in practice.

Chris

[Fair-cooled]

[Fair-cooled]

I know the answers juniorberger. You are the one that wants to know, otherwise why are you wasting peoples time.
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‘74 Super beetle, originally from California until 5 years ago.

Seize the day...not the Engine...

[Rob Combs]