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manifold heat solutions and supporting temp data
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oprn
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PostPosted: Sat Jun 12, 2021 7:51 am    Post subject: manifold heat solutions and supporting temp data Reply with quote

Finally getting back to finishing my exhaust system for my single port 1600 sand rail project. The last step was to rig up the intake manifold heat. It appears to me that the correct direction of flow is right to left based on the stock muffler and the way the heat sink casting on the intake is done. This in my case would put the outlet of the heat riser system a long way from the muffler (normal end point) so I chose to just dump it overboard.

Anyone done that? How did it work? Too much flow? Too much noise?

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PostPosted: Sat Jun 12, 2021 8:21 am    Post subject: Re: manifold heat solution Reply with quote

I imagine that the heat riser exhaust being "dumped overboard". Will sound a little funky.

Why not tie it into the Tri Y 2-4 exhaust pipe? That way the heat is drawn through the intake manifold for better heating and flow.
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PostPosted: Sat Jun 12, 2021 8:28 am    Post subject: Re: manifold heat solution Reply with quote

For it to really work properly you need to hook it up to somewhere else on the header/exhaust/muffler. It doesn't matter where really

The way you have it causes a massive exhaust leak and it won't work right either.

I would connect it to one of the other header pipes
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PostPosted: Sat Jun 12, 2021 9:57 am    Post subject: Re: manifold heat solution Reply with quote

One other thing that just came to mind.
if you leave that heat riser tube dumping overboard.
One small pop out the exhaust system. And you may start a fire in the tall Canadian dry prairie grass. Shocked
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PostPosted: Sat Jun 12, 2021 8:23 pm    Post subject: Re: manifold heat solution Reply with quote

On the stock exhaust, the negative pressure on the left side by the tailpipe pulls the exhaust through the heat riser.
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PostPosted: Sat Jun 12, 2021 8:32 pm    Post subject: Re: manifold heat solution Reply with quote

what happens if you keep what you have... but weld the exhaust side shut. then fill it most of the way with a liquid with a high phase change number?

or... tap into the fresh air outlets your probably not using. if its enough heat of course.
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PostPosted: Sun Jun 13, 2021 3:32 am    Post subject: Re: manifold heat solution Reply with quote

67rustavenger wrote:
I imagine that the heat riser exhaust being "dumped overboard". Will sound a little funky.

Yes it will sound like a large exhaust leak.
67rustavenger wrote:
Why not tie it into the Tri Y 2-4 exhaust pipe? That way the heat is drawn through the intake manifold for better heating and flow.

That would involve 5 to 6 feet of tubing to get it to the top of the engine. My concern is that the added restriction will reduce the flow too much.
[/quote]
67rustavenger wrote:
One other thing that just came to mind.
if you leave that heat riser tube dumping overboard.
One small pop out the exhaust system. And you may start a fire in the tall Canadian dry prairie grass. Shocked

Very valid concern! Grass fires is one of the reasons I have designed this exhaust system to be above the engine. I am planning to put a small lawnmower style muffler in the end of the dump tube to quiet it down and to act as a spark arrestor. Also this car has a skid pan that extends behind where the 1/2" dump pipe stops and sideways to protect the pushrod tubes.

evanfrucht wrote:
For it to really work properly you need to hook it up to somewhere else on the header/exhaust/muffler. It doesn't matter where really

I would connect it to one of the other header pipes

frenchroast wrote:
On the stock exhaust, the negative pressure on the left side by the tailpipe pulls the exhaust through the heat riser.

As far as connecting it to one of the other exhaust tubes - that will not work. That is the exact reason that 99% of aftermarket exhaust systems will not heat the intake manifold properly! You need a difference of pressure to get flow. All other exhaust tubes will have virtually the same pressure in them.

Now to address the "negative pressure pulling the exhaust through" comments - nowhere in an exhaust system is there ever a negative pressure. Especially the stock one! There are places where the pressure is LOWER than it is at the exhaust valve but never negative. The rare exception may be a short runner open tuned exhaust but even then it will only be at a specific resonant RPM and only a few ounces negative. Anyplace in an exhaust system that you drill a hole upstream of the final chamber in the muffler will produce a positive pressure. That said, the best place for me to incorporate this heat riser outlet into the exhaust system would be to drill a hole in the final stage of my muffler and route it there. That would duplicate very closely the STOCK VW set up. Dumping it to atmosphere may produce too much flow but that is easily fixed by restricting the outlet size.

Chickensoup wrote:
what happens if you keep what you have... but weld the exhaust side shut. then fill it most of the way with a liquid with a high phase change number?

That would virtually stop all flow and all heat transfer to the intake manifold and would be no different than a heat riser plugged with carbon deposits.

Chickensoup wrote:
or... tap into the fresh air outlets your probably not using. if its enough heat of course.

???
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PostPosted: Sun Jun 13, 2021 4:45 am    Post subject: Re: manifold heat solution Reply with quote

Somewhere on this forum I recall someone doing this exact thing complete with the lawnmower muffler and reading that it did not work out. I believe it was on a turbo engine though and I suspect there was a resulting reduction in exhaust pressure that delayed boost at the bottom of the RPM range... ???
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PostPosted: Sun Jun 13, 2021 5:57 am    Post subject: Re: manifold heat solution Reply with quote

oprn wrote:

Now to address the "negative pressure pulling the exhaust through" comments - nowhere in an exhaust system is there ever a negative pressure. Especially the stock one! There are places where the pressure is LOWER than it is at the exhaust valve but never negative.

It can be called negative pressure. Bottom line is there is a pressure differential and the lower pressure area does some pulling. One thing you might try is an expansion chamber. This could create a negative pressure wave that pulls exhaust through your heater. Otherwise it could just act like an exhaust leak.
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PostPosted: Sun Jun 13, 2021 8:22 am    Post subject: Re: manifold heat solution Reply with quote

Tie the 'downstream' end of manifold heat tube into the exhaust, do it so it functions like the factory system.

The factory exhaust used the 'venturi effect', with the exhaust gasses passing rapidly by causing vacuum at the tip/opening of the heat tube.
Just like with carb jets, or vacuum pumps used by chemists, or any number of applications..

There are specific instructions from VW about how deep the little chrome peashooter is to be inserted into the muffler, in order to ensure that the heater tube get's it's vacuum 'pull'.
Unless the gases are getting actively sucked out by passing exhaust, the soot builds up and plugs the heat riser tube.

Put it in to or after the collector, have the tube enter the secondary pipe at an angle to increase this scavenging effect.

A couple of people have done this to an aftermarket exhaust to good effect.

The way all of these aftermarket exhaust companies attempt to set this up is a total joke and the tube will just plug up in no time.
Shows how they have no clue..
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PostPosted: Sun Jun 13, 2021 10:48 am    Post subject: Re: manifold heat solution Reply with quote

Clatter wrote:
...There are specific instructions from VW about how deep the little chrome peashooter is to be inserted into the muffler, in order to ensure that the heater tube get's it's vacuum 'pull' ...

Exactly! Look at how the German engineers routed the little tube so that its end will go right INTO the input end of a peashooter:

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And then, they created a Venturi with the baffle holder:
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Maybe you could work a peashooter (or part of one) into your very interesting exhaust system.
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PostPosted: Sun Jun 13, 2021 11:14 am    Post subject: Re: manifold heat solution Reply with quote

So how is the stock Bus single outlet muffler do that then?
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PostPosted: Sun Jun 13, 2021 12:51 pm    Post subject: Re: manifold heat solution Reply with quote

oprn wrote:
So how is the stock Bus single outlet muffler do that then?

It only needs one outlet to create the pull from the other side. The other peashooter doesn’t play a role in it.
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PostPosted: Sun Jun 13, 2021 1:07 pm    Post subject: Re: manifold heat solution Reply with quote

oprn wrote:
So how is the stock Bus single outlet muffler do that then?



Probably like a stock single type 3. One side connects to the heater box on the RHS.

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PostPosted: Sun Jun 13, 2021 1:53 pm    Post subject: Re: manifold heat solution Reply with quote

It will still work if connected to another header tube. It's just a small exhaust tube that heats up and warms the manifold. Yes, routing it in such a way that a low pressure area will help pull the gasses through the preheat tube faster is the "best" way... but sometimes the design of the header will not allow this due to clearance issues, or it just becomes impractical. Such as too much hose or pipe interfering with other components, etc.

IMO it will still do its job, since exhaust gas will fill the tube and warm the manifold either way... metal conducts heat. I'd keep it simple and connect it to one of the other exhaust tubes but just farther away from the flange at head, and then see how it works. If you need to alter it you can do that after some testing.

Or go through the hassle with really long awkwardly bent tubes and route it like a stock one is designed.... and it might work a tiny bit better.... but a long skinny tube also has more length to dissipate heat and cool down before doing its job.... also a free flowing aftermarket header won't respond to the design that same way as VW intended on there stock system. The large dump style stock muffler is a low pressure area but a small perfomance muffler like you have will be different.

I think you can figure out something that will work. It just needs to go from a higher pressure area to lower pressure area. Just before the tail pipe or into an expansion chamber or muffler are solid options.
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PostPosted: Mon Jun 14, 2021 5:35 am    Post subject: Re: manifold heat solution Reply with quote

evanfrucht wrote:
but a long skinny tube also has more length to dissipate heat and cool down before doing its job....

Your thinking on this one is backward. The long skinny part is the discharge side after it has done it's job heating the intake so any cooling will actually enhance flow and make it work better.

I agree that it needs to go from a higher to lower pressure area, that is a no-brainer and that is also why taking it to one of the other equally pressured exhaust tubes has never and will never work properly. I don't know how you keep missing that! I do not see how there could ever be a lower pressure place to dump it than to atmosphere. My concerns are two fold. First is that it will flow too much and get the manifold too hot and second that I will start a grass fire with it.

That said, I would be happier to have it exit in the muffler and I have lots of 1/2" pipe so am going to give some serious thought to putting it in the outlet side of the muffler. Which by the way will be very close to atmospheric pressure.

Well it's obvious that no one responding here has tried this so... let's see what happens... off into the unknown! Thanks for comparing theories.
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PostPosted: Mon Jun 14, 2021 8:05 am    Post subject: Re: manifold heat solution Reply with quote

oprn wrote:
evanfrucht wrote:
but a long skinny tube also has more length to dissipate heat and cool down before doing its job....

Your thinking on this one is backward. The long skinny part is the discharge side after it has done it's job heating the intake so any cooling will actually enhance flow and make it work better.

I agree that it needs to go from a higher to lower pressure area, that is a no-brainer and that is also why taking it to one of the other equally pressured exhaust tubes has never and will never work properly. I don't know how you keep missing that! I do not see how there could ever be a lower pressure place to dump it than to atmosphere. My concerns are two fold. First is that it will flow too much and get the manifold too hot and second that I will start a grass fire with it.

That said, I would be happier to have it exit in the muffler and I have lots of 1/2" pipe so am going to give some serious thought to putting it in the outlet side of the muffler. Which by the way will be very close to atmospheric pressure.

Well it's obvious that no one responding here has tried this so... let's see what happens... off into the unknown! Thanks for comparing theories.

I think you're misunderstanding me as I wasn't that clear.

5 inch past the header flange is a lower pressure area that 1 inch past it was my main point, even if only slightly. If you dont believe me I don't know what else to say.

For some reason I didn't realize you are using a stock preheat manifold. I thought it was all from scratch with a different carb and custom manifold or something. Yes longer tube length would not matter after it heats up the initial length of tube that runs under the carb. I don't know your exact design limitations, as you are building a custom vehicle, so I was just throwing it out there as a potential concern.

You also don't have as much back pressure as a stock muffler to begin with so that is working against you too. But I think that's not such a big deal.

Another major design factor on the stock system is placement of the tube inside the muffler and then sticking it out just behind where the tail pipe exits inside the muffler (the precise placement about 1 inch or so behind that pea shooter outlet could be the single most important aspect.) A venturi effect is created and it helps to pull/scavenge the gasses through and out into the atmosphere. So basically it's not just as simple as routing from high to low pressure... that will improve it but it might still not work as well as you expect compared to the stock setup. On the other hand, perhaps the exact placement inside the muffler is not so important? I think real life testing is the best way to determine this.

And yes the pressure changes at many different points in the exhaust system. If you took a pressure measurement at small increments, let's say every inch of the exhaust tubing, and charted it out, you would see this.

Also I haven't put much thought into it, but if you were to pair the cylinders correctly, perhaps based on the the firing order, order of exhaust pulses, etc. It might work in such a way that it would promote scavenging through the preheat pipe.

And yes it will still work to an extent either way because the exhaust heats up and metal conducts heat regardless. Even if gas flow through the pre-heat pipe is minimal, it will still get hot. Will it work as well or as fast? NO, but once fully warmed up you might not notice.

Here's one idea that would be fairly simple and not involve much work. Pretty much leave it how you have it but just stick a little lawn mower muffler on the end of the half inch pipe Laughing If your only concerns are it getting to hot or starting a fire... IT WILL NOT GET TOO HOT, that is a false concern, the cold intake mixture will be cooling it down at the same time plus most of the heat stays in the actual header even on the stock system. You could just buy a mini two stroke spark arrestor muffler, the kind they use for weedwackers that clear brush, and slap it onto the end, that takes care of your one valid conern, which is unlikely to happen anyway, but it's still a good safety measure.
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PostPosted: Mon Jun 14, 2021 11:55 am    Post subject: Re: manifold heat solution Reply with quote

oprn wrote:
So how is the stock Bus single outlet muffler do that then?


I'm not familliar with bus muffler, but found a pic titled "NOS Bus 1500cc muffler with part number" in Samba gallery from none other than EverettB. Based on the little concentric tube ending at the outlet, it appears alot like the same trick as Type 1 uses:

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PostPosted: Mon Jun 14, 2021 12:08 pm    Post subject: Re: manifold heat solution Reply with quote

evanfrucht wrote:
5 inch past the header flange is a lower pressure area that 1 inch past it was my main point, even if only slightly. If you dont believe me I don't know what else to say.

For all practical purposes the pressure will be the same. The biggest difference will be the pressure pulses will be weaker but it would take instruments far beyond what you and I have access to to measure it.

evanfrucht wrote:
Another major design factor on the stock system is placement of the tube inside the muffler and then sticking it out just behind where the tail pipe exits inside the muffler (the precise placement about 1 inch or so behind that pea shooter outlet could be the single most important aspect.) A venturi effect is created and it helps to pull/scavenge the gasses through and out into the atmosphere. So basically it's not just as simple as routing from high to low pressure... that will improve it but it might still not work as well as you expect compared to the stock setup. On the other hand, perhaps the exact placement inside the muffler is not so important? I think real life testing is the best way to determine this.

I am not too sure how much actual venturi effect there is. Just from memory the Bus muffler does not have the shapes and insert length you mentioned but it works. (Ok I see now from MrGoodtunes' post that it does at least have the tube)The strongest venturi effect I have seen on a stock carb is 270mm Hg which is a bit over 5 psi so if your pea shooter venturi is 1/3 that efficient (that's generous) we may see 1 1/2 psi.

evanfrucht wrote:
Also I haven't put much thought into it, but if you were to pair the cylinders correctly, perhaps based on the the firing order, order of exhaust pulses, etc. It might work in such a way that it would promote scavenging through the preheat pipe.

I have put some thought into it. Opposing cylinders is the correct pairing however all you will get from that is a brief back and forth pulse that may effect the temperature of the riser pipe for a few inches up on both sides but you will never get a true flow through especially at any speed above a fast idle. At that point the pulses will be so frequent as to bring flow to a virtual stand still. The only thing that may work in this case would be to extend the pick up pipe into the exhaust flow, cup one side toward the exhaust valve and away from the exhaust valve on the other side and try and capture a bit of the energy of those pulses to create a one way flow. I believe someone on this forum has tried that.
evanfrucht wrote:
Here's one idea that would be fairly simple and not involve much work. Pretty much leave it how you have it but just stick a little lawn mower muffler on the end of the half inch pipe Laughing If your only concerns are it getting to hot or starting a fire... IT WILL NOT GET TOO HOT, that is a false concern, the cold intake mixture will be cooling it down at the same time plus most of the heat stays in the actual header even on the stock system. You could just buy a mini two stroke spark arrestor muffler, the kind they use for weedwackers that clear brush, and slap it onto the end, that takes care of your one valid conern, which is unlikely to happen anyway, but it's still a good safety measure.

If you go back a couple posts, yes I covered that.

Here is something not discussed up to this point. The greatest need for manifold heat is at low engine speeds and light throttle conditions. That is when the intake velocity is low and the fuel drop out and pooling occur. This is also when the muffler pressure is the lowest but this pea shooter venturi effect would be the least. So - it seems that even the stock system may not be ideal. Think about that a bit...

Thanks for the feed back and thought given, it all adds perspective.
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PostPosted: Mon Jun 14, 2021 12:35 pm    Post subject: Re: manifold heat solution Reply with quote

oprn wrote:

I have put some thought into it. Opposing cylinders is the correct pairing however all you will get from that is a brief back and forth pulse that may effect the temperature of the riser pipe for a few inches up on both sides but you will never get a true flow through especially at any speed above a fast idle. At that point the pulses will be so frequent as to bring flow to a virtual stand still. The only thing that may work in this case would be to extend the pick up pipe into the exhaust flow, cup one side toward the exhaust valve and away from the exhaust valve on the other side and try and capture a bit of the energy of those pulses to create a one way flow. I believe someone on this forum has tried that.


They didn't make too many of them, but the 1973 VW Thing is designed exactly like that and it works pretty well. I also made the "collector cup" design like you're explaining to get manifold heat to my centermount IDF and I had to hammer them down a bit to keep the manifold from getting overly hot. Look up "1973 VW Thing Stock Exhaust" to see how they did it.
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