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manifold heat solutions and supporting temp data
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nogoodwithusernames
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PostPosted: Mon Jun 14, 2021 12:38 pm    Post subject: Re: manifold heat solution Reply with quote

Would it work if you put the riser outlet into one of the header pipes but had it bent so the outlet was parallel to the exhaust flow? I *think* the exhaust flowing in the header pipe would "suck" the air through the riser tube?
If it were just Tee'd in like all the aftermarket mufflers it would just pulse back and forth but this could maybe work?











*I am not a fluid dynamics engineer so don't sue me if it blows something up Laughing
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Clatter
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PostPosted: Mon Jun 14, 2021 12:52 pm    Post subject: Re: manifold heat solution Reply with quote

It's common to use the venturi effect by tapping into exhaust flow to scavenge - usually it's done for PCV reasons.

All you need is to have a small tube coming into the secondary pipe past the collector.
Have it come in at an angle, and stick into the exhaust a bit.
Cut the end accordingly..

Wish i could find the thread..
Been done here a couple of times here already.


Just the little back-n-forth flow you might get from the tubes they weld on near the #2 and 4 pipes won't do anything.
WTF were they thinking.. Rolling Eyes
Well, it will do something..
It'll clog up the heat riser tube.. That will happen for sure. Smile

It's important to have good flow thru the tube.
Otherwise that sucker plugs up tight.

Isn't it a right of passage in order to own a VW?
To have to spend hours un-clogging a heat riser tube..
To struggle with chemicals and a frayed clutch cable in a drill and/or a torch..?
Thought it was mandatory..
They must've changed the rules. Think
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PostPosted: Mon Jun 14, 2021 1:27 pm    Post subject: Re: manifold heat solution Reply with quote

Having one end of the pipe come into the header at a farily sharp angle in the direction of exhaust flow a good idea for sure.

The collector acts as a venturi. The velocity of the gas speeds up as it exits the collector. They even have collectors that are designed off this principle, sometimes called "venturi collectors"

That area might be something to think about
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PostPosted: Mon Jun 14, 2021 2:10 pm    Post subject: Re: manifold heat solution Reply with quote

Angled tube idea points out how there's more to it than just pressure differential. It's about an area of Physics known as Fluid Dynamics and something call'd Laminar Flow (vs. turbulant flow). The fact that VW engineers put the output end of the heat riser tube concentrically in the middle of the final outlet seems to be because of the pulling effect being strongest there, just ahead of the Developing Velocity Profile area shown in this pic from Wikipedia:

Image may have been reduced in size. Click image to view fullscreen.
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PostPosted: Mon Jun 14, 2021 2:28 pm    Post subject: Re: manifold heat solution Reply with quote

Clatter wrote:
Wish i could find the thread..
Been done here a couple of times here already.

Couldn't find it either, but I did find some of the pics in another thread:

https://www.thesamba.com/vw/forum/viewtopic.php?t=711562&highlight=manifold+heat
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PostPosted: Mon Jun 14, 2021 3:27 pm    Post subject: Re: manifold heat solution Reply with quote

I could not find a picture of the stock Thing riser treatment but it appears Vintage Speed uses a form of the "cup collector" idea.

Now we are getting some action! Yes good pictures of them stuck into 4/1 collectors and I get that. Way better than the typical factory header out there! However that was not the original question, I asked if anyone had just dumped it to atmosphere and how did it work? I know there is one person out there who did but I don't believe he ever explained why he changed it.

All we have done so far is discuss other options which is good, I don't deny that. And a few have put out "I thinks" which is good too. We need to think and not just be parrots repeating the status quo over and over. So in the department of "I think", let me repeat that I seriously doubt that even with the best designed venturi outlet, as long as it is ahead of the muffler the pressure differential will never match atmosphere. From that stand point I have no doubt that dumping directly like mine is now will work as far as flow goes. I am concerned about other thing like noise, fires and long hot tubes snaking around where I might want to do maintenance. Got enough of them happening already!

This "Freeing Willy" idea of mine is not cast in stone and can be changed in a heart beat but I do want to try it. I like simple! It may only last for the first fire up and the sound will change my mind...
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PostPosted: Mon Jun 14, 2021 4:23 pm    Post subject: Re: manifold heat solution Reply with quote

I don't see why your idea wouldn't work, but the Briggs and Stratton sound would likely get real old real fast for me, even with a lawnmower muffler on the outlet, unless the rest of the exhaust drowns it out.
Try it and see what happens, having done the "into the collector" mod myself I can say from experience it works exceptionally well, the base of the manifold gets way hotter than a perfectly functioning stock system.
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PostPosted: Mon Jun 14, 2021 4:33 pm    Post subject: Re: manifold heat solution Reply with quote

Im pretty certain i have seen a pic of the scoup inside the exhaust pipe here, but didnt save it

I think it was the last vw attempt to preheat the intake.
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PostPosted: Mon Jun 14, 2021 5:46 pm    Post subject: Re: manifold heat solution Reply with quote

chrisflstf wrote:
Im pretty certain i have seen a pic of the scoup inside the exhaust pipe here, but didnt save it

I think it was the last vw attempt to preheat the intake.

You have indeed seen that pic. I did to.

One side had the little scoop facing into the exhaust flow from the port.
The other side faced away, dumping the heat riser exhaust with the opening facing rearward and exhausting the heated gases out the exhaust.

I hope I explained that well enough for the minds eye to see it.
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PostPosted: Mon Jun 14, 2021 5:54 pm    Post subject: Re: manifold heat solution Reply with quote

You know what would be very useful? If we all took a few minutes on our fully warmed up engines and took heat gun readings on the intake manifolds, posted the temp, the exhaust style and make, mods to the heat riser if any and the ambient temp.

This would give us a base line to go on to say "Did this work better or that?"

What do you think?
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PostPosted: Mon Jun 14, 2021 6:02 pm    Post subject: Re: manifold heat solution Reply with quote

oprn wrote:
You know what would be very useful? If we all took a few minutes on our fully warmed up engines and took heat gun readings on the intake manifolds, posted the temp, the exhaust style and make, mods to the heat riser if any and the ambient temp.

This would give us a base line to go on to say "Did this work better or that?"

What do you think?

I can do heat readings on a stock 1600 SP. This engine utilizes a stock Lierentz silencer and pea shooters. Heat riser effluent exits out the right side pea shooter. I'm not sure if that makes a difference.
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PostPosted: Mon Jun 14, 2021 8:29 pm    Post subject: Re: manifold heat solution Reply with quote

Perfect! Yes direction will make a difference - at each end - but I propose for consistency that we all take our readings on the aluminum casting in the very center. That would be just left of the upright of the tee up to the carb, opposite the generator. That should be close to center and then it matters not which way the flow is on your engine.

Now I am well aware that infa-red heat guns are accurate + - about 10* but I don't think that is an issue here. We just need a ballpark number.

Thanks!
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PostPosted: Wed Jun 16, 2021 11:05 am    Post subject: Re: manifold heat solution Reply with quote

Can't help with temperature data 'cuz I run dual carbs, I even cut off and plug'd the intake manifold heat exhaust tube:

Image may have been reduced in size. Click image to view fullscreen.

What I can easily do is a test of this assertion:

oprn wrote:
... pressure differential will never match atmosphere ...

So I removed the bolt and as much as I could of the asbestos wrap I had stuff'd around it 7 years ago, when I put this stock muffler in. Upon cranking up my 1600dp engine, bits of remaining asbestos blew out the stubby tube. None came out my slightly alter'd peashooter. Solid evidence Opee's assertion is correct.

BTW - Early stock mufflers ran the tube out left peashooter, the switch to right was 1971-72 (based on Wolfsburg West part numbers 113251053AJ & 113251053AK).
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PostPosted: Fri Jun 18, 2021 12:00 pm    Post subject: Re: manifold heat solution Reply with quote

My heat risers are routed from exhaust 2 to exhaust 4 on a single quiet pack 4 into 1 header, with an EMPI centremount progressive manifold - on this I think the riser tubes are a little larger diameter than stock.

Because all the cylinders do not exhaust at the same time, the hot gases actually make it up the heat riser to the manifold.

How do I know ? If I spill oil on the heat riser pipe, it boils off with smoke.

It may not be as good as specific stock designed system, but it does work.

One day I will measure the temperature.
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PostPosted: Sun Jun 20, 2021 5:37 pm    Post subject: Re: manifold heat solution Reply with quote

67rustavenger wrote:
chrisflstf wrote:
Im pretty certain i have seen a pic of the scoup inside the exhaust pipe here, but didnt save it

I think it was the last vw attempt to preheat the intake.

You have indeed seen that pic. I did to.

One side had the little scoop facing into the exhaust flow from the port.
The other side faced away, dumping the heat riser exhaust with the opening facing rearward and exhausting the heated gases out the exhaust.

I hope I explained that well enough for the minds eye to see it.

My header has this type of system on it, sorry I didnt take any pics before reinstalling it. It has enough flow where it gets hot enough to burn the coating off the new heat riser tubes I just installed.
Last time I took a heat reading the aluminum center section of my weber progressive intake was reading 112 degrees about halfway between the carb and bottom.
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PostPosted: Mon Jun 21, 2021 11:14 am    Post subject: Re: manifold heat solution Reply with quote

Just caught this now and might have a few thoughts to add.

-You will get a lower pressure the farther down in the system away from combustion you go. Just simply by being a long tube away you will have lower pressure. That pressure will suck the flow through while the high pressure at the head will be the highest pressure.
-I would be afraid that you would be working backwards by putting a muffler on the outlet tube for the heat and therefore adding back pressure. You would be fighting the flow, not helping it.
-You might do well to check the photos on the VS systems. They have an option for manifold heat and it involves little scoops inside the pipes, directing flow either downstream or scooping it up into the system. You can do the same thing by simply putting small deflector plates inside the system on a set of headers. I have seen this done and I recall the guy mentioning that the important one is the intake scoop for the system. I would think that a similar deflector in the outlet side would not hurt and would give that venturi effect.

Chris
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PostPosted: Mon Jun 21, 2021 11:47 am    Post subject: Re: manifold heat solution Reply with quote

On my draw-thru turbo, I run engine oil thru the manifold to pre-heat with .

Dual benefit. It cools the oil, and it warms the intake.

I actually run the oil supply line to feed the turbo thru the intake first.
That way the oil going to the turbo is always colder than engine oil. A real benefit to a turbo that has no other cooling.

And the heat imparted in the manifold makes here run real nicely.

I wonder why folks don't rout engine oil thru the heat riser jackets more often?
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PostPosted: Mon Jun 21, 2021 11:56 am    Post subject: Re: manifold heat solution Reply with quote

Tom, for your application that sounds really neat! As for why more people don't do it, I recall seeing a comment to the effect that it tends to make warm up slower. Can't speak to it personally, though I would love to have a turbo motor in my upcoming beetle project!

Thanks!

Chris
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PostPosted: Mon Jun 21, 2021 2:57 pm    Post subject: Re: manifold heat solution Reply with quote

Yes ccowx, that type of system to capture the pulses instead of using differential pressure is mentioned several time in this thread already and I think is a viable alternative.

Ohio Tom the way you are doing it for sure makes sense and I have no doubt works for you. The temperatures involved will be lower all around though and slower to respond on start up as ccowx said. I think it's a good idea in the warmer climates but could be less than adequate where ccowx and I live.
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PostPosted: Wed Jul 07, 2021 8:53 pm    Post subject: Re: manifold heat solution Reply with quote

I finally got the engine running today, too many interruptions in the last month. It is not idling yet so can't really set the timing or mixtures properly. Seems no fuel is getting through the idle circuit as is stays running at mid rpms and if I hold the choke partly on so the carb has to come off again.

Anyway that is not the subject of this post, the exhaust and heat riser are. I am pleasantly surprised at how quiet the exhaust is. I would compare it to the stock Bus single outlet system but maybe about 30% louder. This is going to be a treat after the dual cannons!

The heat riser seems to be working well, lots of flow. Another surprise is that I cannot hear the heat riser outlet above the rest of the engine at all! I have not run it long enough to see how hot it will get but it looks promising. The intake is warming up nicely even with only 2 and 3 minute runs.

The exhaust system has to get wrapped! No way around it, too much heat up there were I am trying to work. I have burnt myself twice already just trying to set the carb and timing. It's a real hazard for anyone moving around the back of the Buggy too especially the grandchildren!
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