Aftermarket Exhaust Heat Riser Ports

[DurocShark]

I should put ports in quotes... "Ports" The exhaust I bought for the 1835 has the flanges for the heat risers, but they're just welded to the outside of the exhaust! There's no openings into the exhaust at all!

I was thinking about taking the manifold to a muffler shop to port the right one into the exhaust where it is, and on the left one run a tube down to the collector. Is this possible? I thought about doing it myself using a torch and brazing rod, but thought I'd ask here.
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No boom today. Boom tomorrow. There's always a boom tomorrow.

[FeelthySanchez]

The p/n is a multiple-use app, & they are left un-drilled for those folks w/ '62 & earlier types.
So ...... jus' drill 'em. Use the 2 ports as drill guides, & note how the RT side port is much larger in diameter:

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[DurocShark]

In your pic you can see there's a tube running to a downstream location in the muffler. Both being at the same spot relative to each other means little exhaust will actually flow. That's my concern and what I'm not super comfortable doing myself.
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No boom today. Boom tomorrow. There's always a boom tomorrow.

[FeelthySanchez]

It's the other way 'round: muffler (upstream) feeds pressure to heat riser.
Different sized heat riser ports = a pressure differential between L & R sides: THAT is what causes hot gas to flow thru the riser.
Seeing a bit of confusion here, so maybe shoot me a PM & I'll try to walk ya thru it, or perhaps make a house call to knock it out - I'm in NW OC & it's not a tough job.

[DurocShark]

I'll try drilling them out first. Thanks for the offer.

I'm just worried since this engine is getting a progressive. They tend to be super sensitive to manifold heat. It's normally not an issue using factory exhaust, but this 1835 is going in the baja while I rebuild the 2180. Ultimately it's going in the 64 that will get a more stock exhaust. So this only has to last a year or so.
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No boom today. Boom tomorrow. There's always a boom tomorrow.

[Frank Bassman]

So let's think about this for a second. Are you saying that in a stock muffler the point of high pressure is the bottom tube from the can going up, and the low pressure point is at the port near the head? I always thought it was the other way around.


Also that in a header with the collector modification, the opposite is true, with the low pressure being the joint at the collector? Looking at some modified headers, the small riser tube added is facing outward, in the direction of escaping gas. This through a scavenging effect, creates a "negative pressure" area and promotes flow since the head port is a positive pressure area. Is this what you mean?

-Frank

[DurocShark]

[DurocShark]

This article spells it out pretty clearly:

http://www.aircooled.net/making-weber-progressive-dfev-work-aircooled-vw-engine/

[ashman40]

Take a look at the pics in this thread:
https://www.thesamba.com/vw/forum/viewtopic.php?p=3552812
Here's one pic from that thread:

This side ends at the collector. It is positioned where the gasses merge together and the pressure is lowest. This creates a "sucking" effect and pulls the gasses from the other exhaust port thru the intake passage. I think you are looking to duplicate what that person did with their headers.

If you were shopping for new headers I think aircooled.net actually sells a service to add similar tubing to a set of headers. Or at least they used to.

There is a less intrusive version of this which just adds short sections of tubing at the exhaust port facing towards or away from the exhaust port. The one facing away from the port creates a lower pressure area. I don't think this version is as effective as the above pictured version but is probably better than just drilling a hole into the exhaust tube.

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AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}