Two types of manifold heat riser gaskets?

[beetleman217]

I see 2 pairs of these gaskets in my 40 hp gasket kit. Which should I use? Why are they different? Thanks

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If all else fails, stop using all else

1977 Westfalia
1961 Beetle

[Michael Fischer]

Use 1 of each.

[drscope]

The one with the small hole is supposed to be used in hot weather or hot climates.

The one with the big hole is supposed to be used in colder climates or colder weather.

The bigger hole allows more heat into the heat raiser.
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[KTPhil]

I thought you used one on each side, in order to encourage one-way flow through the heat riser. But I forget which one goes on which side. By "side", I don't just mean left/right, but which goes on the side with the 1/2" external exhaust tube vs. the side directly at the manifold. I think VW changed this through the years.

[79SuperVert]

I remember reading that the small hole one is used on the side of the heat riser where it exits the manifold to re-enter the exhaust stream, and the large one is used on the side where the hot air enters the manifold. Dr. Scope, you have tons of experience as a mechanic on these cars, which is why I'm very interested in what you say. So if you're in a cold climate you should use large diameter gaskets on both sides, but in a warm climate you use one of each?
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[tasb]

Yes, but like the rest can't recall which side gets which. The gasket sets only come with one small hole gasket. My guess is drivers side gets the small hole gasket.
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1957 Kombi low mileage 36 hp governor equipped M 178 Slow Drag Winner 2014, 2015, 2018

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[79SuperVert]

My Bentley for 61-65 says the gasket with the smaller hole goes on the left side. It says they started installing the smaller gasket beginning with chassis # 3223145 and engine # 5042363. It doesn't say anything about putting the smaller gasket on earlier engines.
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Central Jersey VW Society

Wanted: Art Collins VW (Savannah, Georgia) items - license plate surrounds and other items. Also ivory "AM", "FM" and "SW" buttons for a US Blaupunkt Frankfurt.

[KTPhil]

Not to be repetitive, but at some point the exhaust flow changed from right-to-left, to left-to-right (or vice versa). I don't have my Muir book but I think it was listed in the "changes through the years" pages. This would mean the gaskets should be reversed for those models.

[Helfen]

Like most of you here, I always thought that the small hole gasket was meant to restrict flow for warm climates. But think about this; How many heat riser tubes have we seen that are plugged? Plenty for my own experience and there are plenty of topics of this on Samba. Because heat riser tubes always plug up it leads me to believe there is dead space, or equal pressure on both ends of the heat riser. Could it be possible the small gasket was put there to get some movement through the tube by restricting one sides pressure. Pressure- air, water, electricity, always flows from greatest potential to least. Something to think about.
D.

[KTPhil]

That is exactly right, and why the small gasket must go on the proper side (which swapped at some point over the years).

I don't fully understand the details, but that long thin tube on one side is there to properly time the exhaust pulsesd through the heat riser. Think about how properly designed headers help scavenge the exhaust using the pulses to manage the inertia of the gases for best flow. The heat riser uses the same thinking to force more of a one-way movement. It's actually probably more of a "two steps forward, one step back" sort of thing as the pulses travel, but the net directional flow is what they are after. A restriction at one side will help with this.

I read it in a manual or bulletin but haven't been able to find it so far. Most of my manuals are still packed from a move, and online searches have not found it yet.

[drscope]

I was always told to swap them out from summer to winter by the old timers when I was messing with this stuff years ago.

Now I'm wondering.
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Mother Nature is a Mean Evil Bitch!

[Helfen]

[KTPhil]

The late Muir book states: "Use the small-holed gasket (if there is one in your kit) on the left."

All Bugs I remember have the small tube on the left side like this 36HP muffler:

So that seems to be the norm.

I'll have to wait until I get all my manuals out to find the comment about it changing sides at some point.

So you can see in the photo how the left side feeds to a low-pressure point in the main muffler body. So the heat riser gas flow must be right to left. The smaller hole maintains pressure in the heat riser, allowing the lower pressure in the thin tube to extract the gas and force flow from right to left in the heat riser.

[Culito]

It might vary by manufacturer, also.
So the small hole goes on the side with the tube? This must only be an early engine thing, I haven't seen this in any 1600 exhaust kits.
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[beetleman217]

I found this information on Rob&Dave's site:

"One further point - your muffler kit should come with small flange gaskets for the two ends of the heat riser, one on either side. Originally VW had a smaller hole in one gasket and a larger hole in the other, to control the amount of gas flow in the heat riser. If your kit has the same sized holes it's no problem (the heat riser will just run a little hotter), but if it has the small/large hole arrangement, the small hole goes on the DOWN side of the heat riser - that's the side with the curved pipe into the front of the muffler. I can't tell you which side that will be - I've seem replacement mufflers are made which work in either direction - the curved pipe can be on either side."
_________________
If all else fails, stop using all else

1977 Westfalia
1961 Beetle

[herbie1200]

This is a good point of view: my NEW manifold is completely clear and the noise (with two large-hole gaskets) is perfectly audible and disturbing.

My '63 has this kind of sound: "TOW - t -t -t - TOW! - t - t - t - TOW! - t -t ...", 1 big TOW! for cyl.2 and 3 little "t" for other cylinders.

BUT I'm scared to put the small-hole gasket into descending part of the heatriser: would this favorite clogging?

[KTPhil]

I don't think that will clog it. Clogging happens when the pipe gasses cool and deposit as soot, and then it gets baked on. The small hole gasket will ensure flow THROUGH the riser, not just dead air, making it less likely to gather deposits.

Clogging also happens when bored white people try to dance, but I can't help you there.

I had an aftermarket muffler that actually had a weld bead on the riser flange where the tube connects. In effect, they put the restriction on the flange, so I didn't need the smaller gasket. At first I thought they were just sloppy, but now I can see they were smart!

To avoid clogging, use the pre-heat inlet hose on the air cleaner, and let the flap close by gravity. Adjust your choke for only the richness you really need. Keep your spark plugs clean and gapped, valve adjustment and timing right on. And adjust the depth of your tailpipe resonators; this helps set the correct back pressure in the muffler, which also affeects heat riser gas flow.

And I would make it a habit every few years to pull the carb (not a bad idea to clean it at that time anyway), and while you are at it, pull the manifold and roto-rooter it out to maximum ID, just as a maintenance task.

[tasb]

I was going through my intake pile the other day to put some up for sale and tested the risers. It was interesting that about half of the 1500-1600 single port intakes were clogged while none of the 36 hp were clogged- I had 8 of 36 hp variety.
_________________
Roads Scholar
1957 Kombi low mileage 36 hp governor equipped M 178 Slow Drag Winner 2014, 2015, 2018

1965 hardtop Deluxe Microbus owned since 1990 M 620 factory 12 v 1500cc

1961 (October)Single Cab- Road Trip Workhorse

Member# 2059

[KTPhil]

[drscope]