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GreyhoundBeetleC2A
Samba Member
Joined: April 24, 2025
Posts: 7
Location: TX
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 Posted: Tue Apr 29, 2025 8:02 am Post subject: Heat Riser tubes cut off |
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Hello, and thanks for the invite!
I boought a 74 BEETLE with the 1600cc engine (AE serial code) and it looks like the previous owner cut off the heat riser tubes to install a non custom muffler.
I want to add a stock muffler (to hook up the heater boxes) but I'll need to get the Back plates for the muffler to heat riser connections.
I live in Houston, don't plan on driving the Bug in the Winter anyway, the inlet tubes of the risers are not obstructed, do you see any issues in driving it in this configuration?
Thanks
Tom |
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andk5591
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Joined: August 29, 2005
Posts: 16797
Location: State College, PA
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| Posted: Tue Apr 29, 2025 8:05 am Post subject: Re: Heat Riser tubes cut off |
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If you are running a center mount carb, you REALLY want the intake heated. If you are going to replace the intake, try to find a good original with clear riser tubes. There is also an intake heater out there, but I have never used it.'
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Woodie 69 VW woodie (Hot VWs 7/12).
"John's car" 64 VW woodie - The first ever
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hobthebob
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Joined: December 08, 2021
Posts: 457
Location: Austin, TX
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| Posted: Tue Apr 29, 2025 8:07 am Post subject: Re: Heat Riser tubes cut off |
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| Well, I have a 67 with a 1600dp, center mount PICT 30/31 and 009. No heat riser tubes to speak of, also cut off while living its best life in FL. The car runs fine, always has, and it came from south Florida. I now live in Austin TX and drive my car year round with no issues at all. YMMV |
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busdaddy
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Joined: February 12, 2004
Posts: 52589
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Tue Apr 29, 2025 9:52 am Post subject: Re: Heat Riser tubes cut off |
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While it will "run OK" without heat risers it'll never compare to how much better it runs and drives with working manifold heat. Once you experience a car with all the factory stuff present and working you'll never want to go back.
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EVfun 
Samba Member
Joined: April 01, 2012
Posts: 6073
Location: Seattle
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| Posted: Tue Apr 29, 2025 11:44 am Post subject: Re: Heat Riser tubes cut off |
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| GreyhoundBeetleC2A wrote: |
Hello, and thanks for the invite!
I boought a 74 BEETLE with the 1600cc engine (AE serial code) and it looks like the previous owner cut off the heat riser tubes to install a non custom muffler.
I want to add a stock muffler (to hook up the heater boxes) but I'll need to get the Back plates for the muffler to heat riser connections.
I live in Houston, don't plan on driving the Bug in the Winter anyway, the inlet tubes of the risers are not obstructed, do you see any issues in driving it in this configuration?
Thanks
Tom |
I think there may be some confusion here. What is it you want to hook up? Are you trying to restore the car heater, or the intake manifold heat riser?
The heater hoses are the two black flex hoses running from the fan shroud down through the rear engine tin to connect to the heater boxes. Thanks to Themrfreeze for this picture:
The intake manifold heat riser tubes are the small lower two tubes in this picture that connect to the exhaust system. Thanks to PolarBearVW for this picture:
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| Wildthings wrote: |
| As a general rule, cheap parts are the most expensive parts you can buy. |
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oprn
Samba Member
Joined: November 13, 2016
Posts: 14583
Location: Western Canada
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| Posted: Tue Apr 29, 2025 5:12 pm Post subject: Re: Heat Riser tubes cut off |
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I don't think he is confused. He is talking about it in conjunction with a muffler change.
| busdaddy wrote: |
| While it will "run OK" without heat risers it'll never compare to how much better it runs and drives with working manifold heat. Once you experience a car with all the factory stuff present and working you'll never want to go back. |
To all of you who think your center carbed type 1 VW engine runs fine without heat risers listen up to busdaddy. He is giving you the honest goods here. If you don't believe him it's because you just don't know what you don't know and you will never know until you experience it.
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hobthebob
Samba Member
Joined: December 08, 2021
Posts: 457
Location: Austin, TX
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| Posted: Wed Apr 30, 2025 9:19 am Post subject: Re: Heat Riser tubes cut off |
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| That's good stuff right there. When I have the time and money, I'll one day get that intake with heat risers. Until that day, I don't know what I don't know, and it drives fine, always has! :p |
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zerotofifty
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Joined: December 27, 2003
Posts: 3520
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| Posted: Wed Apr 30, 2025 5:45 pm Post subject: Re: Heat Riser tubes cut off |
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| oprn wrote: |
I don't think he is confused. He is talking about it in conjunction with a muffler change.
| busdaddy wrote: |
| While it will "run OK" without heat risers it'll never compare to how much better it runs and drives with working manifold heat. Once you experience a car with all the factory stuff present and working you'll never want to go back. |
To all of you who think your center carbed type 1 VW engine runs fine without heat risers listen up to busdaddy. He is giving you the honest goods here. If you don't believe him it's because you just don't know what you don't know and you will never know until you experience it. |
Granted, but I reckon most VWs has plugged heat riser tubes. sure they do transmit some heat when plugged by conduction of heat by the metal, but they do tend to get plugged with soot and rust quickly. In a warm climate the problem this creates in minimized.
Cutting them of course negates any conduction of heat by the metal
*****Note that there are two different gaskets used for connecting the heatriser to the exhaust (muffler).
One of the gaskets has a tiny hole, the,other a big hole The tiny hole MUST be placed on the correct side for proper heat flow thru the tube, AND VW design changes on the muffler during production caused the side for the small hole gasket to be changed.
The small holed gasket goes on the side of the preheat tube that is fed by the pipe on the muffler, NOT the side that is fed by the pipeless muffler flange. The muffler pipe and pipeless flange changed sides at some point, so the small holed gasket side changed. ONLY PUT THE SMALL HOLE GASKET ON THE SIDE THAT THE MUFFLER HAS THE PIPE TO FEED THE HEAT RISER. The big holed gasket goes on opposite side!!! This will assure hot gas flows thru the preheater tube.
***** IMPORTANT DETAIL.....
See above image
the muffler side with the pipe is on the left shown here, but some mufflers have the pipe on the right. the small holed gasket goes on the side with the pipe, in this case the left side. gasket #13 has the small hole, the right side uses the big hole gasket, which is #14, and this goes on the side of the muffler that has the pipeless flange, which in the case of this muffler is the right side.
Always put the small hole gasket on the side of the muffler with the pipe, big holed gasket on the side with the pipeless flange
This here photo below shows a muffler with the pipe on the right side rather than the left, so in this case, the small hole gasket goes on the right side!!..
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busdaddy
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Joined: February 12, 2004
Posts: 52589
Location: Surrey B.C. Canada, but thinking of Ukraine
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oprn
Samba Member
Joined: November 13, 2016
Posts: 14583
Location: Western Canada
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| Posted: Wed Apr 30, 2025 8:42 pm Post subject: Re: Heat Riser tubes cut off |
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Looking back I don't recall ever having a heat riser tube plug off. I have acquired used ones that were but we never had it happen on our cars. I wonder if it is because we always ran a thermostat. Plugged with carbon to me indicates a cold engine running an over rich mixture which would naturally lead to carbon deposits. I have taken apart lots of VW engines with the combustion chambers, pistons, valves and exhaust ports with heavy black carbon deposits. Likely all caused by running too cold and too rich.
Engines running at a proper temperature and proper mixtures just do not soot up like that.
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Abscate
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Joined: October 05, 2014
Posts: 23624
Location: NYC/Upstate/ROW
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| Posted: Thu May 01, 2025 2:52 am Post subject: Re: Heat Riser tubes cut off |
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That’s getting memorialized….
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baldessariclan
Samba Member
Joined: October 14, 2016
Posts: 1971
Location: Wichita, KS
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| Posted: Thu May 01, 2025 3:42 am Post subject: Re: Heat Riser tubes cut off |
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| zerotofifty wrote: |
*****Note that there are two different gaskets used for connecting the heatriser to the exhaust (muffler).
One of the gaskets has a tiny hole, the,other a big hole The tiny hole MUST be placed on the correct side for proper heat flow thru the tube, AND VW design changes on the muffler during production caused the side for the small hole gasket to be changed. |
One point of clarification (because I know this particular detail tends to cause some confusion & angst at times):
As far as I can tell, the two gaskets w/ different-sized holes (i.e. VW part no 113 251 263 w/large hole; VW part no 113 251 265 w/small hole) were only used on earlier engine + muffler combos — e.g. early D, H, L code engines.
Later engine & muffler combos used only the gasket w/ the larger-sized hole at both R & L locations (i.e. 2 x VW part no 113 251 263). — e.g. on later D, H, L code engines, plus AB, AC, AD, AD, AF, AH code engines. Ref. parts catalog listings below:
http://oacdp.org/type1part/2021.png
http://oacdp.org/type1part/2023.png
http://oacdp.org/type1part/2024.png
I suspect that the gasket w/ smaller hole was employed primarily just to limit the amount of exhaust gas flow (and thus heat transfer) through the heat riser tubes for the smaller displacement engine and carb combos — they didn’t need so much manifold pre-heating.
Later engines though, with their larger carbs and displacements, required more manifold pre-heat to deal with the corresponding increase of fuel+air mixture volume, and thus used the gasket w/ the larger hole at both locations, for more exhaust gas flow (and heat transfer) through the heat riser tubes.
Note also that the flow of exhaust gasses through the heat riser tubes is primarily dependent upon and caused by the overlap between end of the exhaust tip and internal tube in the muffler. A low-pressure point is developed there, due to the accelerated exhaust gas flow through that constricted overlap region. This lower pressure is what helps to “suck” the exhaust gases through the heat riser tubes. Ref. service bulletin below — text is in German, but the picture gives a good idea of how it’s supposed to be set up:
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Last edited by baldessariclan on Thu May 01, 2025 7:08 am; edited 2 times in total |
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Abscate
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Joined: October 05, 2014
Posts: 23624
Location: NYC/Upstate/ROW
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| Posted: Thu May 01, 2025 7:06 am Post subject: Re: Heat Riser tubes cut off |
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The number of aftermarket mufflers with completely foolish heat riser ports that don’t work is astounding
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oprn
Samba Member
Joined: November 13, 2016
Posts: 14583
Location: Western Canada
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| Posted: Fri May 02, 2025 6:46 pm Post subject: Re: Heat Riser tubes cut off |
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Ah yes but… to make them work right costs money and they would not be competitive in the market. 99% of air cooled VW owners don’t have a clue how important proper heat riser is and as long as the engine runs, could care less. All they want is a cheap exhaust.
For proof of that just walk down the row at any VW event and look at the engines. Or go through the photo gallery here…
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EVfun
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Joined: April 01, 2012
Posts: 6073
Location: Seattle
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| Posted: Sat May 03, 2025 7:45 am Post subject: Re: Heat Riser tubes cut off |
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| oprn wrote: |
Ah yes but… to make them work right costs money and they would not be competitive in the market. 99% of air cooled VW owners don’t have a clue how important proper heat riser is and as long as the engine runs, could care less. All they want is a cheap exhaust.
For proof of that just walk down the row at any VW event and look at the engines. Or go through the photo gallery here… |
I have wondered if those double exhaust port connected aftermarket systems could be made to work good enough for warm weather owners using the small hole and large hole gaskets.
The incorrect heat riser setup hits each port with a blast of exhaust pressure, trying to make the exhaust gas flow one way and then the other many time per second. Little to no flow happens.
The side with the small hole metal gasket would tend to have less of a pressure pulse. Since going through the heat riser the exhaust gas exiting the intake manifold should be cooler and reduced in volume. Perhaps the 2 different size gaskets would establish some flow from the large hole side to the small hole side.
My Buggy has a Dansk reproduction split Thing exhaust on it with the extended heat riser tube on the right side, so I cannot test this idea.
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| Wildthings wrote: |
| As a general rule, cheap parts are the most expensive parts you can buy. |
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baldessariclan
Samba Member
Joined: October 14, 2016
Posts: 1971
Location: Wichita, KS
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| Posted: Sat May 03, 2025 9:39 am Post subject: Re: Heat Riser tubes cut off |
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| EVfun wrote: |
I have wondered if those double exhaust port connected aftermarket systems could be made to work good enough for warm weather owners using the small hole and large hole gaskets.
The incorrect heat riser setup hits each port with a blast of exhaust pressure, trying to make the exhaust gas flow one way and then the other many time per second. Little to no flow happens.
The side with the small hole metal gasket would tend to have less of a pressure pulse. Since going through the heat riser the exhaust gas exiting the intake manifold should be cooler and reduced in volume. Perhaps the 2 different size gaskets would establish some flow from the large hole side to the small hole side. |
Yeah, I’ve seen that theory proposed from time to time in these forums, but I personally find the concept to be pretty doubtful…
However, if someone was willing to do some testing and produce fairly credible evidence for the effect, that would certainly be interesting — e.g.:
W/ a properly set-up & fully functional stock muffler & heat riser arrangement, using large hole hear riser gaskets on both R & L sides, use infrared thermometer or similar to take temp readings on both sides of the heat riser tubing, to obtain a “baseline performance” set of data.
Next slide the appropriate exhaust tip far enough out where it no longer overlaps the internal tube in muffler (i.e. to negate the effect it has on exhaust flow through the heat risers), and replace one of the large hole heat riser gaskets w/ a small hole one (on whichever side you think will work). W/ that arrangement, re-measure the temps on each side of the heat riser tubing, and compare to your original baseline readings.
Just an idea to think about…
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1971 Standard Beetle — fairly stock / driver
baldessariclan -- often in error, never in doubt... |
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zerotofifty
Samba Member
Joined: December 27, 2003
Posts: 3520
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| Posted: Sat May 03, 2025 6:20 pm Post subject: Re: Heat Riser tubes cut off |
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| baldessariclan wrote: |
| EVfun wrote: |
I have wondered if those double exhaust port connected aftermarket systems could be made to work good enough for warm weather owners using the small hole and large hole gaskets.
The incorrect heat riser setup hits each port with a blast of exhaust pressure, trying to make the exhaust gas flow one way and then the other many time per second. Little to no flow happens.
The side with the small hole metal gasket would tend to have less of a pressure pulse. Since going through the heat riser the exhaust gas exiting the intake manifold should be cooler and reduced in volume. Perhaps the 2 different size gaskets would establish some flow from the large hole side to the small hole side. |
Yeah, I’ve seen that theory proposed from time to time in these forums, but I personally find the concept to be pretty doubtful…
However, if someone was willing to do some testing and produce fairly credible evidence for the effect, that would certainly be interesting — e.g.:
W/ a properly set-up & fully functional stock muffler & heat riser arrangement, using large hole hear riser gaskets on both R & L sides, use infrared thermometer or similar to take temp readings on both sides of the heat riser tubing, to obtain a “baseline performance” set of data.
Next slide the appropriate exhaust tip far enough out where it no longer overlaps the internal tube in muffler (i.e. to negate the effect it has on exhaust flow through the heat risers), and replace one of the large hole heat riser gaskets w/ a small hole one (on whichever side you think will work). W/ that arrangement, re-measure the temps on each side of the heat riser tubing, and compare to your original baseline readings.
Just an idea to think about… |
Well VW figured it was good to have a small gasket and a large gasket at least on some of its cars. I figure there is likely good reason for that, and reason it has to do with heat flow via gasses. Or maybe VW just did it to fuck with us?
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oprn
Samba Member
Joined: November 13, 2016
Posts: 14583
Location: Western Canada
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| Posted: Sun May 04, 2025 2:53 am Post subject: Re: Heat Riser tubes cut off |
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Thinking back a long way I can only remember the little/big gaskets on the 1200cc engines. I don't remember seeing them on the 1500/1600's.
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baldessariclan
Samba Member
Joined: October 14, 2016
Posts: 1971
Location: Wichita, KS
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| Posted: Sun May 04, 2025 5:11 am Post subject: Re: Heat Riser tubes cut off |
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| zerotofifty wrote: |
| Well VW figured it was good to have a small gasket and a large gasket at least on some of its cars. I figure there is likely good reason for that, and reason it has to do with heat flow via gasses. |
I agree, and am thinking that the gasket w/ the smaller hole was probably primarily used to limit or “meter” the total amount of exhaust gas flowing through the heat riser tubes — i.e. to keep them from getting too hot. The earlier, smaller displacement engines and carburetors only required so much manifold pre-heating — less than the later, bigger motors.
On the other hand, what so far I fail to see is how 2 gaskets w/ different sized holes could be used to somehow “pump” or otherwise cause the flow of exhaust gasses through the heat riser tubes - ? (as seems to be sometimes claimed, here and there in these forums). I mean, that concept just doesn’t make any sense to me.
However, I could be wrong about that, and thus would be interested if anybody ever tests the supposed effect, and can show that it does indeed actually exist and work. If so, potentially means a lot for folks running non-stock style mufflers! At this point though, I still remain pretty “dubious” about it all… 
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