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No heat risers?
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uhhrace
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PostPosted: Mon Nov 23, 2015 11:06 pm    Post subject: No heat risers? Reply with quote

Bought a new exhaust that doesn't have any flanges for the heat risers to bolt onto. Can I just block off the heat risers? And will it noticeable affect how the car runs? I know it brings warm air to heat the carb, but I live in San Diego so I don't know if it ever really gets cold enough for that to be an issue.
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Tim Donahoe
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PostPosted: Mon Nov 23, 2015 11:50 pm    Post subject: Re: No heat risers? Reply with quote

If you have dual carbs, it's not an issue. But a single carb? Now that's another animal.

Tim
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PostPosted: Tue Nov 24, 2015 5:29 am    Post subject: Re: No heat risers? Reply with quote

Outside temp is not that relative when it comes to a fairly high velocity mix of gas and air. On a hot day if you blow on your wet arm, its still feels cold. You will see icing on the outside of the intake.....even with risers, you will still see some.

X2 what Tim said. I just converted a future buggy to dual carbs for one of those reasons.
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volksworld
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PostPosted: Tue Nov 24, 2015 7:20 am    Post subject: Re: No heat risers? Reply with quote

even exhaust systems that HAVE flanges are a problem...including stock mufflers that arent designed correctly internally to actually allow a FLOW of exhaust through the heat riser
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PostPosted: Tue Nov 24, 2015 8:04 am    Post subject: Re: No heat risers? Reply with quote

volksworld wrote:
even exhaust systems that HAVE flanges are a problem...including stock mufflers that arent designed correctly internally to actually allow a FLOW of exhaust through the heat riser


Does anyone make a stock exhaust that is designed correctly for the heat risers flow?
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PostPosted: Tue Nov 24, 2015 9:04 am    Post subject: Re: No heat risers? Reply with quote

Dansk that i have is correct
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uhhrace
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PostPosted: Tue Nov 24, 2015 10:32 am    Post subject: Re: No heat risers? Reply with quote

andk5591 wrote:
Outside temp is not that relative when it comes to a fairly high velocity mix of gas and air. On a hot day if you blow on your wet arm, its still feels cold. You will see icing on the outside of the intake.....even with risers, you will still see some.

X2 what Tim said. I just converted a future buggy to dual carbs for one of those reasons.

So icing on the outside of the intake, will this freeze the gas/liquid inside the intake, or just slow it down on its way into the engine?
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Volks Wagen
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PostPosted: Tue Nov 24, 2015 10:45 am    Post subject: Re: No heat risers? Reply with quote

uhhrace wrote:
andk5591 wrote:
Outside temp is not that relative when it comes to a fairly high velocity mix of gas and air. On a hot day if you blow on your wet arm, its still feels cold. You will see icing on the outside of the intake.....even with risers, you will still see some.

X2 what Tim said. I just converted a future buggy to dual carbs for one of those reasons.

So icing on the outside of the intake, will this freeze the gas/liquid inside the intake, or just slow it down on its way into the engine?


It cause the fuel to drop out of vapour type form and condense in the intake, which will lean out the vapour but might gather to give globs of fuel droplets at times, so you'll get rough running.
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OLD VW NUT
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PostPosted: Tue Nov 24, 2015 11:04 am    Post subject: Re: No heat risers? Reply with quote

The stock style heat risers help to keep the fuel atomized on its way to the heads and intake valves. Carb icing usually shows up at the outside base of the carb first - once you see icing on the outside you can bet there is more than that on the inside. Severe icing will plug jets and even interfere with the throttle butterfly. The car will either run like crap or not at all.

Very few manufacturing clones of VW stock mufflers build into their product the proper plumbing that will allow enough exhaust gases to heat the intake manifold to prevent icing. Some do.

Check out the pic below - a grab from the gallery. That little tube on the left will likely create more exhaust flow than simply perching the riser connection on top of the #4 exhaust port. There is very little flow from those - usually found on mass produced headers. You can make your own heat riser setup by putting one heat riser next to #2 or #4 exhaust port and run the other side to the exhaust collector on a header setup. If you are looking for a stock muffler find one plumbed as this one is.

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


Aircooled.net sells mufflers that are close to OEM. One with left hand preheat and one with right hand preheat. I have no idea if one is better than the other. Ask John about that.

http://vwparts.aircooled.net/Muffler-GERMAN-1966-71-Type-1-LH-Pre-heater-p/113-251-053ak.htm

http://vwparts.aircooled.net/Muffler-EUROPEAN-1966-71-Type-1-RH-Preheater-p/113-251-053aj-rh.htm

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

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PostPosted: Wed Nov 25, 2015 4:27 am    Post subject: Re: No heat risers? Reply with quote

Easy to check if yours is working, after eng gets warmed up check temp of the heat tube on both ends, if u can hold one end u r getting no flow of exhaust gas. On orig good ones i used to swap the 'cooler'end flat gasket 4 one with the small hole in summer to drop intake runner temp as hotter temp isn't needed then.
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volksworld
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PostPosted: Wed Nov 25, 2015 9:55 pm    Post subject: Re: No heat risers? Reply with quote

vanram the leistritz muffler pictured by old vw nut was the best one on the market but they are no longer available... what you cant see in that picture is that the heat riser tube ended directly in the center of the left tailpipe opening...this allowed the flow of exhaust through the tailpipe to "siphon" exhaust through the heat riser tube....ernst mufflers were not set up like that and were terrible...i've seen kadrons like that but the steel was very thin and they didnt fit very well...never tried a dansk...40 years ago real empi headers ran the heat riser tube directly into the center of the collector but i havent seen anyone do that since then
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Tim Donahoe
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PostPosted: Wed Nov 25, 2015 11:58 pm    Post subject: Re: No heat risers? Reply with quote

One thing not mentioned: the exact placement of your pea shooters is very important. If you stick them in too far in some mufflers, you can interfere with the gasses going to the heat riser. Check your Bently for the measurements when installing the pea shooters.

Tim
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talljordan
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PostPosted: Fri Nov 27, 2015 8:13 pm    Post subject: Re: No heat risers? Reply with quote

Tim Donahoe wrote:
One thing not mentioned: the exact placement of your pea shooters is very important. If you stick them in too far in some mufflers, you can interfere with the gasses going to the heat riser. Check your Bently for the measurements when installing the pea shooters.

Tim


This is one thing that has always bugged me. Why couldn't VW and the aftermarket folks just add a little stop tab....
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Tim Donahoe
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PostPosted: Sat Nov 28, 2015 12:41 am    Post subject: Re: No heat risers? Reply with quote

Jordan, I guess they just figured people wouldn't be keeping these cars for decades, and didn't think it necessary to provide a fail safe tab to prevent the issue.

The information is in the Bently, though.

Tim
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