Exhaust Heat Riser Question

[greasemonkey54]

I think its called the heat riser, either way I want to remove that piece on the passenger exhaust manifold that has a tube connecting to the intake tube. The truck is a 86 with a 305. I am going to a open breather and wanted to remove the contraption from the manifold, how does it come off, can it come off?

[454Man]

I'd leave it if you plan to drive during the winter months :-)

[rich weyand]

Don't take it off if you plan to drive at temps below about 45* F.  Vaporizing gasoline cools the induction system by taking from it the heat of vaporization.  You can freeze the carb/throttle body.  Also, the carb/throttle body will take frickin' forever to warm up without it, resulting in poor mileage and poor performance.  There's a reason the General put it there.

[Irish_Alley]

to add to what rich said, in the winter with snow (even with out) you have to sit there and idle for a couple minutes with the choke on just to be able to drive then once you are driving you still have to deal with the cold air. the heat rise will pre-heat the air and let things warm up faster and is more of a auto choke if you would. unless your going just for looks and dont care if it stalls out while driving because it too cold.

[rich weyand]

I put a heat riser on my headers, and on the coldest winter day, intake air warms up within a minute, and you can hear the idle settle down within two minutes.  Then I'm good to go.

http://users.rcn.com/weyand/smalls/dsc03923small.jpg

[Irish_Alley]

you could also keep the old parts and put them back on in fall/winter. also rich how did you manage that? nice ideal

[454Man]

I ruined 2 engines in the winter B4 i wised up. It will cause a lean condition.
Rich this is intriguing... What size pipe is that? More details and pics. I just run the hot air house down between to primaries to pull hot air.

[rich weyand]

Here's a closer pic: http://users.rcn.com/weyand/smalls/dsc03924small.jpg

OK, what I did:

1) I got a stainless steel exhaust tip: http://www.amazon.com/dp/B000LG3DBG/ref=pe_175190_21431760_C1_cs_sce_dp_1. This is a perfect diameter for the stock heat riser pipe.

2) I had a local machine shop machine off the part of the turndown exhaust tip that stuck down below the tube, so it would lay flat against the header pipe.  I also had them cut three slots 1/2" wide and 1/2" deep across the tube on the same side as the turndown opening.  This is trivial stuff on a Bridgeport with a 1/2" square-end end mill, and the machining cost was $20.

3) I cut the standard downtube into pieces.  I cut it 1/2" from each curve, so I had elbows with short straight sections plus the top piece with the socket for the air cleaner flange through the first corner, which has to be tight to clear the valve cover.

4) I got a piece of 1.5" flex exhaust pipe http://www.summitracing.com/parts/wlk-36319/overview/ and cut straight sections to join the curves together.  I clamped the modified exhaust tube to the header and fitted the parts.  It takes some planning and some jiggling to get it to route nice and look OK.

5) I marked all the pieces so I could put it back the same way, and then I glued all the pieces together with JBWeld, and put it back on the truck.  Lined up all my registration lines to get the same setup, then let it set up overnight, then primed and painted with Rustoleum.

It works great.  The downturn opening and the slots are up against the header pipe and let in hot air right off the pipe.  The trick was to cut up the original heat riser pipe into curves.  Keep the air cleaner flange socket through the first curve in one piece, though.  That bend to clear the valve cover is pretty tight.

[greasemonkey54]

I know it is supposed to but I have not noticed any ill effects when I switched my caprice to headers. I just want a cleaner look to under my hood.  My truck has always been touchy and wants to stall when I first start driving without warmup time in the winter. lol

[454Man]

It's there...Even if you don't notice it. I run mine below 60°

[Stewart G Griffin]

Not wanting to start an argument necessarily, but is this device really for warming up the carb?   i don't think so, myself.

[454Man]

Mainly for introducing warm air into the system for a faster engine warm up and good fuel/air ratio.

Sent from my SGH-T769 using Tapatalk 2

[Irish_Alley]

Stew your thinking of the old style that will redirect exhaust from one manifold under the intake to the other side. This style pre-heatz the air before it goes into the Carb for a better mix and helps the fuel vaporize better

[rich weyand]

Even a hot engine in cold environments can suffer carburetor icing.  http://en.wikipedia.org/wiki/Carburetor_icing  This applies equally to injection systems.

Airplane piston engines all have a similar setup to ours, that is controlled via cable by the pilot instead of by a vacuum thermostat. 

This control is labeled "CARB HEAT".

The other advantage of carb heat is that the carb can be tuned better, because it does not have to run over such a wide range of temperatures.  The inlet-air temperature is controlled by the thermostatic air cleaner, which means the carb will not have to operate well with inlet air below the set-point temperature.  Finer tuning of the carburetor is possible, for better mileage and more power within the temperature range. This consideration does not apply to injection systems.

[chengny]

I think its called the heat riser

GM called it the "heat stove".  It is only useful if the Thermac system is still installed and operational.




The TAC system, Fig. 82, is designed to improve carburetor operation and engine warm-up conditions. It achieves this by keeping the air entering the carburetor at a temperature of at least 100°F., or more.
Carburetor air temperature is controlled by a pair of doors, Figs. 83 thru 85, located in the air cleaner snorkel, which channel either preheated or under hood air to the carburetor.
Preheated air is obtained by passing under hood air through ducts surrounding the exhaust manifold, causing it to pick up heat from the manifold surface. The heated air is then drawn up through a pipe to the air cleaner snorkel.
Underhood air is picked up at the air cleaner snorkel in the conventional manner.
The two air mixing doors work together so that as one opens, the other closes and vice versa. When underhood temperature is below approximately 86°F., the cold air door closes, causing the hot air door to open. Hot air from the exhaust manifold stove is then drawn into the carburetor. As the underhood temperature increases, the cold air door begins to open until the temperature reaches approximately 115°to 130°F, at which time the cold air door is fully open and the hot air door is fully closed.
The doors are controlled by a vacuum motor mounted on the air cleaner snorkel. This motor, in turn, is controlled by a sensor inside the air cleaner which regulates the amount of vacuum present in the vacuum motor according to air cleaner temperature. Whenever manifold vacuum drops below 5---8 inches, depending on the unit, the diaphragm spring in the motor will open the cold air door wide in order to provide maximum air flow.
The vacuum motor and control door assembly in the left snorkel on outside air induction units does not have a sensor and is controlled only by manifold vacuum. This snorkel remains closed until full throttle is obtained. With manifold vacuum at 6-8 inches, the door will open, allowing maximum air flow.