What is this flapper valve blocking my exhaust

[clevelag]

After 17 years of storage I've finally decided to do the restore on my 68 Wag.

I pulled the Buick 350 today and when I disconnected the exhaust pipe from the passenger side exhaust manifold this little POS was sandwiched between the two. It's frozen shut so I've had almost half blockage on that side of the engine for who knows how long. What the heck is it?

http://s377.photobucket.com/user/grantclev/media/Removed_zpsbobrmkwv.jpg.html

[Heavy_Metal_Thunder_81]

It's called a heat riser. It blocks off that side of the exhaust to force hot exhaust through a passage in the intake manifold to the other side exhaust. It is used to heat up the intake manifold for better cold engine drivability and faster warm-ups. As it warms up the valve opens and allows exhaust to flow normally.
Most people knock out the valve and plug the holes then reinstall.

[Probesport]

Yep thats exactly what I did. Removed the flapper, threaded the guide holes and blocked with bolts/copper RTV.

[KaiserMan]

Yep thats exactly what I did. Removed the flapper, threaded the guide holes and blocked with bolts/copper RTV.

I've never had one of these that worked on any of my Buick 350's. The above is exactly what I've had to do with them all. Works fine.

[nograin]

That one looks pretty intact. Assuming you're doing a true restoration, if you can free it up, as said it will help with warm up. The coil is a bimetal which opens the valve when warm. The counterweight helps keep balance and IIRC helps it open when the rpms go up.

[FSJunkie]

No heat riser: you have to be gentle on the throttle until the engine FULLY warms up or it can hesitate, stall, or backfire.

A functioning heat riser: you can do whatever you want through the entire warmup period. Floor it if you want. Start the engine, put it in gear, and take off at whatever throttle you want.

When I was young and stupid in high school I saw that heat riser as a restriction to performance, so I spot-welded it wide open. I pulled the valve back off a few years later and ground off my weld to make it operational again. Runs 100% better.

One of those little things that helped the cars run great when they were new, but either seized from neglect (you're supposed to spray the shaft with graphite oil every 15,000 miles) or that owners removed because "it's unnecessary". Owners then complain that old carbureted cars don't run well...so they get aftermarket EFI. If owners left their heat risers and thermostatic air cleaners alone and maintained them, aftermarket EFI wouldn't sell nearly like it does.

[Probesport]

While I agree that a functioning heat riser in a carb'ed vehicle is beneficial, a fantastic running carb vehicle is no match for a decently tuned EFI setup.

Carburetor vehicles never ran great, even perfectly built carburetor cars. They run acceptable for most environments and when tuned for a specific purpose can run very good.

You simply cannot match mechanically what can be done with EFI. It's not even the same sport. While the 360 is far from a powerful or efficient engine, you can gain quite a bit from being able to control the entire aspect of it.

[babywag]

With a well tuned carb, with a proper functioning choke, they can be eliminated as well with no ill effects.
Removed both of them from mine, way before I converted to EFI.

They aren't a necessity, and there are many vehicles out there that run just fine without them.

[JeepJeepster]

Wired it open on the FSJ we had. Never really drove it in winter weather but it always started right up. Soon as you tapped the throttle to get off high idle it was ready to roll.

Its there to hold back heat to help warm up the passenger side exhaust manifold. The intake pulls air from around the exhaust manifold when its started and the engine is cold, thus pulling warm air into the intake. Just helps the engine warm up quicker.

[nograin]

On a positive feedback EGR as used in the later wags, there might a slight effect. They most certainly help speed the warm up process and if the carb is tuned properly for full operating termperature, then it will be less wasteful to use it. I'm not going say I haven't run without, my car doesn't have one, and nor does it have a choke. I manage although will be putting on a carb with manual choke sooner or later.

As far stoichiometric goes, all it indicates is chemical balance. Not least emissions, not most efficient, not most powerful. The AFR for best power and efficiency will vary with load. The least pollutants will vary depending on which pollutants are of the most concern.

There's a graphic in this thread RFS forum
Heat Riser effect on wideband? page 2

[serehill]

LOL

It only allows the engine to warm up faster then after that it is of no use. It does not in any way affect overall perfomance after worm up at all? I've blocked mine & the ports running across the intake for the best performance throughout.

So you are warming up your engine less than 5% of the time it operates. No use in suffering to operate for 5% of the time. Mine is in the southern hemisphere & works just fine. There is no real noticeable warm up delay compared to overall performance. The heat riser & exhaust valve loss for 5% is nothing. This also greatly improves starts when hot without crossover heat.

Interesting that the valve also increases back pressure in the exhaust manifolds & intake while cold to warm transition. Since the exhaust gasses are running backwards past the 2 rear cylinders on the right side. Thus creating back pressure how do you think that makes the engine run? The exhaust manifolds design is for the exhaust to run in the opposite direction..
Increased back pressure & back flow on 2 cylinders. Runs better

[gpcl16]

For what it's worth, I've seen heat riser valves installed on cars as old as a 1961 Thunderbird, before any emissions controls or fuel milage mandates were in effect. My '63 Galaxie 500 with an FE 352 was supposed to have one but a spacer was put in it's place at some point in the past. The only ill effect I ever had was that the hot air choke was very slow to open. It took about 10 minutes of running to open fully, and this was with a brand new choke stove and pipe installed and brand new choke thermostat.

Fast forward several years, after getting my '88 GW I discovered that the valve was frozen shut causing reduced power, milage, and running hotter than ideal. I wired open the valve and fixed all problems at once. Later on when I had the exhaust apart for an engine rebuild I drilled out the valve and used two bolts and RTV just like Probesport. Well in my case that ended up causing an exhaust leak that drove me crazy so I pulled it again and used a pipe thread tap on the two holes and put in some allen head plugs that fit flush with the sides. No problems ever since.





I would recommend running an electric choke if it doesn't already have one and ditch the valve if it's not working. Create a spacer or modify the valve.

[nograin]

Rick - Exhaust can't flow backwards- just more slowly forward. It has to move from high pressure to low pressure. With a high overlap cam, it can and often does get sucked back into the cylinder and even into the intake manifold because of the late exhaust valve closing. This really isnt an issue with a most stock or RV type cams.

Too often 10 minutes can be my entire drive and in the chilly and cold season obviously want to help warm up as much as possible. With an aluminum intake aiding the cross over is far less an issue. It's one of several reason's my car hasn't had a valve in it. (of course it did originally)

If it comes to a choice of stuck shut or none, the choice is obviously go without. I totally agree that if its not free to move, it will cause problems more serious than slow warm up ever will cause.

[FSJunkie]

This has nothing to do with emission control.

Ever wonder why engines need richer mixtures when they're cold? It's because the carburetor or TBI dribble raw, liquid fuel into the intake manifold and it just flows into the cylinders. Liquid fuel doesn't burn well, so you have to dump more of it into the engine to get it to run. All that liquid fuel washes the oil off the cylinders and wears the hell out of them and the rings. What little fuel is vaporizing and burning will condense back to liquid whenever the throttle is opened and manifold pressure drops, which is why cold engines like to stall when you open the throttle.

The quicker you can get that manifold warm, the quicker you can lean the fuel mixtures back out and stop dribbling liquid gasoline into your cylinders. If the manifold was warm all the time, you'd never need a choke on your carburetor or have cold engine enrichment on your TBI! Your engine would last longer, not stall when its cold, and drive better. Good fuel vaporization makes for good fuel distribution to all cylinders, which makes for more power. You actually need to continue heating the manifold a little even after the engine is warm, because the liquid fuel turning to vapor absorbs heat and chills the manifold like refrigeration.

The heat riser isn't a potato in your exhaust. It just restricts flow through the outlet of the right manifold, forcing more exhaust to flow through the crossover passages in the cylinder heads (part of the center exhaust ports in the heads) and intake manifold to the exhaust manifold on the other side. The crossover is small, but at low engine loads and speeds like encountered in normal warm-up, the change in backpressure on the right cylinders is minimal. Should the engine be accelerated and the crossover become restrictive, the increased backpressure will blow open the heat riser like the blow-off valve on a turbocharger. It acts as a backpressure regulator. The actual backpressure on the cylinders is not high. That's not the heat riser's job. It's just directing the exhaust to take a different path and is designed to relieve the backpressure if it increases beyond a designed limit determined by the bi-metal spring and the weight arm.

I welded my heat riser open several years ago because of advice I received on this forum. My engine always ran and drove flawlessly through the warm-up period, so long as I was easy on the throttle. If I was too heavy on the throttle, the fuel would condense back to liquid in the manifold and the engine would backfire and hesitate. I since undid my weld and put the heat riser back in operation. I can now start my engine in below freezing weather, let it warm up for 10 seconds, and FLOOR IT if I so desire without any hesitation what so ever. The engine actually has MORE power. That's the way they should drive.

And that is why I don't listen to people's advice any more.

[JeepJeepster]

Very interesting information there.

I personally had no idea that exhaust could 'cross over' from the passenger side to the drivers side...

The valve seems to have its uses for DD's driven in colder weather. For those that drive them once a month on pretty days....