I have a 86' F250 with a 351w HO. I'm installing an Edelbrock 1406 carb. Whomever had the truck before me pretty much disconnected all the emissions. I went to put the new cab in today, and the part in question (see 1st pic), which sits right of the carb, below the throttle body, in the intake manifold, is in the way. The vacuum line was never attached to the part. I've spent hours looking on line at emissions parts, but cannot find anything to give me a clue what the part is. You will see the pic of the intake manifold. The part was bolted into the hole next to the intake opening. I mangled the part taking it out. The piece that sits in the intake was badly crusted up.

 

That's a valve that controls the flow through the exhaust crossover in the manifold. My 84 302 had the exact same one in the stock intake manifold.
Since it obviously not working, you could just cover the hole with a block off plate, or stick the valve back in.

I think you will find differing opinions on here as to whether the exhaust crossover is actually needed or not. You've obviously been running without it, as I believe the valve is normally closed (requires vacuum to open).

 

He lives in New Mexico, so I am assuming it will never see cold weather. So he probably doesn't need it. But if he just covers the hole with a plate, it will be on full blast all the time.

Doesn't this little door work in conjunction with the heat riser in the opposite side exhaust manifold? If that exhaust manifold heat riser is open all the time, then he probably could get away with the little door open all the time. If it became a problem (hard starts when the weather is hot and the engine is hot) he could pull the intake and put the restriction plates in place that come with the intake gaskets.

 

Since he said that most of the emissions stuff was previously removed from the truck, I assumed that the exhaust valve in the opposite exhaust manifold is also not functioning. If there's nothing forcing exhaust flow through the crossover, it probably makes very little difference if the crossover valve is open or closed. I have no experience with this stuff, so I'm certainly no expert.

 

Well he said the carb was hitting that valve and why he removed it so if he puts in back the carb will not fit .......
....... unless he adds a spacer between carb & intake to raise the carb to clear the valve.
He would need to get longer studs. 2 nuts jambed to remove & install the studs and can use all thread rod to make new studs.
Dave ----

 

Thanks for the responses. When I pulled the valve out, the actuated door was closed and completely baked/gummed up. I've decided to cut all the top pieces off the valve, reinstall the plate with the door intact left open. . . If I have issues I will close it and see what it does. In case I have issues, does anyone know exactly what the valve is called or have a part number? I've googled exhaust cross over valve, heat riser valve and several other variations and cannot find the part.

Also, I live in northern NM at 8400 ft. Our summer temp high is 90, and even that is rare. On average the summer temp is 75-80. But winter it is cold' can get well below zero. With that said, where do you all foresee an issue: warm summer or cold summer temps with the valve taken out?

I've been looking at aftermarket intake manifolds and it looks like many don't have the opening for the valve. Which I assume means that many don't have the exhaust cross over in the intake? If that is the case, I may simply buy a new intake. Thanks for all the consideration.

 

Pull the Ford Intake and install an Eddy intake for that carb. that's what I did....

 

Ever been in the desert during the winter? It can be colder than a witch's gazink.

But not all of NM is desert, there are cities that are a mile high or more, because the Rocky Mtn's extend into NM

Taos is 7,000 ft., and there are ski resorts in the area.

 

A carbed engine has lots of bandaids so it runs well in all conditions. The system you are messing with is one of them. Your intake manifold is called a "wet manifold" since it has air AND fuel flowing through it. The fuel is atomized and mixed with the air, the engine cannot properly burn liquid fuel, it has to be a vapor. The problem is in cold weather when the engine is first started, the intake manifold is cold. When the air vapor hits the cold metal of the manifold it condenses and turns back into a liquid. It then rolls around the bottom of the intake, suddenly all going into one cylinder and causing it to miss fire and run rich. Some of the other cylinders are starving and running lean because they are lacking the fuel that just went in the other cylinder. This is what makes an engine run so rough and buck and jerk when it is cold.

To help combat this problem, the factory blocks off the exhaust on one side with a heat riser valve in the exhaust manifold, and this forces it up and underneath a passage in the plenum right underneath the carb. This creates a "hot spot" and when the fuel vapor hits this spot it will tend to stay in vapor form. This makes the engine run much smoother when it is cold and warming up.

Of course the racers will tell you heat is a bad thing, and they run without this feature. But they are also running their engines for 20-30 minutes trying to warm them up enough to where they can race. No one wants to fiddle around with a cold natured beast in a everyday driver. So take that in consideration when taking advice from racers and aftermarket companies that want to sell you "performance" parts.

I just went to fall 2018 Hershey a couple of weeks ago. We were able to get there in time to see the vintage race car demonstrations. It just so happens the night before we had a cold snap in the weather, it was about mid 40's-50's outside. We did not get to see some of the cars go around the track because they could not get them to run. You could hear them starting up in the pit area and then cough and sputter and then die. They tried several times with some of them, and then gave up. The wet manifold problem is the exact problem they were having, except they did not have any heat to help them out.

 

Joe, You can have issues both when hot & cold.
As Franklin said when cold hard to run right till you have some temp in the motor. When hot you may have a hot start issue as all that heat under the carb boils the fuel out of the float bowl when you shut down the motor even just to run into the store and back out.

An aftermarket manifold does have a cross over it just works a little different.
You have a valve in the intake others as Franklin pointed out have a valve on the outlet of 1 manifold. This closes off when cold and forces the hot gas thru the intake. Then when warm / hot the valve opens up and the exh goes out the Y pipe. Note some times this valve can also fail closed and cause a hot start issue.

Do you need the cross over? Good question and you will get all different answers. I will say the only way to know is give them both a try and see what works for you.
As for the race cars not starting when cold they also have non-stock cams, large carbs, race fuel, etc. that don't help it start / run when cold. Had a buddy with a Jeep he sand drag raced and had a heck of a time getting it to start at 1 race because it was cold.

On a race motor you want the fuel mix to be a cool as you can get it but want the motor temp up around 200*f, just ask Smoky Yunick (bless his sole).
My non-ford drag motor, the intake cross over is blocked to keep the intake / fuel cool and never had an issue starting it but also did not race it when it got that cold.
So as you can tell heat can be good & bad.
Dave ----

 

In my case, I had heat-related trouble while the engine was still running, not just after shutdown. In both cases, the engine had just worked hard climbing a long steep grade fully loaded (the truck, not me). While driving slowly on flat ground, not working hard at all but with lots of heat still present under the hood, the engine just died.

I'm almost positive this was caused by excess heat radiating from the crossover passage, affecting the carb. I don't know if the fuel boiled over or became frothy or whatever, but it certainly seemed heat related. Sitting for about 45 minutes was enough to restore normal operation.

As beneficial as this heat source is on a cold engine, in my case it was too much when fully warmed up and working hard. I think changes in modern fuel chemistry are part of the equation, too. I should note my engine (8600 GVW '84 351W 2 bbl) has NO control system for the crossover passage. There's no butterfly on either exhaust manifold, nor any valve on the intake manifold. The crossover passage is always open to exhaust flow, although in theory if both legs have equal backpressure (Y-pipe to single exhaust), not much is forced through this passage. I guess the design logic at the time was this basic, uncontrolled set-up kept the crossover passage within a certain temperature range and that was good enough.

Even on temperature-controlled systems, there's still a major shortcoming. There's no true feedback of the temperature where it really matters, just underneath the carb. For example, consider the temperature-activated butterfly valve on one exhaust manifold, designed to force exhaust through the crossover passage. The temperature feedback comes from this external valve on the back of the exhaust manifold. I guess this was considered good enough, meaning a certain temperature range there was designed to translate to the desired range under the carb. Factor in age or a sticky valve (very common) and the area under the carb may easily end up far too hot or cold.

Ideally the control system would have been designed to take its feedback from the actual temperature under the carb, but that would have added complexity and extra cost. Performance wise that would have been the best of both worlds, with plenty of heat when cold, but not too much when hot. Wishful thinking on my part...

In my situation, with the non-controlled system, my "fix" was to reluctantly block off the crossover passage. No more heat-related fuel issues, but I've noticed driveability is decreased a little bit on mornings below freezing. Generally if I let the truck warm up for 2 or 3 minutes it's good. It's a small trade-off to avoid heat-related fuel issues in the summer. My present set-up has me wait a few minutes safely in my driveway during the winter versus a repeat of being stranded who knows where in the summer. I should also note my truck is not a daily driver, typically used only in the winter on the few snowy days we get in western Oregon.

 

They did usually still have some control over the passage. There are restrictor plates that come with the intake gaskets, and there is a chart were you look up your application, and they will tell you no restrictors, one on the left or one on the right side or restrictors in both sides. I believe this was also used in conjunction with carb spacers and those thick cardboard gaskets with the plastic bushings. They fiddled with the combination of heat valves, no heat valves, and carb mounting to get it to perform the way they wanted, there are probably several combinations that would work ok.

I have found on the engines I have setup, no exhaust valve, restrictors in both sides, a carb spacer AND the factory aircleaner with the heat pipe from the exhaust manifold works well. You would think with no exhaust valve, restrictors and a spacer that the manifold heat would not matter, but it does in my setups. I don't mind waiting to let it warm up a minute or so, but when I want to go, I don't want stalling and sputtering down the road, and carb freezing in cold damp weather.

 

There was an exh valve that worked off vacuum all be it think not Ford and worked off a temp switch.

As for no valve and flow remember where the exh is coming from.
It comes from 1 side then the other so it pushes back and forth to heat the intake.

I am happy the 300 six does not have this heat issue and I am running a hot water heat to the bottom of the intake with the EFI exh manifolds.
Dave----

 

Most all engines have this issue in some form or fashion. As you probably know, your six was originally setup with the exhaust manifold and the intake manifold under the carb touching each other, to introduce a hot spot. The EFI engines did not need this hot spot, since multi-port fuel injection has a dry intake manifold, air only. No fuel to drop out.

 

You are right and why I have the hot water heater.
I just don't remember seeing a lot of posts on hot start for the 300's of boiling fuel in the carb like the v8's.
And if I do have an issue of too hot a carb I can bypass the hot water part and have a cool intake manifold.
Dave ----