Block Exhaust Cross Over on 413 Engine

[RKC]

1963 413 Engine on Imperial: I have the intake manifold removed from engine. Before installing I some questions. There is a lot of information about blocking off the exhaust cross over to help prevent vapor lock. Fel-Pro 1215 is a metal pan gasket with the ports blocked, but you have to add a gasket on both sides. YouTube shows mechanic taking tin and covering the hole. Questions: Has anyone done this before? Is this a good idea? How has it affected the automatic choke? Thanks for your input!

 

[413]

It’s really not a good idea. Here is why.

with that heat crossover blocked:
-the choke will stay on way too long
-your plugs will be dark
-the fuel won’t get atomized and it will stumble and hesitate until you have been driving for 30 minutes plus.
-gas mileage will go down.

I was drag racing a stock 440 and this trick was recommended, so I blocked it, the car was slower, more inconsistent, used more fuel, coukdnt pull away from a stop sign smoothly until it got some heat in the intake.

even in the 80+ degree weather it still was not any good like that.

seems to be fine on a higher compression race car with a large cam and carburetor.

Vapor lock and heat soak problems are helped greatly with ethanol free gasoline.

 

[CBODY67]

With age and use, there can be some carbon build-up in the passage, which accomplishes the same thing already.

IF the automatic choke thermostat is slow to open, it can be because not enough of the hot exhaust gases' heat is heating the intake manifold so the choke thermostat can open as it should. Closing the heat passage would only make it worse!

UNLESS you change to a new carb with an electric choke, best to leave everything alone. Chrysler B/RB engines of that vintage had some hot restart issues anyway. From back when they were NEW and gas had lead in it!!! Follow the starting procedure mentioned in the Owners Manual (1/3 throttle or so to start the engine) for best results. With time, you'll learn what the engine likes, so pay attention to that, too.

With cast iron cyl heads and intake manifold, no need for the paper side gaskets on the tin valley pan gasket. BUT if you have an aluminum intake, they can prevent the harder tin from imprinting INTO the gasket surface of the aluminum intake. Aluminum and cast iron have different expansion rates, so the paper helps them to move against each other as that happens.

BEST thing to do is to ensure the ignition system is at its top condition and make sure the plugs fire as easily/quickly as they can. If an electronic ignition upgrade might help that, so be it. Similar with fine-wire electrode spark plugs, or some with a cut-back center electrode.

What you also might do is to minimize the size of the insulator under the intake manifold itself, to allow more ambient air flow under the intake manifold for better heat dissipation. That insulator had been a bit controversial as it is either a heat insulator or a damper to prevent certain harmonics in the tin valley pan gasket as the engine runs, helping keep from cracking in the stiffening bead lines. But it also blocks airflow under the manifold, anyway.

In prior times, it could be a bit popular to block that heat crossover passage for allegedly better WOT power. But on carbureted engines with aluminum heads and no heat crossover there anyway (as its not needed with EFI, which the heads were designed for, OEM), that lack of heat makes the initial starting when cold a bit trickier to make happen in the morning, by observation. BUT as the aluminum heats up quicker, the heater works a bit quicker.

Sorry for the length, several dynamics at work in the hot re-start issue.

Happy Holidays!
CBODY67

 

[57fury440]

Blocking the heat crossover should not have any effect of the initial start on a cold engine. It will have an effect once it starts.

 

[CBODY67]

Will not affect the engine firing-off, but will affect drivability on a carbureted engine as the hot spot in the intake manifold plenum will stay cold until enough engine heat migrates into that area. Consider, too, that moving air/fuel will be colder than ambient air temperature.

 

[1966newport]

done it on many summer only drivers

 

[fury fan]

I have not experienced vapor lock on any of my cars, not even in 90+F days.
So I presume the main question from the OP about vapor lock is actually for a hot restart.

From what I've read modern fuels evaporate more easily, which means our carbs boil fuel out more readily.
The intake manifold is going to heat-soak from the heads a bit after shutoff due to lack of airflow from the fan (by whatever routes that circulates out of the engine compartment).

You could try a thick insulating gasket under the carb - but I don't know if you'll find one that fits an AFB of '67-older.
If you have a modern Eddy/AVS carb - those should still be available at speed-shop outlets.
IIRC there is a fuel filter from the 80s that has a 3rd nipple on it for a return to the tank - you could run a return line to the tank, but you'd need to figure out how to get a fitting on the tank, or the filler pipe, or into the fuel sender assy (all of which are do-able with suitable bulkhead-type fittings).
A return line would allow some of the hot fuel to go back to the tank. You fuel pump needs to supply above that amount for the engine, though - you could make a drilled restrictor plug in that return line if necessary.
But that really only helps the fuel between pump and carb, though - the fuel in the carb is still trapped by the needle/seat.
You could install an EVAP system (OEM-type charcoal canisters are still available) but you'd need a carb with a bowl vent. And this really only helps capture the fumes, it doesn't really prevent vapor lock.


I blocked the heat crossover on a bigblock once. I got such a nasty exh resonance around 2000 rpm (I have an X-pipe setup) that I immediately drove back down teh street and unblocked it. Exh systems are all different, so YMMV on that.

I have had 2 smallblocks plug up the crossover with carbon, and both ran like crap like that.

Due to the disadvantages others have mentioned, I would not block the crossover in an attempt to fix vapor lock.

 

[413]

Yes the small blocks that clog the crossover with carbon just run terrible like that. Then like a miracle they run good again when you clean it out and get it hot again

 

[Outsider]

I always block for racing and use race carbs with no choke, but that means need to be on the throttle at start until it's warm. No need to use the paper gaskets that come with the blocked port race pan. I make sure the intakes fit with no gaskets before use, or mill surfaces to make them fit, and then only use Black RTV on both sides of pan to seal.

On street cars I always leave the heat riser port open otherwise there would be no proper auto choke capability.

If vapor lock an issue I would focus on cooling the fuel from the pump up with some of the various heat shielding sleeves and or line re-routing and perhaps a heat insulator between the carb and manifold.

 

[cbarge]

I have blocked the crossover on a few big blocks.
No issues.
The difference is I run Edelbrock carbs with an electric choke.
My car is out up to late November even if there is frost on the windshield.
The electric choke works as it should as it is not affected by the blocked crossover.
In the hot summer months, the temperatures at the carb dropped by half and no boiling of the fuel in the float bowls and no need to run an electric fuel pump.
I do run heat sheathing on the fuel lines.
Another 20 to 50 degrees savings.
With a cooler denser fuel, I am able to run a bit more timing without any ping.
Hot or cold, no long crank times either.
Hope this helps.

 

[RKC]

I have blocked the crossover on a few big blocks.
No issues.
The difference is I run Edelbrock carbs with an electric choke.
My car is out up to late November even if there is frost on the windshield.
The electric choke works as it should as it is not affected by the blocked crossover.
In the hot summer months, the temperatures at the carb dropped by half and no boiling of the fuel in the float bowls and no need to run an electric fuel pump.
I do run heat sheathing on the fuel lines.
Another 20 to 50 degrees savings.
With a cooler denser fuel, I am able to run a bit more timing without any ping.
Hot or cold, no long crank times either.
Hope this helps.

View attachment 572425

View attachment 572426

Where did you purchase the sheathing insulation for the fuel line? Did you cover from the filter to the carb?

 

[cbarge]

Where did you purchase the sheathing insulation for the fuel line? Did you cover from the filter to the carb?

You can buy the fuel line sheathing from Summit or Jegs, etc.
Sparkbplug sheathing serves the same purpose.
Yes I covered the line from the filter to the carb.
Cheers.

 

[RKC]

You can buy the fuel line sheathing from Summit or Jegs, etc.
Sparkbplug sheathing serves the same purpose.
Yes I covered the line from the filter to the carb.
Cheers.

I found some on Summit. Which size would I need for my 413 engine, .375, 5/8, or 1 inch diameter?

 

[cbarge]

I found some on Summit. Which size would I need for my 413 engine, .375, 5/8, or 1 inch diameter?

5/8 should work with some wiggle room.