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Benefit or not: Blocking the exhaust manifold warming ports under the carburetor

Started by joeceretti, April 18, 2014, 11:11:07 AM

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joeceretti

I imagine this must have been discussed. I have noticed that the exhaust manifold warming port running under the carb causes the fuel to boil when 346 flathead engines are up to temperature.

Does it make sense, with these ethanol containing fuels, to block these ports?

No amount of heat shielding of the fuel lines and exhaust manifolds prevents this problem from occurring. It seems to me that blocking or partially constricting these ports would solve this problem, but would it cause other problems?

Scot Minesinger

The short answer is no detrimental effect has been discovered that I know of.

There is an article in the self starter on this where it was done with a 50's era Caddy (likely the 331) and it did not do much good. 

I have the intake manifold off my Caddy now, and I do not plan to block it off, although now would be the time.  Maybe I should reconsider?

The only person who reported a good cure to this boiling gasoline off out of the carb was a gentlemen who installed an electric fan behind the grille with a wind up timer.  When he shut the car off he twisted the timer to ten minutes and the fan ran for ten minutes after shut-off, never draining the battery.  You could test this by parking your car after hot, opening hood and directing fan on it then start after 20 minutes and see if it helps.

I know the flatheads have the fuel line adjacent to exhaust manifold.  If there is anyway to re-route it that would help, because heat shields only work well when car is moving.

Then there is the originality thing.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

joeceretti

The problem I have noticed... I have a perfect radiator now, I think better than new. I have a perfectly functioning fuel pump. I feel the carb and it is cool, I wrapped the exhaust manifolds in heat shield and even after a long run I can put my hand on them. Yet STILL I can hear the fuel sizzling inside the carburetor. It can only be from those exhaust warming ports. Designed for fuel with no ethanol and an octane rating of 40-50.

If I crank the engine a lot the entry of fuel eventually cools the internal components enough that it starts but that is hard on the battery, sometimes draining it.

Blocking these ports should not have any effect on originality when being judged, they are not in any way visible.

I just don't like second guessing the engineers. Maybe in this case, because of modern fuels, they should be second guessed.

INTMD8

Not sure on your particular engine but they are blocked on my 59 390, as well as removed the valve from the drivers side exhaust manifold outlet.

I've been driving the car lately, about 300 miles in the last 2 weeks. Pump the gas once and it fires right off (temps in the high 30's). I haven't had any problems from lack of heat that I can tell and I don't plan to drive the car in sub zero temps.

"Cadillac Kid" Greg Surfas 15364

Guys,
The flat heads are a very different animal from the OHV motors.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

joeceretti

Greg's got that right. They sure are. I don't think warm ups would be a problem with a flathead with these ports blocked execpt in the coldest of cold weather. I suspect they were there more to help warm the low octane fuel that came with all kinds of impurities. I am just surmising though.

Steve Passmore

Joe, There was one reason and one reason only for these heats transfer chambers, when the car was an every day runner people would jump straight in and off they go, the engine and fuel had to get to working temp in a flash.  With the way we use them now its not necessary.   My cars idle a while when I get them out the garage and we are generally lighter on the gas pedal than way back then. It just takes that little longer to warm up if you block them off.

Personally I have never had a problem with the flatheads.  Buicks had a flap inside the manifold that when cold would divert the hot exhaust to the carb, when warmed up re-divert it out the pipe, however I would weld them open on mine preventing gas's getting to the carb usually because the flap valve would be rusted up or the heat spring broken. never had a problem with them gone either.
Steve

Present
1937 60 convertible coupe
1941 62 convertible coupe
1941 62 coupe

Previous
1936 70 Sport coupe
1937 85 series V12 sedan
1938 60 coupe
1938 50 coupe
1939 60S
1940 62 coupe
1941 62 convertible coupe x2
1941 61 coupe
1941 61 sedan x2
1941 62 sedan x2
1947 62 sedan
1959 62 coupe

Raymond919

My '49 had a hot start problem after being driven a while. It wouldn't re-start for about 20 minutes or so. I bought new intake manifold gaskets from Olsen's with the cross-over passage blocked going under the carburetor. I also installed a phenolic (sp?) gasket under the carburetor which was 1/4 inch thick, and removed the heat riser valve installing a metal spacer instead. The problem is gone. I did this early last summer and the car started perfectly the rest of the summer. No more cranking, it just ran immediately upon turning the key. I also have an electric fuel pump installed near the gas tank but didn't have to use it. That's saved for those times when the car hasn't been started for long periods of time. The gas evaporates from the carburetor and the electric fuel pump replenishes the fuel missing from the float bowl. Last time I used it, the car had sat for 3 1/2 months without being started. I turned on the pump for about a minute, then pumped the gas pedal to set the automatic choke and pushed the starter button. It didn't even crank, it was just running instantly.
Another unexpected benefit was that the new engine paint didn't burn off the intake manifold in the vicinity of the cross-over area under the carburetor. It stayed a nice Cadillac blue like the rest of the engine.
Ray Schuman
# 26141

Jeff Rosansky CLC #28373

The car fuels will vaporize much more easily than the old fuels.  I can use autofuel in the airplane but have to be concerned about vaporlock.  Not really a concern with Avgas.
Jeff
Jeff Rosansky
CLC #28373
1970 Coupe DeVille (Big Red)
1955 Series 62 (Baby Blue)
Dad's new 1979 Coupe DeVille

cadillacmike68

I'm thinking about having them blocked in my 1968. But then I would also have to have the heat valve on the right side welded open otherwise I'll blow out that side of the exhaust! I have my car already converted to full dual exhaust, so it should both breath easier and not have that super hot crossover right under my float bowl.


Regards,
"Cadillac" Mike