I say if she's hot, she can call it whatever.Block it. I'm in LA area. I don't even have a choke on my old vehicles.
It's December 11 and it was 68 degrees... Local Weathergirl calls it a winter cold spell.
Intake manifold, heat crossover.
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autoxcuda
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in LA here… they’re all swimsuit models.
Dan Georgino
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Electric choke.
MopaR&D
Nerd Member
This... I've run engines with the crossover blocked in below-freezing temps and they do just fine, as long as the tune is good you shouldn't even need to spend much time letting it warm up. The last engine I left the crossover open it would frequently boil the gas in the carb even with 1" plastic spacer and the intake manifold would be BURNING hot to the touch. Not good for performance, or really anything at that high of a temp. The only time you might run into an issue is if you're using an Air-Gap intake (which doesn't have a heat crossover anyway) and driving on the freeway in below-freezing temps. But you're in Cali so that's a non-issue.
Hot-air intake, like the dual-snorkel air cleaners from the 70s with the heat riser off the exhaust manifold/header, does more for gas mileage and faster warmups anyway. Modern gasoline evaporates like crazy it doesn't need help like the stuff back in the 60s-70s-80s did.
Dan Georgino
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Yes, my Gas was boiling over, and a messed with the exhaust manifold butterfly valve by spraying some lubricant, and that fixed it for now anyway.
autoxcuda
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crossover blocked.
I ran a single snorkel air cleaner with heat tube since someone replaced my OE 68 340 left exhaust manifold with a 73-up heat stove type… it probably helped some. But wasn’t anything amazing in negative 10 degree Iowa weather
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MopaR&D
Nerd Member
Yeah -10 in the midwest might need more help lol... I had a dual-snorkel air cleaner off a 1972 440 I ran on a 360 with air-gap and it helped a lot but the few times I drove it when it was around 10-15 above zero it was struggling a bit. I bypassed the temp control valve and had it running with the doors open or closed by manually hooking up a vacuum line. Also was running shorty headers so I cut up a factory heat stove and steel-zip-tied it to the #1 primary tube.
No matter the argument, some people will never agree that blocking the cross over is a good thing. Leaving it unblocked does not one single thing for performance. It's all about cold weather fuel mixing and cold weather driveability and wait for it..........EMISSIONS. As long as you give the engine time enough to warm up, it will run fine, even in the coldest climates with the exhaust cross over blocked, plus, the proof is THERE regarding performance from keeping the mixture cooler, even when the engine reaches operating temperature. There's zero reason to leave the cross over open, unless you're running a stone stock engine and even then it will show benefits from blocking it off. You will simply not have the faster warm up when the engine is cold and in cold weather. Big whoop.
All the engines I build, I fit carbs with no chokes, usually TQs. With some engines depending on design, it is possible to partially block the exh xover. So that the intake gets a small amount of heat. It is called a compromise; I do this on some engines, depending on intended usage. I fit a steel plate in the xover port in the gasket, & drill a 1/2" hole in the plate.
Dan Georgino
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Thank you, great tip. I think I will try that.
EL5DEMON340
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put a thin .010 steel shim stock behind that gasket on the head side, that gasket will burn trough after a couple hundred miles.
340six
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I would blocker up.
If using the original thermostatic spring controlled choke leave it open or the choke will stay on to long. If using and electric or manual choke you can block it off
MopaR&D
Nerd Member
When I blocked the crossover on the 360 in my truck I fabbed some tiny "plates" out of 14-gauge(ish) mild steel I had laying around that would drop into the ports on the heads just enough to sit flush with the intake mating surface. Globbed them up with high-temp orange silicone, stuck them in the ports then laid the intake gasket over top with another dab of silicone in between for good measure. Been running that way for at least a year and no indication of burn-through. The crossover ports (in my late-70s 360 heads at least) tapered down a bit from the mating surface so there was a bit of a "shelf" for the plates to sit on, made sure they couldn't somehow fall down in the ports and cause mucho destruction.
Dan Georgino
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That's just it, it boils my gas. So I need to block
Dan Georgino
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Electric
make sure that you get rid of the heat controlled valve in the exhaust manifold or fix it open. If not when cold (closed) there will be nowhere for the exhaust to go!!! But yes another vote for block it - some Eddy manifolds don't even have the passage in the intake manifold.
Dan, normally you can solve that by using one of the thick carburetor insulator mounting gaskets. They are over 1/4" thick and help keep heat off the carburetor.
Dan Georgino
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I have that. Still boiled. I have lubed the exhaust manifold valve, and now it works good. Probably stuck closed. Now moves freely. Thanks
It's possible that was it, especially if it took a while to exhibit the problem.
Dan Georgino
Well-Known Member
No, it's clean.
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