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Old 02-21-2023, 05:09 PM
wbnapier wbnapier is offline
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Default Pros and Cons of filling the exhaust crossover?

Hello,

Mine is unfilled, and I use the hot air choke with success on my tri-power.

I do have an electric choke ready to go.

Many seem to block the opening with with a metal plate.

Others fill it with moltem aulminim.

I've heard one guy just wad aluminum foil in there, which of I found to be the most genius.

Do you do both sides?

Is is true performance or reliability gain and that it keeps the fuel cooler?

Does i have an advantange in warnming and atomizing the fuel?

Any info you have would be appreciated.

Thank you.

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Old 02-21-2023, 05:43 PM
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Heat from the crossover is one factor of three that helps vaporize and atomize the liquid fuel to a combustible gas.
The other two is velocity thru the venturi and the amounts of fuel added.

If you reduce or eliminate one of these factors you will have to increase the other two to the corresponding degree.

This matters little or nothing at all for the race crowd, they starts at 4000 rpms and drives only a quarter of a mile at the time and could care less for drivability or fuel economy.

For anybody that has some insight in the principles of the combustion engine, how it works and why, knows the intake gasket steels are kids stuff and the molten aluminium fill in the siames channels in the heads are "racers only" when tuning headers for max performance beyond 5000 rpms.

FWIW

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Old 02-21-2023, 06:56 PM
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I always blocked mine. I never noticed anything other than a cooler intake manifold. Cool dense intake air makes more horsepower the way I see it. I regularly started my cars in freezing temps with no problem. I think the fuel is atomized by the venturi. Vaporization is another thing. Not sure how much effect the crossover has once the engine is fully warmed up. Seems like the purposed of the crossover is to warm the intake quicker, on start-up, in cold weather. This warms the intake charge up a little when the chambers are ice cold. Helps the pig light up a little better. Especially on emissions mixtures. All probably splitting hairs over very little consequence. Do what makes you sleep well. Lol!

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Old 02-21-2023, 07:04 PM
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I would agree with Kenth; for a street car the thermostatic divorced choke is hard to beat for reliability and ease of use. Also, if you plan to drive the car in the cold a heated intake is not a bad thing.

I filled the 96 heads I had with molten aluminum - not the easiest task.

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Old 02-21-2023, 09:38 PM
wbnapier wbnapier is offline
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What about wodding up aluminum fool?

Also, the aftermarket alimium heads seem to go without that area.

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Stump Puller Cam
Muncie M22W 1st-2.56 2nd-1.75 3rd-1.37 4th-1.00
3.55 Rear Differential
Front: 225/60R15 Height: 25.6"
Rear: 275/60R15 Height: 28"
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Old 02-22-2023, 01:13 AM
Goatracer1 Goatracer1 is offline
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Aluminum foil will burn up after a while. I also vote for keeping the cross over. You won't see any performance gain on the street.

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Old 02-22-2023, 02:14 AM
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I'm a kid, so I put one stainless block in the driver side, at least allows some heat to reach the intake, warm up takes a couple minutes longer, my experience is the engine is happier sitting at a light with the AC on in 90 degree heat without exhaust flowing under the carb with today's fuels.

My guess is not many people have operational thermostatic valves in their exhaust systems anymore either.

I believe carbs like to be warm, not so sure they like to be roasted. And always seems like open crossovers in warm climates leads to people looking for the best carb insulators they can find. All depends on the driving you do I think.

I think a lot of the things engineers did 50 years ago was based on the fuels available at the time, the physics haven't changed ... but the fuels have.

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Old 02-22-2023, 04:46 AM
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Take the car for a spin, any day, hot or cold, drive at normal highway speed, stop a little quickly in a safe place and touch the carburetor. It is hardly hot, rather cold, and that is due to the rush of air thru the venturi. Without the crossover, it would be even colder and if the air were moist, in the worst case, there could be ice formation in the venturi which interferes with the carburetor's function. Those who advocate a cold carburetor and a cold intake have probably misunderstood the meaning of denser air, it is the AIR TO the carburetor that should be kept cold (dense) not the carburettor/intake itself.

FWIW

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Old 02-22-2023, 08:57 AM
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I've been thinking about this more. I think we can all agree that it makes sense for a racecar in Florida and not for a bone stock car in Canada. So what's the break point? Dataway made some good points about changes since the cars were designed. Some fuel has ethanol in it. Ethanol content varies. Engines have Fe/Fe, Fe/Al, Al/Al parts. Also agree that it should be blocked for fuel injection? Warming the intake helps when the engine is cold and carbureted. What's a good intake/carb temp target when it's fully warmed up? Aluminum intakes warm up quicker but also dissipate more. Lots of variables for blanket statements I believe.

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Old 02-22-2023, 09:33 AM
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One of the three dumbest things I have done with a car since I got my first one in 1959 was blocking the cross-over on a street-driven car!

The other two?

(1) putting an electric choke on wife's car which was equipped with an automatic transmission
(2) thinking I was good enough to make a Pontiac 301 with factory turbo run with a basically stock 1970 4 cylinder Toyota

Jon

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Old 02-22-2023, 10:10 AM
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Quote:
Originally Posted by carbking View Post
One of the three dumbest things I have done with a car since I got my first one in 1959 was blocking the cross-over on a street-driven car!

The other two?

(1) putting an electric choke on wife's car which was equipped with an automatic transmission
(2) thinking I was good enough to make a Pontiac 301 with factory turbo run with a basically stock 1970 4 cylinder Toyota

Jon
What was the result? Cold start problems?

I've always heard, and believed, that Pontiac had a superior design with the valley pan. It keeps the hot oil off of the intake manifold. Is there another reason for it? Seems to contradict the hot manifold theory. Would the hot oil make it past the target intake temp?

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Old 02-22-2023, 11:28 AM
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Quote:
Originally Posted by JSchmitz View Post
What was the result? Cold start problems?

I've always heard, and believed, that Pontiac had a superior design with the valley pan. It keeps the hot oil off of the intake manifold. Is there another reason for it? Seems to contradict the hot manifold theory. Would the hot oil make it past the target intake temp?
No, city driving for the first 30 minutes. Engine would stall at every stop sign/light. And my "heel and toe" techique is not as good as it was 50 years ago.

A carburetor with a manual choke finally was the solution. Pull the choke about half way at every stop sign/light for the first 30 minutes.

Jon

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Old 02-22-2023, 11:38 AM
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Quote:
Originally Posted by carbking View Post
No, city driving for the first 30 minutes. Engine would stall at every stop sign/light. And my "heel and toe" techique is not as good as it was 50 years ago.

A carburetor with a manual choke finally was the solution. Pull the choke about half way at every stop sign/light for the first 30 minutes.

Jon
Got ya. That is bad.

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Old 02-22-2023, 11:43 AM
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If you block the crossover, on a stock vehicle, you have to remove or disable the heat riser. Correct? I have always done it on cars with headers. So this just occurred to me.

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Old 02-22-2023, 12:36 PM
wbnapier wbnapier is offline
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I live in San Diego and have a cast iron tri-power intake. There is a e-choke conversion available if I ever filled in the crossovers.

I run E10 91 octane, I use phenolic spacers, and the carbs do get hot to the touch.

Do any of the after-market aluminum heads use these hot air crossovers?

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3.55 Rear Differential
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Old 02-22-2023, 01:22 PM
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I have a 65 with the factory intake and factory AFB. I filled mine, and would concour with Carbking that you definitely have to let the motor warm up (mine up to at least 160 deg coolant), warms up in about 5 minutes, but after that mine definitely runs better than not filled. I did switch to an electric choke. This is strictly speaking about spring - summer driving, with 10% ethanol fuel. Idle quality in hot weather is also much improved. It also helped a lot with the fuel evaporating out of the fuel bowls. I had another car with the same exact set up but cross over not filled, and the next day when you would go to start the car, the carb would be dry. I'll be building another motor for another car, and will do the same thing again.

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Old 02-22-2023, 03:07 PM
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I did quite a bit of testing on mine. It's a 68, with a 71 704 carb, choke stove. Blocked the driver side crossover passage so exhaust can still get to the choke stove .. but yeah, it's not forced through. Had to adjust the choke link a bit more than normal, but after an extra five minutes of warm up the intake is warm enough to fully open the choke.

I also run an OEM air cleaner with the pre-heater installed which helps with warm up, and also when intake air drops below a certain temp at any time.

I don't know about fully filled crossovers as I've never had them ... but my setup seems to be a good middle ground. I'm more likely to be driving in 80 degree weather than 50.

Kenth ... you live in freakin Sweden Of course you need an operating crossover, it never gets above 50f there .

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Old 02-22-2023, 04:45 PM
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Quote:
Originally Posted by Cardo View Post
I have a 65 with the factory intake and factory AFB. I filled mine, and would concour with Carbking that you definitely have to let the motor warm up (mine up to at least 160 deg coolant), warms up in about 5 minutes, but after that mine definitely runs better than not filled. I did switch to an electric choke. This is strictly speaking about spring - summer driving, with 10% ethanol fuel. Idle quality in hot weather is also much improved. It also helped a lot with the fuel evaporating out of the fuel bowls. I had another car with the same exact set up but cross over not filled, and the next day when you would go to start the car, the carb would be dry. I'll be building another motor for another car, and will do the same thing again.
How did you block yours?

K

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Old 02-22-2023, 04:57 PM
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Dave at SD Performance filled it when he did the heads. I believe it's with melted aluminum.

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Old 02-22-2023, 05:05 PM
Goatracer1 Goatracer1 is offline
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JS the valley cover is not to keep oil from heating the intake. It is to keep the hot intake from heating the oil.

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