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Engine buffs: why do our engines need to warm up?
#1
Hey folks,

When I start my daily driver, it fires right up, ready to drive off. Now I don't know about your 7123 but mine needs nearly a minute of warming up time before it can idle properly.

Why is this? I'm looking for technical explanations :-)

Cheers,
Vincent.
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#2
its a @Don C question! So i'm sure he'll come up with a tech answer!

for my part i'd say its all about atomisation.
The carbs on these v8 spray a significant amount of fuel and when cold, its lots of fuel in liquid state.
Loads goes wasted too and mix in chamber isn't well balanced.
That's another plus for the EFI. No more holding the engine with the pedal.

73 modified Grandé 351C. Almost done. 
71 429CJ. In progress
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#3
(06-01-2018, 01:35 AM)Vinnie Wrote: Hey folks,

When I start my daily driver, it fires right up, ready to drive off. Now I don't know about your 7123 but mine needs nearly a minute of warming up time before it can idle properly.

Why is this? I'm looking for technical explanations :-)

Cheers,
Vincent.

Because your engine does not burn liquid fuel. It burns vaporized fuel. It takes heat to change a liquid to a gas.

73 conv. 460, D0VE large valve heads, Performer RPM manifold, Voodoo 227/233 cam, Holley 950 HP carb, C6 trans, 3.25 trak-loc.
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#4
(06-01-2018, 06:48 AM)TommyK Wrote:
(06-01-2018, 01:35 AM)Vinnie Wrote: Hey folks,

When I start my daily driver, it fires right up, ready to drive off. Now I don't know about your 7123 but mine needs nearly a minute of warming up time before it can idle properly.

Why is this? I'm looking for technical explanations :-)

Cheers,
Vincent.

Because your engine does not burn liquid fuel. It burns vaporized fuel. It takes heat to change a liquid to a gas.

Bingo. Carbs don't vaporize fuel well without heat. Fuel injection does a much better job cold and direct injection even better still.


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#5
So where does the vaporizing happen then? In the carb? Does that get warm enough? What if you have a thick spacer? Or in the intake?
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#6
That is why you have the heat stove on the exhaust manifold with the tube to the air cleaner snorkel in a closed system.

Thanks,
mustang7173 Thankyouyellow

"Courage is being scared to death but saddling up anyway" -- John Wayne
[+] 1 user Likes mustang7173's post
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#7
So where does the vaporizing happen then? In the carb?

Mainly yes, but when warm, the intake helps with the inside heat. The carbs also have a special shape that helps accelerating the air to create myst.
Another problem on v8's is the distance from the fuel source and the chambers. When cold in winter even if the myst is "ok"
there is some condensing of the myst on intake wall returning liquid before it can reach one cyl chamber. As Hemikiller pointed out, a direct injection removes this distance.

73 modified Grandé 351C. Almost done. 
71 429CJ. In progress
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#8
A cold engine needs a higher fuel to air ratio than a warm engine, this is because it cannot vaporize the fuel as fast as a warm engine.
A carburetor cannot easily adjust for this, most have a choke that can restrict the incoming air to create more vacuum and allow the engine to take in more fuel. Because of this the car cannot perform well until it has warmed up and the choke has been opened back up.
In a Fuel injected car the fuel injectors are just set to add the extra fuel as necessary, this allows the engine to be ready almost immediately.
 
I am using an EFI setup and don't have to wait for the motor to warm, acts like a modern day car.

-john
(jbojo)
351C 4V cc heads, 10.5 : 1 CR, 290 Herbert cam, Flat top forged pistons, forged connecting rods, Atomic efi,
C6 with Gear Vendor overdrive, 3.89 Tru Trac, Hooker Super Comp with 2 1/2" Pypes Exhaust.        

Some Mod pictures can be seen at:

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#9
Good explanations. Fabrice is right on about the fuel condensing on the walls of the intake manifold, one of the biggest problems with carburetors.

Which raises the question, why do throttle body fuel injection systems work so much better than carburetors? It's all about fuel atomization. Carburetors work by the air flow through the carburetor pulling fuel out of the carburetor nozzles in droplets, not really well atomized. The throttle body injectors spray the fuel into the air stream in a fine mist. As John said, the F.I. system adds extra fuel, when cold temperatures require it. This compensates for the condensation on the walls of the intake manifold, without restricting the air flow. Closed circuit systems, with O2 sensors, work better, more accurate at adjusting the fuel quantity. Injectors right before the intake valves work even better, with direct injection into the cylinders being best.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
[+] 1 user Likes Don C's post
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#10
That all makes it very clear guys, thanks for explaining! Didn’t think that snorkel is important for starting up. Many cars don’t have it. Does the snorkel make a big difference for starting up or was it more an environmental thing?
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