Vapor lock question

[85lebaront2]

Jim, keep going and I will come up there and strangle you. You are giving me flashbacks to high school and studying the gas laws!

[Gary Lewis]

85lebaront2 wrote

You are giving me flashbacks to high school and studying the gas laws!

PV = NRT?  I did that from memory and I don't think my memory is what it used to be, but I really can't remember.

[ArdWrknTrk]

But they're not wrong....

Most of us understand.
Spewing nonsense isn't helping the OP with his vapor lock, nor providing other readers with the information they need to better understand how heat works.  

[viven44]

I wasn't go to say much more but thermodynamics has a couple more considerations... all of the below is just my opinion, not facts.... some of the below is extrapolating from thermal simulations I have come across in my line of work

Steady state thermals
---- This is the key care-about in designing just about anything. Semiconductors or engine/fuel heat management..
-Conductive heat dissipation
--- I honestly don't think a thin layer of rubber or fancy reflective coating is going to help in continuous operation aka steady state, especially if there is no air gap. If there is an airgap between coating and the actual fuel line to be shielded, that is immensely helpful... all the heat shield wraps benefit from the fact that there is an airgap from an imperfect wrap... so don't wrap it too well ;) (Air is a very poor conductor of heat) 
--- The actual fuel flowing in the lines is the best heat transporter/dissipator of all. This is really where I think a return fuel line is super helpful. The fuel is at a vastly lower temperature and liquid heat transfer is very effective.... the flip side is that one might argue that the fuel in the tank could become hot over time with a return line as the fuel would have picked up a lot of heat from the lines... but then if the tank is really full and is also being constant cooled by airflow from the vehicle driving maybe this may not amount to much.
--- Radiative and convective heat dissipation --- again not probably helpful in steady state if the coating is in contact with the fuel line... but very effective at shielding if there is an airgap.. If the fuel line is sitting next to an exhaust manifold... there is value in having a heat wrap that is reflective... but an airgap is probably a more critical first order factor.
Transient thermals
---- this is transient spikes in temperature caused by sudden high power scenarios. Not applicable to engines/automotive I would think.. only mentioning this because I do think the reflective materials can help shield from low duration/high power heat sources.... and also to mark the difference between it and steady state behavior. In steady state even poor conductors and reflectors will eventually "load up"... but then if there isn't much mass to load-up maybe there is value... I can see Jim's point of "thickness being the enemy".

All the parts are sitting in a big oven.. I am sorry but its all a big crap shoot anyway... The common sensical things to avoid vapor lock is to run fuel at higher pressure and avoid boiling scenarios (either from vacuum on the suction side of the pump or from excessive temperature spikes beyond what the flow of fuel can handle)

With what I have done and the discussion above, I have realized a couple of issues (no return line and also black rubber/in-contact with fuel line). Again so far so good even in extreme hot days. Maybe because my 460 drinks enough fuel to keep the fuel flowing ;)

[ArdWrknTrk]

Which is why Gary's reflective braided sleeve is effective.
It provides an air gap, a reflective surface... and perhaps some air flow through the braid.
Remember, nearly 100% of underhood heat (other than block & heads) is radiative heat.
No matter what anyone wants to think it is a wind tunnel under hood.
Maybe a wind tunnel that starts out at 100°C/212°F or whatever, but by the time the coolant reaches the radiator outlet it better be a lot closer to ambient if it is going to have capacity to do it's job.

And I agree entirely that fuel flowing in the line is carrying away a lot of heat.
That is why the hot fuel handling vapor separator is offered with a 0.090 orifice "for problematic vapor lock"
Once bypassed back to the tank it has substantial surface area to dissipate some of that heat.

With a carburetor that's float bowl is vented to atmospheric we can't make the float valve too strong, and run higher line pressures
Gary essentially did, when BB was carbureted, by running the later in-tank FDM's and a return style FPR where the old vapor separator was......

Transients.
I'm used to energetic chemistry and working with rocket motors.
You probably don't even want to know what kind of pressure and temperature spikes get instrumented in a combustion chamber.
Unfortunately ablative surface treatments are mostly a one shot deal...

[viven44]

Yeah I was going to say ... make a shield thin to remove thermal mass.. but make it too thin it won't have structural integrity.... didn't know that can be handy... makes sense though.. about half the rocket has 'left the chat' by the time it has 'escaped'... rocket launch and 1/4 mile racing do have a lot of similarities...  

[mat in tn]

soooo...... foil duct tape? 

[ArdWrknTrk]

Over a glass fiber braided sleeve and we're back to Gary having gone the route of not re-inventing the wheel.

[Gary Lewis]

I have it on the dip stick, which touches the header at times, the engine wiring harness as it goes from the fender liner over the header to the engine, and on the fuel lines near the header.  Doesn't even show that it has touched the header.  And it is easy to apply given the velcro closure.

[ArdWrknTrk]

I didn't know that your dipstick was actually touching.
I remember how tight you said those things were.