Home » Public Forums » GMCnet » Vaporlock baseline temperatures
| Re: [GMCnet] Vaporlock baseline temperatures [message #211778 is a reply to message #211760] |
Fri, 21 June 2013 09:13   |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma:
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Senior Member |
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Mike,
Got it! I like the idea. My main concern was the material used for the return line and since you've used steel that's not a concern.
Using rubber at the filler junction doesn't worry me either as there's probably minimal pressure at that point.
How hard do you think it would be to run the steel fuel return line run through the dash air evaporator? It could even make a few
loops to cool the fuel on the way back to the tank.
Regards,
Rob M.
-----Original Message-----
From: Michael Morton
I'll try and answer some of the questions raised about my mod. Rob, a “T” at the inlet would return the fuel to the tank
just fine but I was also interested in capturing and returning any bubbles or vapor that were present in the fuel line. The filter
housing is a larger diameter than the fuel line so any vapor is likely to collect in the top of it, that is why I tapped off of the
top of the housing. I installed a 90 deg fitting on top of the filter housing and a straight fitting into the side of the filler
neck, both were TIG welded into place. The filter housing was easy, mark the top with a Sharpie remove it and drill a hole. The
filler neck required removing a section. The very early models are 3 pieces and the center section can be removed but most of the
filler necks are 2 piece setups and as Jim B told me it seems that GMC hung the filler neck and built a motor home around it. It's
next to impossible to remove so I cut it to remove the section to be welded
and reconnected it with a piece of 13/8 filler neck hose. It is already connected with one piece of rubber hose and a connection on
the other end gave it some flex which helped since I used a steel line for the return. It sounds hard but the hardest part was
removing and reinstalling the wheel well liner to gain access. That filler hose is an odd ball size and I had to order it online. I
used a standard steel brake line, like you see hanging at the auto parts stores. The only pump I use is the original mechanical
pump. I had previously added an electric pump just forward of the fuel valve to fight vapor lock, it helped some but didn't
eliminate it. Now I just use it to prime or fill the carb for starting after sitting for a while. And no, I haven’t operated
it at a high elevation, I have had it in the NC mountains and several trips to Florida with no problems. Also, had a question about
a regulator or restriction being needed. A carb really doesn’t need much pres
sure, just enough to trickle into the bowl when the float drops and opens the needle valve. Think of your lawn mower, it
doesn’t even have a fuel pump, just gravity feed from a tank mounted a couple inches above. High wing airplanes are the same,
not even a fuel pump, just gravity feed, and when in a steep climb the fuel tanks are not much higher than the engine at all. All we
are interested in doing is keeping the fuel bowl full, the mechanical pump is pumping 3-5 psi thru a 3/8 fuel line and even with
tapping off a return there is still more than enough to fill the bowl. My engine is putting out a lot of power, 10 to 1 compression
pistons, Edelbrock aluminum heads and intake, Mondello cam, etc. I'm sure it is flowing much more air, and fuel when I step on it,
than a normal 455 and I have never seen an indication that it is not getting enough fuel. (and I step on it a lot!) Can you say
Redneck tire truing?
Now for the disclaimer, everything I have said refers to a carburetor, fuel injection is a whole different beast. Fuel injection
does require higher and constant pressure, I'll leave that to someone else.
Mike
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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