Home » Public Forums » GMCnet » Vaporlock baseline temperatures
| Re: [GMCnet] Vaporlock baseline temperatures [message #211812 is a reply to message #211760] |
Fri, 21 June 2013 12:16   |
GMC_LES
Messages: 569
Registered: October 2009
Location: Montreal
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Mike
I feel the need to comment, not to discredit you, but to point out a few things that can responsible for our varied results.
1) You are running 10-1 compression which requires a better grade of fuel (super). It is a well known fact that running super often reduces the risk of vapor lock. It is also easier to find super without ethanol poisoning so your choice of fuel is one of the reasons for your success.
2) A mechanical diaphragm type fuel pump is more tolerant of bubbles in the fuel and they are typically not vulnerable to cavitation. They will continue to maintain a constant fuel pressure with or without the bubbles in the fuel. Most electric fuel pumps that suffer cavitation will have a difficult time maintaining fuel pressure until the cavitation has passed.
There was a thorough discussion here several months ago about how the stock fuel pump reacts with vapor lock. This discussion suggested exactly what mike has done.
3) in extremely hot driving conditions, recirculating the fuel from the top of the engine back to the tank has the potential to add heat to the fuel tanks unless a method for fuel cooling is provided. Of course fuel recirculation is a better solution than letting the fuel boil in the carb and fuel line on a stock factory configured system, but it only prolongs the inevitable if you are going to be several hours in hot traffic.
Les Burt
Montreal
On 2013-06-21, at 7:37 AM, Michael Morton <memorton@charter.net> wrote:
>
>
> 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 welde
d
> 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 pre
s
> 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 Morton
> 1975 Eleganza (Sloopy)
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Les Burt
Montreal
1975 Eleganza 26ft
A work in Progress
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