Home » Public Forums » GMCnet » Vaporlock baseline temperatures
| Re: Vaporlock baseline temperatures [message #211760 is a reply to message #211128] |
Fri, 21 June 2013 06:37   |
Michael Morton
Messages: 21
Registered: July 2004
Karma: 0
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Junior Member |
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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 pressure, 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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| 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: 6
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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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| Re: [GMCnet] Vaporlock baseline temperatures [message #211789 is a reply to message #211756] |
Fri, 21 June 2013 09:46 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Senior Member |
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| Jim Bounds wrote on Fri, 21 June 2013 04:12 |
Mike,
Can I install a 3 port mechanical fuel pump and use the return from it to set up the same condition? A friend of mine here in Florida has done that and feels it is a major addition to his system
Jim Bounds
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________________________________
From: Michael Morton <memorton@charter.net>
To: gmclist@temp.gmcnet.org
Sent: Thursday, June 20, 2013 5:36 PM
Subject: Re: [GMCnet] Vaporlock baseline temperatures
Guys, I just can't believe that everyone keeps trying to over engineer this vapor lock problem. I have posted a couple times how I cured my problem and been told it wouldn't work. After rebuilding, restoring, and racing many different things for the last 40 years, I believe in the KISS principle. (keep it simple stupid). I started racing dirt bikes, moved into go carts, drag cars, road race cars, have build 2 motorcycles that hold land speed records. But my first love is airplanes. I am a licensed aircraft and power plant mechanic and an airline captain. I have raced an airplane at Reno, flown airshows in several different aerobatic aircraft and presently maintain several war birds that I fly at shows. My main hobby is restoring antique aircraft, just finished rebuilding the 300hp engine on my airshow aircraft. Lost count of how many aircraft engines I have rebuilt over the years. I'm just saying this to show that I am no dummy when it comes to
mechanical things. I read
about coolers, tank insulation, in tank pumps, and many more ideas. All that is required is a simple fuel return line. Just tap and install a fitting in the top of the fuel filter housing at the carb, install another one in the fuel filler neck, located in the engine compartment under the drivers seat and connect the two with a 1/4 inch line. I did this 2 years ago and haven't have a hint of vapor lock problem since. Now I just use my electric fuel pump to fill the carb after a long sit to make it start easier. With the fuel constantly flowing there is little chance for vapor lock and if vapor does form it is routed back to the fuel tank. I did say to install the fitting on the top of the fuel filter housing, didn't I? This maintains reliable fuel to the carb bowl. Most carburated and fuel injected aircraft use a fuel return to combat vapor lock. All the cars I own I have bought salvage and rebuilt so I know them inside and out, my BMW, and Ford F150
with fuel injection use
fuel returns, hell even my carburated 1985 Jeep CJ7, and 1966 AC Cobra use a fuel return. Just keep it simple, install a fuel return and enjoy your ride. After all, we are dealing with a motor home built in the 70s using 50s technology, it's not rocket science.
Sorry to toot my horn, but this is not my first rodeo.
Mike Morton
1975 Eleganza (Sloopy)
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When I got my coach five years ago, it had severe vapor lock issues right from the get go. I happened to mention this to Dave Lenzi while talking to him about copper exhaust manifold gaskets and Dave suggested using the Toronado AC equipped fuel pump with the bleed off. I have done a whole laundry list of things to combat the vapor lock, EXCEPT that.
The vapor lock is virtually gone, but still rears it's ugly head now and then. I think Mike's solution takes it one step further than the fuel pump thing, as it takes the line from the pump to the carb out of the equation. That will be my next step in, hopefully, finally solving this problem. If that doesn't work, I will eventually go with the in tank pumps.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| 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
Karma: 0
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Senior Member |
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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)
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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Les Burt
Montreal
1975 Eleganza 26ft
A work in Progress
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| Re: Vaporlock baseline temperatures [message #211838 is a reply to message #211128] |
Fri, 21 June 2013 18:11 |
Michael Morton
Messages: 21
Registered: July 2004
Karma: 0
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Junior Member |
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Les, When running aluminum heads it is generally accepted that you can run about 1 point higher compression without detonation problems. I have my timing set as high as I can and not get any ping, I usually run mid grade fuel and have no problems. I occasionally run 87 and if it is really cheap stuff, I will hear a little pinging, usually not. Some have suggested running the fuel pump with an extra outlet for the return. My way of thinking is that the only place that the fuel comes in contact with the hot engine is the fuel pump, I see that as a major source of heat and that setup would do nothing for the hot fuel between the pump and carb. I think that pulling the return just before it enters the carb is the best way to go. Some have suggested a fuel cooler setup, I like the KISS principle and don't like the idea of adding another possible leak source under the hood, I don't want to make it more complicated when this seems to work fine. I'm not saying this will work for everyone but it certainly has eliminated my problem.
Mike
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