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Mustang drag cars launching and fuel spilling out the rear filler tube.

1204 Views 22 Replies 13 Participants Last post by  pateryan56
During the summer I watched quite a few 65-70 Mustangs at drag strips and noticed that quite a few that were really quick cars had fuel splash issues of fuel coming out the rear fuel filler cap area as they launched off the line.

What are some really good ways to stop that from happening aside from going to a custom fuel cell. My car will probably see high tens to low elevens so that is a concern.

I appreciate your input guys and thanks!
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1965 Mustang GT. 11.898 @ 113.646, all motor, three pedals
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…and run less than 1/2 tank of fuel. It’s gonna climb back up the filler neck either way, all we can do is minimize the spillage.
 

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My gas cap has double gaskets and the vent is closed. The fuel tank vents out the quarter trim. I have a glass fuel filter mounted near were the vent line ties into the filler neck. The fuel filter acts like a shock absorber when pulling G's and stops most if not all fuel from escaping. A mandatory fix that had to be done so I could continue competing. I fill my tank to the top before every event.

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I got a filler tube from a junkyard years ago I think it was a 70's Galaxie wagon. No it's not vented and car runs fine bur cap hisses a lot when opening.
I am in the process of venting it , waiting for a check valve and will connect it from filler tube to back panel where factory pop-open cap is
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pop-open cap is.
 

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I ordered a fuel filler neck online and plan to put the flapper in my stock neck.
 
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The track threatened to ban me from racing for leaking gas out the back when I launched. I didn't even know it was leaking. I got the 71 mach 1 new and improved flip up gas cap that is not the cap, just a cover. It has a screw on gas cap under that. It fits my 65 like it was made for it.
 
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The track threatened to ban me from racing for leaking gas out the back when I launched. I didn't even know it was leaking. I got the 71 mach 1 new and improved flip up gas cap that is not the cap, just a cover. It has a screw on gas cap under that. It fits my 65 like it was made for it.
That sounds cool. Have a pic?
 

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From a performance aspect, some type of vent MUST be provided at the tank to replace the used fuel.

I installed a new 65' fuel cap on a stock tank system and went for a spirited ride climbing one of our PA mountains after installing the newly modified motor. As I approached the top of the mountain, the car sputtered and died. It had spark, but the carb was bone dry-no fuel. I could hear the electric pump running and was thinking WTF? No cell service there. I then thought about the new part added and unscrewed the cap. Air rushed hard into the tank! I put the cap back on, started the car, and drove on.

I thought about the situation on the way home. The supply and return fuel lines are 1/2" ID and the fuel pump is a healthy Magnafuel 350, which matches the performance level of the motor. The tank was near full. I had created a huge vacuum with the new 700hp motor! It consumed so much fuel that it couldn't get enough to replace the fuel used. I welded a large AN fitting on the top of the filler neck and routed the looped hose under the car. That cured the vacuum issues, so the moral is Don't Suffocate Your Fuel Tank!

On a hard launch it still would vent some fuel on the track when near full. I never did find a permanent solution (even a loop didn't help) but a 1 way check valve or maybe using an inline fuel filter (like Nailbender) might have helped.
 

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When I first started drag racing I also had that splash out issue, so on my 70 with the pop-open fuel cover, I removed the spring loaded mechanism inside and put a "non-vented" screw on cap (Wanted the stock look on the outside). The filler neck goes to my fuel cell, which is vented with a roll over vent valve on the cell, then AN braided hose with a few loops to under the car and a small K&N filter to keep any dust from getting sucked in. Not a drop ever escapes out now.
 

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During the summer I watched quite a few 65-70 Mustangs at drag strips and noticed that quite a few that were really quick cars had fuel splash issues of fuel coming out the rear fuel filler cap area as they launched off the line.

What are some really good ways to stop that from happening aside from going to a custom fuel cell. My car will probably see high tens to low elevens so that is a concern.

I appreciate your input guys and thanks!
Stick this in the rubber hose....
 

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Stick this in the rubber hose....
Hey, that's really spiffy. My '70 Mach 1 definitely has the fuel splashing issue. Looks like the check valve is a good solution.
 

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I see that Tanks, Inc also have a similar 2" valve but nothing larger. The 65/66 filler tube hose is 2.25 OD, so one might have to improvise for either diameter to work properly.
Dang, same here, its 2.25" for 67-70 also. Maybe some modification is possible- maybe print a ring for a larger OD...if there is printer plastic impervious to gasoline. My local library will do 3D printing for next to nothing according to my son.
 

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Dang, same here, its 2.25" for 67-70 also. Maybe some modification is possible- maybe print a ring for a larger OD...if there is printer plastic impervious to gasoline. My local library will do 3D printing for next to nothing according to my son.
PVC is "gasoline proof". Grab a stub piece of Schedule 80 2" PVC.... it's 1.913" ID and 2.375" OD. Cut a "ring" to go around the valve... a little bit of sanding and maybe so mild heat will allow it to fit over the 2" check valve. Stuff it at the bottom of the hose just before it hooks to the tank. Finit.
 

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Discussion Starter · #17 ·
Stick this in the rubber hose....
That is awesome! I am not sure what the inner diameter of a 67-68 filler neck hose is but I am going to measure mine tomorrow. I am going to get one if it fits! Thanks for posting that!
 

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Discussion Starter · #18 ·
PVC is "gasoline proof". Grab a stub piece of Schedule 80 2" PVC.... it's 1.913" ID and 2.375" OD. Cut a "ring" to go around the valve... a little bit of sanding and maybe so mild heat will allow it to fit over the 2" check valve. Stuff it at the bottom of the hose just before it hooks to the tank. Finit.
Another good idea! I will try that also.
 

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Bart, unless this quick search revealed another internet untruth..
View attachment 870114
This related to PVC HOSE which I would never use in a petroleum application. PVC pipe material is impervious to gasoline because there is not enough BTEX in gasoline to swell PVC and cause permeation, especially in a non-continuous contact application.
 
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