fuel tank collapsing

Just freshened up the blown altered and noticed the sides and top of the tank have been sucked in. While not totally collapsed it is very noticable. The vent is not plugged/covered and it's a little smaller than dime in diameter. Looking at some pictures of the car leaving I can see that fuel is spewing out the bottom of the vent at the hit. The vent is near the back, underneath the cap. The tank is about 7gallons and I'm really surprised to see this. Two passes ago we throw a rod out in the lights, picture of that run shows tank in good shape at the start. The car ran 6.78 197 but seemed lazy after the hit.

Ideas?

 

Sounds like you might need a larger diameter vent .

 

If the vent is located in such a way where the fuel sloshes out at launch then obviously it's not venting at that time. Even if it isn't sloshing out it may still be covered with fuel and not venting properly. If you have to fill it that full then it sounds like you need a larger tank with a larger vent while your at it.

 

I am no expert but if the loading of a run pushes the fuel to the back if its blocking the venting process then it may create a vacuum , kind of reminds me of how they put windage plates in sumps to stop the oil being pushed to one end and leaving the oil pickup dry.

 

Fuel tank

Find someone who runs one that works, Copy it, and Baffel it as necessary. There is HP to be found or should say used, with the right tank. There are certain places you need to spend the money. and other places you can get by with. Maybe you can find a print somewhere. Do some research It,s winter. Good luck Don

 

when i worked for barklages on their pro-mods mark wanted to teach me the 'ozark glug test'... and i said 'the what??'

barklage-'you know the glug test'

me-'what the hell is that? are you making that up?'

barklage-'you know... you fill your tank up with liquid and hold your hand over the outlet. turn it up so the outlet is pointed down and let your hand go'

me-'and??'

barklage-'if the tank doesn't 'glug' while the fuel is running out... then it's ok'

only in the ozarks... can't make this stuff up folks

 

Not only in the Ozarks, anywhere where there is a barn, barnyard logic will apply!

My guess is: if the vent goes up into the neck, the tube is more than likely dented from the funnel!
On a blown motor, minimum vent tube is 1/2" x .049 wall, .402 I.D.
We've used 3/4" x .049 since the days of the 12-71!

If you are not sure, go to the hardware store/home store and buy a 3/8" plastic hose about 3' long, then slide it through vent tube.
I've fixed a lot of stupid stuff through the years

 

Is the tank at the front of the car and wedge shaped? There's alot of downforce at 200 mph.

 

Well I think we found the problem. Took the tank out and both the top and the bottom of the vent looked clear. Seems it was blocked within the vent tube a couple inches from bottom. The tube also is looped inside the tank. Apparently, when I drained it still had fluid in the loop which over the past 3 months turned into some crusty mud like crap. Should be able to expand tank back out. We will be putting a vent through the top however.

Yes it is in front and angled somewhat but it has a weight bar and some tubes in front of it to break the wind.


Thanks everyone