vent size recomendation

i have a back halve outlaw 10.5 car with a kb 526 with the mag 44 sticking out straight out the front cover towardes the grill [motor out of a rail],i have two 5 gal cells upfront teed to my waterman lil berta pump,two 5 gal cells are probley overkill but its a done deal,what size vent would be suited best for this set up thanks for any advice,steve

 

I ran in to a issue once witht the vent being to small. I would not run anything smaller than a 6 in each tank, I would really thinks a 8 would be the best. Are you returning the fule back to both tanks? Make sure that you keep both tanks full for you will have a problem.

 

im returning fuel to 1 tank ,both tanks are plumbed togather,thanks for your reply!

 

I to battled mid track fuel problems most of the year. Changed about everything but the rear tires trying to figure it out. Finally found it in September........yep....fuel tank vent not big enough. I went overkill and installed two 1/2" vents. Sure can breath now!

Hope ya hear what I'm saying.......blessings........Ron Clevenger.

 

I would not run less than 1/2 of the outlet size.

If each tank has a -12 outlet then run at least a -6 vent.

 

venting

the outlet coming out both tanks are 1 1/6 to the pump,is it best to to run a breather on the vents or just a bulk head fitting with a braided hose coming off and running down beside the tanks,thanks for the replys,steve

 

If you have to run a vent, and you know you do , why not run a vent the size of your outlet, (say 1.250 inside), and be sure you have enough, it certanly can't hurt. you got to do it any way, why wast time and money, do it right the first time!

 

That's why I said 'at least'... If you have room for a larger vent, then by all means have the larger vent.

I prefer to have a breather, just make sure it isn't restrictive or else you may go lean.

 

If the total vent area is half the area of the fuel outlet size, you'll never have a problem. Why? Because air flows through an opening much easier than liquid. You don't need a very large hole to let the same volume of air into the tank as the fuel leaving. Half the area is much more than plenty.

Also, if you're returning fuel to the tank, that liquid being forced in is helping to replace what is leaving. That puts less demand on the vents. In fact, even if you return fuel to the pump inlet, that lessens the demand from the tank too. For example, if you're pumping 12GPM but only using 8GPM, the 4GPM left over is part of that next 12GPM through the pump and it only needs to take 8GPM from the tank. Less fuel actually removed means less air that needs to enter.

I'd be worried that a gigantic vent might more easily slosh or spill fuel. Ya don't need it under the tires or catching you on fire.

Remember, the sizes that the fittings are rated is the OD of the tube size, not the ID of the hose or fitting. -12 is listed as 3/4", but that isn't the ID. Here's a chart that I use based on the ID of the fittings for each.

Size ID Area
-16 .85 .57
-12 .62 .30
-10 .49 .19
-8 .39 .12
-6 .30 .07
-4 .18 .03
-3 .15 .02

Spud
www.fuelinjectionenterprises.com

 

Vent Placement

One word of caution, assuming your running an intake with some sort of burst panel.
Place the vent hose inlet in a position where if the burst panel goes the ensuing fireball and heat will not be drawn to the fuel tank. I have seen this happen and it gets real ugly, real fast. Also make sure you place the vent inlet below the lowest part of the fuel tank, just in case you ever go on your top the fuel will stay in the tank.

 

Oh MY GOD, Stop trying to reinvent the weel, how hard is it to put a big vent in compaired to a smaller one????? This has been gone over on this site at least 3 times, and if you know how to build a fuel tank there wont be any sloshing and spilling!

 

would 2 JAZ # 8 an tip over valve breather vents in both tanks be enough ,this way i wouldnt have to run a hose and be safe to,it only comes in a # 8,steve

 

Well, then...this subject has been covered here before and I guess there can be no further input on the topic. Everyone should just put a vent in their tank the size of their forearm. We're not sure why, but it's "just as easy" so what the heck.

There's nothing wrong with having a reason behind the choices you make. I was merely explaining a good rule of thumb for folks to use when choosing a reasonable vent size and thought people here might be interested in what I thought. Sorry if my reasoning offended your sensibilities 'eli'.

I'm assuming not everyone here would want a vent in their tank big enough to put their foot in. The front door to my house isn't 9 feet wide for a similar reason.

Spud
www.fuelinjectionenterprises.com

 

Ya and I'll bet your company has filters for all the sizes you talk about , and you will be stuck with them if one size fits all????

 

Oh, I get it...you're the resident "cranky old guy" here, aren't you?

Vent filters?! I carry no such thing in any size. Sorry, no conspiracy there.

Could it be that my post was simply motivated by a desire to share a logical, rational approach to answering the vent size question that was asked? Since I don't have a reputation of being a "web-board bastard", I'd appreciate the benefit of the doubt from you.

Thanks,
Spud
www.fuelinjectionenterprises.com

 

now see what you started steve, aka prost632, with that simple to answer question.

 

Spud, I liked your reply. Makes more sence then the Wilie Coyote way. LOL

 

ronnie

blownzr1,im feeling bad about right now,but i was always told theres no stupid ?s ,and not knowing alot about my new combo and being an X nitrous guy,i have a lot of STUPID QUESTIONS.i would have called you but the last ? i asked you ,you didnt return my call. i can keep a secret you know!!!!!

THANKS ALL FOF YOUR REPLYS!!!!!

 

For what ever it's worth: We recently did a little research on the subject of tank vent size. Our flow bench has a #12 vent on the tank and is similar in size to a large F/C tank, the instrument are digital and read to 2 decimal places. The system was flowing 11.38 gal. at 8000 rpm, we changed the vent to a #6, which would be very small, but really saw no measurable differences (to our surprise). Most people use a #10 or #12, which would seem to be very adequate, although I recently saw a top running car that had two #12 vents. That setup would probably pass the "glug" test.

 

Ok now for something a little left of centre, I have seen a few fuel tanks blown up like balloons after breaking the blower belt, I am assuming this is happening because the fuel pump is baulking for a nano second and a pulse wave is developed in the fuel outlet of the tank.

Now I didnt get in there and measure the vent tube, but a larger vent would favour this not happening surely.

As I said left of centre.

Ray