Fuel tank construction
 

I am getting ready to have a fuel tank fabricated for a 26 Corsa I’m rebuilding. I have gone round and round trying to make decisions on a couple things. I have the original tank as a template. It is roughly 90-100 gallons and has a welded in 3/8” pick up. It also has 4 baffles spaced evenly throughout it.

I was curious as to what thickness material everyone is using for the tank. Is the standard 1/8” enough or are people using something thicker to prevent damage from the beatings these boats take?

Here’s the big one that has been driving me nuts searching through old threads looking for a definitive answer. Pickup and a return bung. I was thinking about having a 5/8” pickup tube installed so I never run out of supply. The motor that is going in the boat for the time being is a N/A carb 468 with a mechanical pump however I have a bunch of parts to put together a blown 540 that I was thinking about running Holley EFI on. Can I run the larger pickup on the 468 in the meantime or is there an issue with running a pickup that is to large for what the engine needs. I also was curious if it would be a good idea to have a second bung welded in for a return line on an efi setup so fuel can go directly back to the tank. This bung would be the same size as the pickup and capped in the meantime until needed. The pickup and return would be in the engine compartment so I don’t believe it’s a USCG issue.

The shop that is going to build the tank does a lot of tanks but is not specifically in the performance business so I wanted to get all of my ducks in a row before I drop the old tank off to have the new one built.

If I’m overthinking all of this that is an ok answer as well as it is definitely a bad habit of mine I just want to make sure I’m doing this correctly the first time.

put big npt bungs on the tank,,then you can put any pick up tube size you want.btw,5/8" fuel pick up is fine.

TylerG,

Can't disagree with this. Your fuel system is only as big as the smallest fitting. Don't make that the very first thing the fuel has to pass through AND the one fitting you can't change.

Another way to configure your plumbing is to run your fuel return back to the filter before the pump. Many filter mounts have at least two "ins" and "outs". This is how Weldon recommends.

Thanks. Brad.

If you return right before the pump and not the tank, you will need to put a fuel cooler on the return side. I had to do this. If I have to idle over 20 mins in no wake areas my fuel overheated and then would not idle and eventually the engine would die. I just installed 4" oil/power steering coolers after my sea pump.

Thank you for the reply’s. What about 2 3/4” npt bungs welded in then using a 3/4 to -10 adapter with a 5/8” tube welded on to the npt end and cut to the length needed to make the pick up. Aside from the custom pickups that Eddie Young was making at one point I haven’t seen a lot of custom larger pickups so I don’t know if this is an ok way of doing it. I was only thinking about welded in pickups because that is what the tank originally had but I do like the more conventional thread in style

I have seen a lot of boats rigged with the fuel returning to the filter head but I did hear of issues like Rookie is describing. Which is why I wanted a return fitting in the tank if I’m starting from scratch.

thats fine

If I were starting from scratch, I would install a 1/2" npt bung for the pickup tube and a 3/8npt bung for the return. This will support a thousand hp or more. Line size depends on what type of pump you are using. If you are using a standard mechanical pump, they don't pull very well from a large, long fuel line. The diaphram only moves so much fuel each stroke and it takes forever to get it primed. Electric pump doesn't really care.

Returning the fuel to the filter head on a EFI engine is a proven way to induce vapor lock. Return it to the tank.

Snap, others,

https://cimg8.ibsrv.net/gimg/www.off...a11fd1850.jpeg

So this is exactly how I’ve got my fuel system set up. I’ve shared this photo with a handful of people, and nobody has mentioned a hazard of vapor lock. But, since you mention it….

https://cimg3.ibsrv.net/gimg/www.off...728193d3b.jpeg
(Older pic. I’ve since cleaned it up as best I could reach, and the pickup line is now AN connection.)

I obviously do not have a return bung on my existing tank, which is full-ish with fuel, and removal of the tank is an absolute non-starter. What would be the plan for adding a return bung if I wanted to go that route, or am I just stuck with it?

Thanks. Brad.

They make a "T" fitting that you splice into your fuel fill hose that will return to tank. I have friends that did not have the issues I had when returned to filter head. I was returning right before the pump bypassing the filter head. Circulating the same fuel over and over. My electric pumps would run hot. This was after 20-30 minutes idle time. You can always try it and see if it works.
Example:
https://www.speedwaymotors.com/Inlin...yABEgK8QPD_BwE

Removing the return from the filter head and returning it to the tank was a proven fix for the 454 and 502 mags that suffered from vapor lock. Yours will probably be just fine since your lines aren't right on top of the engine getting heat soaked. You will just have to try it and see. As Rookie said, you can always return it through the fuel fill hose with a tee. I have also pulled the fuel sending unit and drilled a hole through it to fab up a return when the fill hose wasn't accessible.

Rookie,

https://cimg5.ibsrv.net/gimg/www.off...6bbd6e78f.jpeg

I have access to the full hose on top of the tank, but I’m betting that hose would be a farqing nightmare to get off, and I’d have to cut it and use that cutoff as the splice between the tee and the fill bung.

Did you have a fuel cooler when your pumps ran hot while idling? I will have a cooler in my plumbing, between the fuel rail and the regulator.

Tyler,

Sorry for the slight detail, but this might be handy info for you, too.

Thanks. Brad.

See above...

Rookie,

Speaking my language. :ernaehrung004:

Carry on….

Thanks. Brad.

Is anyone running the anti-siphon valve when going with the larger pick up tube?

I've always had mine built with 3/16.

XLint,



I installed one on the output port of the fuel pump. I removed the one that was on the pickup on the tank. It had about a 1/4" hole through it. :rolleyes::picard1:

Thanks. Brad.

Don’t worry about a de rail this is all great information. I’m a marine tech in my early 20s so I’m fortunate enough to be surrounded by a lot of knowledgeable guys but when it comes to the high performance stuff I’m limited to the stuff my dad has owned over the years, one local performance shop that has been awesome as far as setup and parts sourcing, and these forums. Im always interested in seeing what other people are doing.

The comment about big npt bungs was enough to get me thinking about using the adapters and making my own fuel pickups. Im sure this idea has been done before but prior when I thought of thread in pickups I had the image of a super restricted stock style that made a hard 90* turn and choked down fuel flow that I see every day.

I was worried about the 5/8” -10 combo being to large for a mechanical pump but for the N/a setup I think I’ll start out with a -8 to 3/4 adapter with a 1/2” tube welded on. I can always make the larger setup if I need it down the road.

Fuel pickup ideas
https://www.offshoreonly.com/forums/...k-up-tube.html
.
https://fueltankparts.com/collection...nt-pickup-tube

Awesome!!! Thank you.

Will be ordering 1.

Sorry for the derail OP.

1/4 inch minimum is the way to go , The cost difference for material is minimal. I’d insert an extra bung for an extra pickup so one pickup is Main other is reserve. One thing I’ve learned with fuel gauges on boats during my 50 years is their worthless when you drop below a 1/4 tank.

Piece of mind to know you have 15-20 in the tank if you run out on the main pickup.

Tommy,

There have been a handful of times since buying our PQ that we have come into the ramp on pucker, thinking we were sucking fumes. During our ongoing rebuild, while addressing the tank pickup sitch, I called Florida Marine Tanks and came to discover we have a 90gal tank, when I was thoroughly of the opinion it was around 60gal, and that the fuel gage sender is a 12" unit, which only reaches the bottom of the "square" portion of the tank. Anything below that, that which reaches into the vee of the hull, below the bottom of the square sides of the tank, is out of sender, which he said was good for about at least 15, maybe 20gal. We have 15-20gal of fuel when the gauge reads empty. Go figure.....

Thanks. Brad.

Thats was a project I`d rather forget .

https://cimg1.ibsrv.net/gimg/www.off...964c600b4d.jpg
https://cimg3.ibsrv.net/gimg/www.off...685b5dd111.jpg
https://cimg5.ibsrv.net/gimg/www.off...4395cbf28b.jpg
https://cimg0.ibsrv.net/gimg/www.off...44eed2dc2f.jpg

-10An for return and supply.
3/4 bungs.

The return to filter is the less desirable way to do it. Returning to tank is always better and allows you to use the entire cell as a cooler. If you don't have access to the tank or dont want to risk drilling you can always dump the return in the fuel fill neck, usually 1-1/2"

I remember when you first came on the site and excited about your new flat deck. Next thing we know you’re cutting up the floor, at the time I thought to myself what a rude awakening to buying a big expensive Hole in the wallet.

Whoops you did it again .