Hmmm, good thought. I had thought of the purpose of these baffles from many different perspectives. The dimensions of the corner cuts were somewhat randomly devised based on other tanks that I've seen on the web. They do serve a stiffening/fabrication purpose, they do limit the amount of fuel bashing against my formed ends, but they may be a little large for the limit of fuel movement in a corner. At this point, I could easily reduce their size (for the bottom ones, not the top ones) and that would fix the cell fuel load better.

They are 1.5" on a side, what do you think about 1/2 that size? My only other concern is that as the size of the hole decreases, the stress on the baffles increases. I don't want the bashing of the fuel to rip the baffles out of the tank over time. Boat guys weld them in all the way around. I don't think a street car sees this sort of abuse (up and down through the waves and such).

Oh man! That looks awesome!! Well done Craig. No ideas on the baffle bit, but are you going to polish the thing at least?

No seriously. Are you?

No, this is not getting polished...there is no point (first time readers won't get this joke). It'll get black powder coated maximally.

Here's what I did - added some corners to: A. strengthen the wall/baffle connection and B. reduce the size of the hole to 1" square (ish). We'll call this the Dupuis modification.



You can see the reduction in size.



That's as good as it gets. Oh and for those that are wondering - TIG is very difficult to make work/pretty inside a 7.5" X 16.5" opening...so the welds are a little ugly.

A little ugly by professional standards perhaps, but considering the tight quarters (and that they're 10x better than mine at the best of times) they've got me in awe.

I'm thinking that the gaps in the stitch weld would have pasesd more than enough fuel from one partition to the other, even with your engine at full song, but what you've got is way better than the big empty box the car came with. What happens when a little sediment falls to the bottom of the tank and plugs off the gap, though? Better too much hole than too little.

I wouldn't be concerned with 1/3 of a half tank of 50 litres smashing those baffles off, no matter HOW hard you corner. Stronger is always better, but you're right - you're not dealing with 400 gallons in rough seas.

Having trouble visualizing- where does the pick up sit? Should there not be a low spot in the tank where the fuel can collect so you don't accidentally starve it when doing hard corners with a low tank?

Here's a shot of the pick-up sump before I blocked off the corner and tacked the return line to the baffle. Unless I'm going around a high banked oval the wrong way, I should be fine.



Just for fun I gave the baffles a good slug last night...just got a sore hand . I was able to stand on the tank end on and nothing moved (no jumping ...that would have crushed it).

Part of the hole sizing relates to the rate of fill of the tank (and I was only using the EPA rate of 37 L/min). In my research I found out that most tanks (even the pick-up truck ones) are not baffled except around the FI pumps. I was surprised by this - some of the designs that I did see were mostly just holed plates to settle the wave of fuel down (diffuser). Some use half height gates - mostly for boats or planes, the hot rod stuff is mostly a "well, this works" sort of engineering that I don't really like. One thing I would do differently is have a lip bent on all sides. Welding a corner when you can't see it is nasty.

With the two lines out, I should be able to clean the tank if needed. Much of the welding had to be done with the short cap on the torch and left handed to boot. These baffles are also 7" inside the tank - frick, couldn't see it half the time and for sure had a heck of a time getting the rod to dip into the puddle. New tank of gas and we're doing end tanks tonight!

Filling the tank should be fine no matter what - you're going to have large holes at the top of the tank, so at worst it'll spill over there and fill the next cavity.

I would be surprised if modern tanks are baffled at all, since they're plastic. I'm not sure how the most modern returnless systems purge the air that gets picked up by the pump but there must be a way. With the older systems any little slugs of air would just get passed through the rail and back to the tank, ideally. The pressure shouldn't blip for more than a second, and you shouldn't be cornering hard on less than 1/3 of a tank anyway. In the 780 with the old defective in-tank pump, I sometimes got fuel starvation (and near stalling, sometimes not-so-near) when I hit the brakes and the low fuel level rushed to the front.

On a welding note, I've been puttering around with the TIG on an RC project and have swapped hands with much success. Left handed torch, right handed filler just seems easier to me now that I've tried it. I still suck, but I bury the tungsten far less than I did!

I've seen plastic baffled tanks for aircraft...but I guess it makes sense to not worry too much about it as tanks are also no longer just large boxes, but wrap around stuff. Now I'm thinking about head room in the tank. I suspect that the usual volume of 10% (5 L in my case) wouldn't matter much as it could expand up into the fill tube - they did nothing in the original tank. Makes one wonder if this isn't all just a lot of over-thinking. In the 240 filler neck that I have there is a simple vent. I'm guessing that the vent attaches to the tank by the fill neck? I've been thinking that the fill pipe will be welded to a doubling plate, then attached to the tank. That way I can weld it all the way around (inside and out) and make the tank connection even stronger. Thoughts?

The one in the beetle is connected to the fill tube by a large rubber hose. Same with most pickemup trucks that I can think of. I don't suppose you'd thrown that into your plans, have you? A rigid pipe sounds like a nightmare to get into and out of the car. Maybe I'm misunderstanding? A nipple installed the way you're suggesting sounds like just as much overkill as the rest of your system, so in that case it's just about right.

With the OG tank did you ever have fuel puking out the cap, be it just after you filled it up and parked it in the sun on a hot day, or during vigorous driving? Where did the stock tank vent? Obviously if it's drum tight the fuel pump will eventually starve (it sure did on my 242 when I mistakenly plugged the vent during the B21A period)

If you're concerned about vapour volume, maybe the vent from the tank could pass through another box of some sort on it's way from the top of the tank to the inlet of the filler? On the 240 there is a series of vents, check valves, and rollover valves that vent the tank to the charcoal canister, etc. Any vapour is probably taken up by the canister in that case. The 122 tank certainly leaves a lot to be desired in terms of safety...

OK for the third time - the old tank didn't not leak a drop due to expansion. I'm using a fire hose barb connector welded to the tank and a short rubber hose to join to the filler neck. Should be a big upgrade, I'm also installing a roll over valve for the vent.

Mmmmmm...powder coating.

Ya, don't need to do anything, but polishing is out due to the weld puckers. Sure they are small, but they are still there. If the tank didn't have the baffles, then I'd be tempted, though it makes no sense. Just a nice black PC will be nice. I'm also doing the battery box when done.

Seriously? Haha, I missed the first two. Sorry!

I deleted them. Our wireless was flaky and I lost the same post twice. So I had a couple of blank posts up for a while.