I have an early car but wanted to run some vintage stuff with my friend. I replaced the steel tank with a 944 fuel cell. I used the stock filler tubes no problem. There is no appreciable difference in fill time between my cell and a standard fuel tank.

Stock location is good but let us remove the flapper and the restrictor plate. It would be an advantage in enduro's.

To give some perspective on this, with the OEM restrictor in, our first attempts at refuelling took about 4 minutes for a 5 gallon can. With better venting, and some modifications to the can, we got this down to about 2 minutes and change. With the filler neck gutted, and the cans modified with a larger hose, we can now drain 5 gallons in 50 seconds or less. In our upcoming 9 hour enduro, we'll need to take on between 60 & 65 gallons of fuel - means 12 to 13 cans of fuel. Modifying the filler neck will save us minumum of 15" in the pits (45 + minutes from our baseline configuration!). That's about 5 LAPS. Giving that up versus the SE30's and Miatas that we are competing against in E2 would be suicidal. This is one of the reasons we're running this enduro under GTS-1 rules - so we can legally make this modification.

While I am all in support of limiting mods to make competition level, and more simple/cheap in Spec, this does not affect Sprint races, and handicapping the whole class versus other E2 competitors seems cruel .

I agree with Eric. There will be absolutely no advantage in normal Spec races with this modification except allowing some in the pits to refuel their cars faster getting them to grid on time (something we need at times - right guys!). You don't have to do it is this rule and it does nothing for you on the track. It should be a no brainer allowed modification. The only advantage I see is the drop in bicep mass in drivers not having to hold 50lb jugs up so long to fuel up cars. May affect our arm wrestling.