RCR40 Fuel Tank Capacity

[Pasha Saleh]

Does anyone know the exact capacity of the tanks? I’ve got a mismatch between fuel sender (Speedhut) and fuel gauges (Smiths) where it reads 2/3 when totally full, then sweeps randomly back and forth form zero to 2/3. I’m thinking of using a unit like Meter Match to see if I can make it more accurate but would need to know the tank capacity to calibrate.

I filled the tanks with fuel cell foam to mitigate sloshing so watching the needle move around like that was unexpected. It happens even when stationary so may not be related to sloshing.

 

[bryanf]

By measurement I calculated their volume at about 11.9 gallons if you could fill the entire tank including the upper section.

https://www.gt40s.com/threads/bryans-rcr40.52988/post-553134

 

[Pasha Saleh]

Awesome, thank you! Now I’ve just got to figure out why I am getting 4 mpg!!

 

[Alan Lofurno]

I’ll see if I can find my notes, but my recollection is that mine are 8.5 to 9 gallons each. I never run more than 55-60 miles on each. Another problem I realized this year is that as there are no baffles, that as the tank gets lower I was starving the fuel pump on long down hills, hard braking, or when I was waiting at a light on a down grade.

 

[Pasha Saleh]

Thanks, Alan! So does that mean you are seeing MPG in the 5-6 range? I keep thinking something must be wrong with my math!

 

[Alan Lofurno]

5-6 seems a bit low - unless you are on the race track! I get 11-13 mpg. I check it almost every time I refill and it’s always in that range. All back road driving. Can I assume that you would notice if you had a fuel leak? I ask because my left tank had a pin hole at a weld seem that leaked. (Chris welded that for me).

 

[Pasha Saleh]

I have had all kinds of carburetion issues (4 x Weber 48IDA) since fuel had sat in the floats for a year and a half between the engine being completed and dynoed and when we were finally ready to install it. This resulted in stuck floats, a tailpipe fire, etc. So it could be my MPG may settle down to a more reasonable range once I've got it all sorted. I just added phenolic spacers under the carbs and it completely changed the character of the car -- solved the backfiring and fuel percolation issues. A real dramatic improvement. As for fuel leak, I doubt it since I assume the garage would smell of fumes and there is no smell at all even right up close to the sponsons. Doesn't surprise me that Chris fixed your tanks -- not only is he a mechanical whiz but one heck of a generous guy with his time!

 

[Neil]

5-6 seems a bit low - unless you are on the race track! I get 11-13 mpg. I check it almost every time I refill and it’s always in that range. All back road driving. Can I assume that you would notice if you had a fuel leak? I ask because my left tank had a pin hole at a weld seem that leaked. (Chris welded that for me).

You did not mention if the fuel tank was rendered inert before welding or not so I'll remind everyone that welding on a fuel tank is a quick trip to Valhalla unless it has been thououghly purged with CO2 or nitrogen. Emptying the tank is not sufficient; the residual fumes are explosive with the right fuel/air ratio. A young mechanic in Buckhannon, WV burned down a whole Chevy dealership by welding on a gas tank-- he learned the hard way.

 

[Pasha Saleh]

Ran out of gas today on the left tank and it took 8.3 gallons to fill it back up. I was on a slight uphill incline, so what gas was left was all in the back on the opposite end of the pickup tube. This seems to match perfectly with Alan's estimate of 8.5-9 gallons. I asked RCR the question and they weren't sure and thought it was "close to 15 gallons", which is way off. From the experience today, 9 gallons total with 8.5 gallons usable seems to be the answer.

More distressingly, the car only ran 34 miles on the 8.3 gallons it took to fill it up...4.1MPG!! Can this be possible? Running 4 x 48IDA Webers with all jetting spec'ed by Jim Inglese and it is running really well -- no smoke, hesitation, etc. But how can the fuel economy be this terrible? It makes the car almost unusable!

 

[Neil]

If you stand behind the car and your eyes are watering, it is running pig rich. Find someone with an air/fuel ratio meter and find out for sure quick. If that is true, you are washing the oil off the cylinder walls and wearing out your piston rings in a big hurry.