Quote:
Originally Posted by 1ntCobra
That got me thinking, the 427 S/C had a 42 gallon gas tank probably meant for long endurance races. And that is not probably the type of race that the 427 raced in much. So would you actually want to fill the tank all the way for a shorter race? And if you balanced the car with a full tank of gas, would it still handle correctly on a nearly empty tank of gas? I kind of remember reading something about such a problem with a Cobra, but don't remember where I read it.
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The gas tank is always a pretty nasty problem in a race car. You want the tank to be as close to the center of gravity as possible. That way, as the fuel load changes, the CG doesn't change.
Putting the gas tank behind the rear axle is a really bad place to put it. If the gas is behind the rear axle, it actually "levers" over the rear axle and takes weight off of the front wheels as it tries to lift the front wheels up. This, of course, transfers "extra" weight to the rear wheels in the process. You end up with a car that has the CG constantly changing. Not to mention, having the gas tank in the back is more dangerous in a rear end collision. At least it makes for a fun ride!
You can put the gas tank above the rear differential. (A pretty good place to put it). The gas tank is centered over the pivot point of the car (the differential is the actual pivot point the car steers around) and so this lowers the north/south polar moment of inertia. In other words, the car "points" quicker into a turn. Of course, this also moves the gas tank closer to the CG of the car...which is always good. The Shelby Series One put the gas tank there.
There ain't no free lunch, however. By putting the gas tank over the differential, you automatically have raised the gas tank high into the air. This, of course, causes problems in roll. As your car goes into a corner, it rolls. The higher the weight is up in the air, the "easier" it is for it to make your car roll too far--and the harder it is to control the roll as you loose fuel.
That is why they put the "ship in a bottle" gas tank in the Ford GT down the center of the cockpit tunnel--very low in the car. I think that is a really good place for it. It is well protected; placed very close to the CG so changing gas level doesn't upset the car too much; it is low so the roll centers don't change.
No free lunch again. It is extremely hard to package, and about impossible to service without lots of swear words and taking the entire car apart. Also, a center tunnel gas tank is impossible in a front engined car--the transmission has to go there.
David
