Why have fuel tanks near engine compartment?

Hi Jeff, I think it partly comes down to packaging remember the 911 is rear engined not mid, everything is moved back slightly and it has rear seats no other place left for the tank other than the frt. If you look at the size of the tank(s) in the 308 thru the 360(they hold more vol. than a 911) they take up a lot of space. There wouldn't be room up front for the tank and probably still keep the slope of the frt sheet metal on the V8 fcars not to mention the conveniance of the storage vs behind the seats. There is more width in frt of the engine than there is in the frt of the fcar, again packaging.
Also frt impact is more critical in the engineers mind, the tank being in the middle of a car is safer in the event of frontal crash or for that matter a rear impact(Ford Pinto fiasco, the tank was ahead of the rear bumper). IIRC VW had a problem with exploding fuel tanks in the Beetles because of the location in the frt of the car.
Also, fires in ferraris are not really related to the fuel tank, but more to plumbing to the engines and into the tank. regards, Vern

 

I remember seeing "stingray" vettes running in autocross back in the '70s: with a big front engine and that huge rear tank, their handling shifted as the tank emptied. Putting the fuel tanks near the centerline keeps the weight distribution stable.

Think how many refueling fires we've seen in F1 over the past year.

In a racing car, the fuel tanks would be racing cells, and a roll-over or side impact wouldn't have the fire risk that the side mounted regular tanks in street Ferraris seem to have. But racing fuel cells don't last long enough to put on production cars.

 

Um, in 1972 the 911 had a 21 gallon tank. 308s have a 18.5 gallon tank. So um.. yeah.

 

I would say the location of the fuel tank is much safer in the rear of the car rather than in the front.
This has to do with the predictability of an impact rather than with engine location, radiating heat and what have you.
In fact, if you pay attention, just about every car, irrespective of the engine location, has the fuel tank placed inside the wheelbase, in front of the rear axle (i.e. inside of the safety cage).
That is the area of the car that is less likely to be crushed in an impact, in most cases.
On the other hand, car fires are usually generated by leaks in the engine compartments, not by fuel tank leaks.
The firewall, in theory at least, should give you time enough to exit the car in case of such fires.

 

All valid points.

Basically, when the engineers sit down to design the car, they take many aspects into consideration. At some point, they have to figure out a place to put everything. Car design (like everything in life) is all about tradeoffs. There is no perfect location for anything. (Similarly, there is no perfect car: high performance, comfortable, reliable, beautiful and totally affordable.)

In the cases of Ferrari, Porsche, Corvette, the location of the tanks simply work in the packaging to hit the engineer's designated list of priorities. They all work just fine. If the Ferrari had the Porsche's tank, it wouldn't have a spare tire in front (no room.) The C5 Corvette's and 328's tanks are nearly identical (twin tanks.)

At least we aren't talking about Mustang and Pinto tanks. Just remember, over 1.5 million Mustangs went out with rear-mounted tanks that also served as the floor of the trunk! (Pintos got all the press, but more dangerous 'Stangs were produced.)

 

Jeff, is more like the engine is closer to the fuel tank Not the fuel tank close to the engine, I know what you're saying, no matter how you look at it they are still close together. About 99% of production cars out there have the fuel tank located in the rear of the car, but sometimes as we all know engineers and car designers sometimes like to relocate the engine from front to rear, therefore, since the fuel tank is originally there, now the engine is closer to the fuel tank. So it is just a design for who knows, maybe weight distribution?

 

Can't say for the 308, but on the 328 it's about 200 lbs tail heavy -- which is one reason why the 328 has fatter rear tires.

(The weight distro is one of the first things I check -- A Jeep wagoneer and a Celica AllTrac both have AWD -- but the one that isn't nose-heavy handles a lot better in the snow (e.g. the limits of traction).)

 

1+. I think it has to do more with weight distribution than anything else.

 

Sorry didn't go back that far on the 911, from the mid 90s 911s have had tanks that hold around 18-19 gal down to 16-17 in the later cars. the Fcars have been around 21 in 348/355 to 25 in the 360.
That wasn't the main just of the answer anyway it was a side note, If you read what I said you would know I dealing with packaging and safety issues. So um...yeah what.

 

Jeff, As far as I know you are correct in the location on the fuel tank, not being a Porsche guy I'm not sure but can't imagine they would want to pronounce an already overly tail happy car by putting more wt. back there. hahaha
My previous answer was just an opinion based on design and packaging. When you bring in weight distribution there could be something to that but in a street car I'm not sure that is as high on the engineers list vs. the sloppiness(artwork in design) of the frt sheet metal on the Ferrari. The benefit of that rear weight bias is better on the track and better for braking, I would think that is one of the reasons why the Porsche is known for good braking(all that rear weight going to good use)a good anti dive mechanism. The best race car design at the moment is to have the majority of the cars wt. between the axles and behind the driver partly for aerodynamics but also for better handling and braking(thinking of an F1 design). With the way the frt of the 355, for example, is designed I'm not sure you would have room up frt for the 20 some gal. fuel tank and a storage compartment too let alone the spare in the older 308 & 328s altho you could move everything back where the fuel tank would have been. I still think(for safety in frontal collisions) I would rather have my fuel tank(s) behind me and not in frt, hahaha. Just my opinion.

 

The Ford GT and the Acura NSX use a mid-mounted tank (similar to Ferrari, although not exactly the same) and I have read the reason for both was to minimize weight distribution change as the tank emptied. I think those who commented on this being the reason are on the right path, since it's likely those 2 cars both got the idea from Ferrari!

 

That can't be right....I've never been able to fill my tank with more than 14 gallons of gas....

 

The factory claims a 21 gal. fuel tank for the 1975 Porsche 911S. Just looked at my sales booklet from the old days. So, if we assume about 6.9 # per gallon, this is not a large percentage weight of the whole car. Kind of reminds you what a perfect fuel ethyl octane is for a motor car.

I am not able to find documents from my old 1972 911T just now, but I would think it was similar.

One reason we may think of the Porsche tank being smaller is the fact that the fuel guage shows dead empty when there are still about 3 or 4 gallons left in the tank. It will run a LONG LONG say after it indicates low fuel.

Back on the subject, I personally cannot think of anything more scary than having the fuel tank as part of the cars side frames (like the Ford GT Lemans cars or many F1 designs).

I am going to make a personal message to Ralph Nader to remind him where the fuel tank was on the Corvair.