I just got my HE engine completely rebuilt with fireball heads. The car is now incredibly powerful both setting off and if you hit the gas around 80. But it only does 10 mpg ... not even that sometimes ... 9.5.

Occasionally I get a whiff of gas when starting the engine... do you reckon the mechanic retarded the timing? I asked him and he replied with a smirk ... "it's a fireball head, did you ever hear of a fireball? They were designed for power."

Should a fireball give more than 10 mpg or is my engine tuned to PERFORM? what do you reckon?

Rudy

 

To clarify, ALL 5.3 HE engines have the May Fireball cylinder heads. They were introduced mid-1981

You should not smell raw gas. Whatever the problem is...could be many things....needs to be fixed. This could certainly be part of your poor fuel economy and can certainly be dangerous.

An XJS V12 HE, in good order and driven gently, should get about 12-13 mpg in city driving and about 18-21 mpg on the highway.

If your driving mostly in the city and "using all 12 cylinders", so to speak [grin], then 10mpg is entirely plausible.

Cheers
DD