hey there
im still debating on the engine i want, but I wanted to know what the major differences between a 350 and 400 SBC was ( aside from ci)

Is there any *possible way* i can get semi decent fuel economy out of a 400 SB? If for instance i put fastburn vortec heads on it)

any ideas?

 

stock cam, sure

do some mods....then they will all suck, if you want economy buy a cavalier....the difference between the 2 motors all built up can't be more than 1mpg if that while day to day driving

 

If you want mileage get an LS1.

 

i drive a stock 400 with remanufactured Q jet carb and i can tell you that it eats gas, and alot of it, so it is not driven much anymore

if you are after gas mileage then you want a smaller engine for sure


good luck

 

go for the 400 when my 350 goes thats what im building for about $3,000 i can put together a 500hp at the crank motor that can take a beating all day long and not break a sweat

 

one thing with 400's....though i dont know how hard yours will be run, when we build them as race engines....we ALWAYS plumb the intake from the water jackets right at the front by the thermostat...back to the back two cylinders with some braided lines....for some reason...the 400 blocks dont cool the back two cylinders as well as the other 6....the back 2 always overheat and burn up. not that its any big deal...but something to keep in mind if it'll really have the ballz run off of it.

 

This is a good topic for debate. It depends on the horsepower level and the type of fuel you plan to burn.
Another thing to think of it is not just the gas mileage but the price of octane.
If the engine is to only use 87 octane gas, then a mild 400 would probably yield more horsepower per mile per dollar than a 350 of the same power level.
Here's another way to look at it: If both a 350 and 400 were built for 375 HP the 350 would probably get better mileage at cruise than the 400 but would need 91 or 93 octane gas. Like Xpndbl3 said: Both will get close to the same mileage. And like Nelapse said: the only way to get decent mileage with a high horsepower level is to use a newer technology engine.