Why is it that forced induction engines are typically smaller than their naturally aspirated, more humble counterparts.

For example, the non-forced induction Cobalt Sport featured a 2.4L 170hp engine, while the LSJ and the LNF are featured on smaller 2.0L blocks.

Also, the Porsche 911 Turbo is a twin-turbocharged 3.6L flat-six, as compared to the Carrera S or 4S which features a 3.8L flat-six.

Volkswagen's NA 2.0L vs the 1.8L turbo.

The only thing I could think of is "They designed the smaller block to deal with the tighter tolerances needed for forced induction," and "Uh... well if the engine's smaller there's more room for a blower or a turbo?"

Obviously, these are answers I pulled out of my ass. Help please.

 

better gas/unnecessary power unless you got the money to spend.

 

Hehe... you'd be hard-pressed to find people on car forums who say "unnecessary" and power" in the same thread...

 

because you don;t need more displacement to make more power with f/i. it keeps the power levels between car models similar

 

Usually they are shorter stroke to allow the motor to rev faster.

 

usually they lower the compression by a smaller stroke on the crank.so smaller stroke =less displacement.for example,the LSJ and L61 have the exact bore but the stroke on the L61 is more making it 2.2 as to a 2.0

 

good example is the corvette. 7.0l for the z06 and 6.2 supercharged for the zr1.

i believe the reason as cited by gm perfomance division was that the cylinder walls would be too thin to boost the 7.0

 

Also the 640hp LS9 has the same block as the 430hp LS3, cost reduction and similar design = better things for cheaper.

 

X2. The bore is usually the same but they decrease the stroke so there is less time for the piston to go up and down. Creates more HP that way. ( revs faster )

 

Ok, the reason they are smaller displacement is smaller stroke means more air can be forced without the possibility of bending rods, there is less 'leverage' pushing down on the whole assembly.

Usually F/I engines are square or over square(more bore than stroke).

 

Yep like a Sportbike motor.

 

while this is true, this is only the casewith that particular instance. usually the bore od the engine isnt the issue, but the stroke of the engine is lessened when adding boost. the LS motors are an exception

correct!

 

all the reasons above, and because with FI, you don't need the displacement to make the power.

 

Moreso there is less reciprocating mass to interfere with forcing **** in it.

A turbo v-8 makes more power than a I-4 turbo.

It is more about how much air can something ingest than displacement.

 

well, yes, steddums, a v-8 will always make more power, just saying that per cylinder.. yadda yadda.

 

Wow... this is good info. Thank you everyone.

 

Another idea here when it comes to OEM applications. They MAY be going with smaller displacement to get better fuel economy/emissions when off boost in order to compensate for increased emissions/fuel consumption when on boost. Basically trying to "fix" the averages.

 

mm...possible, but since the engine is usually de-stroked, its rotating assembly wont really weigh any less, so you wont really see an improvement in fuel economy