Inline fours (I4) are not inherently balanced like the flat-four (F4) is. In fact, I4s are the worst motors for noise, vibration, and harshness (NVH). These are most commonly taken care of with a counter-rotating balancing shaft that cancels harmonic inbalances. I wouldn't try to pump up a four-cylinder without a balancing shaft.

On the other hand, horizontally opposed (flat) engines are completely balanced by design. They are the smoothest engines PERIOD

-Jim

 

Well, considering a new Lancer Evo 7 runs 0-60 in 5.0 flat (according to some magazine) but it does the 1/4 in 12.5 thats faster than a ferrari F360 (12.8 in the same magazine)

Thats freakin fast.... I hope the STI is that fast.

I also think I would rather get the STI than the Evo b/c of the horizontally opposed engine... it seems as though it would be safer at higher rpms... especially b/c of the short stroke.

 

Advantages to a H4 Engine?

Hope this isn't a repeat, if so I am sorry. Why a Horizontally Opposed Engine? What are the advantages? If there are great advantages then why not see more Boxster-Style engines in other cars?

-- Rich

EDIT: Rich, I'm sure it's a repeat, but I can't find the thread either.
I split a DSM topic the went way off track and merged it with your question.

 

Flat engines give better midrange punch in terms of power distribution. In the Suby's case, the center of gravity is lower as well. Boxers can be found of Subies, Porsches(which Subaru used to use as an advertisement-same config), various touring motorcycles, etc etc. Also, the boxer does not need counterbalancing on the crankshaft. There are various reasons why we don't see more boxers in my opinion, such include: the cost to have two separate heads as opposed to an inline, servicing is a little trickier just do to spacial arrangement, etc

 

Yea, I suspect cost is the primary reason as that seems to govern just about everything. I do like that boxer engine, though! I think the lower center of gravity and no need for counterbalancing are huge benefits and, IMO, are well worth any cost difference.

 

DannyM5,

All engines require "crankshaft balancers." These are the flat, round parts of the crank that are one each side on the connecting rods. They offset the momentum of the pistons as they move up and down.

You will notice that these are very small on the flat four compared to other engines. This is because of the horizonatlly opposed design and light weight rods and piston. These facotrs allow for a lighter crank which is very, very good. Anything that rotates in a power train should be light, and carries it's weight as close to the center of rotation as possible. Less torque will be required to accelerate a member with these characteristics.

-Jim

 

All the above is true. Also to add, the flat 4 has such a short crank and is thus inherently stronger overall although with Japanese forged cranks, this is rarely a weak point.