First, let me say I am a not a big fan of balance shafts because of the reliability issue/maintance issue. However, let me first say that many people will talk about a balanceshaftless car having lots of vibration and that is true to some extent.

Now, I know that many people at this point are kind of wondering why I would bring up such a overly debated topic? Simple new information.

So as I was working on my Daily Beater putting togeather the crank pulley's it instantly became clear that one of the reasons a 944 is so much rougher running without balance shafts then other cars is because it doesn't have what every other large non/balance shaft 4 cylinder cars have. What is it your asking? Simple a harmonic balancer on the crank pulley

http://en.wikipedia.org/wiki/Harmonic_balancer

Well, shortly after thinking about this problem I was wondering to myself why I have never noticed that 944's do not have harmonic balancers before? So I started to dig in my pile of S2 parts from my engine. I get to the bottom of the rubbermaid container to find my 944 crank pulley assembly. There it is a 944 harmonic balancer on the AC/Alt pulley from my 944S2. Porsche had clearly added a harmonic balancer to the S2 motor. I am guessing to add more refinement because in reality the 3.0L pistons etc.. are all about the same weight.

So why does this matter to you? If your running a race car it really doesn't but on street cars if you want to reduce the vibration simply add a S2 harmonic balancer and reduce some of the unwanted vibrations. I personally think that its not bad without the balancer but just wanted to let people know about this option if you have a street car.

It does answer my question of why I always thought my S2 was a smoother motor then any 944 I had previously been inside. Its clear now is because it had an extra advantage over a normal 944 motor.

 

but the S2 still had balance shafts...

there was probably something else with the 3L engines that warranted the balancer, maybe the rods were known to be somewhat out of spec or something. the 968s with the same crank and basic block used a dual mass flywheel but no balancer.

 

The 944 S2 3.0L has a harmonic balancer in addition to balance shafts. The S2 balance shafts are different than the 2.5 BSs, and the 2.7 BSs are different too.

The 968 did not have a harmonic balancer but had a DMF instead, like Spencer said. It also has balance shafts. I think these shafts are the same as S2 shafts but I'm not certain.

I have a harmonic balancer on my 968 because I deleted the DMF. I tried running it without the BSs one time (for a few seconds to check timing belt tension) and it vibrated like a mother. They all need BSs.

A harmonic balancer is the same as a BS, it just has a weight at the front instead of at the middle, and there's only one of it, compared to two BSs. I'd say stick with the original config dude.

 

Balance shafts are used to counter the mass of the pistons moving up and down as the engine rotates.

Harmonic balancers are used to reduce torsional vibration of the crankshaft (the crankshaft will twist when excited at it's natural frequency).

In conclusion, harmonic balancers and balance shafts exist for completely different reasons, so you can't use "one or the other". The harmonic balancer/dual mass flywheel prevent crankshafts/oil pumps/timing belts/valvetrains/etc from breaking, and the balance shafts stop the engine from vibrating up and down.

The 3.0 liter engines probably needed a harmonic balancer more than the 2.5 liter engines because the crankshaft is different. Technically they should also have heavier balance shafts if the pistons weigh more, but IIRC they don't. The cancellation provided by the shafts sized for 2.5 liters must have been called good enough not to make a new part.

 

I thought shat was the past tense of ****....

 

And an old question it is.....

For a street car, keep them.
My feeling is porsche paid Mitsubishi royalties for a reason rather than just sticking a harmonic balancer on the engine.

 

I've benn wondering if anyone has modified a Fluidampr to fit a 944/951/968 engine.

 

Harmonic balancers are a pretty hotly debated item. SAE consensus tends to lean towards the primary use being to reduce vibrations for the sake of driver comfort. Although oddly enough a lot of high end race motors (see Hitech and similar) swear by them. It's worth mentioning that the more common name for these is a torque damper, which is really more appropriate when considering their function. Long story short, they do not accomplish the same thing as a balance shaft, which is an out-of-balance shaft that opposes the vibrations created by other out-of-balance rotating assemblies in a motor, namely crank/piston assemblies and cams. Jerk is the dynamic's expert's most worthy adversary. I'm deliriously tired. Other topic worth debate, if removing a torque damper is bad for a motor, then switching to a lightweight flywheel is similarly detrimental as a heavy flywheel will function much the same way as a torque damper.

That's enough for one post me thinks.