Flywheel Question, Is lighter better? Options

[ScottD914]

(IMG:style_emoticons/default/idea.gif) Gentlemen and Ladies;
I've spent the winter rebuilding my 1.8 up to 2142 (or there about). The
question I would pose is about the weight of the flywheel I need to purchase.
My new Eagle Rods and KB pistons are much lighter than the stock equipment
from 1974, does the sum of the mass in the case need to correspond with the
mass of the flywheel somehow? I've seen two choices: 17lbs and 12 lbs. Your
thoughts? Thanks. ScottD

[pcar916]

(IMG:style_emoticons/default/agree.gif) with these guys.

I'd do it even though a four-cylinder will be a little more susceptible to some vibration because there are 33% fewer fires per revolution of the crank. The lighter weight will produce less shear in the crank, but in any case don't romp on and off of the throttle a lot with the engine unloaded.

My 6.75lb flywheel has done just fine since 1999, and that's combined with an early push-style 911 clutch and pressure plate (like yours but 225mm... unless you've converted from the 215mm) in a 3.6L car.

I was an avid Porschelist/Rennlist guy back then and when I put out a post like yours the response was almost uniformly "Don't do it!". Turns out few had and it was just popular opinion that the idle would suffer and the 901 would wear out or break quickly. Neither happened.

Their reasoning, and my initial concern, was that since the original pressure plate and clutch-pak in a 993 is ~55lbs then approx. 33% of that would be foolish! The entire setup I have in the car now is less than 20 lbs... I think I remember 18, but I can't remember the exact number. I'll weigh 'em again during a transmission swap in a week or two.

I'll never go back to stock parts in my machine especially with FI. That said, with huge cams and big carbs, low speed streetablility could suffer.

Good luck!