Light Flywheel

[Moss64C]

Anyone have thoughts on drilling the outside radius below the ring gear for additional lightening of the flywheel? I think some of the early 911's had this done from the factory. I've already machined the outer radius but would like to get to around 12lb flywheel.

Mike Moss 64C

[raygreenwood]

Unless you are drag racing...in general....lightening the flywheels on type 4 engines is not a great thing. It removes a lot of the enertial mass that the engine was designed to work with using the stock stroke. It can lose a lot of its down low torque potential.
Also, though the 2.0L 914 flywheel was forged....just from my experiences....lightening the flywheels excessively really weakens them, makes them more prone to warpage and cracking as they no longer have the nescessary mass to absorb and shed heat, especially in street driving and high clutch usage. Ray

[The Rookie]

wow i didn't know that. i had about 12lbs shaved off my flywheel. so would that be counter productive for a 2270cc engine. my engine was orignally from a 75' 914 2.0 and it's goin back into my 914.

[Twystd1]

Ray, I beg to dissagree.

I have cut down at least a dozen flywheels for friends that drive 914s. Some are stock engined. Some are radical type IVs.

The 1.7s and 1.8s work really well with 14LB FWs.

The 2.0s work great with 12 LB FWs. And all of these are street driven. All these guys drive their cars hard. These guys aint pinky fingers.

The best part is using engine compression to slow me down. High compression and lightened flywheels really help.

AND I haven't seen one of these warp or crack due to lightening.

I figure if you know how to drive. The lightening only costs about a 20% wear factor from slipping the clutch a little more from a complete stop.
And most guys don't drive their 914s more than 10 - 15K miles a year.

90% of the material I remove is from the outside edge of the FW. I simply radius the back side on a lathe. Rebalance it... And voila... Insta 12 or 14 LB flywheel.

I can use a mill and get em down to 9 LBS. For racing only. I have seen 6 lb clutch and PP combos on race cars.... Again not for street.

Thats my experience.. So thats all I know....

Cheers,

Clayton

[raygreenwood]

Sounds like pretty good experience. The 2.0 should do the best as its forged...but I have seen plenty of cracked ones that were lightened...(mostly the cast 1.7/1. from this especially if you drive a lot of stop and go traffic in very hot areas. It just looses too much mass to handle the heat.
It also will mostly have problems ...in my experience...when you get into racing clutches that have drastically higher clamping pressure. Some of the cracking tended to be in areas near the bolt holes where material removal got a bit heavy handed.

The real issue is mass. Though you get quicker spool up.....you get less torque on that rpm spool up. Torque is a result of not just cylinder compression and expansion pressure.....but is also a result of rotating mass at velocity. There have been some anecdotal findings I have read here and there that if the mass of the flywheel is reduced too much that it may induce some crank flex because there is not enough mass to counter the throws of two inner most pistons of the crank on their powerstroke. These were speculations based on observations.

Then again...even if it does cause limited problems...if the performance improvement is what you expect and the life expectancy is nominal....go for it! Its cheap and easy. Ray

[Piledriver]

Stick a 228 Vanagon FW in it, 14 lbs from the factory, forged, and a bit around the edge that could be removed w/o structural issues.

All it requires is reaming/install the input shaft bearing.

At one point you could get a new 228 FW/PP/disc for a Vanagon for what a proper plate alone for a 914 would cost.

(Which is why I have been running one or the last ~5 years/100K++ miles... I have adjusted it twice, but I think the locknut got lost)