Most Twin Cam Engines use a direct acting tappet which is commonly adjusted with shims and this is the classic defitiniton of a 'flat' tappet engine.

The XK Jag engine is typical as is the Lotus Twin Cam, Ford BDA, DFV, most Coventry Climax Race engines. They are commonly adjusted using a ground shim between the tappet and valve. the Alfa sud engine is unusual in that it uses a flat tappet that combines a screw adjuster.

I think the standard 996 has a hydraulically adjustable direct acting tappet.

The 906 Solid lifter is a variation on this design as it uses a small lash cap for adjustment. This style of lash cap has become quite a common replacement for the heavier tappet in a wide range of race engines.

The reduction in ZDDP that ocurred in most oils around 5 years ago does cause flat tappet engines specific problems.

I believe that around 1200ppm is needed to ensure that adhesive wear does not take place.

I believe that current SAE standards limit this to around 800ppm which is just not enough.

(I hope my figures are correct)

If modern oils are used during 'break-in' then damage is very likely and either cam lubes are essential or carefully formaulated Break In oils are vital.

We used to use Valvoline 20/50 racing and for years had no issues. The new VRI had a roughly 50% reduction in ZDDP and since it introduction we swapped to Joe Gibbs Drive XP4 and again have had no issues.

There are now several high ZDDP Race Oils on the market as well as additive concentrates from Lucas Oil, Redline and a variety of other companies.

Some care is needed as excessive levels of ZDDP can cause bearing pitting and other damage.

I think the maximum level is around 2000ppm but I am sure that there is better information than this with a little more research.

I am sure that this is quite a problem for the classic car industry and we all need to be using the correct grade of oil with sufficient anti wear and anti scuff additives.

After discussions with others on several Porsche forums and research into products that are on the market, I've decided that the very least that I can do is to change my selection of oils to those that still contain what appear to be the "older" adequate levels of ZDDP.

As mentioned earlier in this thread, there are Joe Gibbs oils that apparently have higher levels of ZDDP. Also, you can get ZDDP levels up in the 1300 to 1400 ppm with products from Brad Penn, Motul, and one Mobil 1 formulation, Mobil 1 V-Twin, which still runs the higher ZDDP level. My curiosity wonders why some oils can still contain the higher ZDDP levels when the US EPA mandated lower levels in order to prevent damage to catalytic converters in automobiles? I can understand why Mobil 1 V-twin would be exempt since it is meant for motorcycles, which currently are not required to use catalytic converters; but, how do Brad Penn, Motul, and Gibbs oils circumvent the regulations? Is it because they are meant for "racing" conditions which do not require the use of catalytic converters (yet)?

And, while the M1 V-Twin oil is only available in the 20W50 which works for the 911 engine, the oil does not contain friction modifiers since motorcycles normally have a common oil sump shared between the motor and the clutch. So, what impact does the lack of friction modifiers have on engine performance or longevity?

Mainly, fuel economy,.....:)

No change in engine wear provided a good oil containing high-quality base stocks and a proper additive package is used. Naturally, regular oil changes are required, but you already know that. :) :)

Ernie:

The really long answer about 20W-50 oils is here: http://forums.pelicanparts.com/porsche-911-technical-forum/367300-ultimate-motor-oil-thread-why-we-hate-cj4-sm-oils.html

A shorter answer is that the oils that go to 40 or 50 weight are not covered under the EPA mandate since the cars that use these heaveier oils do not have catalytic converters that are subject to the EPA extended warranty requirements.