Quote:
Originally Posted by RussMcB
So, are all of these "acceptable" for 99% of us here (except the Racing 4T)?
I chuckled to myself when I first assumed our cars were "domestic", then reconsidered when I remembered where the engines were built and designed. :-)
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Marc Haibeck's (
zr1specialist.com) site contains an excellently presented write-up estabilshing the oil specifications at the time of the LT5 introduction. In short, the article establishes ZDDP levels at the time of the engine's
debut as 1200/1300 parts per million (PPM) of phosphorous and zinc additives.
Bearings aside for a moment, perhaps the most critically demanding areas for lubricity s the
cam lobe and lifter contact surfaces. And, well established levels of ZDDP were added such quantities to boost lubricity enough to provide adequit protection for motors with cam lobes sliding directly on the fixed lifter faces. But, the down-side was the fact that the phosphorous and zinc compounds were recognized as being detrimental to the effective longevity of catalytic converter and by extension air quality.
Roller tappets was the answer to the high levels of lubricity (ZDDP) required for the critical cam/lifter contact. And, over time, as newer engines w/ their reduced lubricity demands replaced older motors with their flat tappets, ZDDP levels were increasingly reduced in subsequent (API) specification releases.
Coincidentally, along with reductions of the phosphorous/zinc additives, a rise in the number of cam lobe failures was documented, and reduction of ZDDP was at the tip of the controversy. A huge debate ensued (and continues today) between engine builders and experts retained by the (oil) manufacturers (no surprise there) as to the exact cause of failures.
Questions of cam lobe surface hardening procedures and recommended cam break-in procedures and oils and the application (i.e., racing with unusual spring tensions, etc.) was all thrown into the cloudy soup of causal analysis arguments (and continue to be hashed yet today, if only at a reduced noise level).
Lubricant failures tend to be insidious. So, wear on parts due to inadequate lubrication is often difficult to pinpoint exactly in the longer term (of time and miles); complicated by other factors such as oil change intervals, average engine loading, heat, cold, short vs. long haul history, etc.
On the one hand... mitigating factors for wear is the lack of valve actuator linkage and the mass associated with that. (For example, the actual lifter in the LT5 measures only about a centimeter in diameter and about 2 cm long. It is housed in a titanium(?) lifter shell which makes the actual contact with the cam lobe.) And, the
valve weight due to the smaller size of the valves for DOHC apps vs. a 2-valve arrangement. Spring tension is reduced resulting from these factors which further reduces friction in the valve train.
On the other hand... Custom (higher) lift and faster rise intervals associated with increased lift, especially when combined with higher rev limits (approaching 8000 rpm on some builds adds to lubricity demands at the square of the increase in rpm above those typical of OHV motors. I have personally observed the lifter shells of LT5s that have worn through and shattered - testimony to the severity of friction between the cam lobes and the lifter bodies of these motors.
Maybe Pete or Marc can post some pix of such destroyed lifters?
The "take away" (for me, at least) is:
1) the original spec from Lotus was for oil with ZDDP in the 1200/1300 region.
2) Significant evidence exists to suggest less is not more, when it comes to ZDDP and these motors.
3) Cam lobe and lifter wear is insidious. By the time trouble is detected, it is often catastrophic.
4) The LT5's are expensive and much more labor intensive to fix than other (OHV) motors with a single internal cam. Most would agree that it makes sense to avoid "experimenting" with certain aspects, including (especially) OIL/lubrication; choosing rather to rely of the experience of experts (or at least significant evidence resulting from known applications).
In short: ZDDP additives in PPM quantities significantly higher than that specified for the latest (and especially for non-competition or aggressive driving situations, is highly recommended.
ALSO! in a survey of driving habits of ZR-1 owners, now several years old, I was shocked to learn that ~ 60% of them seldom if ever tickled the stock rev limiter (7100 rpm), and a good many of them admitted they seldom if ever reved to 6000 rpm! Well, in that context, is it any wonder the experience with various engine fills (not to mention mileage) having various ZDDP concentrations would be all over the map??
WAXERS vs. WARRIORS... The experiences and so too recommendations could legitimately vary considerably.
So... I guess if you drive your Z like it was intended, then it would be important to choose oils (synthetic included) with closer to the original (Lotus) recommendation: 1200/1300 PPM. But, if you baby your baby - parades or cruising to cars n coffee (primarily), then maybe you don't have to worry about it so much??