Dan Di Cesar
Do Older Engines Need Oil With ZDDP Additives? In my opinion, YES !
In classic cars and hot rod engines, use a high-zinc motor oil all the time, there has been a lot of confusion in the last few years about lowering the zinc and phosphorous levels in modern oils and how these lower levels relate to Classic and performance engines using standard flat tappet lifters-that is, just about every car built before the eighties. The concern involves the use of the new lower zinc/phosphorus-content ILSAC (multi-viscosity) oils, readily available at auto parts stores everywhere, and how compatible they are with these older engines.
What is high-zinc motor oil ?
Zinc dialkyldithiophosphate (ZDDP) is the most common zinc- based additive and is used primarily as an anti-wear agent to prevent premature engine wear. It also provides corrosion and oxidation protection.
However, because the zinc and phosphorus levels found in ZDDP can negatively affect catalytic converters, it has been phased out of motor oil formulation in recent years.
Reducing ZDDP has drawback, as classic-car owners have found. Older vehicles with flat-tappet camshafts and, in particular, engines that include high-tension valve springs or other modifications that create high pressure, can suffer premature wear due to reduced ZDDP levels.
For best protection, classic car owners, engine builders, and gear heads typically use high-zinc and high-phosphorus motor oil to offer protection for flat-tappet cams, lifters, and other components during engine break-in, racing and driving.
ZDDP anti-wear additives are heat-activated, meaning they provide wear protection in areas of increased friction.
As temperatures rise and surfaces come closer together, ZDDP decomposes and the resulting chemistry protects critical metal surfaces. When parts move during operation, any sliding or motion takes place on top of or within the ZDDP ant-wear film, which reduces metal-to-metal contact. This is especially important in engines with flat-tappet camshafts orr engines modified to create more horsepower. High-tension valve springs used in racing applications, also increase the potential for cam wear and requires additional ZDDP.
The design of flat-tappet cams make them especially vulnerable to wear. As the name indicates, the tappet-or lifter- is flat ( see picture below) During operation, the cam-lobe (see picture below) slides rapidly over the tappet, increasing friction and temperatures.
A thin oil film is the only barrier that prevents the lifter and cam lobe from welding together.
If the oil film fails or provides insufficient wear protection, the components can eventually wear the flat-tappet cam and affect valve operation.
Engine power and efficiency can decline if the flat-tappet cam cannot lift the valves enough to adequately charge the chamber for ignition or release exhaust fumes. Because most V-8 engines of the muscle-car era came standard with flat-tappet cams, the problem is especially prevalent to classic cars, sports cars, and hot rod owners.
Roller cams came out in the eighties for the American V-8 engines, are differentiated by rolling contact rather than sliding contact. Although costlier roller cams are common in the most modern vehicles, and are now retrofitted to hot rod owners. unfortunately nothing for our MG's, or other British cars.
Personally for racing we have been using Valvoline VR-1 Racing oil SAE 20-50 (non Synthetic) and for the longer endurance races we add a can of STP oil treatment which has ZDDP. We have been using Valvoline racing oil since 1965 with success.
In my street MGB and my 65 Ford Mustang I use the Shell Rotella T SAE 15W-40 (non Synthetic) it has a 1200 ZDDP level.
A list of motor oils and there zinc,phos, and ZDDP levels can be found in our magazine Dipstick ( pun intended !! )
The question of choice remains with you. If you wish to continue with the use of a Mineral based oil which is less expensive, or you may want to step-up to a Synthetic grade giving higher zddp levels than mineral oil. It came to my attention that a local Quebec company Pro-Lab based out of Thetford Mines has developed a 20W50 Vintage oil has higher levels of zinc, phos, and zddp, more than the standard oils on the market. It is sold through Robert Pieces Anglaises in Laval.
Moss motors is also offering Vintage motor oil and ZDDP engine additives.
I have not tried the other brands of oil but I would recommend going with the SHELL ROTELLA T 15W40 and a container of STP oil additive for the extra ZDDP for the added protection. I believe the PRO-LAB 20W50 oil would be next on the list, and is on more economical route while still maintaining protection for your engine. Shell oil is available at Cdn. Tire, Wal-mart, and auto parts suppliers.
Contribution: Amsoil,MGB PowerTune, Tribolgy, Joe Gibbs racing, LN Engineering, Pro-Lab