I have also been wondering about which oil would be best with a Flat tappet cam and lifters... Here is some reading about different oils and filters...
I am thinking of going to Synthetic oil..
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Oil and Filters and oil info...
Regular Replacement Filters
Manufacturer Filters
This is usually the best choice for your vehicle.
Aftermarket Filters
These are filters made by companies like Fram,Wix, Motorcraft, Lee, AC/Delco, Bosch, Casite, Hastings, Pennzoil, Valvoline, and Purolator. The quality of these filters varies greatly. In many cases the auto manufacturer uses these filters themselves. Private label filters are made by these companies as well.
Trade Brand Filters
These are filters made for the oil change industry. They are actually no worse than the poorer quality aftermarket filters. You can't buy these at an auto parts store but you'll see them used at many of the quick oil change places.
Premium Filters
Some manufacturers of synthetic oil also make so-called synthetic filters. These are high priced and have not been proven to provide any benefit over a high quality manufacturer of aftermarket unit.
In-depth reviews on Oil filters
http://www.frankhunt.com/FRANK/corvette/articles/oilfilterstudy/oilfilterstudy.html
http://www.frankhunt.com/FRANK/corvette/articles/oilfilterstudy/oilfilters.html
This guy was threatened with legal action by a major oil filter manufacturer, so you know he's on the right track. This resulted in the division of his web site into a fact page and an opinion page. I'm sorry, but I can't disclose the name of the major oil filter manufacturer.
Bypass Filters
Bypass filters have been used on diesel truck engines for years. On cars they are a messy solution to a non-problem. Forget it.
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Synthetic Oil
Advantages of Synthetic
Synthetic oil was originally developed for high performance racing engines. Mobil tried to popularize synthetic oil for passenger vehicles back in the early 1970's. At the time, Mobil was promoting 20K or 25K oil changes with synthetic, but they soon backed down from this. Synthetic oil is a good choice if you have a vehicle with a high performance engine (in fact synthetic is required for many of these engines). It is also a good choice if your vehicle is operated in extremely cold climates. It has higher resistance to breakdown caused by heat and it flows better in extreme cold. Unfortunately for the synthetic oil industry there is virtually no advantage to using synthetic oil in a non-high performance engine that is operated in moderate climates. You probably could go a bit longer between oil changes with a synthetic, i.e. following the normal service schedule even if you fall into the severe service category, but I wouldn't advise this. In short, synthetic may give you the peace of mind of knowing that you are using an oil that is far better than necessary for your vehicle, but it won't reduce wear or extend the life of the engine. The mistake some people make it to wrongly extrapolate these benefits onto normal engines operated in mild climates, with the ultimate lack of any knowledge being manifested with statements such as "synthetics provide 'Peace of Mind,' or 'Cheap Insurance,'" or other such nonsense.
Extended Change Intervals
Most manufacturers of synthetic oil advise users to not exceed the manufacturer's recommended oil change interval. Part of this is self interest (they don't want to be liable for any damage) but the real reason is that synthetic oil, while it does have certain advantages, still becomes contaminated.
Be extremely wary of synthetic oil companies that offer to pay for your repairs if it is determined that their oil and their extended change interval recommendation caused the problem. Think for a moment of the incredible hassle you would have to go through to prove responsibility for an engine problem. Who would pay your legal bills? Who would pay for replacement transportation during the battle? The more bizarre the warranty the poorer the product is a good rule of thumb.
API Certification, Phosphorus & ZDDP
Never use a non-API certified synthetic oil (there are many of these on the market). The problem with the non-API certified synthetics is that they contain too much phosphorus (in the form of the additive ZDDP (Zinc Dialkyl Dithiophosphates)). The API has limited the amount of phosphorus because phosphorus shortens the life of the catalytic converter. These oils are fine for snowmobiles, motorcycles, and older cars that don't have a catalytic converter, and the extra ZDDP does provide additional wear protection. Unfortunately, the marketers of some the non-certified oils do not explicitly and honestly state the reason for the lack of API certification. You can check the status of API certification on the API web site. Be certain to go not just by the manufacturer name but by the actual product as well. This is because a manufacturer will sometimes have both certified and non-certified products. Suffice it to say that Mobil 1, Royal Purple, Castrol, & Havoline all make synthetic oils that are API certified and that can be purchased at auto parts stores and other retail outlets. Amsoil has one product line, XL-7500 that is API certified, but it's other lines contain too much ZDDP to be certified and should not be used in vehicles with catalytic converters.
Amsoil
Amsoil actually makes some very good products. The negative image of Amsoil is due to their distribution method (MLM) and their marketing approach. If Amsoil products were competitively priced with Mobil 1 and other synthetics, and if I could buy them in a store, I would not hesitate to use their XL-7500 synthetic as opposed to Mobil 1. What upsets me about Amsoil is that they didn't disclose until recently (and then it was by accident) the real reason that their oils (except for XL-7500) are not API certified. In the past they came up with all sorts of bizarre excuses about the reason for their lack of API certification and this greatly contributed to the distrust that people have of the company.
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Engine Flushes--The Latest Scam
Engine flushes pump heated solvent through your engine, supposedly to wash away sludge. But regular oil changes with detergent oil already take care of the sludge problem. And if you actually have an engine that is full of sludge the last thing you want to do is do an engine flush because the sludge can clog the oil passages and destroy the engine completely. These flushes are completely unnecessary. All they do is wash the money out of your wallet. As Click and Clack state: "This is what's known in the business as a "profit center." Something the garage can use to beef up the amount each person spends per visit. So unless you've got a very old car, and are trying to solve a specific, sludge- or carbon-related-problem, I'd skip the R-2000." These engine flushes usually sell for about $130. The victims are people that think that they are doing something nice for their vehicle by cleaning the engine. In fact a dealer or repair shop that tries to sell you an engine flush should be avoided for all service because they are untrustworthy.
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Check Your Oil
Check your oil level at least every other fill-up. It's easy to become complacent about this, especially because few modern vehicles burn much oil. However there are still a few vehicles that have serious oil burning problems and owners have wrecked their engines by running out of oil.