hi all , i just purchased an 81 w/ stock motor. its finally a childhood wish come true. i will probably take delivery next week sometime but im lining up service items ahead of time. i have been looking at oil threads for the past 2 hours and dont really have a definitive answer. i understand this motor is flat tappet , thus benefiting from higher ZDDP, but on the other hand , its catted and i dont want to fry the cat. ive been looking at the brad penn 1 10w-30 with the added zinc, and also the brad penn regular 10w-30. they are both blends which is what i want.  does this motor need that boosted zinc? car looks like it has the OEM cat in it. i can only guess its not gutted, but who knows.

ill post pics when she finally gets here

The cats back then weren't sensitive to zinc.  I use Valvoline VR-1 10w30 dino oil.  I can order it at O'Rielly's.  Plenty of zinc.

Don't buy the ZDDPlus additive. It has too much zinc.

thanks , that was my line of thinking..   so if i decide to go with an aftermarket highflow in the future such as magnaflow... would those be adversely affected or would the increased flow design make it somewhat immune?

I'd ask Magnaflow.  You still have a flat tappet cam.  Maybe no cats...

hey one more thing....  on the 81's with the early CCC , the cats didnt interface with any of the computer stuff right?  so deleting it wouldnt affect running parameters like we have on cars now?  it was only basically fuel delivery and timing correct?

just for the good of the forum knowledge in general , i have attached the response direct from DA lubricants regarding this issue

Steve,

Thank you for contacting D-A / Penn Grade / PennGrade1 Lubricants and for your inquiry.

I have been fortunate enough to have spent considerable time discussing ZDDP and the effects of phosphorus in automobile catalytic converters (Post-1975). It is widely known that phosphorus volatizes and acts as a ‘chemical poison’, reducing catalytic converter effectiveness and life span. As a matter of fact, many industry formulation chemists have been hard at work searching for ways to replace or reduce the use of (ZDDP – zinc dialkyldithiophosphate).

When an application (like your 1981 Corvette) utilizes pollution control equipment such as a catalytic converter, the oil must be formulated to be compatible with the exhaust catalyst (lower phosphorous to avoid catalyst ‘poisoning’). Today’s modern passenger car engine oils are a complex mixture of additives and base oils that are required to provide good engine lubrication and increased fuel economy while reducing emissions.  They accomplish these goals in a number of ways including utilizing lighter viscosity base oils, higher concentrations of friction modifiers and reduced levels of certain functional additives.  Unfortunately, these same characteristics can have a negative effect upon oil in numerous applications. Today’s stricter emission requirements have caused the need to reduce the amount and type of anti-wear agent used in the oil (ZDDP) in order to lower the oil’s phosphorous content and help prevent catalytic converter ‘poisoning’.  This has raised questions about the ability of newer engine oils to provide the needed anti-wear protection to critical engine parts.

The additive element that is ‘controlled’ in motor oils is phosphorous, not the zinc.  High levels of phosphorous in motor oils are detrimental to the components of the catalytic converters used on today's modern vehicles to reduce emissions.  Therefore, to minimize catalyst 'poisoning' the American Petroleum Institute (API), the organization that sets the standards for engine oil quality and performance, has established limits on the concentration of phosphorous in engine oils designed for use in vehicles equipped with catalytic converters.  Zinc and phosphorous are integral elements in the anti-wear additive used in motor oils so when the phosphorous concentration is reduced the zinc also is reduced.  However, because of the chemical composition of ZDDP, the zinc concentration in motor oil will typically be slightly higher than the phosphorous concentration.  Oils meeting the most current API Service SP category that also meet the ILSAC GF-6A classification and are considered 'Resource Conserving' have phosphorous concentrations that are limited to 0.08% wt maximum (800 ppm).

Steve…bottom line, our PennGrade 1® Synthetic Blend High Performance Oil SAE 10W-30 is an unlicensed engine oil due to its typical 1500 ppm of Zinc, 1400 PPM of Phosphorous. The aforementioned levels constitute its ‘enhanced’ antiwear package. The level of phosphorous alone in the PennGrade1 High Performance Oil could be detrimental to the performance of your 1981 era catalytic converter, especially if you are experiencing any ‘blow-by’ / burning oil. Typically we do not recommend PennGrade1 High Performance Oils in vehicles manufactured after 1975, the year catalytic converters were first mandated, but over the years we have received feedback from many individuals utilizing PennGrade1 in last model systems without issue. They would much rather replace the catalytic converter (if they even had to) than any of their valve train componentry. To be honest, your stock catalytic converter has likely seen better days, and although I would certainly run PennGrade 1® Synthetic Blend High Performance Oil SAE 10W-30 if it were my 1981 Corvette, the caveat must be expressed.

Sorry for the lengthy response Steve….I simply wanted to convey all my thoughts on the subject. Please call me direct should you have additional questions,

Ken Tyger

Sorry, I don't think that guy has a clue what kind of cat you have.  I'm pretty sure we still had "normal" levels of zddp in our motor oil back in 80-81.

Corvette Central list a 1976-81 converter.

https://www.zip-corvette.com/76-81-magnaflow-catalytic-converter-federal-emissions.html

thanks , seems im piecing together that path forward through the jungle of opinion and info sources. yes i would assume they wouldnt list a cat for out cars if they knew they were going to be destroyed from higher zddp/phos levels.  or at least they would say "this is the possible affect , buy at your own risk"

I have been running Mobil 1 10w-30 for almost 20 years with no issues, although I have only added about 20,000 miles in that time.  I always figured; IF, the synthetic caused abnormal wear the engine would still long outlast me given the yearly milage.   

The only issue with synthetic, for me, was since it is "thinner" it had a higher rate of seeping through the existing gaskets.  When I had to replace gaskets I changed to ones made for synthetics.

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