Only guys like them could FUBAR a oil viscosity test like they did
I learned a long time ago to make sure any new engine being dyno tested on an engine dyno or a chassis dyno are broken in properly to insure the ring seal is completed and the rings are seated properly Zero to no more than 10 % leak down done with the motor warm or hot
I wonder if they had that block honed with a torque plate and the proper head gasket under it so it would hone properly

But, ZDDP is the kicker - if you've got a flat-tappet cam you for sure need the high-zinc oils

In general, no you don't NEED high zinc oil.

It depends on the application, mostly the cam and valve springs.

Something like my 51 Plymouth's stock flathead does not need it, never did and never will. A stock 318/225 nope.

Something with a high/aggressive lift cam and the appropriate springs, yep.
The

Synthetic oils will leak out of a engine that has no leaks with petroleum based oils
I wouldn't switch any old muscle car motor to synthetic oils due to the fact they were designed to run on petroleum oils

Anyone telling you there would be negative effects, other than on your bank account, is someone to pass by when advice is being handed out.

I've got a 70 Challenger T/A with a slightly built 340-6 ,I've always used conventional oil,but wondering if a switch to synthetic will have any negative affects? Thought I'd ask before doing it!
Thanks

Just a simple question; you say you have always used conventional oil, so how many oil related issues have you had over the years?

And haven't we have beat on and raced our Mopars for over half a century with lesser quality oils than we have available today with good success?

And here is an interesting point that was brought up in a similar thread on another board; ALL modern oils have a significant amount of synthetic additives (including conventional oils) to make them what they are. How much more synthetic material would you think is necessary?

Today's engines are vastly different in design and tolerances than our old dinosaurs. And demand different oils than our old dinosaurs. Who here is going to put 0-10 in their Mopar? The ultra thin viscosities is one of the main reasons for the proliferation of synthetics for daily drivers.

All oils have an API rating. That is the 'starburst' typically printed on the back of the container. Today's rating is SN. That is a much, much higher rating than our engines have ever had access to which translates to much, much better oil. For comparison, the now obsolete rating at the time most of our engines were built was SD. And it's interesting to note that whether the oil is syn, blend, or conventional, the rating is the same. The only real difference for most (not all) of our older engine applications, is the cost.



IMHO, Valvoline VR-1 is the best oil for most of us who are not racing and for many who are. It is cost effective, readily available, has ample flat tapper additives, and has proven itself in countless engines including mine. I run it in my Hemi and my wedges. Nearly 7,000 RPM, heavy valve springs, flat tappet cams and many street years of street miles with the occasional visit to the track. Absolutely no oil related problems. Ever.

What is there to improve on?

i have some pennzoil 60wt racing oil in the cardboard cans..........