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

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.

So it's a worthwhile switch for older motors?

Unless you are leaking oil already it is a worthwhile switch.

Ok thanks!

Synthetic will clean better and gunked up or coked deposits can be cleaned away over time and you’ll have a new leak. That’s the only downside other than price.

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

Try it and tell us how well that worked out for you.

Modern synthetics do not cause leaks. Early formulations did, to some extent.

If it's a flat tappet cam I would be more concerned with zinc content. Some of the high zinc oils like Brad Penn are semi-synthetic.

I was told years ago that all multi weight oils, 5W20Wt,10W30WT and so on, all were based on semi synthetic technology

any more, all one can do is read the "fine print" on the bottle, unless the label states the oil is for flat tappet cams, such as the Joe Gibbs stuff.

Use Brad Penn or Driven semi with zinc.

The MSDS will tell you what it is made of. Just because someone said something doesn't means they know anything.

keep in mind, the super thin [wt wise] oils are for modern engine clearances, which are much tighter.

This.
On the Engine Masters the 20/50 even made more power, over the thin stuff
But in that case it showed it was the right oil for that motor.

Yeah, their conclusion was that the thicker 20W-50 aided ring seal in that engine.
I was a bit surprised that it picked up power vs the thinner oil, but there it was...
Whether there was an issue with that engine's ring seal wasn't analyzed.

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

I agree, I would be concerned about the zinc content as well with a flat tappet cam.

Me too, I just wondered if that engine which was quoted to have "a ton of laps on" (Dyno), would be equally as worn when compared to a used street / strip or a drag race engine that's made 100+ passes