Synthetic has no base oil impurities like conventional oil made from crude, hence it is heaps better oil normally, but from what i've read good quality mineral oils are more than enough for a piston car engine. I'm pretty sure synthetic is basically made from a condensed petroleum gas like ethylene.
In any case there is no need to run Mobil 1. There are cheaper variteies around like Valvoline and Castrol. I use Castrol Edge 10W-60 in the Monaro and the Cross8, but use standard 20W-50 Valoline in teh Premier.

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If we all had the same (good) taste, who would buy all the Fords?

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Originally posted by HK1837

In any case there is no need to run Mobil 1. There are cheaper variteies around like Valvoline and Castrol. I use Castrol Edge 10W-60 in the Monaro and the Cross8, but use standard 20W-50 Valoline in teh Premier.

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Byron when you talk at about the monaro and the cross8... is the monaro a CV8 or VZ or an earlier model...

For a long time I have used valvoline XLD 20-50 in the VT and its seems fine on the last service I did I brought Valvoline Engine Armour 10-30 which was on special which is a synthetic blend .
Changed oil and filter and took it for a drive and noticed an imedediate difference the motor seemed a lot smoother and felt like it had more power probably due to the thinner oil, I will be buying valvoline engine armour again for sure. I will use the XLD still in the older cars.

for reference of those driving old flat tappet equipped engines, steer well clear of synthetic oils.

the most important thing is a high zinc content, which is hard to find since catalytic convertor days.

It poisons the catalyst, epa doesnt like it so most common oils dont have enough to keep the camshaft happy.

the zinc is important as a "sacrificial" surface for highly stressed metal on metal actions (such as lifter to lobe)

Blokes were using diesel oil for a while (detergents can upset a 400,000 mile stocker, but you wouldnt care about the cam anyway) but the epa is onto them too now with more and more passenger diesels on the market, oils designed for harleys were the go also but im not sure anymore (bikes were exempt from emissions compliance and obviously didnt run cats)

Also, backward compatible "s" ratings dont mean s*** as far as zinc content.

Im told penrite make a specific oil with high (compared to everyone else) zinc content but ive not seen it near me.

I was using shell helix 15/50 but they sneakily dropped the zinc content and relabelled it (bought up all the old stock i could find in the meantime)

Then you start getting into stuff like Brad Penn, Kendall etc which costs a pocketful (but its cheaper than replacing camshafts)

may not necessarily matter to a stock s***box, but put some valvespring in it and aggressive lobes and it certainly matters.

Roller cams are a different matter of course.

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11.38@117mph

will go quicker

Edited by user Tuesday, 20 July 2010 6:43:04 AM(UTC)  | Reason: Not specified

This topic has had a lot of discussion in classic car circles in the U.K as well.
The consensus view here is that there is no benefit in running a 70's pushrod motors on modern semi synthetic oils. One argument I have seen is that the old oil pumps are designed to work with thicker oils, so putting thinner modern oil in may reduce the efficiency of the pump.
I use a classic blend 20W50 in my HQ. It makes sense as this is what it was designed for.