Chevy Big Block 427 L72 Spec Engine

Should this Chevy Big Block 427 get 10W-30 or 20W-50 motor oil? (photo credit:

A reader asks: My street rod has a 1967-vintage Chevy big block 427 (L72 spec) with solid lifter cams. This car runs only in the summer and has an estimated 450 horsepower. I would like to run AMSOIL Z-Rod in this engine, but I’m really torn between 10W-30 and 20W-50. There’s so much debate on the internet about which grade to use. Can you offer any thoughts?

Answer: This is a very contentious and well-worn subject, but there is actually no wrong answer. There is no downside to going with 10W-30 or 20W-50 motor oil in your engine. It really comes down to personal preference. As your engine does put out significant horsepower, we would lean toward using 20W-50.

If your engine sees very light duty or is built exceptionally tight, 10W-30 would be fine. But again, if you twisted our arm, we would give 20W-50 the nod for the thicker viscosity.

Regardless of which viscosity is chosen, AMSOIL Z-Rod is formulated expressly for older engines. Packed with 1440 ppm of zinc and 1320 ppm of phosphorous (serious anti-wear additives), Z-Rod is a superior choice for classic engines. These anti-wear agents make Z-ROD Oils especially suitable for engines with flat tappet camshafts.

Motor oils specified for modern cars and trucks are anemic by comparison with zinc and phosphorus levels averaging in the 800 ppm range. Today’s cars and trucks have emissions equipment that do not react well to high zinc and phosphorus levels. Therefore the latest motor oil specifications take a different approach to wear control.

But as emissions equipment are a non-issue for classic engines, this motor oil has no formulation constraints. The 100% synthetic base oil of Z-Rod provides tremendous shear strength and maintains consistent viscosity, regardless of high engine temperatures or hard operation.

There is absolutely no downside to going with a synthetic oil like Z-Rod in vintage engines. You will not see increased oil consumption or leaks. Z-Rod Oils also contain special additives that condition seals to extend their life.

As vintage cars tend to retire for the winter, AMSOIL also gave Z-Rod a healthy dose of anti-rust and corrosion agents. So you can rest well knowing your baby is well-protected whether she’s running or not.

So regardless of whether you opt for 10W-30 or 20W-50, you will have done your engine a favor by choosing the AMSOIL Z-Rod Motor Oil series.