syntec 18.88 5qt, M1 22.47 5 qt. I guess that if the castrol 0w 40 was there, it would be a no brainer, but there's only 5w, 10w. Same for the others. BTW, the rotella is 5w 40. I put oil into 2 LS1 camaro's, a Vortec suburban, 4.3 liter s10, ZX2 and ZX3 fords. The last 3 get pennzoil dino, sometimes a couple of quarts of synth mixed in for the fords. I've been putting in M1 10w30 into my SS, and 5w30 m1 into the wifes Z28. w/ a 20% rise in price, I don't know if it's worth it. Are any of the other 3 worth the premium over dino oil? should I bite the bullet and stay w/ the M1 in the LS1's?