[north]

The 455 nomenclature in 70 was confusing. None of the factory brochures refer to any of the 455's being an HO but some other factory literature did. There were two basically different engines:

The lower performance engine was only offered in the B bodies, rated 360 horse and like the 69 428-360 it was a 2 bolt main, small valve heads (basically the 400 2bbl high compression heads), 4 bbl, with a small single snorkel air cleaner with no chrome dress and the 066 cam.

Optional on A, B, G was a higher performance version with large valve heads (same 10 or 10.25 ratio compression, depending which factory spec you read), larger valves, 067 cam, dual exhaust and a dual snorkel air cleaner. On the B and G it was rated at 370 horse but on the GTO it was rated 360, apparently the GTO's chrome valve covers and air cleaner lid cost 10 horsepower!

What was missing on the B and G from previous years was the traditional HO big inch engine with the long branch manifolds and chrome dress. This is reflected in the option price of the 455's in 1970

The basic 455-360 in the B cars was standard in the Bonneville and was a $105.32 option on cars that had the 400-290 as standard equipment, this was the identical price for the 428-360 in 69 Catalina's. The 455-370 option on the B's cost $97.49 on a bonneville versus the 69 428 HO costing $149.55 on a bonneville.

Similarly on a GP the 455-370 (the only 455 offered on a GP) was $57.93, the exact same price as a 69 428-370. However the 69 428-390 was $176.94 extra.

I think the change in 70 to sort of split the features difference between the true 428 HO engines of previous years and the regular 428's was smart. By dropping the HO manifolds and special higher flow exhaust pipes of the 428-390 and the chrome dress up kit they were able to substantially lower the cost of that higher output engine.

If you think about it the cost of ordering the "good 455" on a Bonneville was really only about $65 if you were going to order duals anyhow on the base 455.