What are the differences between 1988 454 magnum and 420 engine both from mercruiser? I was told the 420 is better??? Please advise?

From what I have been told they are two very different motors. The 420 will make more HP, and they have better parts in them. I believe same crank and pistons but the 420 I was told has roller rockers and so on. The Mags came I think in a few different flavors from 365hp-385hp? The 420 is obviously more.... I am sure that you will get some much more definative info....

Jon

Pretty much what Audio said. Roller rockers, cam, intake, carb. Not sure about CR, but I can check. Bottom end/block is about the same.

I believe the HP420, HP425, HP465 etc were the early "HP" motors. better parts for the High Perf engines.

Holley 800 carb, Wiend single plane intake, hotter cam, Crane gold roller rockers, high perf. exhaust system.

Does anybody know anything else about a 420? Are they still available? Please advise.

Thanks

Other than the exhaust. looks like it would take just over $1100 to convert a 365 Mag into a 420. using Summit racings catalog.
Then another $1719 for some Aluminum Edelbrock heads. How much more hp would the heads give you?
$2000 for Brodix heads
$2200 for Merlin and just a little more for Dart heads

The 420 also has the "188" casting rectangular port heads & matching Team G single plane intake manifold..... no, the 420 is no longer made, but can be duplicated... better cams are available today for it. Bare head castings now are about 700.00 each here (new) and used are not much cheaper, so aluminum heads are a good & comparitive replacement.

Get a crate 502.My 2 cents.

the 420 cam is the crane #h-228/312-2s-14t1.2 or part number#132561 in the crane cataloge 228/236 duration at .050 114 lobe seperation 530/551 lift.i would upgrade to a rollerfor not much more money but a lot more torque and horsepower from th same bottom end.use a dart single plane with an 800 holley jetted up alittle