[Cliff R]

I'll put this out there as a "general rule of thumb" for a street engine build.

If you find your new build wanting, needing, liking or responding well to having to run much more than about 10-14 degrees initial timing you missed the cam choice vs the CID/compression ratio a bit.

With about 10 degrees initial timing your engine should make at least 12-13" vacuum at 700-750rpms. Take a gander at a hand held vacuum gauge and note where the "green", "yellow" and "red" zones are at if you think I'm off base here.

Of course it doesn't mean that the engine woln't run OK, nor does it maean that you can't start "crutching" it with a LOT more timing and pig-rich carburetor. That's been going on for decades and how a LOT of us make a living with custom tuning carbs and distributors. This industry caters to "bling" and just about everyone associates "menacing" idle quality with improved engine power and performance, when in many cases nothing could be further from the truth.

Attached is an overlapping dyno sheet I've put up here many times. The 455 at 9.3 to 1 compression had a "rougher" idle with the smaller XR276HR cam than it did with the custom ground HR cam I recommended to the owner to replace it. It also made MORE power at every RPM and quite a bit more upper mid-range and top end power. Even the very experienced engine "builder"/dyno operator was amazed at how much better the big 455 ran everyplace with a much larger cam in it on a wider LSA.

Just some food for thought when it comes to choosing cams for the big 455 engines..........