[Cliff R]

"The bigger 284 is usually done before 5500, it will probably have no issue making 500 HP, but there are better cams."

I've witnessed dyno runs with both the XE274 and XE284 cams in 455 engine builds. Both of the engines were well prepared, good pistons, rods, "ported" factory iron heads, etc.

The 455 using the XE 274 cam was topped with 6X heads, mildly ported, factory intake, and they borrowed my carb for the testing. It cranked out a whopping 412hp and DONE by 4800rpm's. The peak torque number was decent, over 500ft lbs, happened at 3200rpm's but clear down to 414 ft lbs at 4900rpm's, which simply means it's a "turd" in the upper mid-range and top end and threw all it's power at you in a very narrow RPM range.

I had no input in the 455 that used the XE 284 cam, we didn't even know what cam was in it the day of the testing, it was just in line in front of me and they couldn't get chit of power out of it, so we watched for hours as they messed with it trying to get decent numbers.

Most pulls were barely 400hp and it never did hit 500tq. It was using ported 7K3 heads, Street Dominator single plane intake and 850cfm carb. They finally settled on 430hp and nudged a little over 500tq out of it.

I thought the numbers for both builds were "low" for the combination of parts, but they were on the same dyno I use, same operator, etc. Matter of fact my first 455 with 6X heads, iron intake, q-jet etc went on the dyno right after the XE284 cammed 455 and cranked out 455.4 hp on the first pull and 530tq..........