Thread: Death rattle

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I have a 92 Chevy 454 crate motor with a mild hyd cam that I bought from a guy who couldn't get it running right.

It has a Holley 3310 on an Edelbrock Performer manifold.

After fixing the modified (can yoy say "butchered"?) HEI and straightening out the carb "modifications", etc, etc, I finally had it running decent but way fat.

AND, I couldn't get rid of the detonation "rattle". If I retarded it enough to take away the detonation it wouldn't start!!

To make a long story shorter, I rejetted the carb this pasy weekend (it's still a little rich) and guess what? The detonation is gone!!!!

The motor now needs more advance! I was so sure the damper ring had slipped that I had given up using a light and was timing "by ear", so I have no idea where the timing was (is), but the difference is night & day.

Have any of you ever experienced this?

I feel I should add, that while I'm no genius, I have been building and tuning my own engines for 55 years and have designed and brought to production an aftermarket Pontiac block. I've been involved in engines that produced some serious power, but I've never run into ANYTHING like this.

Any ideas?

Wow, at first i was thinking cam timing but if rejetting fixed it great.I was part of a project that somehow the cam was installed on the wrong mark on the gear and it ran like that.

BTW a 454 in a Seville, now thats cool.

Cam timing was my first thought, but when you have a problem, it's usually the simple things.
I did all the obvious "fixes" first then decided to rejet, and BINGO!!

Much to my surprise the problem was gone. I was just wondering if anyone else had run into something similar. As I said, I've been doing this for a while (my first cars serial number was in roman numerals) and had never run into anything like this before.

That's the trouble with picking up someone's failed projects, you never know what hidden "improvements" he forgot to tell you about.
I think I'd check the cam timing even if it seems to be running okay.