[HWYSTR455]

Was trying to avoid commenting here, but couldn't help myself.

Ok, you can't just toss the stiffest springs in to prevent det, you have to actually know what the timing curve is. And just to say, there are other factors that cause det, not just timing. Like what temp you run at, static CR, rich/lean, final drive ratio, etc. (and cam as you just recently found out)

You need to plot your timing curve to start, determine the area, load, etc that the engine is experiencing det, and then target that area for changes. If you don't approach it methodically, you're just making matters worse.

Put a timing light on it, with the vacuum advance disconnected, and rev the engine from like idle to 3500, in increments of 500 RPM, and record the timing. That will give you a baseline.

Key tuning areas are initial, total, rate (curve), and vacuum, and you tune in that order.

So then take it for a drive, note at what RPM you experience det, and the conditions, and record that value. Then look at your baseline recordings for that RPM, and put springs in it that addresses that area.

I attached a chart from a 455 iron head combo I had that was very close to 10:1, and accelerating, and driving in top gear. Should give you an idea of the process. You can see the range where I was experiencing det, and how I targeted that area to control it.

Make sure you're not going lean. Try stepping up 2 or 4 jet sizes and see how it runs, and if it experiences det the same as before. Don't run higher than a 180 t-stat, and in extreme cases, you may want to run a 160 t-stat.

In general, it's a trial and error thing, but by just tossing the heaviest springs in there, you are impacting many areas of operation, and will most likely suffer in other areas.

.