cruise speed valve rattle input.

[ManicMoparchanic]

Sorry if something here already.
Since engine build been easyish on engine, but the other day running 70 on hyw floored to pass a truck heard loud valve rattle, tried again after truck just to see if I heard what I thought,it was.
Stock bottom build on 1964 225, have 1976 head decked 60 off with big valves. Now I used stock cam, lifters, rods, valve springs. And, atm a 600 holly on a super six intake. Should I have installed the heavier RV valve springs, or could this be a timing advance problem. Never knew solid lifter to rattle only at power demand, have had hydraulics float before. Any ideas? Thanks
:sign3:

 

[ManicMoparchanic]

Sorry if something here already.
Since engine build been easyish on engine, but the other day running 70 on hyw floored to pass a truck heard loud valve rattle, tried again after truck just to see if I heard what I thought,it was.
Stock bottom build on 1964 225, have 1976 head decked 60 off with big valves. Now I used stock cam, lifters, rods, valve springs. And, atm a 600 holly on a super six intake. Should I have installed the heavier RV valve springs, or could this be a timing advance problem. Never knew solid lifter to rattle only at power demand, have had hydraulics float before. Any ideas? Thanks
:sign3:

Also forgot, still running the 1 7/8 exhaust pipe, hoping to remedy today/ tomorrow..upgrade to 2 1/2 with Thrush turbo 2 1/2 in/out muffler.

 

[RedFish]

Spark knock only when under load is typically timing related, like vacuum advance failure.
Running too hot can cause it too.

 

[ManicMoparchanic]

Spark knock only when under load is typically timing related, like vacuum advance failure.
Running too hot can cause it too.

Car has always ran mid/high warm side, but never hot, before, and after build.

 

[67Dart273]

I agree with Red, I doubt this is "valve rattle" but rather spark knock, otherwise known as pinging.

Did you have the head and or block deck milled, and is there some chance that either had previously been milled?

Until you map out the timing curve, you don't KNOW what it is advancing.

Too hot plugs, too hot engine, too much compression/ low octane gas, too much timing advance, or too lean of a fuel mixture

 

[ManicMoparchanic]

I agree with Red, I doubt this is "valve rattle" but rather spark knock, otherwise known as pinging.

Did you have the head and or block deck milled, and is there some chance that either had previously been milled?

Until you map out the timing curve, you don't KNOW what it is advancing.

Too hot plugs, too hot engine, too much compression/ low octane gas, too much timing advance, or too lean of a fuel mixture

First mill on head 60 thousandths. Runnin a little rich, need to rejet front barrel or go with smaller 4 bbl. Next trick to upgrade exhaust and install factory hei distrib. Thanks for input, for sum reason didn't think bout pinging...doh, now I'm the new noob..lol