So I've now replaced my fourth valve spring in about 4 years. These are Manly springs. My mechanic had recommended them for my LT4 heads, after his testing indicated that the stock ones were insufficient. I have a CC-304 cam.

I never had a problem with any GM springs. I didn't replace all of them because I forewarned myself by buying two replacement springs last time and kept the spare in the glove box.

Sure enough, the spring on the exhaust valve on cylinder #6 broke.

The typical symptom led me right to the problem:
1) Running on 7 cylinders...
2) Boost/Vacuum gauge fluttering


Each time, the mechanic will say something like..."9,000 RPM???" or thereabouts. Of course, it will break for absolutely no reason whatsoever at any RPM. I did notice that twice it was very cold outside in the mornings, but the car wasn't cold when the springs would break.

Note: Don't install Manly springs. Find other, reputable brand.

That's my personal recommendation.

Oh, and Manly doesn't do squat to replace or guarantee them....of course.

 

Are you sure your "Mechanic" installed the springs properly. That's a very mild cam to be breaking springs.

 

Manley springs are A-okay.

 

Do you have the slightest idea how FEW valvespring MANUFACTURERS there are???

If the mechanic wasted his time checking the stock springs and you had any thought of reusing them with an aftermarket cam then neither of you knows enough to be playing with this. I would bet the spring was just insufficient, LOTS of "gurus" like to missmatch the valvetrain.