Valve Spring Replacement

[James W.]

I am curious as to the benefits of changing the valve springs in my 327/300 hp engine. The car and engine was restored/rebuilt back in 1981 and has seen about 8,000 miles since then. I am now starting to drive the car more and it seems to be kind of week in the RPM range say from 3500 to 5000. Are the valve springs week and would a new set of valve springs help or is there a better solution, maybe a tune-up and distributor re-curve? When it was rebuilt, I installed a different set of distributor advance springs to aid in getting the advance in sooner as described in a post recently.

Any comments... Duke, John, Clup? What do you recommend?

Thanks,

James West
Omaha, NE.

[William C.]

Re: Valve Spring Replacement

I'd start with a general tuneup, including a chack to insure the secondaries in the carb are working properly. It's hard to wear out a set of valve springs by not using them, especially on a hydraulic lifter engine as even the open valves will tend to close over time, reducing spring load as the hydraulics leak down.

[Duke W.]

Re: Valve Spring Replacement

I agree with Clup. I don't think there's anything wrong with the valve springs.

With the OE heads (no port work or fancy valve job) the 300 HP engine makes peak torque at about 3000 and the power peak is probably in the range of 4000-4500 and then it will drop rapidly. With some head work everything is upped by about 500 revs with up to ten percent more peak power, and it should pull usably to 5500.

If you really think the engine is weaker than it should be above 3500, especially if you get any misfiring, then look at the usual distributor suspects - end play, wobbly breaker plate, or worn shaft bushings. An easy way to do a quick check is just to free rev it to 5000 with a dwell meter attached. If the dwell reading falls off more than two degrees the distributor needs to be overhauled and blueprinted.

You didn't say what carb is has, but checking secondary opening is always a good idea. Holley's can be problematic in this regard. The AFB has a simple mechanical secondary opening that can be adjusted to be sure the butterflies open all the way, then check that the seondary air valve moves freely.

Duke