Valve springs! Stock 327/350hp Weak?

[Ken K.]

I want to replace my weak valve springs on my 1966 327/350hp Vette. I think the original part number of the spring is: 3735381. What is the specs. of the original spring? (Lift, open, and close pressure) I see .550 lift and .600 lift springs, but I just need the stock size.
My question is, What type of spring should I put into the car? Everything is still stock on the car. (Cam, valves, rockers bolts are still the "press" in fit type.) Is there any aftermarket springs that will work better? (without missing up my cam or rocker towers)? Thanks

[Joe L.]

Re: Valve springs! Stock 327/350hp Weak?

Ken------

The GM #3735381 springs have the following specs:

closed= 78-86 lbs @ 1.66" installed height
open= 170-180 lbs @ 1.26"

These springs are still available from GM.

You could use the 1967+ small block spring, GM #3911068, which is also still available. This spring has slightly higher pressures than the 3735381.

With a stock cam, I would recommend using only one of the two above-referenced springs. Springs with higher pressure won't do you much good and may do you a lot of harm with respect to increased cam lobe wear.

[Duke W.]

Re: Valve springs! Stock 327/350hp Weak?

[Early 327 valve spring, 3735381]
closed= 78-86 lbs @ 1.66" installed height
open= 170-180 lbs @ 1.26"

For comparsion the 3911068 spring is:

76-84 lbs @ 1.70"
194-206 lbs @ 1.25:
free length 2.03" (381 free length is 2.08")

The primary difference is rate. The early spring is nominally about 233 lbs/in, and the 068 is nominally 262 lbs/in.

The later spring should provide a bit more valvetrain limiting speed, but should not pull pressed-in studs.

I would also recommend the later spring for post '66 cam designs, which would include the late 300 HP cam that is also the replacement for the early 300 HP cam and the LT-1 and L-46 cams since the 068 was the OE spring for these cams.

Duke