Valve springs

[John Pelkofer Jr]

Hello and happy holidays,

I am restoring a set of cylinder heads on a 1966 427/425
for a customer. He supplied me with a set of valve springs part# 3916164.
Can anyone tell me the application for these springs, the correct installed
height and pressure at installed height. Thank you all in advance for any and all advice. John

[Duke W.]

Re: Valve springs

I'm not familiar with that part number, but this subject was thoroughly vetted last summer and the consensus is that the best spring to use is the 3970627, which is the "second design" that showed up circa 1970 as a production and service replacement for the earlier, weak design. This second design is a dual spring as opposed to the earlier single spring/damper design.

They may come as an assembly with a built in retainer and umbrella seal.

Go the links at the top of the page and click "archives". Search the part number listed above to find the discussion, which was sometime last summer IIRC.

Duke

[Duke W.]

Re: Valve springs

I'm not familiar with that part number, but this subject was thoroughly vetted last summer and the consensus is that the best spring to use is the 3970627, which is the "second design" that showed up circa 1970 as a production and service replacement for the earlier, weak design. This second design is a dual spring as opposed to the earlier single spring/damper design.

They may come as an assembly with a built in retainer and umbrella seal.

Go the links at the top of the page and click "archives". Search the part number listed above to find the discussion, which was sometime last summer IIRC.

Duke

[Duke W.]

Re: Valve springs

The 3916164 valve spring you referenced is the first design L-88 spring. Assuming you are using a repro of the original L-72 cam you should NOT use these springs. They are too stiff and will cause excess valvetrain loading and possible lobe wear problems in normal road use. And I DEFINITELY don't recommend the L-88 cam for a road engine. It's a racing cam and only belongs on a racing engine with headers and open exhaust. It's a terrible choice for a road engine.

As you will see from the valve spring thread in the archives, the L-72 heads need to be massaged, especially on the exhaust side and the exhaust valve seat opened up to accept a 1.88" valve.

Other than the above head modifications and maybe a set of high strength aftermarket rods, which may be cheaper than Magnafluxing, replacing the bolts, and resizing the OE rods, all OE or OE equivalent parts will create a very strong high performance road engine with broad torque bandwidth that will produce useable top end power to at least 6500 while retaining the L-72's reasonable idle and low speed operating characterisics.

Also remember that these early Mark IV blocks need a camshaft with the rear bearing groove and the correct "three hole" rear cam bearing. This subject has also thoroughly discussed and is in the last year's archives.

Duke

[Duke W.]

Re: Valve springs

The 3916164 valve spring you referenced is the first design L-88 spring. Assuming you are using a repro of the original L-72 cam you should NOT use these springs. They are too stiff and will cause excess valvetrain loading and possible lobe wear problems in normal road use. And I DEFINITELY don't recommend the L-88 cam for a road engine. It's a racing cam and only belongs on a racing engine with headers and open exhaust. It's a terrible choice for a road engine.

As you will see from the valve spring thread in the archives, the L-72 heads need to be massaged, especially on the exhaust side and the exhaust valve seat opened up to accept a 1.88" valve.

Other than the above head modifications and maybe a set of high strength aftermarket rods, which may be cheaper than Magnafluxing, replacing the bolts, and resizing the OE rods, all OE or OE equivalent parts will create a very strong high performance road engine with broad torque bandwidth that will produce useable top end power to at least 6500 while retaining the L-72's reasonable idle and low speed operating characterisics.

Also remember that these early Mark IV blocks need a camshaft with the rear bearing groove and the correct "three hole" rear cam bearing. This subject has also thoroughly discussed and is in the last year's archives.

Duke

[Clem Z.]

Re: Valve springs

164 are not so bad as installed they are 116# @1.880 vs 105# @1.880 for the 627 BUT the problem is the 164 are only 317#/inch where the 627 are 450#/inch so over the nose you would be light on the pressure with a stock lift cam

[Clem Z.]

Re: Valve springs

164 are not so bad as installed they are 116# @1.880 vs 105# @1.880 for the 627 BUT the problem is the 164 are only 317#/inch where the 627 are 450#/inch so over the nose you would be light on the pressure with a stock lift cam