I'm looking at new heads for my Mark IV 454s. Thinking about Dart p/n DRT-15100112. My engines are stock, no mods. Original cam, flat tappets.

I'm concerned the spring rate may be too high on these new Dart heads. Does anyone know what the stock spring pressure is on Mark IV 454 heads?

ThirdBird,
What is the year and rating on the original engine?
Bob

rm,
1989 454/365 horse.

My book says, and this is without the damper, single spring 24-75584, closed at 1.88"=74-86lbs. open at 1.38"=288-312lbs. Installed at 1.875.

My heads have dual springs.

ThirdBird,
That spring is GM part # 3970627
1.487"
105 # seat force @ 1.880"
350 # nose
Stack @ 1.280"
450 #/in rate
Carries a 3964264 retainer
Bob

Thanks for clarifying that Bob, Ive found that quite a bit of the info in this Merc manual is bogus. Their cam specs for one, Im not surprised the spring info is wrong too. That didnt seem right.

Formula31,
You are correct, there is a great deal of incorrect information in the Merc manuals including camshaft spec on certain engines. It's my understanding that Merc sometimes issues service bulletins with corrections, but that material goes to dealers.
Bob

If you're doin new heads, you should just do a new cam at the same time also. Its only a couple hundred $$$ more and a couple hours more work.

Thanks rm.