DM91RS

I know some of you (F-BIRD'88 in particular) have ported and had good results with these heads (416 or 081) casting # installed on a 350.

I have read about and done porting on a set of each. I have not seen mentioned what size springs and how much lift people are using with these particular heads. The spring seats look pretty small in diameter to be machining to a larger size as the material falls away pretty quickly once you start going outside the 1.25" stock diameter. I might try to run a cam with .510" lift and would really like to not have to machine the spring seats if possible. I will shorten the quides for clearance and new seals.

I have read that over .500 lift you should go to a larger diameter spring and have also read of others running up to around .530 lift on the 1.25" size (not a stock spring though)

I need to do the same thing to a set of Vortecs also so I guess the info would apply there too?

Thanks

DM

Stekman

You don't HAVE to, but it helps. The factor spring pocket can accomodate a 1.26" OD valve spring. Depending on what cam you are running, I would run whatever is recommended. For example, if you were to run a Xtreme Energy hydraulic flat cam, the 981 springs would probably suffice, MAYBE the jump to the 986 springs. If it were the Xtreme Energy hydraulic roller series, either the 986 or 987 springs are recommended.

The 981's are designed to fit in factory spring pockets, so no enlarging of the seat is really needed. Both the 986 and 987 series share the exact same 1.43" OD, so machining would be needed.

There ARE however springs with pressures and rates very similar to the 986 series, but are of the factory spring pockets. A set I have and plan on using on a set of Vortec heads are the Isky 235-D valve springs. These are 1.26" OD.

Max lift is created and allowed by 2 things. The first is the problem with factory heads, Vortec, 416, 081, or otherwise. There is simply not enough room, at the factory installed height, between the bottom of the retainer and the top of the guide boss. At roughly .480", give or take, the retainer slams into the guide boss causing most usually catastrophic failure of something. The other thing is the actual amount of lift alloted by the springs themselves. There is a point where the spring's individual coil windings actually makde contact with eachother, physically preventing the spring from compressing any further. That is what is known as coil bind. To find out the maximum allowed space a spring will offer, take the installed height, subtract the coil bind, then subtract about .060" of safetey clearance, so the formula looks like this:

Installed height - coil bind - .060 = max lift allowed by valve spring.

The same theory applies to all cylinder heads. The only thing that would really change is the fact of self aligning or not. Another thing to consider: replacing the pull out studs with screw in ones (and maybe guide plates).

DM91RS

Stekman...thanks for the info.

This info is basically for 2 engines. The cam choice is a ZZ4 which I already have. I was planning to run 1.6 rollers but this isn't written in stone. Max lift would be .510 exh with 1.5's or .544 with the 1.6 rockers. If I could get away with the smaller diameter springs by running .510 lift max I would consider that. I seem to remember that Dyno Don was running Manley 1.25" springs on his Vortec's with a ZZ4 cam with 1.6 rockers.


I have screw in studs for both and plan on new seals with guides being lowered. Are telflon seals the best or are there better ones that would fit the available guide machining tools sizes. Seems like they were .500 and .530 diameter. I have never used the telflon seals before so I have no experiance with them and how they last. The stock Vortec seals are working well for me after several years.