formula350sd

iTrader: (2)

Im going to be changing valve springs this year im looking at 986 or 981 comp springs Im leaning towards the 981 because of the higher open pressure and the lighter seat pressure I will also be using a comp rev-kit


my question really is can I really go wrong with either the hot cam is really mild and both springs should be useable with a larger if I choose down the road is there any real advantage to having the 986?

sofakingdom

iTrader: (1)

The 981 is a 1.25" spring; stock diameter. It's good for lift only up to about .500". It will fit virtually all stock heads, without modification, except Vortecs. It's really not enough spring for the HOT cam, unless you only use 1.5 rockers.

The 986 is 1.45" diameter. It's ALTOGETHER more spring. It's capable of up to about .550" lift. However, ALL stock heads will require machine work to use it. Clearly it's enough for larger cams.

Yes the HOT cam is pretty mild.

There is no advantage to lighter seat pressure. Valve float is caused by the valve bouncing off the seat, which is directly due to inadequate seat pressure. That's why Comp recommends the 986 as the "upgrade" spring even for cams that the 981 is technically adequate for; it just does a better job than the smaller spring, period.

A rev kit has nothing to do with that.

The HOT cam is too small for a rev kit to make much difference.

formula350sd

iTrader: (2)

Allright then well I am only using 1.5 rockers and for me the rev-kit is more of cheap insurance

Although I dont think it would be aproblem the 986 open pressure seems low but maybe Im thinking in overkill mode

sofakingdom

iTrader: (1)

Compared to what?Against what?

If you live in Florida, you don't insure your house against earthquakes; you insure it agains huricanes. Likewise, if you live in California, you don't insure your house against hurricanes, you insure it against earthquakes. In Minnesota, you build your house to absorb and hold heat; in Texas you build it to reflect and shed heat. And so on. "Insurance" is only of value if you expect that the bad thing that it insures against, is likely (or possible) to happen.

A rev kit is a specific remedy for a specific situation (lifters losing contact with the cam), which if you don't have it, it's a waste of time and money. That mild little stockish cam isn't likely to generate that.

What do you expect to happen, that a rev kit will help with? What experience have you had with that mild cam that indicates a need for it? I.e., why are you so determined that you're going to use one, but you haven't even made the most fundamental and important decision (valve springs) about things in that sphere of concern yet? If you don't know, or you're not REALLY in a situation that it does anything, then all it will do is make you car faster by way of weight savings concentrated in the area of the driver's wallet.

The 986 spring is the better choice, period. This is assuming of course, you're willing to get the heads worked on. If you're not, then the 981 is about all you can use, unless you go with the beehives. Which is also not a bad idea.

Alternatively, if you just want more spring pressure than the 986, use the 987 instead. Same size as the 986, just one more step up in strength.

formula350sd

iTrader: (2)

In case of pushrod or rocker arm failure (not likely I know) the revkit will hold the lifter in the bore and I picked it up for next to nothing I figured I may need it eventually so why not it may not be nessasary but neither are 4 bolt mains or aluminum heads in alot of mild builds

The spring pocket is a non issue I'm more than willing to do things right and send heads out for machining I was more looking for info and other peoples insight on spring pressures and rates but for some reason (no offense here) all people tend to do is just throw part numbers around

the 981 should be lighter than the 986, granted it wont handle as much lift because of design, but its lighter weight should be a factor in valve control no?

I know beehive springs are light and come in good rates and have better control than the 986 at high rpm but wouldent the theory apply to a conventional single spring thats lighter


I know all about springs (I used to work in the industry) Im just looking for more insight into why with all the different cams people chose, and all the different springs on the market, why the 986 is always the first and best choice