I got to hit the track again this weekend , also got to run another high 11 second pass (but still inconsistant.)

Anyway my 5 runs were as follows.

12.23 @ 113.5 (hit rev limiter in 2nd) 1.78 60 foot
12.09 @ 114.2 1.72 60 foot
11.92 @ 115.3 1.68 60 foot
12.36 @ 112.8 (hit rev limiter in 1st and 2nd) 1.69 60 foot
12.18 @ 113.7 1.79 60 foot

As you can see I was pretty well all over the place, but most of it was due to experimenting with launch technique. I finally settled on 15 psi in my M/Ts and left footbraking it at about 2800 rpm.

The car is starting to run the way I thought it should. The best 1/8 mile I got of the day was on the 11.92 and it was a 7.73 @ 88.6 mph, my worst was a 7.9 @ 87 mph.

Anyway on to the problem. heading home my valvetrain started making some pretty good noise. The car set the next day and Sunday I pulled it out again and drove it to church. onthe way home the valvetrain noise increased until it "popped", my church is only a few blocks from the house, so I coasted home.

I pop the hood, and there was a big dent outwards on the driverside valvecover. I remove it and am greeted with 2 rockers off their respective studs, studs broken !!!!! to my horror as well, the puchrods are not there, off comes the intake. I find both pushrods broken in half!!! I then examine the other pushrods and see tiny cracks horizontally (as the pushrod sets installed).
I go ahead and replace the bad ones and readjust the valves (after replacing the 2 studs from another set of heads I have).

My set up is a GM 847 cam, K-motion K-800 springs installed at 1.86., Compcams hardened pushrods, comps steel magnum rollers. Which pushrods should I move up to? Or is there something else I should check first?

 

It sounds more like you are getting coil bind. That would cause the kind of damage you describe.

 

Are you still using the stock rocker studs? If so, pull them and install a set of ARP studs. I had the same thing happen to me (stud snapped, pushrod dented the valve cover), but I didn't have any busted pushrods. I was also running the same cam and springs as you. I was using the stock '94 hardened pushrods at the time and they held up fine...no cracks or anything.

Maybe Comp screwed up and sent you regular pushrods by accident?

 

NSA or SA?

 

They are non-self aligned, the guideplates are the ones that come with the AFRs as well as the studs.
The pushrods look just like the stock ones, except for right around the ball (on the tube end) is a scorch mark where it looks like they were heat treated. I would say coil bind as well, but I checked that and have plenty of room. I could have even added almost .005 thicker shim and still had .030 to coil bind.

 

An easy way to check is that non-hardened pushrods scratch easy. So if those aren't scratched at all from the guideplates, they should be hardened.

 

.030 is not enough of a safety margin for me. The minimum I
like to see is .050

.035 does not leave much room for error.

 

It is impossible with my present set-up without having the spring seats deeper, changing valves or keepers, to get .050.
I really have never had trouble with .030.

 

Ok found my math sheet while I was doing the springs, they were installed at 1.78" the coil bind for the K-800s is 1.085 so that leaves me with 0.10 clearance since the lift on the exhaust is the greatest @ .595. So I'm good there even using the coil bind of .050. Don't know why I was thinking I only had .030 clearance, maybe that was retainer to guide clearance.