Im fairly certain the valvesprings are killing performance in my car. I bought the heads used but fresh off a rebuild with some new springs on there of an unknown brand. After a couple thousand miles on the motor i started breaking springs.. one by one i have them break, typically after a long drive where heat plays a part. They appear to be the same springs napa sells for stock replacement. Ive been replacing the broken springs with zz3 springs from GM. I know i should have just changed all of them but that was back when i was at home, lazy, no money, etc

I can only imagine what with the 4 that have broken that the others are on their last legs and their spring pressures very low. This could explain why the engine seems to level off past 4500 rpm (although it runs real strong up to there)

So heres my Q, how do i select valvesprings up to the task? spring pressure and whatnot. The heads are #416 305 h.o. heads with a 214/224 cam with 1.6 rockers delivering a final lift of .474/.498 I regularly run it up to 6 grand. Are the zz3 springs up to the task? (i imagine so)

and anyone had a problem like this and if so what were the results of a spring swap? what kind of perf. improvement?

thanks

 

Any of the major cam mfrs' best 1.25" outer dia springs should work OK. I would strongly recommend NOT using anything from GM, as they seem not to understand high-perf valve springs at all. They have no experience in this matter, since all their racing programs have always used aftermarket ones. I would also avoid "budget" springs with lower cost and bigger claims than the majors, K-Motion for example.

Comp, Lunati, Crane, etc. all supply springs that will work. Comp's part # is 986. Get the right retainers and keepers to go with them.

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"So many Mustangs, so little time..."
ICON Motorsports

 

K-motion part #750 will work good. I think they spec at 130# at 1.750" with coil bind at .610" lift at that installed height.

 

I would also make sure that the valve geometery is right. Factory srings are lame but something else is also contributing to that problem. You are very near the limit for a ZZ3 spring (retainer could also be hitting)