Im swaping in a 87 350 TPI to replace my tired 305. Im gona put a zz4 cam in. I've read about guys using LT4 springs in the stock heads. My question is besides the springs form sdpc2000.com do i need to get the retainers, seats, locks, and shims for the LT4 springs or can i use my stock ones. Move this if needed.

 

LT4 springs are not a direct drop in. The spring pockets need to be enlarged to 1.32" (factory being 1.26"). If you are looking for direct drop in springs, Comp Cams 981-16 is the part number to get. Get all the affiliated hardware as well (retainers and locks). Or, if you do feel like machining the heads for a larger diameter valve spring, the Comp 986 version would be my suggestion. Isky makes the 235-D spring which fits a factory spring pocket but has higher spring rates, more resembling the 986 springs. Either way, get the affiliated hardware, as I said above.

Since the heads have to go to the shop anyway for machining on the guide boss, why not just enlarge the spring pockets for larger springs?

 

Im open for all opinions on what springs to use i just heard about people using LT4 ones. Im pretty much dead set on a ZZ4 cam. About the guide bosses i have to have those machined to make the zz4 cam fit / work? is that what ur saying.

 

Ok ive familerized my self but i still have one question that i need explained. Im gona get the CCA-981-16 from summit to keep the cost of machining down. I want to know what degree of retainers do i need 7 or 10 degree retainers? Also these springs will work with the zz4 cam correct and if i want later can i put 1.6 rollers on? im replacing the push in studs now with screw in ones.

 

NOW the 1.6 ratio rockers comes out...that changes a lot of things.

With the given lift of the ZZ4 cam, with 1.6 rockers, the exhaust becomes about .544" on the exhaust (drawing that off hand, not sure on the exact number...you can calculate this yourself: take the current lift on the exhaust, divide by 1.5. Multiply the results by 1.6). That lift is pushing it with what the 981 springs can take at an installed height of about 1.750" Since that is going to be the rough lift you are going to be attaining, there are no decent springs that can do .550" of valve lift and still be safe with coil bind. I don't think I would stretch on the 981's like that. 981's would take a 1.5 rocker just fine. If it were me, I would upgrade to the 986 series of valve spring if 1.6 rockers were to be used.

As far as the degree of the locking face, either will work. The lock/retainer idea works like a wedge. So the more angle to the contact surface, the better they will "lock," or so goes the theory. Though, I've never seen issues with 7° on the more aggressive engines. You can get either. Just be sure to get both in the same degree. Factory uses 7°.