so i am building a PI motor, i am putting comp xe-274-h cams in it, i know they are for the NPI motor but i got a great deal, so anyways i bolt the cams down and put the heads on the motor and when i turn the drivers side cam without the timing chain attached,it gets to max lift on like the 4'th lobe in and right when it crosses over max lift it like snaps and kicks the cam over. i have no idea what it is any ideas? i am running the comp beehive springs and Ti retainers, stock valves. Please help. Also the pistons I am running are 04 cobra pistons so they are a smaller dish than stock PI motors but larger than stock NPI motors so i dont know if i will have contact. please help, thanks in advance.

 

ttt

 

What position was the motor in. If it didnt have the key on the crank at 12 o'clock then you are hitting the piston. And 04 cobra pistons have a bigger dish.

 

04 cobra pistons have a 13.2 cc dish, the keyway was at 9 o'clock which is whati was told is the safe position, so is there a possibility i bent a valve? thanks for the help.

 

Its not a major deal. It is just the valve spring pushing the lobe back up. There is nothing holding the cam still from turning, so the spring just pushes it around. Put the chains and tensioners on and then turn the motor by hand. The chains will hold the cams in the right spot and they won't snap back on you. check the clearance and you should be fine.

 

any other comments? does anyone know if 274's will have PTV contact if they are degreed in as perfectly as possible?

 

the 274s are a GIANT cam, IMO way to much cam for what your doing. Even with no PTV you still have too much cam for stock heads/stock shortblock.

You MIGHT get away with the 278s since they are the NPI verisions with only .500 lift instead of the .550, but its gonna be close either way, espcially on a car thats getting swapped to a PI setup on a NPI shortblock.

 

the 274's are the npi cams with .495 lift the 278's are the pi cams with a .550 lift you got them mixed up, also i am not runnign a stock shortblock, read the thread, its forged all forged with p&p heads, full exhaust, intake, its a built motor so the 274's should be fine, i understand they are a big cam but the 278's are by far the largest and lift has very little to do with PTV contact its the duration that matters, and the LSA, the overlap period is where it happens not max lift.

 

ttt