Just put in a 581/592 comp cam and stage III heads in my friends 98 z28. Car will barely run but I think that's expected from not having any tuning done yet. But there is some knocking up front that is audible even over the open headers. What could it be??? Everything was put back together the way it should be (this is our 3rd ls1 install) with locktight and everthing else. This car has full port and polish, milled .030, new comp dual coil springs, and comp cam lifters. Could the air to fuel be so off that it causes severe knocking??? Should we have used different push rods because of the mill? Any Dallas/Fort Worth locals with ls1 edit that could make a house call?


HELP

 

what size valves? that much lift on heads milled .030 will possibly need shorter pushrods, but maybe not it will depend some on the valve size.

 

stock valves and pushrods

 

stage 3 heads on a factory bore? You'll definitely need a tune or a blower. LOL set your idle speed at like 1500 rpm and that might handle it.

 

that is an odd stage 3 set of heads with stock valves, but since you are milled .030 but using stock valves piston to valve interference is not an issue. did you get the timing dot to dot? what exactly are the cam specs? if is a comp cams cam going by the lift numbers you posted is is a 224/230 .581/.592 , still what are the specs? do you have a flashing SES light? it could be a lean condition causing knock. please give more details.

 

Yeah that is the right cam and the dots were lined right up. It does start if you crank it a lot. It won't hold idle at all but will rev fine if it starts. The heads were taken to a friend of mine who works at southwest engines in cedar hill. He builds pro mod engines and has been doing heads for 25 years. He said he opened them up as big as they would go and went ahead and polished all of it too. It has open headers and pops a lot when it tries to idle if that helps any.

 

You did not state what the CAM's LSA is but I suspect the LSA has caused low end vaccum loss and thus without a custom tune there will be startup and idle issues since the MAP/Vac values no longer match the PCM's expected values and PCM thinks the engne is in a different running state then what it is.

With open headers it will have a ill effect on what the O2s are reporting what the AFR is.

 

Sorry, it's on a 112 Lsa but your prob right about the a/f and all that