Here's another fun one I've been dealing with. Z06 2650 big cam

[JASON11WS6]

So like the title states. Z06 with a 2650, car ran idled and chopped great. Oil pump ate it and the motor was toast. Rebuilt the motor and it ran great but we had a couple of issues with the head (porting took too much meat out and it leaked coolant). Finally tossed on a new head and the car runs like crap when it's cold now. First start up is negative timing, no vacuum and it pops and bangs really loudly. Once it's warmed up it's fine, it'll drive okay and idle fine. The chop still doesn't hit as hard as it used too but the timing is good. Still surges a bit when going into gear. I've learned a lot about cam tuning the last few months dialing in some big cammed cars so I feel like I can get it.
I guess the big question is what can I adjust during the warm up process that might help out? No timing, no vacuum and it even misfires when cold. Any ideas?

[GHuggins]

Only heads were replaced right? Near baro reading at idle and struggling to run - sound about right?

Pushrods are most likely wrong or you have a vacuum leak, but with it getting a little better with temp, it's most likely the pushrods are too long and keeping valves slightly open. Just went through this on a customers lt4...

[Alvin]

So like the title states. Z06 with a 2650, car ran idled and chopped great. Oil pump ate it and the motor was toast. Rebuilt the motor and it ran great but we had a couple of issues with the head (porting took too much meat out and it leaked coolant). Finally tossed on a new head and the car runs like crap when it's cold now. First start up is negative timing, no vacuum and it pops and bangs really loudly. Once it's warmed up it's fine, it'll drive okay and idle fine. The chop still doesn't hit as hard as it used too but the timing is good. Still surges a bit when going into gear. I've learned a lot about cam tuning the last few months dialing in some big cammed cars so I feel like I can get it.
I guess the big question is what can I adjust during the warm up process that might help out? No timing, no vacuum and it even misfires when cold. Any ideas?

Some Z06's will not let you get into boost in strict SD only.. But a lot will and a lot will. I strongly suggest failing the MAF and getting the VVE rock solid. It makes a huge difference on so many things down the line.

[JASON11WS6]

My first thought was vacuum leak. The pushrods are sized okay, we've checked them but also the car ran on this same set up before. Last year we got the new motor running and we had an issue with the head leaking coolant (slight pin hole from the porter). When we changed it we started having these issues...so again I think vacuum leak but it runs okay when it's warm.
In the end I think it might need some more tuning. I'm going to Ve tune it and start tweaking the vtt before it goes back on the dyno.
I was just hoping maybe there was some warm up tables I could at least take a look at.

[TriPinTaZ]

You know how the OEM valley cover has the port that plugs into the bottom of the OEM blower? If you're still using the OEM valley cover with the 2650, have you verified this port is sealed properly to the 2650?

[GHuggins]

Engine characteristics usually won't change that much just from going from ported heads to slightly less ported heads as I assume the new one is also ported - just not as much as the original one with it only having one of them replaced. VE will change how the engine calculates torque, but it'll run as it did only with negative timing or more timing if it's off 10 to 20 percent. For it to be changed as much as it has you have to have something really different that's been thrown into the equation. Check what Jason said with the vacuum port in the valley pan. You can even smoke the crankcase if you have the ability to do so.