Hello, I have a 79 Z28 with a 355 Chevy smallblock and a TH350 trans. The block and rods are stock, crank is a Scat, Summit 234/244 duration 488/510 lift cam, high vol oil pump, Edelbrock RPM heads, Summit aluminum roller rockers, Dart kool can dual plane intake, headers, Holley 650 double pumper, MSD 6A ignition system, Taylor spiro core 8mm wires, and Mallory HEI distributor. This motor only has about 4000 miles on the rebuild. My problem is that my engine runs very rough and backfires through the carb when starting and once it starts it pops through the exhaust for about 10-20 seconds. I should mention that I don't have a choke either. It is milled off. This all started at the end of last summer and has been getting progressively worse. The car would only run a little rough(no big deal) when I was stopped at a stoplight and was sitting there for a minute or so and this was the start of it last summer. However, as soon as I stepped on the gas it was fine and was fine until such time that the car would idle for about a minute. Then it started to get worse and worse. I connected a vacuum guage to it and it was reading all over the place from about 9-14 inches. Fluctuating rapidly as I remember it right. Basically just jumping erratically all over the place. It was then I noticed that #2 cylinder intake rocker would stop oiling after a long idle period. It would start oiling again if I gave it some gas and it would continue to oil for a minute or so and then stop oiling again. I have plenty of oil pressure due to my high volume oil pump so I figured that I have a bad lifter and I was planning on changing the heads anyway so I figured I would just replace all the lifters as well. Needless to say, changing the heads and lifters did not solve the problem. I even stuck a piece of wire into the lifter oil gallery just to make sure there was nothing stuck in it. I then ran some engine gum and varnish cleaner in the oil(can't remember what brand), but that didn't help either. After that I thought my timing chain might be bad, but I checked it and it is tight. Next I pointed my finger at my MSD ignition because I figured it was the last thing. I followed all of MSD's installation instructions and tech tips and everything looks good except for one thing. MSD says to run every plug wire at least 2 inches away from each other and I don't know how you would do something like that. My wires are pretty much touching coming right out of my HEI distributor and running in the direction of the plug they are going to. My wire looms place the plug wires about an inch apart. In this case I don't think close plug wires are the problem anyway just because the car ran fine before with the wires routed the same way as they are now. Just today I started the car and ran it for about 5 minutes and shut it off and I noticed that some header pipes are noticeably hotter than others. For example, #1 and #7 header pipe is no where near as hot as #3 and #5. The rough idle is so bad now that you really can't drive the thing. I am at the end here. I have no idea what else to do. I hope somebody has some ideas and I am very thankful and appreciative to anyone that can offer some help. I am ready to pull the motor and start all over, which is absolutely rediculous. I am wondering if I have some crud or gun or whatever stuck in one of my galleries going to my lifters. Maybe it is after all that one valve not oiling that is giving me this problem. Thank you for anyone that takes the time to read this long explaination.  

You replaced all of the lifters without replacing the camshaft? I sure hope you took the time to break-in the new lifters very well because using new lifters on a used cam can sometimes be risky business...

Sounds like you need to do your homework on using flat tappet camshafts as you might have one on its way out.  

That is risky,check for shavings in the oil and if there is check bearings.I like using a magnetic oil drain plug to catch shavings.Type in [flat tappet cam failure]lots of information for your next go around.Lobes and lifters once there mated it's for life,they form their own wear pattern together that cannot be disturbed.Good luck and keep us informed.    WIEDER  

Thank you for your advice guys. Yes, I did break in the new lifters correctly. At one point I did think maybe my cam was going south, but all the valves seem to be at full lift. Now I didn't use a dial indicator to measure the exact lift, but just by watching each one they all looked ok. I have watched them all on more than one occasion as well and did not see any change. Also, I would think that it would have to be more than one lobe considering the way the car is running. I guess anything is possible though. I still can't figure out the oiling problem on that one rocker. Very strange. I can't really say if it is related to the extremely rough running condition or not. I still have it stuck in my head that it is an induction problem between spark plug wires. Although, at one time it ran well with the very same plug wires and routing that it currently has. But again, I guess anything is possible. Maybe I should try slipping braided shielding over the plug wires and then grounding the shield and see if that solves the problem. Again, thank you for your help. It is appreciated.  

It will amaze you what an engine will do if an exhaust lobe is going flat and that cylinder is having a very difficult time ridding itself of the spent gases...

I highly doubt it's a spark-jumping problem but you can surely troubleshoot that area if you please.

You can't tell if a cam is on the way out by eye-balling.  Even though the lobe will most likely go away fast, it would have to be ground to nothing and your bearings would already be shot for you to notice a valve not moving hardly at all.  

Sounds like you have a bad camshaft due to the erratic vacuum. The popping you hear on the exhaust and the intake are tell-tale signs of the cam. If it were just plug wires you'd probably already have the infamous Holley fire. You should pull the motor down and go through it due to the contamination of metal fragments.  

it sounds like your cam has started to go south. had the same thing happen to the engine i put together for my 62 two door wagon i tried every thing else then tore the engine down and measured the cam lobes they were bad . replaced the cam & lifters broke it in per specs its all good now.  

Well, I guess it is almost official then. I probably have a bad cam. I will just have to check it with a mic to confirm it to be true, but I am sure you guys are right. I could set up a dial indicator on the valve side of the rocker and turn the motor over by hand and check it I guess. However, I am not sure that I could get a stable or accurate point. I would have to look at my rockers to see if that is possible. I might be able to use the retainer possibly. Not sure, would have to look at it and check. But anyway, thanks to everyone for the help. I really appreciate it. The last thing I wanted it to be was the cam though. I had thought about that, but I was avoiding it hoping that it was something else. thanks again.  

freind went through the same scenerio last summer with his big block chevelle.he rebuilt his numbers matching 396,threw a comp cams nostalgia flat tappet in it,didnt last a week,and it was broken in properly.had to re do the motor again,wiped out 5 lobes,and that was with all comp cams recomendations.go figure.  

Does CompCam recommend ZDDP additive type oils with there break-in instructions? I personally haven't seen that.    WIEDER  

they recommend using their own eos additive.didnt work for my freind though.  

Comp surely doesn't "recommend" EOS when they can instead push their own oil additive package. Someone on the tech line may have had good things to say about EOS before Comp started making their own break-in lube but that had to have been years ago...

Cam failures are VERY RARELY the fault of the manufacturer but unfortunately when backyard joe has to rebuild his entire engine he is looking to place blame on someone else...  

Like I mentioned before,type in {flat tappet cam failure}One of Comp Cams tech articles recommend off road oils after the break-in not there products.Another subject that seems strange to me is that CompCams offers Pro Plasma Nitriding for there cams.Why don't they incorperate this on all flat tappet cams. Please read these articles,the one from HotRod is full of information.GigTG what's EOS,never heard of it,these articles talk about ZDDP {Zinc and Phosphous}anti-wear ingredients.It's not only backyarders havings issues.Again please read!  WIEDER  

EOS stands for "Engine Oil Supplement." GM had (emphasis on the tense) been producing it for many years and many engine builders swore by it as a lubricant that helped flat tappet cams live. I'm pretty sure it's fairly high in ZDDP additives but the quantities probably been reduced in recent years before it was discontinued.

The reason Comp doesn't nitride all of their flat tappet cams is that it would scare away potential buyers. Having flat tappets that cost almost as much as rollers wouldn't look too good on paper. It would probably bring drastcally cut production of flat tappet cams by the aftermarket and the budget-rebuilders, retro-fitters, and class rule engines would suffer...

I guess I do recall Comp recommending certain brands of oil for use with aggressive flat tappet cams but the recent pushes have been to add their supplements as well. I wonder what they're saying now as ZDDP additives are slowly creeping out of Rotella oils. Are they really telling all of their customers to use incredibly expensive race-only oils?  

I run Mobil 1 and now I'm looking at synthetic race oils with ZDDP like Q racing oil at $20.00 a quart!Ouch!They need to make retro rollers more affordable and get the prices down where OEM's rollers are. WIEDER