Well if you look at the motorsport cams they are generally .512 or less except for the x and z but the durations are more than your 268, and the motorsport ones aren't the real "wild" ones either..... or am I mistaken?

I am talking about duration @50. Advertised duration for a typical lobe like that would be 319 to 325 degrees (Hyd. Roller).

ok I see what you are saying

Couldn't have said it better myself, thank you very much!!!!

Example.

My custom cam, on my GT40's is .552/.544 lift with 1.7 ratio peds. It would have been ~.600 but I didn't want to convert to stud-mount, and .550 is about the safe limit for ped's. Duration is ~222/230 and it should clear.

My current cam (that is coming out) is a TFS #1 also being run with 1.7's, its .530/.544 221/225 (if my memory isn't too foggy) and clears no problem, and the GT40's have larger than stock valves obviously.

Duration has far more to do with P2VC than lift does, as peak lift doesn't occur until the piston is well down the bore. Its the valve events when the valve is chasing the piston, piston chasing the valve that cause issue. Radial clearance is another, often overlooked issue as well, and is a very common one with large-valve heads.

^I'm pretty sure the thread starter asked how much lift the stock heads can handle, I don't remember a question of how much lift or duration a stock short-block can handle or whether to replace valvesprings, so knowing they can handle at least .512, that was my post, I wasn't saying I could guarantee anything-but thanks for the lesson. :teeth:

Your words verbatim. You are correct he did ask what lift the stock heads could handle but you answered with the above. I did not try to threaten your tech guru status but I was simply correcting something that was wrong - no harm intended.

On that note do you know if he's had any worked done to his heads in the past? For example lets say a new set of springs were installed and someone never set/checked the proper installed height.

What happens if his springs go into coil bind at .500 lift now? Maybe the heads were milled .040”… or there has been 10 valve jobs done to them unbeknownst to the current owner? Bottom line is there are no guarantees and you must check your stuff and not hold a few tips from an internet forum as gospel.

Good point here. If you use the clay method always check for radial clearance. You must cover the entire relief and not just merely fill it full of clay. Too many times I have heard of individuals checking the p to v only for depth, finding it's within spec and all therefore should be well….

Once the engine is run a valve gets tweaked and the builder cannot figure out how this could have possibly happened with all the ‘clearance’ they initially though was there. I guess it’s a good thing witness marks usually confirm where they forgot to check.

I am not afraid of my tech guru status being threatened, yes, I said that a stock long block can handle .512" lift because I know it can, fabs was not asking about duration and did not give cam specs, he merely asked what stock heads can handle...which I answered-adding that a stock long block could handle it, if anyone else was interested.
Now, I could stay here and give out scenerios of what happens if this..what happens if that, but it has nothing to do with the question being asked, question has been answered, I'll move on. I will add that it sounds like you know what you're talking about, but it seems to be over and above said question.

On my 88 GT i was running a E-303 cam with 1.7 roller rockers, was told it was equal to 529 lift and it ran fine :thumb1:

I wasn’t trying to roast you, as I am sure your help is much appreciated on this forum. I took a somewhat vague answer and tried to paint a clearer picture. Also I was stressing the importance of checking your parts vs. relying on general internet insight to avoid it.

For sure? And you’re going to guarantee this? Ever heard of an 1986 H.O… Maybe with your engine, but what exactly does he have here? Again you never know and can’t be sure until it is verified. Lets say his heads have been milled to china by a previous owner and the I.H is wrong, when he fires up his engine with a new cam and it hits, whose fixing it?

You HAVE to give out scenarios because that’s the reality of life. I see 50+ engines a season and let me tell you wouldn’t believe what’s actually out there. Especially when it comes to valvetrain. Truth is you never actually asked him any more details before ‘confirming’ what will work. SPEEDTOSPARE answered it dead nuts on and went on to even ask about his combination. See below

Stock heads can handle more lift if set up correctly. The question is how much do you need and have they been properly ported to utilize it. If the head is unported or the port job is terrible then it won’t matter much anyways.

Too much information is better then not enough. Hell even G.I Joe knew knowing was half the battle!