ok, if anyone thinks that a complete list of lunati cam specs and springs with rough prices that you will find would be a good post/sticky let me know and ill post a thread about it...i have it all listed. cam specs part numbers for DROP in springs good to .630 lift, and you can get springs, retainers, and locks for well under 200. and this means NO machining on your heads....well anyway...im going with those springs and im looking to do a cam. but im gonna put a set of stainless 1.985"/1.555" valves in the heads too. my question is what is the max lift that i can have with those size valves in the heads? i would like to know what the lift would be with 1.5's and 1.6's, any help is GREATLY appreciated, since i am like a kindergardener when it comes to math...thanks!!!!! let me know on the lunati list and ill post it if someone thinks it would make a good sticky...i think it would since lunati (holley) makes some really really good stuff. i believe that they are grossly underrated...


p.s. im only going with a small cam..its a daily driver/cruiser so im sure that those valves would work with lets say a lunati with
262/270 211/219 .507/.515 112/106 and an operating range of 1600-5600 which should work with my factory stall...

 

does anyone know?

 

I'm still trying to figure out what you said?

Why'd you go with those valve sizes?

 

Max lift will depend on many things, including how far the piston is in the hole, what kind of valve reliefs the piston has, etc. Or are you asking what is the max lift for stock pistons in an unmolested block? Even that has no "fixed" answer, since there are manufacturing dimensional variations. You need to verify P-T-V clearance before you fully assemble the engine.

Lift at the valve will be the same, no matter what rocker ratio you have. The cam lobe lift would be adjusted down to arrive at the same gross lift with 1.6X rockers. Typically, the cam manufacturer tells you what the valve lift will be with a 1.5X rocker, and you calculate the valve lift for 1.6X rockers by multiplying by 1.06667

 

Total valve lift has VERY LITTLE to do with P-V clearance. Interference takes place nowheres near peak lift. It occurs near TDC, nowhere near the lobe center line (which is the point of maximum lift). So, the question you asked has no answer. If you think about for a minute, duration and "intensity" of the lobe have more to with P-V clearance than max lift. Also, the way the cam is degreed in and the LSA play a role. Bottom line is that leaving out tolerances the only reasonable assurance that a given combo of cam, rocker ratio, and head will work in a given shortblock is the knowledge that someone else with EXACTLY the same setup had enough P-V clearance. When you factor tolerances back in, you are left with the advice already given - you need to check.

Rich

 

That cam is tiny compared to the norm around here and the valves are also smaller than the norm. You should have no P-V problems with those on a stock shortblock.

Broken <enter> key?

 

Green96ta, yep, I'd be interested in the Lunati cam and spring specs and prices. Do let me know if and where you post them. Thanks!

 

i was told that going with a valve that big would cause me to lose power is that true?

 

does anyone know? im using stock heads with some very light gasket match porting, and a cc503 cam. would bigger valve be helpful or hurtful?

 

A valve how big? You mean the 1.985" valve you somehow determined you would use? If that was the case, the LT4 head would "lose power" because is has 2.00" intake valves.

You can't generalize about valve diameter. As you go larger, you start to get shrouding and a portion of the flow curtain is restricted. While a larger curtain area means a lower velocity, its not only velocity that determines whether you make power. There's also turbulence and swirl, determined by the port configuration. I'm not sure how anyone could say categorically that a 1.985" intake valve would "lose power".

I doubt you will gain much if all you are doing is increasing the valve size, and not doing anything to the runners.

 

Changing the rocker ratio will change the lift the valve sees.

 

Try reading the sentence immediately following the one you quoted... then you might understand what I said.

He is asking about max lift at the valve, and then asking if the answer is the same with both 1.5X and 1.6X rockers. If, for example, he determines that the max valve lift his particular configuration can handle is 0.600", he can buy a cam with 0.400" lobe lift and use 1.5X rockers, or he can buy a cam with an 0.375" lobe lift and use 1.6X rockers.

The answer to his question - "what is the max lift that i can have with those size valves in the heads?" - is that the max lift he can spec at the valve does not change, whether he uses 1.5X or 1.6X, but the lobe lift would change.