If i take STOCK 5.9 Magnum, and nip .065" outta the quench distance (deck block .040" and run a .025" thinner gasket) will i run into piston to valve issues with a big cam? Thinking a 237/245 with .555" lift and 108 lobe separation. The stock 11cc dish is about .085" down for what thats worth. Is that enough? Or am i notching pistons now too?

Obviously the guides are getting cut.

That's a lot of clearance taken out and a lot more lift and duration added. I'd clay it and find out.

Checking it is the only way you will find out. I doubt if it will even be close to enough room. Also, cutting notches in stock pistons is not a good idea because they are already fairly thin where you need the notch. .200 minimum material left after the cut is what my engine guy wanted for milling pistons, and I wouldn't want to go less on a notch either.

This would be a really stupid issue to hang up my cunning plan...

if it is all together right now you could swap in a pair of light checking springs & see what you have now for a baseline/start.

Yup... could do that. Wish i had the cam handy too...

So you bought the cam cause it was cheap. Is the .555 lift with 1.5 or 1.6 rockers? If it's the number for 1.6s, you could swap back to a 1.5 rocker and 0.520 lift.

The problem that I see is there isn't a lot of installed height for a spring to handle that much lift. I seem to remember 1.625 being about max inst6alled height. So 1.625 -0.060 -0.555 = 1.010 solid height for the spring. The Hughes 1110 looks like it hits coil bind at 1.040.

For sure a Comp 901 won't work, unless you go to longer valves.

Glad it's your problem and not mine!

R.

Thats .555 with 1.6's (.515" w 1.5). I'd hate to lose the lift (and these rockers are pretty much brand new looking), but if 1.5's are dirt cheap... then yeah, thats an option. And lets be honest... even .515" is gonna make some wild power...

Does Hughes (for instance) not sell cams/springs for this application? For stock valves? I'm sure not everyone is buy small cams from them. Surely this issue cant be a hang-up?

Valve lift between a 1.5 and a 1.6 rocker is not going to make or break the piston to valve clearance. The additional duration and tighter LSA is what is going to make the difference. The new camshaft delivers an exhaust valve that is closing later in relation to piston's proximity to TDC, and an intake valve that is opening earlier in relation to piston's proximity to TDC.

If you are going to see interference or insufficient valve to piston clearance it will happen when the piston is 20* to 10* before TDC for the exhaust valve and between 10* and 20* after TDC for the intake valve. The valve are likely to be off the seat less than .2" when interference occurs.

Retarding the camshaft may give way to additional valve clearance for the intake valve. The intake is more likely to interfere simply because it's larger in diameter.

Others will know better, but from what I have read, with lift much over 1/2 inch you have to use dual springs.

R.

Well... even without the invisible gremlins (you KNOW will pop up) taken into account, this is all adding up a bit too fast. I think i'll just clay up the stock short block with the big cam and see where i'm at. Leaving the deck where it is, and just switching to a slimmer gasket will only rob me about .020" or so distance. If its doable i'll just toss it in and run the engine as-is. A slight mill ov the heads and the thin gasket should leave me around 9.5:1 actual CR... which is more than enough without quench.

The springs... well i'll cross that bridge when i come to it.

Brian from IMM is setting me up with Beehive springs on my EQ heads that will allow higher lifts. They do require a 1.320 diameter valve seat cut of .100 depth to get the extra room for lift. The Beehive retainers then have plenty of clearance for rockers, which can be an issue with some setups.