Rockers 1.5 ratio or 1.6???????

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MR JIM

MR JIM

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Running flat tappet solid cam with 573 lift.My question is..the valve springs can handle up to 600 lift ca I go with 1.6 rockers????
 
Maybe, depends on the lash. You're very close to the edge so double check everything.
 
.573 divided by 1.5 equals .382, this is your lobe lift. .382 x 1.6 equals .6112, that would be your lift with a 1.6 rocker. That's too close in my experience. The only real way to know for sure is to know your EXACT installed spring height, put the spring in a vise or a spring testing tool, compress the spring to the installed height plus .6112 minus your lash and measure for coil bind clearance suggested by the spring manufacturer. Don't forget to check for retainer to seal/guide clearance too.
 
59* Smallblock???

If so, take another .020-.025 off for the bad valve train angles. Put a dial indicator on the retainer with your current setup and check lift at the valve. You might be surprised at the number.

Never seen a 59* smallblock, ever get actual theoretical lift, especially on something that big.

BB would be too close and you'd need to check everything for coil bind, retainer interference.
 
What Crackedback said is right on. Because the pushrod is NOT in plane with the lifter body..Small block Mopars lose just about .010 lobe lift (pushrod) at the rocker end of the pushrod. If you will do the math with that in mind you will be right on with the target lift figure, a much more accurate number. The 1.5 vs 1.6 math just does not work for the small Mopar as it is usually done. The design ratio is 1.5 (production), .573 lift divided by 1.5 = .382 lobe lift less the .010 'lost motion' = a truer lobe lift of .372 X the 1.6 ratio = .595 WITHOUT lash. Not knowing MR. JIM's lash figure I will use .020. which gives a much truer lift fingure of .575 . My XE275HL Comp is listed at .525 lift. Doing the math less the .010 with 1.6 rockers gives a lift at the valve of .544 and .544 is exactly what my dial indicator reads off the retainer when I degreed the cam in. I always use 1.6 rockers with small Mopar, it will give back the lost lift that is lost due to the bad geometry inherent with the small Mopar engines. (59 degree). the terrible geometry losses. Especially with the smaller cams. If you are running a .480 lift camshaft you really only have .465 lift at the valves, and that is ok if that is what you want. But if you want .480 lift use the 1.6 rockers and you will have a true .496 at the valve. This is FYI.
 
I'd be more concerned with spring pressures than the lift. Maxxing out a spring is a fast way to kill them. A higher ratio means the spring has to work harder to control the valve... Then you're compressing it further.
 
Moper, you are absolutely correct, I agree with you about the increased 'stress' the higher ratio rockers impart to the valve springs. I was giving an explaination as to why we can't accurately use the standard method of calculating the as installed lift, of our cams . It will not be correct. I don't build my engines with a 'plus or minus' rule...nothing wrong with getting the right number. JMHO.

Terry
 
Also remember to check your valve to piston clearance if you increase the lift. Watch for any other valve train clearances such as pushrod to head, rocker to retainer, pushrod to rocker, ...
 
All good advice above, maxing spring pressure equals shorter life and less control, actual lift, etc...

I wonder, are the heads capable of flowing well at this lift? If they are, I'd look into new valve springs that can take that lift easier than what is on there now. Remember also, the increased rocker ratio creates a more intense acting cam. (More on the spring)
 
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