I rounded from 18lbs to 20lbs assuming you had 2.19" Int valves. Of course, part of the valve contact seat face will not have pressure on it, as well as the tulip stem area. But it's better to over estimate a little on the potential impact of boost on the valvetrain.

Brad's peak HP curve is going to be higher for sure. He may have to re-prop to take advantage of the new cam. Would also reduce his cruise rpm...or give him a faster cruise speed at his old rpm.

Either way, this new cam is significantly larger than the stock HO cam. Make sure you post up some vids of your new exhaust running.

Hey Dan, how aggressive were your flat deck 540 cams?

Brad's 145lb seat springs may be on point for the cam and expected peak rpm of say 5400-5500.

But the lift is getting on the higher side, and I suspect the 496 is still using the stock lifters?

that does seem a bit light on the spring pressure, I run more than that on smaller cams. remember that it is a roller cam so a little more than it needs does not give up anything vs too little that may cause the valve to bounce on the seat. being hydraulic you cant go crazy but I would still rather have more than I need vs the negative effects from too little.

My cams were always as easy on the valvetrain as possible.
Bad kitty engines had low spring pressure (220#) solid roller and I suspect the intake valve bounced and lit a fire in the intake melting the intercooler.
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Rookie,

Obviously, no way of knowing for sure, but I don't know if the engine has ever been apart. Merc OEM springs are 90 lb seat pressure.

Thanks. Brad.

I've built a few marine engines,stock gm lifters live quite nicely at 160lbs on the seat.I got a set of heads in for rebuild,hyd. roller and springs were set up at 200lbs,had over 250 hours on those.
your motor should have a t a min. 160lbs,thats how I set up my engines I posted a pic of,,14yrs now and still running.

I used to leave exhaust valve seals off on all the blower engines I build, when I first got my dyno, I had my old Baja 548 on it and made countless pulls NA with blower off, i had headers off and saw quite alot of oil that migrated down exhaust valve stems, now if its low boost, like 6, 8 lbs, I use exhaust seals but take spring off, if its race stuff (mud, drag blown etc) or 9, 10, 12+ lbs of boost OR NA on e85 or methanol, I still leave them off with idea these guys dont properly warm them up and the extra lube will help keep valve stem from galling.

Id be scared to run 145 seat and 383 open (If Im understanding rookies math correctly) with a 232/244 @.050, 115+5 LSA, .617"/.627 cam, glossing thru your threads, your putting a steel crank in and better rods? Boosted that cams gonna carry past 5400, Ive seen stock 500 efi cams pull to 5800/ 6000 boosted on a procharged 502 500efi (with upgraded valve train), unless your bottom end is the "limit" of rpms, Id let it pull to where power dcecayed, thats where all your speeds gonna come from , rpms.
i had a cam that was ever so slightly bigger then your specs at one time, turned it 5800 blown at 8, 9 lbs, had like 150 seat/430 open, cam had damage from lofting on back side of lobe at 120 hours. Do you know what your valves weigh, not sure on a 496 how they compare to what I had, I wanna say my valves were 155/ 160 grams. I typically run 170 seat/450 open on most na stuff to 5800 and 190, 195 seat and 490 open on marine stuff thats blown but usually 8/9 psi or more and rev limiter at 6000. Spring rate decays hot too. BUT on other hand,you been getting away with much less BUT with a stock cam. Smitty

A spring checker will give you the information you need. And looking at the spring you can usually determine the make.
Someone removed the exhaust seals, maybe they changed springs.

My head guy would insist on 200-225 hydraulic, 275 solid. . That bit me in the ass only once with comp lifters that couldn`t take the pressure but Johnsons should be able to handle that with an easy lobe. Otherwise I never had a single valve train issue ever.

My valves got beat up pretty good on the Bad kitty Engines.. I think probably also due to insufficient valve spring pressures or too much lash? I don`t believe the lash was checked after break in.


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