Rookie,

So, I'm not overly familiar with the numbers and how they relate, and I don't see these numbers anywhere on the spec for these springs, but the builder has referred to them a "145lb springs", whereas the OEM 496 springs were "90lb". Read that for what it's worth. It reads to me like they are ~50% heavier than OEM.

For the cam, we went with 232/244 @.050, 115+5 LSA, .617"/.627" lifts. This cam was formulated based on stock 496 heads with 5lbs boost @WOT. The builder has polished on the heads a bit, but has not done any significant material removal, for fear of running into water passages, as they are known to be fairly thin-walled. HE feels this cam will be just about all the stock heads will support.

Thanks. Brad.

The 90lb and 145lbs springs refer to the closed seat pounds of force when closed. Supercharged, at 5 psi boost...you lose about 20lbs spring force when the int valve is closed...as the 5psi wants to open the valve.

Maybe tMa quoted 90lb spring was for the smaller 496 cam...that had a 204° @.050". Something like that.

90lbs seat is pretty light for 5psi boosted system. It means a 70lb net seat pressure.

Tartilla,

That's kinda what I thought. From everything I've read and been told, the 90lb springs were way to light for a marine application. Again, back the fact that the engine is actually a truck engine that was designed to spend 95% of its life at 1700RPM, right? I have to wonder how much HP is being left on the table, even without considering boost factors, with these marshmallow springs in the stock HO. It's interesting that Merc saw fit to change the cam, addressing the marine application aspect, but not the valve springs. I guess I can get the not messing with the cast pistons thing, but the valve springs are a relatively easy swap, and the heads have to come off to swap the cam.

Thanks. Brad.

Tartilla,

We were running ~3.5lbs @ WOT prior to the failure. We have reduced the ProCharger wheel diameter by 1/4", so we could expect to see another 2-3lbs (1lb/.1" wheel diameter, as per ProCharger tech), but we also modified the intake to improve airflow, which will reduce boost while actually providing more air to the cylinders. The net expectancy is somewhere around 5lbs. We'll see.

That's also some interesting math, there. It's not that I don't believe you, but I'd like to see the math that makes 5lbs of boost into a 20lb change in net spring pressure. Physics. It's a b!tch....

Thanks. Brad.

If my engine builder told me I`ll be running 145# springs on a blown engine he`d be fired on the spot.
You better double check that .

Dan,

Those numbers came directly from a respected OSO member who's Whippled quite a few 496s before the builder suggested as much. Neither of them are new to the game. We aren't running huge numbers as far as lift or HP expectations. Besides, the engine seemed to run fairly decent as it was with 90lb springs. 145lb springs will fine, if not ideal.

You also have to consider the ProCharger isn't a real supercharger. It doesn't start delivering any real air until it hits 3500RPM or so. That may change a bit with the new pulley, but it won't be by much, I don't think.

Thanks. Brad.

2.19 diameter (valve) has area of 3.767.

2.25 diam (valve) has area of 3.976.

2.3 diam (valve) has area of 4.155

Times the valve head area by pounds of boost and you get your answer

It's 122lb seat pressure.
At a 373lbs/in spring rate. 122lbs + 231lbs (373lbs*0.620") = 353lbs over the nose.

What springs were in it? Apparently someone worked on the heads at some point.