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. :picard1:

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. :ernaehrung004:

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.

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.
https://cimg3.ibsrv.net/gimg/www.off...a6238f08ce.jpg
https://cimg4.ibsrv.net/gimg/www.off...0bd1428f01.jpg

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.


https://cimg9.ibsrv.net/gimg/www.off...d75f6c0064.jpg
https://cimg0.ibsrv.net/gimg/www.off...de457a02b3.jpg

Guys,

Keep in mind we are still running the stock heads and exhaust. Conventional wisdom says we won't see much over 5300, maybe 5400 RPM. We haven't commissioned the cam yet, but he's telling me this cam will help pull more out of the engine at the RPM the heads and exhaust will allow for. I'm being told by several who have dealt with the builder that valvetrain is his guru zone, and he's used to building WAY more engine than mine.

And, yes.... I am kind of leaning on the fact that I had WAY less spring pressure before (unless they were changed at some point; I will ask), and the engine ran fine. I haven't been given any indication that spring pressure had a hand in the piston failure.

I will be seeing the builder today (he wants money to pay the machine shop and commission the cam), so we will be discussing this.

Thanks. Brad.

My advice..... buy a stock take out 496 and go boating. Give me $5k and I'll kick you straight in the balls....this will be much cheaper and painless in the long run....lol

:)

TikiJoe,

Yeah…. We’re WAY past that point. Besides, we weren’t “stock” before the failure. I ain’t going backwards.

Thanks. Brad.

https://cimg8.ibsrv.net/gimg/www.off...d724ae3d0.jpeg

These springs aren't making sense. They are 122lbs @ 1.900" installed height, Max lift on the spring 0.640" your cam is 0.627" and the spring needs more than 0.013" shim to achieve 160lbs seat pressure. Your into coil bind at 1.200". Does the builder know the cam specs?
Please someone correct me if I'm wrong.
https://cimg7.ibsrv.net/gimg/www.off...7f26684244.jpg

are those titanium valves? rarely see ones beat up like that.

Nope.

Rookie,

Your math makes sense. It is possible that we zeroed in on a spring before deciding to go with a new cam, and then it was out of sight, out of mind. I am running this down with the builder.

Thanks. Brad.

Guys,

https://cimg1.ibsrv.net/gimg/www.off...33d9ef13d.jpeg
A block and its internals. The crank is on the front passenger floorboard.

https://cimg3.ibsrv.net/gimg/www.off...fba09ce88.jpeg
Look at that hone….

Gotta get it all to the builder now.

https://cimg5.ibsrv.net/gimg/www.off...f764c86ea.jpeg
The virtually brand new machine the work was done on. Nothing more than a 4 axis CMC bed mill, really, set up specifically to do engine blocks. But it’s still pretty cool. I didn’t get a pic of the honing machine, but it’s pretty cool, too. It can hold +/- .0002” size and taper. Again, pretty cool to me when my interests and profession intersect.

https://cimg4.ibsrv.net/gimg/www.off...084485d47.jpeg
Also got the ACR circuit buttoned up today.

Starting to work on fuel plumbing next.

Thanks. Brad.

The new honing machines are pretty big step up. Sense the rotating resistance etc.

Looking good.

Brad, are you still running the stock lifters with dog bone style roller lifter alignment?

​​​​Not trying to bust your &@!!s here...just seeing some potential factors.

The factory rollers with dogbones only have 0.570" lift before they have issues with the alloted travel on the machined surface for the dogbone retainer. Essentially they can come out of the dogbone on a small base circle from a high lift cam. Different perspectives on this. Some say max lobe loft of 0.350"...some 0.375". Either way...a need to know.

Did I miss that you're getting new lifters too?

One of everything .. I`m jealous !!!
:D

Tartilla,

Builder mentioned a long time ago that we don’t need to address lifters as long as they are in good shape, which they are. Again, that was before discussing a new cam. My math says .369” lobe loft on the exhaust. I’ll run it by him. Well back off the cam numbers if it’s gonna be an issue.

Thanks. Brad.

..messed up my edit. Oh well. Lol.
Basically it said…
Many have used the gm dogbones on the old crane cam cams up to .610/.632 …..but yeh, always ck in case.

I would buy new lifters. Even if old ones are good for the application. I would go with Johnson’s. Cheap insurance.

I know everything adds up in cost doing this build, but I too would go with new lifters. Have seen many fail in many different engines for various reasons. Who wants to tear an engine down to replace them, seems like somewhat cheap insurance to keep from ripping motor apart later.

Not to mention you're asking these used lifters to perform at their maximum effort. What would the inspection plan be to ensure the cam/lifters are healthy?

Perf GM BBC stock lifters are not that much $$.

Then you could sell your used cam/lifters as a set. Recover some $$. If they are gtg...then they have value. Otherwise...they aren't worth putting in with a higher intensity cam.

Guys,


This is a .365” lobe loft cam. We are looking at .369”. There’s somewhere in the .050-.100” range clearance at apex.

Thanks. Brad.