Fast Cam Accel Rates & Stud Flex: A More Nuanced Discussion of Stud Girdles & Shaft Rocker Thresholds?

[NewbVetteGuy]

On the subject of "when should someone start considering a stud girdle" or "When should someone dig deep into their wallet for shaft rockers?", I often hear the really simple explanation that they're needed for "high rpms and/or high spring loads, when you can't afford a shaft mount rocker system". -This is often translated to the even more simple "use shaft mount rockers when running solid rollers; stud-mount when running hydraulic rollers."


I'm interested in a slightly more nuanced discussion of the subject.
My best guess is that the energy / loads exerted on the rocker / valves are the best indicators and that should be a combination of the velocity of the valve train (RPM and accel rate /actual speed) and the weight of the valve train, right?

I have to think that a heavier valve train with really aggressive lobed hydraulic roller can still be in a situation in which a stud girdle is going to be a useful thing to have. (Think the Comp QXI lobes with fast accel rates and big lifts for a hydraulic roller.)


So what are some rules-of-thumb that a normal human can use to guestimate when they should consider moving from simple stud rockers to adding a stud girdle or moving to a shaft mount rocker system? (Something more nuanced than: "When you move to a solid roller".)


Adam

[SupStk]

I've considered stud girdles or shafts mandatory for solid rollers and girdles a good addition for most performance applications. The easiest way I can think of for helping with that decision is put a dial indicator on the stud and turn the engine over with the assembled valve train. It's then up to you to decide how much deflection you are willing to live with before addressing the issue.

[CamKing]

When we get over 350lbs of spring pressure at max lift, I recommend a stud girdle.

[Stan Weiss]

Mike,
Does stud diameter come into play?

Stan

[CamKing]

Mike,
Does stud diameter come into play?

Yes, that's just what I recommend on a SBC with 3/8" studs.
There's a lot of limited circle track classes where we have to run right on the edge of what's reliable.

[NewbVetteGuy]

When we get over 350lbs of spring pressure at max lift, I recommend a stud girdle.

My PAC Beehive 1219x @ 1.200" open (at my max lift on your HR70375-71360-110 cam with 1.6 rockers) = 349.5 lbs... I guess I'm good by 1/2 a lb?
(7/16" studs)

-I just find it amusing how ridiculously close I am to that number.


Adam

[NewbVetteGuy]

Mike,
Does stud diameter come into play?

Yes, that's just what I recommend on a SBC with 3/8" studs.
There's a lot of limited circle track classes where we have to run right on the edge of what's reliable.

Have a similar recommendation for 7/16" studs?

-It DOES make sense that the recommendation would be based upon the cam MFGR's recommendation on spring open loads as that's already factored in the RPM, cam ramp accel rate, and rough weight of the valve train, huh?




Adam

[NewbVetteGuy]

The easiest way I can think of for helping with that decision is put a dial indicator on the stud and turn the engine over with the assembled valve train. It's then up to you to decide how much deflection you are willing to live with before addressing the issue.

I like this recommendation, too as it's simple enough for someone like me to do.
BUT, aren't the loads significantly different on a running engine? (go up with the RPM squared, I think...)


Adam

[Steve.k]

When we get over 350lbs of spring pressure at max lift, I recommend a stud girdle.

Mike what do you think about the pedastal type rockers like scorpion makes for Ford. There's no provisions for girdle and they say good to 550 open pressure? Do you think the slot in pedastal offers enough support?

[SupStk]

The easiest way I can think of for helping with that decision is put a dial indicator on the stud and turn the engine over with the assembled valve train. It's then up to you to decide how much deflection you are willing to live with before addressing the issue.

I like this recommendation, too as it's simple enough for someone like me to do.
BUT, aren't the loads significantly different on a running engine? (go up with the RPM squared, I think...)


Adam

I would fully expect the valve train to act differently on a running engine, and probably not for the better.

One instance comes to mind on a Super Stock SBC i did years ago. As you’d expect this was a solid roller with decent springs. During the dyno warm up and initial pulls I left the girdle off so there would be less to do on retorquing the heads. After covering that I installed the girdle and on the power picked up about 27 horses. The only difference was the girdle, so removed it and retested. Down the same amount.

Used to run a 351C in SS/J. That engine would deflect 7/16 studs over .015” when doing the rollover test.

[CGT]

The easiest way I can think of for helping with that decision is put a dial indicator on the stud and turn the engine over with the assembled valve train. It's then up to you to decide how much deflection you are willing to live with before addressing the issue.

I like this recommendation, too as it's simple enough for someone like me to do.
BUT, aren't the loads significantly different on a running engine? (go up with the RPM squared, I think...)


Adam

I would fully expect the valve train to act differently on a running engine, and probably not for the better.

One instance comes to mind on a Super Stock SBC i did years ago. As you’d expect this was a solid roller with decent springs. During the dyno warm up and initial pulls I left the girdle off so there would be less to do on retorquing the heads. After covering that I installed the girdle and on the power picked up about 27 horses. The only difference was the girdle, so removed it and retested. Down the same amount.

Used to run a 351C in SS/J. That engine would deflect 7/16 studs over .015” when doing the rollover test.

That's interesting. I have on a few occasions when dynoing left the girdle off in between rocker changes ect. Didn't really see anything that jumped out at me from leaving it off. But, it was hydraulic, lower valve spring pressure. But who knows, it could have skewed results somehow. I guess on an engine that appears to be way overcammed with a bunch of spring pressure….try a pull with the girdle off?

[n2xlr8n]

I like this recommendation, too as it's simple enough for someone like me to do.
BUT, aren't the loads significantly different on a running engine? (go up with the RPM squared, I think...)


Adam

I would fully expect the valve train to act differently on a running engine, and probably not for the better.

One instance comes to mind on a Super Stock SBC i did years ago. As you’d expect this was a solid roller with decent springs. During the dyno warm up and initial pulls I left the girdle off so there would be less to do on retorquing the heads. After covering that I installed the girdle and on the power picked up about 27 horses. The only difference was the girdle, so removed it and retested. Down the same amount.

Used to run a 351C in SS/J. That engine would deflect 7/16 studs over .015” when doing the rollover test.

That's interesting.

Yes.

Not terribly surprising, though. I have heard that SS/ camshafts are plain nasty- valve loft and all.

[dfarr67]

I should have reached for the 7/16 ARP studs in the first iteration- would have saved $$ in the long run.