Cam Setup For L31 350 Vortec

[L31MaxExpress]

I'm favorably impressed by much of what you've accomplished and appreciate much of the knowledge you've shared; but here, I Disagree in both application and principle. Again, and like a dyno, Spintron don't lie. Also, (understatement) I have more respect for GM Vortec heads than you seem to. Opinions.

I'm selective; not one size fits all. Overall, stamped RAs (including OE) work rather well and live long, even in extraordinarily harsh conditions; reference GM's L31-based "602" CT350 campaign.
FWIW, stamped RAs are good candidates for cryo as well as for lapping-in their pivot-balls.

Cheap "roller tip" RAs are known to fail at tip with short MTBF; when that roller tip affects friction reduction little-to-none. Accident looking for a home; Not always so durable. Every motor/build don't rate top-quality full-roller RAs; and cheap full-roller RAs carry too great a risk for failure. Your $ your motor.

Notwithstanding my above positions, I do also run quality full-rollers; when and where they're practical.
I wish crane RAs were still available new; I still have sets of gold race. I wish they'd continued to develop their hybrid which was essentially a gold race But, instead of a roller-tip, was shod with a precision tool steel slider "shoe."

I have found stock ones wear very quickly, using oils today. My L31R was eating on them heavily with under 30K miles on it. Also work on a 2019 L31 powered generator that was eating on them noticeably. I miss the factory GM LT4 rockers myself. Was easy to pickup a set of them on a car someone was building for a truck engine. The LT4s had a nice net lash system as well when using the OE rocker studs for them. I actually prefer the net lash when using a stock base circle cam.

 

[Schurkey]

I'm favorably impressed by much of what you've accomplished and appreciate much of the knowledge you've shared

TOTAL agreement.

stamped RAs (including OE) work rather well and live long, even in extraordinarily harsh conditions; reference GM's L31-based "602" CT350 campaign.
FWIW, stamped RAs are good candidates for cryo as well as for lapping-in their pivot-balls.

"Stock" rocker arms work really well...depending on RPM and spring pressure.

I have heard--on a Pontiac forum--that it's essential to lap-in the rocker balls to the rocker arms on Comp Cams roller-tip rockers. Guys I trust on the Pontiac forum have had repetitive problems with rocker-ball/rocker failures on the roller-tip rockers. This seems to go away with appropriate lapping. (I've never done it.)

Cheap "roller tip" RAs are known to fail at tip with short MTBF

True for most all low-budget auto parts, especially the Chinese sort.

Notwithstanding my above positions, I do also run quality full-rollers; when and where they're practical.

The last two engines I've built for myself, and the one in-the-works are all getting Comp Pro Magnums. None of these engines really "need" full-roller rockers, although the cylinder head design is somewhat unusual and Comp makes full-roller rockers especially for the intake side of those heads, so it's kind of a no-brainer to use them on the exhaust side too.

I have found stock ones wear very quickly, using oils today. My L31R was eating on them heavily with under 30K miles on it. Also work on a 2019 L31 powered generator that was eating on them noticeably.

That really surprises me. My expectation is that the spring loads aren't that high, and neither is the RPM.

I miss the factory GM LT4 rockers myself. Was easy to pickup a set of them on a car someone was building for a truck engine. The LT4s had a nice net lash system as well when using the OE rocker studs for them. I actually prefer the net lash when using a stock base circle cam.

Net lash saves a lot of time/hassle/headaches over adjustable, if a person isn't familiar with the adjustment process. I didn't know that LT4 was net-lash.

 

[L31MaxExpress]

TOTAL agreement.


"Stock" rocker arms work really well...depending on RPM and spring pressure.

I have heard--on a Pontiac forum--that it's essential to lap-in the rocker balls to the rocker arms on Comp Cams roller-tip rockers. Guys I trust on the Pontiac forum have had repetitive problems with rocker-ball/rocker failures on the roller-tip rockers. This seems to go away with appropriate lapping. (I've never done it.)


True for most all low-budget auto parts, especially the Chinese sort.


The last two engines I've built for myself, and the one in-the-works are all getting Comp Pro Magnums. None of these engines really "need" full-roller rockers, although the cylinder head design is somewhat unusual and Comp makes full-roller rockers especially for the intake side of those heads, so it's kind of a no-brainer to use them on the exhaust side too.


That really surprises me. My expectation is that the spring loads aren't that high, and neither is the RPM.


Net lash saves a lot of time/hassle/headaches over adjustable, if a person isn't familiar with the adjustment process. I didn't know that LT4 was net-lash.

Rocker stud on the right is out of a stock 1996 LT4. Same setup as a 7.4 or 8.1L vortec. The later 4.3Ls have an aluminum rocker stand like a LS engine. I have seen someone cut down a couple of pairs of those stands and use them in a 350.

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[L31MaxExpress]

This is a later 4.3 pedestal mount.

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[L31MaxExpress]

Saw this clip a month ago or so.

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[tayto]

Saw this clip a month ago or so.

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that would be an excellent way to modernize stock heads. however you would still need to get rocker bosses machined down and tapped

 

[L31MaxExpress]

that would be an excellent way to modernize stock heads. however you would still need to get rocker bosses machined down and tapped

On a stock TBI or Vortec head sure. On a LT1, LT4 or aftermarket aluminum that came with screw in-studs, would work just as he shows. I am considering trying this with my cam swap. I like the idea of a more ahaft mounted setup to prevent rocker deflection without relying on guideplates.

 

[tayto]

On a stock TBI or Vortec head sure. On a LT1, LT4 or aftermarket aluminum that came with screw in-studs, would work just as he shows. I am considering trying this with my cam swap. I like the idea of a more ahaft mounted setup to prevent rocker deflection without relying on guideplates.

I wish I would have known about this when I did my truck 355 a few years ago. I had a set of compcamps magnum roller rockers that were sitting on the shelf that I used. but this would be much more cost effective now. I had to use non-stock push rods anyway as i had block and heads decked as well as aftermarket cam and LS roller rockers

What do you add to push rod length for preload on GM roller rockers? 0.100" ?

 

[rebelyell]

I'd not seen that clip before now, but long ago had considered late V6 4.3L pedestal rockers (w/roller trunnion or even bushed trunnion) for a DD ... until the issue of adjusting lash raised its head ... then, while also compensating for deck height, gasket thickness etc.
? I don't recall the gent in the video addressing lash ?
? shims under pedestal or between pedestal & trunnion ? ... hassle & expense$ of differing length PRs ?
I soon ceased altogether considering it for either DD or a restricted class CT motor.

Also, in the vid, the gent indicates (@ both 0:55 & 10:56) the stud thread in head is 7/16-20 ... my experience is that it's 7/16-14 ... so, ? Maybe his easylocks/time-serts are actually 14 TPI ? Maybe his head has 20 TPI for RA stud ?

As for OE L31 RA failures, Maybe root cause has little-to-nothing to do with RA itself? ... perhaps something else at play ? dunno ?
As for myself; not seeing or hearing of a significant frequency of OE L31 RA failures.

 

[tayto]

I'd not seen that clip before now, but long ago had considered late V6 4.3L pedestal rockers (w/roller trunnion or even bushed trunnion) for a DD ... until the issue of adjusting lash raised its head ... then, while also compensating for deck height, gasket thickness etc.
? I don't recall the gent in the video addressing lash ?
? shims under pedestal or between pedestal & trunnion ? ... hassle & expense$ of differing length PRs ?
I soon ceased altogether considering it for either DD or a restricted class CT motor.

Also, in the vid, the gent indicates (@ both 0:55 & 10:56) the stud thread in head is 7/16-20 ... my experience is that it's 7/16-14 ... so, ? Maybe his easylocks/time-serts are actually 14 TPI ? Maybe his head has 20 TPI for RA stud ?

As for OE L31 RA failures, Maybe root cause has little-to-nothing to do with RA itself? ... perhaps something else at play ? dunno ?
As for myself; not seeing or hearing of a significant frequency of OE L31 RA failures.

Lash is discussed in the comments. Pushrod length dictates preload, same as LS, so measure push tod length then add what you want want for lifter preload.

The inserts he uses has 7/16 outside thread and M8 inside thread. You could probably source them in 3/8s but anyone I have done you always tap for 7/16 and then the stud goes down to 3/8s