Cam Setup For L31 350 Vortec

[rebelyell]

^^^this^^^
... the coarse end of stud (lower aka head end) has 14 TPI and it's 7/16" aka 7/16-14 ... it's like that no matter how the upper (rocker) end is sized.

I'm not even gonna try this late V6 rocker retrofit into sbc ... it ain't worth the time or expense ... Not for me. And, No, a hydraulic lifter cannot compensate for all those variable heights/lengths/thicknesses encountered when building motors ... more PR lengths and/or ability to shim pedestal heights required.

** and this here tempest in a teapot just triggered an old memory. We built a relative oddity in the CT world. A brand new, one-off straight rail Super Late Model pavement chassis with a 5-star Dodge nose & bumper cover and a true Mopar small block. The car owner insisted on Dodge power. I don't recall which sbm motor that was (perhaps 360A) but it has OE NON-adjustable valvetrain. For those hardheads that insist on that Mopar motor, the aftermarket (perhaps Mancini) offered a conversion kit to convert its NON-adjustable valvetrain into a Fully-adjustable valvetrain. I recall it wasn't cheap. There were some rather smart, experienced motor guys (including a top-shelf T&D maker) involved with that project. If managing that piece with a NON-adjustable valvetrain were so simple; it would've remained so ... It Did Not! And yes, I recognize sbm not same as sbc; but not so very different either.

Again, interesting concept, 'though not altogether new to me; but not gonna bother with it.

 

[Schurkey]

..." very likely got heaps of travel" ...

Likely?

? What if that's not very much travel ?

Likely, if the OEM or OEM-replacement lifters are installed. Not guaranteed, because limited travel lifters are available, and "could" have been installed sometime in the decades since these engines were built. The less travel the lifter plunger has, the more critical the pushrod length.

If a solid/mechanical lifter is chosen ... how would its lash requirements be addressed ?

Not with a non-adjustable valvetrain unless a person was completely nuts, willing to install a custom pushrod on each individual lifter/rocker, and willing to re-do the pushrod length as the system wore.

No, a hydraulic lifter cannot compensate for all those variable heights/lengths/thicknesses encountered when building motors ... more PR lengths and/or ability to shim pedestal heights required.

Yes, and no. The farther away from "blueprint" specs the engine assembly is, the more critical pushrod length becomes...but there's a range of variance around the blueprint specs where the lifter can compensate. For example, the SBC was designed with a 9.25 deck height, and ~.020 steel-shim head gaskets. GM changed nothing in the valvetrain geometry when they went to thicker, composition head gaskets. Similarly, almost no-one would question pushrod length when the block or head decks--or both--got a skim-cut to assure flatness and surface finish, whether or not a .040 or .020 head gasket was used. Of course, things are generally less-critical on Grandma's car compared to a local dirt-track claimer engine, and more still on a Top Fuel dragster.

Pushrod length can be critical, especially if the rockers are adjustable at the pivot point like SBC, and other engine families such as W and Mk IV. Moving the pivot point height changes the way the rocker interacts with the valve tip, AND changes the lifter preload.

Pushrod length is less-critical when the valvetrain adjustment is accomplished with some other means besides moving the pivot point of the rocker up or down. In this case, pushrod length adjusts lifter preload only--and most lifters have lots of available travel. The rocker-to-valve-tip interaction is engineered-into the assembly and doesn't change with pushrod length.

Shimming the rocker pedestal is done...but IF (big IF) the geometry was engineered properly, shimming to raise the pivot, or machining the pedestal to lower the pivot does nothing good for the rocker-to-valve tip geometry, even if it does adjust the lifter preload.

 

[rebelyell]

Likely, if the OEM or OEM-replacement lifters are installed. Not guaranteed, because limited travel lifters are available, and "could" have been installed sometime in the decades since these engines were built. The less travel the lifter plunger has, the more critical the pushrod length.


Not with a non-adjustable valvetrain unless a person was completely nuts, willing to install a custom pushrod on each individual lifter/rocker, and willing to re-do the pushrod length as the system wore.


Yes, and no. The farther away from "blueprint" specs the engine assembly is, the more critical pushrod length becomes...but there's a range of variance around the blueprint specs where the lifter can compensate. For example, the SBC was designed with a 9.25 deck height, and ~.020 steel-shim head gaskets. GM changed nothing in the valvetrain geometry when they went to thicker, composition head gaskets. Similarly, almost no-one would question pushrod length when the block or head decks--or both--got a skim-cut to assure flatness and surface finish, whether or not a .040 or .020 head gasket was used. Of course, things are generally less-critical on Grandma's car compared to a local dirt-track claimer engine, and more still on a Top Fuel dragster.

Pushrod length can be critical, especially if the rockers are adjustable at the pivot point like SBC, and other engine families such as W and Mk IV. Moving the pivot point height changes the way the rocker interacts with the valve tip, AND changes the lifter preload.

Pushrod length is less-critical when the valvetrain adjustment is accomplished with some other means besides moving the pivot point of the rocker up or down. In this case, pushrod length adjusts lifter preload only--and most lifters have lots of available travel. The rocker-to-valve-tip interaction is engineered-into the assembly and doesn't change with pushrod length.

Shimming the rocker pedestal is done...but IF (big IF) the geometry was engineered properly, shimming to raise the pivot, or machining the pedestal to lower the pivot does nothing good for the rocker-to-valve tip geometry, even if it does adjust the lifter preload.

Yup, I've known sbc specs & geometry for a day or two. Not news to me; so why bother ?

As stated, I have no further interest in the suggested V6 RA swap. I don't believe the concept's practical and I have no faith in it; regardless if you or others do. I'm not going to bother with it. And I sure as heck ain't going to pour T&E into chasing after anything I don't believe in. Clearly sir, You and I Disagree on this matter; so, why press it ?

While it seems You and others strongly support the concept; why don't You pursue it and share Your completion (running motor) details here (or on another engine tech forum) ?

 

[L31MaxExpress]

Yup, I've known sbc specs & geometry for a day or two. Not news to me; so why bother ?

As stated, I have no further interest in the suggested V6 RA swap. I don't believe the concept's practical and I have no faith in it; regardless if you or others do. I'm not going to bother with it. And I sure as heck ain't going to pour T&E into chasing after anything I don't believe in. Clearly sir, You and I Disagree on this matter; so, why press it ?

While it seems You and others strongly support the concept; why don't You pursue it and share Your completion (running motor) details here (or on another engine tech forum) ?

I do intend on trying the concept. A 4.3L Vortec is nothing more than a 350 Vortec with 2 cylinder chopped off. Also FWIW the last of the L31 350s put into the later model GMT800s (2003+) had the same setup in them, just impossible to find the OE rocker stands for the 350 here in the US. I opened a 2005 L31 350 up for valve cover gaskets and it had the same rocker setup as the later 4.3L. That later 350 had a lot of changes compared to the US built ones as well, like LS 4-bolt mounts and metric threads on the bellhousing and engine mounts. Those 350s were also EGR deleted, catless exhaust, used the 85mm LS MAF, and had the newer MPFI spider in them from GM. Those rockers give much of the same benifit as a Jesel shaft mount system in terms of valvetrain stability without the complexity of setting one up or the cost. Disadvantage is it is not adjustable, but I need pushrods anyway for the smaller base circle on the new cam.

 

[rebelyell]

I do intend on trying the concept. A 4.3L Vortec is nothing more than a 350 Vortec with 2 cylinder chopped off. Also FWIW the last of the L31 350s put into the later model GMT800s (2003+) had the same setup in them, just impossible to find the OE rocker stands for the 350 here in the US. I opened a 2005 L31 350 up for valve cover gaskets and it had the same rocker setup as the later 4.3L. That later 350 had a lot of changes compared to the US built ones as well, like LS 4-bolt mounts and metric threads on the bellhousing and engine mounts. Those 350s were also EGR deleted, catless exhaust, used the 85mm LS MAF, and had the newer MPFI spider in them from GM. Those rockers give much of the same benifit as a Jesel shaft mount system in terms of valvetrain stability without the complexity of setting one up or the cost. Disadvantage is it is not adjustable, but I need pushrods anyway for the smaller base circle on the new cam.

Great! Convert a conventional L31 w/conventional iron 062 or 906 L31 heads (not any oddball versions of either L31 block or L31 heads that few here will ever encounter) ... deck block at min about 0.010" or 0.025" ... mill heads at least 0.010" ... try a composite head gasket But ALSO a thin steel shim. Put it all together & beat on it ... But Tell us how many different PRs you truly had to attempt. How about build it so that it has an adjustable valvetrain too; a system that's easily And cheaply repeatable? I most certainly want to read all about it (& total $ parts & machine shop labor) ... but 'til then; no further interest here.
Good luck with your project; carry on.

 

[rebelyell]

upHi im going to cam my 1996 c1500 pickup thats got a L31 in it i was wondering if anyone knew if the current valvetrain upgrades im looking at would work and to see what builds other people have done for there cam/valvetrain. (Im already swapping to an 0411 ECU to get it retuned and am wanting an agressive but at least somewhat streetable build.)

Current Parts Im looking At
Cam- https://www.summitracing.com/parts/cca-08-423-8
Rocker Arms- https://www.summitracing.com/parts/cca-1417-16
Rocker Arm Nuts- https://www.summitracing.com/parts/cca-4604-16
Valve Springs- https://www.summitracing.com/parts/cca-26918vcs-kit
Timing Gears https://www.summitracing.com/parts/clo-9-1157

And to mr TStowell ... I apologize to you for my role in what's become a group-hijack of your thread.

 

[L31MaxExpress]

Great! Convert a conventional L31 w/conventional iron 062 or 906 L31 heads (not any oddball versions of either L31 block or L31 heads that few here will ever encounter) ... deck block at min about 0.010" or 0.025" ... mill heads at least 0.010" ... try a composite head gasket But ALSO a thin steel shim. Put it all together & beat on it ... But Tell us how many different PRs you truly had to attempt. How about build it so that it has an adjustable valvetrain too; a system that's easily And cheaply repeatable? I most certainly want to read all about it (& total $ parts & machine shop labor) ... but 'til then; no further interest here.
Good luck with your project; carry on.

You actually make a great point that is valid even for this thread. Pushrod length needs to be correct regardless if the valve train is adjustable or not. I have tools designed to accomplish this feat of re-engineering that you seem to believe is so difficult. Everyone in the world seems to be able to get a non-adjustable valvetrain to work except you. Then again adjusting a rocker arm nut on a SBC is still not correcting the wrong geometry because of the wrong pushrod length in it either. I will measure the pushrod length needed with tools I own to do it, order pushrods in the closest off the shelf 0.050" increment and it will be spot on with standard travel hydraulic lifters. I have owned a couple of setups that needed different length pushrods on the intake and exhaust as well. If you think turning a rocker nut to eliminate valvetrain slack is correcting for all those changes you mentioned correctly, I do not know what to tell you.

 

[rebelyell]

You actually make a great point that is valid even for this thread. Pushrod length needs to be correct regardless if the valve train is adjustable or not. I have tools designed to accomplish this feat of re-engineering that you seem to believe is so difficult. Everyone in the world seems to be able to get a non-adjustable valvetrain to work except you. Then again adjusting a rocker arm nut on a SBC is still not correcting the wrong geometry because of the wrong pushrod length in it either. I will measure the pushrod length needed with tools I own to do it, order pushrods in the closest off the shelf 0.050" increment and it will be spot on with standard travel hydraulic lifters. I have owned a couple of setups that needed different length pushrods on the intake and exhaust as well. If you think turning a rocker nut to eliminate valvetrain slack is correcting for all those changes you mentioned correctly, I do not know what to tell you.

Perhaps you enjoy poking a bear?
Or, just don't listen? You sir, cannot convince me; perhaps someone else can , but not you.
I'm looking forward to your completed, running motor. Although, even then I couldn't Know its "pedigree."
But again, until then I'm done. As in I really don't give a flip. If it works, maybe you author a series of videos & make a few bucks & bathe in your sycophants' admiration; either way, failure or fortune, I don't give a flip. Say what ya want, build a turkey or a trophy, ramble on or defend a doctoral thesis; I don't give a flip. I'm done with this.
Moreover, I apologize for & regret taking part in hijacking OP's thread.
Good luck with your project(s).

 

[TStowell]

And to mr TStowell ... I apologize to you for my role in what's become a group-hijack of your thread.

I dont mind at all ive learned more reading this whole thread back thru then ive learned posting my question, one last question though im going to thru with full rollers and i found a a pair of self aligning rockers that are also full rollers and was seeing what you thought of them or if should go with guide plates and normal full rollers. (Im matching the heads to accept screw in studs). I also am doing the alex parts springs and verifed that it will fit on my heads.

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[Schurkey]

I will not use aluminum roller rockers. Others may disagree.

Consider Comp Cams Pro Magnums, or Crower stainless steel rockers.

You "could" use guideplates instead of self-aligning rockers, but then you'd have to replace the pushrods, too. OEM pushrods aren't hardened, they'll be torn-up by the guideplates. You have to have hardened pushrods.