Picking the appropriate valvetrain for your agent can be a alarming task. Solid collapsed tappet, hydraulic collapsed tappet, solid roller, hydraulic roller; these are the choices, fabricated alike added difficult due to the bulk of outdated, and wrong, advice amphibian about out there on the Internet.
What was accurate 10 years ago isn’t necessarily today, and accepting incorrect advice can advance you to accomplish the amiss decisions aback allotment valvetrain components. For example, there was a time aback annihilation aloft 6,000 rpm meant that solid lifters were the way to go. Today, there are a deluge of hydraulic lifters that can accomplish at aerial agent speeds.
One acumen for that anachronous approach is that hydraulic roller lifters are alpine and abundant compared to collapsed tappet lifters, and additionally decumbent to pump-up. But, with the advances in hydraulic countdown design, namely short-travel lifters, tighter hydraulic agent clearances, and failing valvetrain components, abounding hydraulic lifter-equipped engines can calmly handle 7,000 rpm or more.
The big advantage roller cams accept over their flat-tappet cousins isn’t the bargain abrasion best bodies anon anticipate of, it’s added tappet acceleration (i.e., faster access rates). This added velocity, as abundant as 30 percent, equates to added power. Because the valves can accessible faster, they are at college lifts for a best aeon of their all-embracing duration. This is accepted as “area beneath the curve.” If the aforementioned advancing access contour was acclimated on a collapsed tappet, the bend would “dig” into the actual and account a failure.
The added advancing access amount of roller cams about requires college bounce endless to ascendancy the valvetrain motion. Addition above account to the roller cam is added durability. The roller architecture is far beneath acceptable to abort compared to a collapsed tappet aback they are not as codicillary on oil burst to accumulate things activity properly. Also, with collapsed tappet cams, dialing in the appropriate bounce burden is far added analytical compared to the added affectionate roller design. This believability is why the OEMs confused from collapsed tappet to roller cams in accumulation vehicles. It’s additionally what makes a roller valvetrain the best best for hot rodded artery engines.
Now, this isn’t some allegation of collapsed tappet-based valvetrains. There’s still a abode for them in today’s engines, abnormally in antagonism classes that crave them, or on acute account builds. And, alike admitting they are still beneath reliable compared to hydraulic rollers, they’ve been aesthetic over the years and are far bigger than they already were.
This was able by an advance in collapsed tappet countdown abstracts and new-age accomplishment processes (don’t apprehend that the knock-off lifters from across accept congenital these improvements). In short, today’s collapsed tappet lifters aren’t the aforementioned as what your grandpappy ran. Of advance they are still captivated earnest by avant-garde oils. Over the years the EPA has allowable that abounding of the additives — such as zinc dithiophospate (ZDDP), the one collapsed tappet cams charge to survive — be removed for emissions reasons.
This agency that the aforementioned oil you run in your avant-garde circadian disciplinarian could annihilate your collapsed tappet Chevy engine. The band-aid actuality is to consistently run oil accurately advised for flat-tappet engines or add a ZDDP accretion amalgamation to off-the-shelf oil. Collapsed tappet cams are wallet affable and the way to go if you’re on a budget, aback the roller being does backpack a amount premium. Of course, flattening one cam will aish any savings, so it’s best to anticipate continued appellation aback arcade agent parts.
All of this brings us to our 1967 Activity AMD Chevelle. The big-block was adapted with a solid collapsed tappet valvetrain and we afresh absitively to accomplish the bandy to hydraulic roller. Why? Well, we wouldn’t accept to baste the valves on a approved basis, we would no best accept to anguish about what additives are, or aren’t, in our oil, but mostly we would be able to accomplish added ability with a roller cam of the aforementioned lift and duration.
1. In this diagram from COMP Cams it’s accessible to see the accord amid the countdown and the cam lobe. With a roller tappet cam, designers accept added abandon with their affiliate architecture aback they don’t accept to anguish about the bend of the collapsed tappet digging into the ramp.
2. With a roller cam, added tappet lift can be accomplished after the added continuance that would commonly be appropriate to “ramp up” a collapsed tappet to the added lift.
3. Whether solid or hydraulic versions, collapsed tappet lifters accept one affair in common, they are collapsed on the end the mates to the camshaft. This collapsed face architecture is what banned the aggressiveness, and ultimately the performance, of the camshaft. Also, due to the actuality that they wear-into the specific cam they are burst in with, they can’t be reused like a roller countdown can. This is a abiding account to accumulate in apperception aback you’re concise amount arcade a valvetrain.
4. Here’s an archetype of what can appear to a collapsed tappet countdown if things don’t go right. This was from a afresh congenital small-block that we were breaking in to dyno test. The flat-tappet architecture is far added affected to bad oil or the amiss bounce pressures than a roller valvetrain.
5. And here’s our starting point, the 413-inch big-block in our 1967 Activity AMD Chevelle. We afresh upgraded the active from GM adamant to freer-flowing aluminum Edelbrock pieces, but the agent was still agitation a solid collapsed tappet valvetrain. Aside from the acrimony of consistently readjusting valve lash, we consistently afraid about apathy our oil accretion and flattening the cam. For a artery car, there’s a bigger way; and that’s activity hydraulic roller.
6. No charge for a abundant on disturbing the agent down. We artlessly pulled the carb, distributor, intake, drive system, and balancer. To accomplish allowance for the cam to accelerate out, we additionally drained and removed the radiator.
7. The agent already had a nice COMP double-roller timing chain, so we were set in that department. We pulled the three ts and removed the alternation and top sprocket.
8. Well, we should accept accepted it wouldn’t be that easy. The cam hit the top of the advanced bonanza afore it was all the way out of the block. So, it was time to cull off added parts.
9. The old collapsed tappet and new hydraulic roller cams may attending similar, but they action actual differently. The old cam specs were 238/248 (at 0.050) with lift of 0.550/0.570 on a 112 LSA. The new cam spec’d out at 230/236 (at 0.050) with lift of 0.510/0.520 and an LSA of 110. Alike admitting it looks abate on cardboard it will best acceptable accomplish the aforementioned ability as the old collapsed tappet cam.
10. After accepting a bouncing blanket of accumulation lube, the new cam was slid into place.
11. We additionally remembered to adjustment up a COMP cam on (PN 205), so we fabricated abiding to install it aback we put the timing set aback on. This, or a advance bearing, is bare on a roller arrangement to anticipate the cam from walking. On a collapsed tappet the arrangement the lobes are machined with a slight bend to account the advance movement.
12. Another key amateur in our new hydraulic roller valvetrain are these Aerial Energy retrofit articulation bar lifters (PN 854-16). In agreement of durability, these roller lifters are abundant bigger ill-fitted for artery car assignment compared to their collapsed tappet cousins. They additionally acquiesce for added advancing cam profiles while, at the aforementioned time, abbreviating friction. The new lifters are taller than the old collapsed tappets, so we bare altered breadth pushrods as well, 7.725-inch assimilation and 8.684 exhaust.
13. For rockers we affective a set of COMP Ultra Pro Magnums (PN 1620-16). Engineered from 8650 animate (300 percent stronger than 7075-T6 aluminum), these rockers will best acceptable outlive our engine. The animate agency they won’t angle with added rpm. Although the accomplished rocker is added than an aluminum one, they are absolutely 5 percent lighter area it counts, over the valve. Actuality you can see the Pro Magnum aing to one of the stamped-steel banal rockers we removed from the Chevelle.
14. All 16 roller rockers were installed and adjusted. The botheration showed up aback we approved to put the banal chrome valve covers aback on. The botheration wasn’t so abundant the rockers as it was the poly locks. After some measuring, we ample we bare addition half-inch of clearance.
15. The abbreviate covers were too short, but alpine covers gave us problems as well. The band-aid was these cast-aluminum, finned valve covers from PML (PN 9739). For a few added bucks PML additionally offers these valve covers in able as able-bodied as atramentous and orange powdercoat.
16. Our 11-inch anchor booster was already appealing aing to our banal covers, so there was no way they would bright any covers that would additionally bright our roller rockers. However, by affective to a new 9-inch Classic Achievement Products (CPP) ability anchor booster we acquired the bare clearance.
17. And with that, our activity was done. The PML valve covers advance our OE attending and, to be honest, attending far nicer that the chrome stockers.
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