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Old 04-10-2012, 12:56 AM
Dannyringo Dannyringo is offline
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Quote:
Originally Posted by oldbogie
This has been coming for a long time, it is the reason that the OEMs started switching to roller cams in the mid 1980's and finished up by 1996.

For many years an under the radar agreement left conventional levels of ZDDP in the 15-40, 20-40 and 20-50 weight oils especially those marked for Diesel engines. But now 25 years after the start of roller tappet conversions, that's changing.

Actually modern F/T cams and tappets are being treated to various surface hardening efforts and really aren't suffering failure rates any worse that pre roller history. GM and other engines that didn't use a thrust plate to retain the cam's fore and aft movements clearly suffer worse than engines that positively prevented movements. GM was repeatably sued for cam wear issues clear back to the 1960's and 70's so this isn't anything new. I started using a thrust button in regular flat tappet builds 35-40 years ago and the lobe/lifter failure rate went to zero.

From a spring stand point you're somewhat damned if you don't go to a stiffer spring and damned if you do. A soft spring lets the valve train bounce either from spring harmonics or slight over revving which bangs the lifter into the lobe. A stiff spring stops this but places a higher load on the lobe to lifter interface all the time. I think a 100 pound spring with the valve closed isn't enough. For a mild cam I like to see something more like 120-130 with a damper. Even for a mild engine I like to see a spring with a flat wound damper as this soaks up any random harmonics in the spring without having to use excessive spring pressure to shove these events above the usual rev range. You just have to crowd the advantages on your side when doing a build.

Obviously converting a non roller block to a roller is a time consuming and expensive undertaking. But with the availability of roller blocks with roller cams or of blocks that are machined for roller cams though may use a flat tappet (like GM trucks from 1985 to 1995) that include the machined provisions for a roller cam, there really isn't any excuse to fight the flat tappet wars unless you're building a class race engine that dictates a flat tappet by rule.

Bogie
Hi Bogie:
The springs are Comp Cams 981 springs and they are 1.250S = 110# @ 1.700 / .520 max with 370#spring rate...And they do have a damper...
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