How Does Rocker Ratio Affect Lca?

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member
How does Rocker Raito affect LCA?


To narrow it down we have a 30 over 327 461X heads with the 1.94 valve & flat top piston w/ two valve depressions. The cam has a 112 LCA - Maybe a little wide?








https://www.hotrod.com/articles/roller-rocker-ratio-test/

https://www.onallcylinders.com/2018...rease-horsepower-engine-masters-gets-answers/

https://www.hotrod.com/articles/hrdp-1305-rocker-arm-comparo/
LSAChart01.jpg

both the rocker ratio and compression will effect the results.
LSA lobe separation angle is locked into the cam when its ground and can not change, if its ground at 110,degrees or 114 degrees it will stay that figure
and
LCA lobe center angle, can be changed
if you advance the cam 4 degrees both the intake and exhaust lobe opening and closing points open and close 4 degrees earlier.
if you RETARD the cam 4 degrees both the intake and exhaust lobe opening and closing points open and close 4 degrees later.
opening sooner tends to move the whole power band lower, opening later tends to move the whole power band higher, displacement and your compression effect results,
but a change of about 4 degrees moves the power band maybe 150-200 rpm
the chart above will help you find a closer to ideal lsa in your case thats closer to a 108 lsa and ideally you'll want close to 9.6:1-10:1 on static compression,
to run pump gas with a mild cam, to maximize power
I would NOT worry much about the rocker ratio change as its going to have a rather minimal effect on power, and won't really effect the LCA change unless its a clearance related issue, much less than compression or the cam you selects timing and lift, obviously a set of 1.6:1 ratio rockers allows the engine to breath better but thats mostly the result of potential increased lift not a change in effective duration, the proposed change in rocker ratio is all but meaningless as it has almost zero effect on LCA
most factory cams are already 4 degrees advanced if installed using the DOT-TO-DOT cam timing set install method

http://garage.grumpysperformance.com/index.php?threads/the-mechanics-of-adv-ret-a-camshaft.4532/

http://garage.grumpysperformance.co...lsa-effects-your-compression-torque-dcr.1070/

http://garage.grumpysperformance.com/index.php?threads/calculating-overlap-and-lsa-or-lca-etc.480/

http://garage.grumpysperformance.co...ch-is-best-steel-or-aluminum.3124/#post-12385

http://garage.grumpysperformance.com/index.php?threads/dynamic-vs-static-compression.727/

http://garage.grumpysperformance.co...s-tool-swapping-to-1-6-1-ratio-rockers.14761/


you may have not screwed up, in the cam selection, a wider LSA tends to work better with fuel injection and provide a bit smoother idle at lower rpms,
than a cam with equal duration but a tighter lsa may provide a bit more power.
on something like a cross fire corvette, with throttle body injection,
the wider lsa is better matched.
if you had two cams with equal duration and lift the change in LSA might result in 10-12 hp change in the engine you listed with those heads at best

remember don,t confuse the terms
LSA lobe separation angle is locked into the cam when its ground and can not change, if its ground at 110,degrees or 114 degrees it will stay that figure
and
LCA lobe center angle, can be changed
 
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