From Turbomania Book on Eagle Hydraulic Followers for Type 1
A hydraulic lifter and camshaft combination will provide the engine builder with quiet smooth operation. Regardless of ehat you have been lead to believe, your performance won't necessarily suffer when you install a set of hydraulic lifters. At engine speeds up to 7000rpm hydraulic lifters are actualy more effective than a set of solid lifters.
The reason behind this is simple. Hydraulic lifters run with zero lash. If a hydraulic cam provides .390 lift, you get .390 lift plus the ratio of the rocker arms. A mechanic lifter and cam combination offering .390 will not produce .390 lift in a VW Aircooled engine because of the required valve lash and additional heat growth of the barrels. An initial .390 lift in mechanical lifter/cam installation quickly shrinks to about .360 as the engine warms up.
The duration and valve timing in a hydraulic lifter set up remain constant
because of zero lash feature. The duration in a mechanical installation can drop as much as 20 degrees when the engine reaches operating tempreture. Again the loss is due to engine growth due to temperature.
I know that Aircooled engines have more growth.
I know there is an issue if there is air in the lifter and as the lifters are flat this can be a problem. Bleeding them on insatllation is tricky see
Boston Bobs web site
http://www.bostonengine.com/articles/hydraulicll.htm
also interesting is flow rates on a wasserboxer head interesting on the flow of increased lift due to ratio rockers. Any body any thoughts 1.25:1
or 1.4:1 do I need shorter push rods
The flow bench measures cubic feet of air moving threw each port at a given valve lift. This test was done with a pair of stock AMC heads with varying degrees of porting work.
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Stage 1 Stock Intake Port
Stage 2 Intake Port After Porting
Stage 3 Big Valve Intake Port
Stage 1a Stock Exhaust Port
Stage 2a Exhaust Port After Porting
Stage 3a Big Valve Exhaust Port
Lift Stage 1 Stage2 Stage 3 Stage 1a Stage 2a Stage 3a
.050 24.8 33.0 34.8 18.6 26.4 29.6
.100 47.1 52.2 57.3 36.4 44.1 46.2
.200 89.6 91.4 108.4 68.0 76.2 85.4
.250 115.4 116.7 132.8 83.3 89.5 103.9
.300 125.3 128.5 145.8 95.5 102.7 116.3
.350 137.6 145.3 171.4 104.7 114.4 123.9
.400 * 144.9 158.8 181.3 113.0 125.1 132.5
.450 * 147.8 174.1 186.0 118.6 132.1 137.9
.500 * 154.6 179.0 190.6 121.6 137.5 141.2
*Non-Stock Ratio Rockers