Bottom-Adjusting Hydraulic Lifters
Thread Starter
Staging Lane
Joined: Dec 2001
Posts: 90
Likes: 0
From: San Clemente, CA
Bottom-Adjusting Hydraulic Lifters Bottom-Adjusting Hydraulic Lifters
Hi,
Does anybody have any experience with adjusting hydraulic lifters near the bottom of their stroke? David Vizard claims that this is worth ~20 hp on a 10.5:1 CR, 350 with a 280(seat) cam! The theory goes that the lifters are shortening up due to leakage and any aerated oil. This not only robs lift but more importantly lets the valves bounce off of the seats on the way down because the lifters are not on the low velocity ramp before the valve is at the seat. To correct this issue, he adjusts the lifters to within 0.006” (0.010” cold) of the bottom of the lifter stroke. With this adjustment, the lifter will “go solid” at high rpm and the valve will be “set down in a more controlled fashion”. He claims an increase of “between 200 to 300 RPM more before seat bounce sets in.”
This is the opposite of the Rhoads Lifter concept were the idea is the increase low speed leakage to effectively shorten the cam. Anti-pump up lifters are adjusted near the top of their stroke. This will keep them from holding the valve open after the valves begin to float or bounce on the seat but they also leak down. It seems to me that bottom-adjusting could raise the critical valvetrain speed but will pump up after lose of control. Maybe you could do both with modified lifters?
Solids anyone?
Steve
“How To Build Max Performance Chevy Small Blocks On A Budget!” by David Vizard
Published by S-A Design
Hi,
Does anybody have any experience with adjusting hydraulic lifters near the bottom of their stroke? David Vizard claims that this is worth ~20 hp on a 10.5:1 CR, 350 with a 280(seat) cam! The theory goes that the lifters are shortening up due to leakage and any aerated oil. This not only robs lift but more importantly lets the valves bounce off of the seats on the way down because the lifters are not on the low velocity ramp before the valve is at the seat. To correct this issue, he adjusts the lifters to within 0.006” (0.010” cold) of the bottom of the lifter stroke. With this adjustment, the lifter will “go solid” at high rpm and the valve will be “set down in a more controlled fashion”. He claims an increase of “between 200 to 300 RPM more before seat bounce sets in.”
This is the opposite of the Rhoads Lifter concept were the idea is the increase low speed leakage to effectively shorten the cam. Anti-pump up lifters are adjusted near the top of their stroke. This will keep them from holding the valve open after the valves begin to float or bounce on the seat but they also leak down. It seems to me that bottom-adjusting could raise the critical valvetrain speed but will pump up after lose of control. Maybe you could do both with modified lifters?
Solids anyone?
Steve
“How To Build Max Performance Chevy Small Blocks On A Budget!” by David Vizard
Published by S-A Design
Way to bring back an ancient thread...i know 
I'm about to be doing a head/cam swap and I've been interested in this very topic as well. Has anyone tested this theory in an LS1/6 and found any positive results?
I'm about to be doing a head/cam swap and I've been interested in this very topic as well. Has anyone tested this theory in an LS1/6 and found any positive results?
Roger Vinci sets the lifters deep on their setups. You might contact them to get his input. He has stated that they found more power in doing so, at least that is what I have read.
