Broncobowsher
Total hack
- Joined
- Jun 4, 2002
- Messages
- 35,048
What aluminum heads?
What roller rockers?
What are the specs on the valve springs as installed?
Years ago I had a shop redo a set of heads. Hung an exhaust valve in 30 minutes. That was fixed. Withen a year...
Hung another exhaust valve, had it fixed
Hung another exhaust valve on the other head, pulled both heads and had all the exhaust valves reworked.
Hung an intake valve, had it fixed and had the shop check all the intake valves. Fine after that. The initial setup was wrong and I kept chasing hung valves until I had ALL of them reworked. Stock cam and springs, never lost any lobes.
I am courious about the combonation of parts. Me thinks you have too much spring pressure. Fine for race, not so fine for street. Add in high ratio rockers and even more stress on the lobes.
Why 1.7 rockers are bad on cam lobes... (simplified math to easier follow along)
Lets say you have 200# of open spring pressure with 1.6 rockers. That is 320# on the lobe (ignoring inertia at speed).
Now try 1.7 rockers. Valve opens a little further, that raises the opened spring force a little, call it 220# (estimated). That has 1.7 times the force back on the lifter so 374# on the lobe.
Start stacking a little here and a little there and it can ballon into a failure that no single part would have caused. But as a whole it can't last.
What roller rockers?
What are the specs on the valve springs as installed?
Years ago I had a shop redo a set of heads. Hung an exhaust valve in 30 minutes. That was fixed. Withen a year...
Hung another exhaust valve, had it fixed
Hung another exhaust valve on the other head, pulled both heads and had all the exhaust valves reworked.
Hung an intake valve, had it fixed and had the shop check all the intake valves. Fine after that. The initial setup was wrong and I kept chasing hung valves until I had ALL of them reworked. Stock cam and springs, never lost any lobes.
I am courious about the combonation of parts. Me thinks you have too much spring pressure. Fine for race, not so fine for street. Add in high ratio rockers and even more stress on the lobes.
Why 1.7 rockers are bad on cam lobes... (simplified math to easier follow along)
Lets say you have 200# of open spring pressure with 1.6 rockers. That is 320# on the lobe (ignoring inertia at speed).
Now try 1.7 rockers. Valve opens a little further, that raises the opened spring force a little, call it 220# (estimated). That has 1.7 times the force back on the lifter so 374# on the lobe.
Start stacking a little here and a little there and it can ballon into a failure that no single part would have caused. But as a whole it can't last.