Rocker Ratios...variances
10-06-2015, 06:11 AM
#21
Registered
iTrader: (1)
It wasn't too long ago, BBC's with HFT and HR ran into valvetrain instability in the upper 5k rpm region. If it was spring related, people added more spring psi, but then the lifters ran into stability issues. Leaving you kind of stranded at the same rpm point.
Enter the 1.8 rocker 'less durable' remarks. The 1.8's seemed to make this rpm 'fuss' point happen 200-400 rpm earlier.
Anyway, today's day and age gives us lifters with better internal clearances and valving where the lifters can sustain a higher rpm. Better spring quality with lower weight, has also let us get past this point.
So.....if you have the right valvetrain pieces in place, you can up the rocker ratio ..
Enter the 1.8 rocker 'less durable' remarks. The 1.8's seemed to make this rpm 'fuss' point happen 200-400 rpm earlier.
Anyway, today's day and age gives us lifters with better internal clearances and valving where the lifters can sustain a higher rpm. Better spring quality with lower weight, has also let us get past this point.
So.....if you have the right valvetrain pieces in place, you can up the rocker ratio ..
10-06-2015, 09:06 AM
#23
Registered
iTrader: (1)
10-06-2015, 09:46 AM
#25
10-06-2015, 01:17 PM
#26
I can attest, that there is a significant difference, in the geometry of a Crane Gold, Scorpion, and older style Comp Steel rocker when studied back to back on icdedppls engines, doing valvetrain geometry checks. The sweep patterns, and roller tip placement varied quite a bit between the 3, when setting the rockers up using the mid-lift method.
10-06-2015, 01:18 PM
#27
The first thing anyone should learn in any statistics class is... "You can make the numbers look any way you want"
If you consider 1 pull on the dyno a test (which it should be) and you do 30-40 pulls/day it would get lower. Also, if that is your daily job/passion it is more reasonable.
If you consider 1 pull on the dyno a test (which it should be) and you do 30-40 pulls/day it would get lower. Also, if that is your daily job/passion it is more reasonable.
10-06-2015, 02:31 PM
#28
Registered
iTrader: (1)
Performance 540cid Marine I/O
How would this work:
Custom Spec'd / Ground by LSM
Intake Duration at .050" = 226°
Exhaust Duration at .050" = 228°
Lobe Lift Intake = .300". With 1.7 Rockers = .510"
Lobe Lift Exhaust = .300" . With 1.7 rockers = .510"
Events at .050"
Intke Opens : -1° BTDC
Intake Closes 47° ABDC
Exhaust Opens 48° BBDC
Exhaust Closes 0° ATDC
ICL = 114° ECL = 114°
LCA 114°
Overlap -1°
How would this work:
Custom Spec'd / Ground by LSM
Intake Duration at .050" = 226°
Exhaust Duration at .050" = 228°
Lobe Lift Intake = .300". With 1.7 Rockers = .510"
Lobe Lift Exhaust = .300" . With 1.7 rockers = .510"
Events at .050"
Intke Opens : -1° BTDC
Intake Closes 47° ABDC
Exhaust Opens 48° BBDC
Exhaust Closes 0° ATDC
ICL = 114° ECL = 114°
LCA 114°
Overlap -1°
10-06-2015, 02:56 PM
#29
Registered
What ratio works best with a 3/4 race cam? 1.275's or 1.35's? 
10-06-2015, 03:12 PM
#30
Registered
iTrader: (1)
3/4 Race 1.7's would be 1.275's.
3/4 Race 1.8's would be 1.35's.
They do make 1.6's for the big block, so maybe this is a better bet for a 3/4 race cam......since 1.7's can be considered full race.
3/4 Race 1.8's would be 1.35's.
They do make 1.6's for the big block, so maybe this is a better bet for a 3/4 race cam......since 1.7's can be considered full race.
