[Ramrodd 69]

I have a Shafiroff Ultra Str 540 and am thinking of changing rockers from 1:7 to 1:8. Current roller cam specs are 262/270 [email protected], 715/715 lift and
112 lobe. What would be new #'s upgrading rockers to 1:8. Also, would I see significate HP and TQ increases. Thanks! Bob

 

[Smokey1961]

Lift would be .757

Take lift of .715 divided by 1.7 (rocker ratio) = lobe lift. Take lobe lift times 1.8 (rocker ratio) = valve lift.

Would also need to check valve to piston clearance if you change rocker ratios.

Jeff

 

[Ramrodd 69]

Lift would be .757

Take lift of .715 divided by 1.7 (rocker ratio) = lobe lift. Take lobe lift times 1.8 (rocker ratio) = valve lift.

Would also need to check valve to piston clearance if you change rocker ratios.

Does the [email protected] change or just the lift?

 

[BillyGman]

Does the [email protected] change or just the lift?[/COLOR]

Very slightly, but not enough to change the RPM range of the engine powerband. The extra power ig going to come mostly from the extra lift. How much extra? I don't know. I'm sure it would be realized on a dyno, but I wouldn't expect it to make a night and day difference if I were you.

 

[Wolfplace]

Lift would be .757

Take lift of .715 divided by 1.7 (rocker ratio) = lobe lift. Take lobe lift times 1.8 (rocker ratio) = valve lift.

Would also need to check valve to piston clearance if you change rocker ratios.

Does the [email protected] change or just the lift?

=
Yes the duration at the valve changes slightly you are making the action at the valve more aggresive.
The only thing that does not change is the seat timing assuming you compensate for the lash

 

[Tom Mobley]

Also have to check if the valvesprings are up to the increased lift. check for retainer to seal clearance.