hey guys. i was just whondering if any of you guys knew stock rocker arm ratio for a 90 chevy z71 with a 305? i might put some roler rockers on it just to free up some power because the truck is slow. good ideah bad ideah?

anyways thanks for your help and i look forward to posing more. and check out some of the pictures in my subby and tell me what you think.

 

1.5 Here is a calculator you can use to see what the lift would be if you changed out to 1.6 rocker arms.

http://www.thedirtforum.com/rockercalc.htm

 

hmm... are you sure thats right? i put in the cam and rockers for my big block and it is only saying .578 or somthing like that? is that valve lift? because i calculated m valve lift to be .876 (510 *1.7) that should be how far my valves open right? so whats the .587?

 

All pre GenIII small block chevys came with 1.5 ratio rockers - AFAIK. Big blocks do not have the same specs.

Where did you get the .510 value and where did you get the .578 value?

 

ok i have a .510 lift cam in m big block with 1.7:1 roler rockers, my question was am i getting 867 valve depression or .578 from http://www.thedirtforum.com/rockercalc.htm the link badmofo sent me.

this question was unrelated with my origional question of do you think it would be smart to put stock ratio roler rockers in my stock truck just to free up some power?

but anyways i am getting .867 valve depression in my 454 right?

 

NO.........let me explain

A .510" lift cam is .510" of VALVE lift (or depression.....depending on how you look at it) with STOCK rockers.....a cam manufacturer NEVER quotes lobe lift in the specs, it is ALWAYS valve lift. To calculate actual lobe lift divide advertised valve lift by rocker ratio: .510"/1.7=.300" lobe lift, conversely you can find valve lift by multiplying actual lobe lift by rocker ratio: .300"x1.7=.510" valve lift. if you were to replace the stock 1.7 ratio rockers with 1.8 ration ones your actual valve lift would increase to .540" : .300"x1.8=.540" valve lift

And for your original question.....a roller rocker will always free up horsepower due to a decrease in friction, whether that small power increase is worth the price of the rockers is another question entirely

 

Yeah, what Yelo said.

Always look at the cam spec sheet (always provided with a camshaft). It should tell you what the lobe lift and gross valve lift (with specified rocker ratio) measurements. And, of course, the gross valve lift is the lobe lift * rocker ratio.

 

i understand now thanks alot guys

 

No problem

BTW....that Camp 212º/218º is a REALLY little cam in a big block, my old 454 ran a 248º/256º .635/.635 111lsa....and it idled pretty good !!!, cubes eat cams so the bigger the motor the bigger the cam is necessary to make the most power......yo're probably giving up 50hp with that cam

 

yeah i know its small duration but i wanted it that way because i will be getting a 6-71 for it and i flow tested the heads and thats what the numbers are telling me it wants for 7 pounds of boost. i am kinda in the screw it see how it goes now if it sucks rip it apart and spend another 300 on a cam no big deal mood.