Rocker Arm Ratio

[Gator]

Hey guys I have a quick question; I am replacing all my valve springs and my flat tappet hyd shaft mounted rocker arms. I noticed that there are two rocker arm ratio's one a 1.5 and a 1.6 What do they mean by this? My engine is a 71 340 with .509 purple cam
Thanx

 

[Dart Sport 360]

That ratio is the multiplier for your calculated lift. Its based off the length and geometry of the rocker. Your .509 lift cam is calculated with the stock 1.5 rockers. Your lobe height would be .339" (.509"/1.5=.339")... if you change to a 1.6 rocker your lift would be .542" (.339"x1.6=.542")

That's what I always figured it to be anyway... you would need to check for clearances for sure.

Thanks

 

[deadly dart]

If you have enough clearance between the valves and piston, and enoughspring travel to avoid coil bind, and enough clearance between the bottom of the valve spring retainer and the top of the valve guide, then by all means use the higher rocker ratio. It is worth more power without the negatives of a higher duration cam.

 

[Dart Sport 360]

Yes deadly is right.... I went threw this last winter... I wanted to buy new rockers and yes, more lift is a good thing.... problem is the only way to check is to buy the 1.6's and take the head off and test fit everything.... if my valve hit the piston, or there were other clearance issues, then I was into a bigger mess than I wanted to risk. I bought the 1.5's and stuck with what I knew worked. If the motor had already been out of the car and I could maybe borrow a 1.6 rocker for test fitting than I would have went that way....

 

[Gator]

Well after reading this I now understand the ratio dif and since my engine is still in my car with no plans of it coming out I guess I'll go with the 1.5 ratio... Thanx guys....