Whats the difference between 1.5 and 1.6 ratio rocker arm and how will this effect lift and duration on a cam with 234 dura and 488 lift on intake and exhaust. flat pistons trick flow heads up to 540?

Answer 1

This is a 76 355 engine. The new heads are trick flows with 1.47 springs, 64 cc chambers and 2.02/1.6 valves. Can I use the 1.6 roller tip rockers or stick with 1.5 roller tip rockers? I don't want to lose my lower end torque for high rpm horse power. Daily driver with serious kick, only sees 1/4 mile twice a year.

if its a daily driver you dont want 1.6 rockers stock are 1.5 im running 1.52 rockers in mine gives a little more lift but dosent hurt bottom end see kmjent.com for best price on roller tip rockers these guys are great to work with

Addition to above answer:

In answer to the original question, the difference is as follows:

Your cam has .488 lift with 1.5 rocker arms.

The difference a switch from 1.5 to 1.6 rocker arms will make can be figured out by dividing .488 by the rocker arm ratio 1.5 and that will give you the lobe lift, then multiply that number times 1.6 and you'll have the lift difference at the valve between the 1.5 and 1.6 rocker arms.

In this case: .488 / 1.5 = .325 X 1.6 = .520.

So, changing from a 1.5 rocker arm to a 1.6 rocker arm will give you .032 more lift at the valve with that particular camshaft (from .488 to .520).

Changing the rocker arm ratio won't change the duration, although at any point in the valve open/close cycle it will be opened slightly more as the 1.6 rocker arm accelerates the valve open faster and closes it slower.

Example: The half lift point on a .325 cam lobe is .162, so we do the math again and see that .162 X 1.5 = .243 whereas .162 X 1.6 = .259 which is .016 more at half lift both opening and closing -- exactly half the difference of the change at full lift (.032).