# rocker arm size (does it matter)



## deanhickey (Apr 6, 2015)

Now that my engine rebuild is complete I am thinking of how to get more out of it. I was thinking of increasing the rocker arm ratio. I kept the original size 1.5:1. the cam is a .068 grind flat tappet, bored and stocked to 462 cubes. I probably went a little mild on the cam, but it has great street manners (purrs like a kitten). what would be the pros and cons of a increase to 1.6:1. I would gain some lift but what about the knock on effects? I probably have too much time on my hands thinking about this. LOL
Thanks,
Dean


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## Old Man Taylor (May 9, 2011)

It depends on the heads you have. Higher ratio rockers move the ball of the pushrod into the center of the head. On many heads you must machine the top of the pushrod hole for clearance (with 1.65 rockers). Also the stock Pontiac heads don't flow well above 0.400", which is why most of their cams had that lift.


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## deanhickey (Apr 6, 2015)

Old Man Taylor said:


> It depends on the heads you have. Higher ratio rockers move the ball of the pushrod into the center of the head. On many heads you must machine the top of the pushrod hole for clearance (with 1.65 rockers). Also the stock Pontiac heads don't flow well above 0.400", which is why most of their cams had that lift.


The Heads are #16 (1968) that have been ported. Thanks for the input, you may have just saved me some money.


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## PontiacJim (Dec 29, 2012)

deanhickey said:


> The Heads are #16 (1968) that have been ported. Thanks for the input, you may have just saved me some money.


You may not have any issues with the pushrods contacting the pushrod holes near the top of the head that they pass through with the stock 5/16" dia. pushrods, but then again....... You would only know by putting the 1.6 (1.65?) on to see and look for it.

But, as pointed out by OMT, the rocker arm cup that the pushrod fits into is moved closer inward towards the rocker arm stud to get the higher ratio. This puts additional strain on the rocker arm stud and you definitely want the ARP 7/16" big block rocker arm studs and use poly locks. With bottle neck studs, the high pressures applied to the stud due to the change in geometry would most likely break a bottle neck stud (s) at some point - if you still are using them .

Raising the lift would also mean that you have to know that your present valve springs can handle the lift and have enough seat pressure that the valves don't bounce off the seats at high RPM's when they open and slam closed as the 1.65's will multiply the rate/speed at which the valve opens and closes.

Then you might want to check your pushrod geometry to make sure your pushrods will still work and place the rocker arm end on the top of the valve stem correctly.

Piston top and valve clearance should be OK, but, I would want to know for sure, so this would need to be checked.

So you can do it, but it would have been better to build the engine for the 1.65's where you could check all your clearances during assembly and have your parts installed to handle the steeper/faster action of the rocker arms, and then start with the 1.5's and play around with the 1.65's. This is what I am doing with my 455 build. Setting it up for the 1.65 roller tips, but will first go with the 1.5's for the break-in, run it for a while to get things sorted out, then play with the 1.65's to see if any noticeable changes by installing just intake side, then intake/exhaust, then just exhaust.


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## deanhickey (Apr 6, 2015)

PontiacJim said:


> You may not have any issues with the pushrods contacting the pushrod holes near the top of the head that they pass through with the stock 5/16" dia. pushrods, but then again....... You would only know by putting the 1.6 (1.65?) on to see and look for it.
> 
> But, as pointed out by OMT, the rocker arm cup that the pushrod fits into is moved closer inward towards the rocker arm stud to get the higher ratio. This puts additional strain on the rocker arm stud and you definitely want the ARP 7/16" big block rocker arm studs and use poly locks. With bottle neck studs, the high pressures applied to the stud due to the change in geometry would most likely break a bottle neck stud (s) at some point - if you still are using them .
> 
> ...


Thanks Jim. This is some offseason thinking. Considering the comments I think I will leave it as is. Back to the Old adage , if it ain't broke... maybe I will find a sacrificial Chevy to experiment on. LOL


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