How to Choose Rocker Arms?

[duo_z]

I'm have been wondering how you go about choosing rocker arms. I'm not just talking about roller, or solid, but about ratios and such. I'm building a 289.

 

[D.Hearne]

First you need to know what heads are on it(year and casting numbers) and whether the studs have been replaced with screw in types. Stock ratio is 1.6. You can use 1.7's if the added ratio doesn't get you into spring bind territory. 1.7's add about .030 lift at the valves.

 

[duo_z]

I'm pretty sure they are the stock 289 heads. They are the same ones I pulled off of it. If they were changed before I don't know. I'm running Wiseco ProTru pistons they are flat topped with valve cuts.

 

[2+2GT]

I'm pretty sure they are the stock 289 heads. They are the same ones I pulled off of it. If they were changed before I don't know. I'm running Wiseco ProTru pistons they are flat topped with valve cuts.

Those are stone-stock late 66 heads, they type that require "rail" rockers.

 

[D.Hearne]

Those are stone-stock late 66 heads, they type that require "rail" rockers.

Those are not rail rocker heads. They've got the short valve stems and slotted pushrod guides in the holes.

 

[duo_z]

Thats good to know. My car is a 65' GT, and the block is an early 5 bolt 289. Must have been changed at one point.

 

[D.Hearne]

I read the date codes as March 66 heads. It's hard to see the pushrod slots with the camera angles, but there's something down the holes. The valve stem tops are also hard to identify as well with the camera angle. If you're going to run any cam larger than about a Comp Cam's 268H, then you'll need to replace the stock studs with screw in types. Bigger cams and the pressed in studs don't work well together. The stresses will work the studs out of the heads.

 

[D.Hearne]

I'm pretty sure they are the stock 289 heads. They are the same ones I pulled off of it.

The date code shown in this pic is 6C25, isn't it ?

 

[duo_z]

6G25 date code.

 

[D.Hearne]

6G25 would be the later rail rocker heads, but the valve stems look to be too short for those in your pics. If you do have the pre rail rocker valves, then you're definately going to need to have screw in studs and guide plates installed to run the regular non rail rockers. The stems on the rail rocker heads protrude about a quarter inch above the valve stem retainers.

 

[duo_z]

OK, I'm back on this topic. I'm getting around to needing these parts so I'm going to check it out again. Here are a couple close pics of the valve tops and push rod holes.

So with these heads is it safe to say that these:
COMP Cams K31-218-2 - COMP Cams High Energy Cam and Lifter Kits - Overview - SummitRacing.com
65-9 STOCK 289/302 ROCKER 1965-1969 - CJ Pony Parts, Inc.

Will work correctly with out modification?

 

[D.Hearne]

The cam is compatible with the stock pressed in studs, only you need to watch the compression ratio. No more than 9 to 1 with that cam, or you're going to have to run 93 octane premium fuel at a minimum. As for the rockers, if you're going to pay that much for stock rockers, I would do some looking around and find a set of (rail type)full roller rockers to work with those heads. Or at least buy a set of used stock rockers, those types just don't normally wear out.

 

[2+2GT]

Those are not rail rocker heads. They've got the short valve stems and slotted pushrod guides in the holes.

I told you they were "rail" types. The retainers were a dead giveaway, with the sloped or domed appearance.

His earlier photos were not very useful for looking at the valve tips, though, making it easy to miss.

 

[D.Hearne]

Same retainers can also be found on pre rail heads too. Those look like aftermarket retainers anyway. And with the 12 o'clock camera angle, the valve stems didn't look like rail stems. The stock pre rail retainers are different. Most of the rail retainers I've run across had the 2 pc jobs on the exhaust valves too.