Hot Rods Cast Iron Heads

Quick question guys with the Isky chrome moly pushrods what size rocker arm should I get? How do I determine the size like 1.5 or 1.6 ?

 

I always run the rocker arm ratio recommended on the cam card specifications, they have engineered the cam for that gross lift.
Then when bolting on aftermarket heads or if the block deck or the heads have been resurfaced, always measure for the correct length push rod with rocker arms you're going to run

 

I'd check your valve to piston clearance at TDC and at 10 deg BTC and after TDC. I'd rotate your piston up to those 3 positions. Take your rocker arm and valve spring off one cylinder. Let each valve sit on the piston. Put a 1" travel dial indicator on top of the each valve stem and move the valve upward to see how much travel you have before it seats. That tells you how much you can open a valve before contact occurs.

Then take the amount of cam lift and multiply it by 1.5,1.6,and 1.7 and compare that number to the measurement you got on valve movement before it hits the piston. You need to allow a certain amount of clearance when the valve is at max lift so it does not contact your piston.. Different people will tell you different amounts of clearance.
A lot depends on how high an rpm you plan to rev the engine.

You also need to measure your valve springs and see that they are capable of moving the same distance as the valve lift and still have some room before bottoming out (coil binding). Put a spring in a vise and tighten the vise till it just makes the spring bottom out. Measure the distance between the vice jaws.

Now put a retainer on a valve without any spring and pull up to seat the valve. Measure the distance between the valve seat and the retainer.

The valve seat to retainer measurement minus the bottomed out spring measurement will tell you how much your springs are capable of moving before bottoming out. That measurement is the absolute maximum you want your valve to move.

So you have to find what factor above limits your valve movement and select a rocker ratio that works slightly less than the limit.

If you can use a 1.6, it should help performance better than a 1.5. Get something with a roller tip or full roller if you are going to spend any money.

 

Those numbers relate to the ratio, size is generally a diameter callout along with a length dimension.
As with any part, the intended use and/or combination of components will dictate the ratio, oem rocker ratio is 1.5 for sbc, for a purely street car there's no need for anything else, besides the mfg suggestion, many engine builders may choose ratios, sometimes intake only, sometimes exhaust only, sometimes both.

 

Since both of my engines have guide plates it helps eliminate most sideways pressure. The full roller rockers are very expensive, but stamped steel roller tip rockers are very reasonably priced, and not that much more than stock type quality stamped non roller tip rockers. For the small extra of roller tips I'm happy to pay the price. I'm not a fan of full rollers just because of the extra needle bearings that I think add to another place they might fail. Plus the stamped roller tip rockers fit under stock valve covers, which is a nice bonus.

 

What you said are some good points. The sideways pressure I was referring to is from the perpendicular motion as a rocker arm moves (drags or rolls) across the top of the valve stem, which occurs in all OHV engines . As the rocker pushes down it also pushes the valve stem against the side of the guide (side of the vehicle).

You are referring to sideways as any motion due to erratic movement (front or back in relation to the vehicle which is still a sideways movement as far as the valve guide is concerned) . Just wanted to clear that up, as both are considerations depending on the components selected.

 

I appreciate all the information on here guys. I really enjoying learning as I work through this build. When I get the heads back I will post a quick picture of them.

 

Yes, that's why I like roller tip rockers as they don't drag across the top of the valve stem. Less friction, less wear, and a slight HP gain.

 

Super Stock heads must check at factory port and chamber volumes for the engine/horsepower claimed. It takes hours and hours of welding and epoxy work to build a competitive set of heads that will check legal. Very different thing than what is being discussed here.

 

Speedway double humps vs oe. I had to grind slightly in the exhaust manifolds to clear the valve cover. It's back up and running which was the goal and looks close enough to how I started

 

Speedway double humps vs oe. I had to grind slightly in the exhaust manifolds to clear the valve cover. It's back up and running which was the goal and looks close enough to how I started.
I never knew they made a replica style head to the OE Camel hump. Would you happen to have a picture of your alternator side set up since these do not have any holes drilled? Might want to add these to my SBC 283 one day.

 

No good pics. It is 66, ,67 Chevy truck manifolds and brackets 1967 manifold in my case. Mounts to the front of the manifold, not the side, with a bracket that bolts to the manifold and water pump for the bottom bolt

 

No good pics. It is 66, ,67 Chevy truck manifolds and brackets 1967 manifold in my case. Mounts to the front of the manifold, not the side, with a bracket that bolts to the manifold and water pump for the bottom bolt View attachment 6317231 [/QUOTE]
I see that, thanks for the details on the manifolds and bracket.

 

i still run a set of pro top line alloy sbc heads they were bought out by rhs but i am pretty sure still made in Australia or new Zeeland

 

here are a couple of pictures of my alternator setup in my '40. It uses a stock Chevy mount and adjustment strap. I welded a part onto the drivers side header ( which I built).



These 2 pieces can be used with manifolds or headers , but do not move the alt. up enough to clear the valve cover. They were used a lot in the '60s and maybe '70s. They are not very elegant but could be modified pretty easily.

 

Did you make the 60's style as well? I like those. With my SBC283 the valve covers do hit the back of my alternator.
The cast iron heads that are in the machine shop are a set off a 66" 289 block with the slotted push rod holes.

 

He is using the same Chevy truck lower bracket as I have, with a homemade bracket to support the back with headers. Very nice. I will copy this when I put my headers on, as it provides superior support over the side mount header Mr Gasket bracket

 

Understood, thanks.

 

It's been stroked to 308...