Explain moving the pushrod holes on a Smallblock

I was watching an episode of Enginemasters. Dulcich ported some heads and moved the pushrods to make room for porting. They didn’t do any detailed shots of what he did. Left me confused. So if he moved the pushrod holes, filled them in, and redrilled..... I’m confused. So does this mean you either need to weld or fill the ports where the old pushrod location was? Also, does this just put the pushrod at a funky angle now too? Thanks for the education.

Many heads have the intake port ported enough to go through the wall on the pushrod side enough that the engine builder has to use a tube, half or quarter of the tube, epoxied into the head for the pushrod to clear using a offset intake rocker arm and a offset roller lifter cup moving the pushrod over to clear the new intake port.
Not for the faint hearted or novice unless their willing to take the time, money and effort to do that type of modification properly to work correctly

For sure it’s over my head. I was just trying to understand what they did for pushrod angle. That’s definitely not an easy mod it seems for the novice.

Read up on the 1970 340 6-pak engine used in Challenger T/A and AAR Cudas. This was done on the factory heads to allow porting and they used offset rockers. This led to the development of aftermarket W-2 heads which had the intake pushrods moved a bit more. Bob Mullin did a lot of development work with Chrysler on these designs.

I can't help a lot but here's a set I started. Without moving the pushrod on a set of small block Edelbrock heads I can get them from 243 cfm out of the box up to 318 cfm just by tubing 2 head bolt holes and 4 intake pushrod holes on each head. VERY simple procedure. I always wanted to see how much more cfm I could get out of them by pushing the pushrod over so I put aluminum rod into the pushrod hole and started grinding to open them up. The first test was kinda disappointing but when I get time I will get back on them. Harlan Sharp make me up a set of .350 intake rockers so when I find its "happy spot" I will redrill the pushrod holes.


Untitled by John Cadamore, on Flickr


Untitled by John Cadamore, on Flickr


Untitled by John Cadamore, on Flickr

For those who look at offset rockers with suspicion: look at the Chrysler 331 etc. - made the same way since 1951.
Almost every pushrod British bike engine has huge offset.

I liked that episode. You can get that cylinder head mod done from Indy. INDY also claims some disputed numbers from there CNC port work.

What is done is the pushrod tube is filled in. Steve did it with aluminum shavings and epoxy. Lay the head on a flat surface, mix epoxy, pour & fill into the pushrod hole, let it sit and become soild. Port when hardened & ready. If can also be done with an aluminum rod with an interference fit. I have read some guy did it in this way. He also used a, forgive the lack of a proper name or term, lock tight to help keep the aluminum in place. At this point the port can now be ported wider.

Since the pushrod has to be moved over to activate the rocker arm, the rocker arm itself has to be made offset. So, yes, angles change. But this has been done by most every manufacturer of engines. Here the offset rocker arms or custom offset units are strong enough for most any application. Of course material of the arm maybe the limit as some are better than others under a heavy spring load.

Pushrod angles in the small block are far from perfect. You will loose some lift with the stock angles. If the geometry is off at the rocker, you loose more lift. The MP 48* race block fixes this issue with straightening out the pushrods. But there is still an angle on a left to right as looking at it from the side of the engine.

All of this negitive pushrod angle is still worth the opening of the port. Of course, how far the head can go is the limitation. But the limitation level has been removed for a higher level of possible air flow. And that of course is (potential) power!

The amount of offset has to be carefully calculated for not only clearance but to get the pushrod as straight as possible in the right position. Which more than likely will require adjusting the height of the fulcrum point of the rocker arm for good rocker tip to valve stem workings.

Once all of this is sorted out, even on a stock iron head, X. J, 308, etc... or the factory hp head like the ‘70-340 TA/AAR 6 pack head, it should be a kick ass head for what ever head you start with vs what you end up with. As mentioned earlier, the development of the W2 & W5 Head do not even have a pushrod hole to deal with and require the offset rocker to even operate the head. (Expensive! But worth it IMO when racing.)

I feel the work shown on Engine Masters is a bit adventurous for most guys at home, IF I felt confident on my head porting skills to start with, I’d give it a whirl. It is not a lot of work on top of porting the head. It just the whole job is a lot.

Refer to a pro head porter for more information and possible worth and cost for this mod. If such a mod is worth the cost and added performance over a ported stock casting of what ever head your looking at. A well ported Edelbrock Head does very well. So it may not pay at your level. That’s for you to figure out and I’d do it with a long talk with a pro head porter.
At least “Other Options” can be discussed that may be better. Check your dollars and sense!

IMO, if you're using OE heads, you'd have be getting really serious to warrant needing the offset rockers.

Exactly. If you are going to use an offset rocker might as well go W-2 and be done.

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Exactly. If you are going to use an offset rocker might as well go W-2 and be done. [/quote]
If your trying to make more power start with the best head you can get
Unless the rules you race with say you have to use a stock OEM head

start with the best head you can get
This^^^

I remember T/A style heads had a 0.550" offset rocker arm, a lot of work these days for little return. Unless you were racing a class that specified a factory head had to be run, not a lot of point to doing it really.
I have a truck headed 360, I did toy with the idea of doing it with those and making my own offset arms. But only because I like making that kind of stuff and can do it all myself. Expensive exercise if someone is doing it for me.

The main thing to remember when working with stock heads. The pinch isn’t the main issue that needs addressed