Edy aluminum heads, Harland Sharp rockers, hydraulic roller CC cam. I did not assemble engine.
However now putting heads back together after some lifter and spring analysis.


3 bolts on each bank plus 2 studs to hold down rocker arm shafts. 3/8 th bolts 16TPI.

5 bolts are all about 1.988 inches. One is 2.22. Only 4 bolts had solid washers of .121 inches thick.

Forget which bolts and washers came from what locations.

1.99 inch bolts only give about .367 inch thread depth from entrance into alumni . I suspect assembler of engine had a issue torquing one of the bolts and used a slightly longer one. As said, I forgot what hole,,,it's been weeks since tear down.

I do not believe that screwing into aluminum with only .367 thread depth, minus .121 inch washer width sounds sufficient for 25 pounds of torque without risk of pulling threads. The bolts are 3/8ths inch,,,.367 inches. Edy calls for 25 pounds.

This may work for steel threads,,,in fact just qualifies,,,rule of thumb of having tread depth depth equal to or exceeds bolt diameter. And at that only, if leaving washer out.

My question is, how long of bolts are others using on aluminum heads,

I have some grade 8 bolts of 2.227 inches,,,,still uneasy to use on aluminum,,,particularly if one unknown hole may could already be suspect.

I have some 2.712 inch grade 8's. However they bottom out about .2 before contacting shaft hold down devices. Not certain if bolt shoulder is hitting head threads or if bolt is bottoming in thread hole. Could use washers, but wish not to.

2.5 inch bolts sound about right. Could find nowhere any info on correct bolt lengths..

I would suggest studs. That way you get full thread engagement.
I had one pull the threads out of a stage 6 head, and did a whole lot of damage. I ended up threading it to 7/16"

Edelbrock heads have heli-coils in the #1/3/5 positions.

If you can use the 2.5 bolt without it bottoming in the hole........no reason not to do it.

I like the bolt to reach down into the hole as far as possible.

Aluminum heads = rocker shaft studs. ARP has really nice studs that work. It costs more but with heavy springs you are pulling on steel rather than aluminum.

You could run a bottoming tap into any hole that is still all aluminum and see what you can use for total depth of engagement. I used grade 8 bolts that were longer, but I like the idea of studs.

No bolts just studs here many years zero issues 600+ open pressures.........

The Edelbrock heads come with studs to use in the #2/4 positions that don't have heli-coils in them.

For the OP's application, grade 5 or better bolts would be perfectly satisfactory for the 1/3/5 positions...... Just insure plenty of thread engagement.

Studs would be fine as well, I just don't think there is going to be any real "benefit" in this application.