Do the plugs look over timed? I spray 300 on m5 in a 632 conventional headed motor at 29 degrees of timing and havent taken head gaskets out yet. Compression is at 15.0. When checking timing, do you only check it at idle, or do you rev the engine up? I believe i would be checking the timing from idle to atleast 3500 rpm to make sure the timing isnt moving.

just more thoughts,
fuel distribution
too much timing ?
compression higher than expexted due to small chambers
and lastly change bottom part of grid(if thats the ign)
is it always same spot when it blows

It’s carburetor on alcohol. Belt drive pump with tank up front. Compression may be higher, I haven’t cc the heads. It doesn’t blow in same direction every time. First time both heads blew out up towards the intake right where the missing inner bolts would go. Added inner bolts this time it blew between #6 and #8. Left side was fine. No grid but a msd hvc6 box and coil. I’m leaning toward too much timing, but when my friend got the truck timing was at 36 so i don’t know why it’s a problem now.

Here's my 2 cents worth, on alcohol it's hard to get an engine to detonate, and 36° should not be too high, I run as much compression as I can in 555, 565,572, and 588 and never had any head gasket issues, but I have always used studs and the extra studs under intake. I have found that MSD is not real good with the dial type timing lights. What I would do is to make sure the dowel pins aren't holding the head up, or the bolts are bottoming out in the block before it completely torques the head. Plus I have always used MLS gaskets. I would also CC a head to see where it is, if it's been milled too much the dowel will bottom out, good luck!

is it hurting rod bearings any at all when gasket blows

It hasn’t hurt the bearings yet. Hope it doesn’t.

quote:

It hasn’t hurt the bearings yet. Hope it doesn’t.

likely not detonation