The Ford Barn

ckh · 11-14-2025, 12:20 PM

After a sonic test showing uniform wall thickness, what is the maximum safe
overbore on a 35-36 block?
Thanks,
CKH

KiWinUS · 11-14-2025, 01:44 PM

I try to always have .100”. No matter what year block. Sonic checking is just a good guideline. It too can fail you.

Kurt in NJ · 11-14-2025, 06:01 PM

If it looks like the first picture in the water jacket it can have a hole at .060 like the block in the picture.—- the LB blocks have thin cylinder walls.
The second picture is a block bored to 3-3/8 and the thinnest spot is .220 ( a 59AB block with a long story and one of the cleanest water jacket I have seen)

petehoovie · 11-14-2025, 07:15 PM

Quote:

Originally Posted by Kurt in NJ

If it looks like the first picture in the water jacket it can have a hole at .060 like the block in the picture.—- the LB blocks have thin cylinder walls.
The second picture is a block bored to 3-3/8 and the thinnest spot is .220 ( a 59AB block with a long story and one of the cleanest water jacket I have seen)

ckh · 11-14-2025, 09:37 PM

Thanks for the replies. I bought this block (not an LB) some time ago. It had ben freshly

bored .060 over stock. I haven't had it sonic tested yet. Assuming there is no core shift, is

.060 over stock pushing the limit?

Bored&Stroked · 11-18-2025, 11:50 AM

Sponsored Links (Register now to hide all advertisements)

You should be fine with a .060 overbore. With that said, always have the block magged and then pressure tested. I've seen a lot of "good blocks" end up with issues after thorough testing.

richard crow · 11-19-2025, 07:58 AM

back in the day 060 was the limet after that they would tend to run hot

Flathead Fever · 11-19-2025, 02:12 PM

.060 should be fine. I had a friend that bored one .100, that was pushing the limit. I'm not sure I would want one bored that mush unless you were just going to race it.

ckh · 11-19-2025, 03:10 PM

Thanks to all for your replies. You have now given me the info I need. I bought this block several years ago and had it magged, head surfaces, pan rails etc. No cracks
anywhere. The next step will be a sonic test which I should be able to have done
locally in Las Vegas where I live. If the sonic test shows no core shift, I should be able
to pressure test it myself as finding anyone in Las Vegas to pressure test any flathead
is a loseing proposition.
Thanks again for all your help.
The Ford Barn come thru again.
CKH

11-14-2025, 12:20 PM	#1
ckh Member Join Date: Oct 2013 Posts: 31	Advice needed: 35-36 21 stud block After a sonic test showing uniform wall thickness, what is the maximum safe overbore on a 35-36 block? Thanks, CKH

11-14-2025, 01:44 PM	#2
KiWinUS Senior Member Join Date: May 2010 Location: Charlotte NC KiWi-L100 available here Posts: 3,418	Re: Advice needed: 35-36 21 stud block I try to always have .100”. No matter what year block. Sonic checking is just a good guideline. It too can fail you.

11-14-2025, 09:37 PM	#5
ckh Member Join Date: Oct 2013 Posts: 31	Re: Advice needed: 35-36 21 stud block Thanks for the replies. I bought this block (not an LB) some time ago. It had ben freshly bored .060 over stock. I haven't had it sonic tested yet. Assuming there is no core shift, is .060 over stock pushing the limit? Last edited by ckh; 11-14-2025 at 10:49 PM.

11-18-2025, 11:50 AM	#6
Bored&Stroked Senior Member Join Date: Jan 2011 Location: Central Ohio Posts: 5,906	Re: Advice needed: 35-36 21 stud block Sponsored Links (Register now to hide all advertisements) You should be fine with a .060 overbore. With that said, always have the block magged and then pressure tested. I've seen a lot of "good blocks" end up with issues after thorough testing.

11-19-2025, 07:58 AM	#7
richard crow Senior Member Join Date: May 2010 Posts: 1,908	Re: Advice needed: 35-36 21 stud block back in the day 060 was the limet after that they would tend to run hot

11-19-2025, 02:12 PM	#8
Flathead Fever Senior Member Join Date: May 2010 Location: Yucaipa, CA Posts: 1,492	Re: Advice needed: 35-36 21 stud block .060 should be fine. I had a friend that bored one .100, that was pushing the limit. I'm not sure I would want one bored that mush unless you were just going to race it.

11-19-2025, 03:10 PM	#9
ckh Member Join Date: Oct 2013 Posts: 31	Re: Advice needed: 35-36 21 stud block Thanks to all for your replies. You have now given me the info I need. I bought this block several years ago and had it magged, head surfaces, pan rails etc. No cracks anywhere. The next step will be a sonic test which I should be able to have done locally in Las Vegas where I live. If the sonic test shows no core shift, I should be able to pressure test it myself as finding anyone in Las Vegas to pressure test any flathead is a loseing proposition. Thanks again for all your help. The Ford Barn come thru again. CKH