Cylinder Wall Thickness Sonic Checked My 428 CJ Block

[dozz302]

I just finished sonic testing a 428 CJ Block. The thinnest point I found was at the bottom of one cylinder at .138". That one spot about 3/4" from the very bottom on the Minor thrust side. Very small isolated spot then the numbers started going up. All other numbers were pretty stout. I'm assuming this block could safely go .060" over? Currently standard bore. If I remember all 8 Major thrust sides (thinnest measurements) were between .185" and .235". Did 8 points per cylinder. I was kind of surprised that the cylinders do seem to have a little bit of meat. At least on this one.
I have no plan on going .060" over.

[jayb]

I think that block could easily go .060" over - Jay

[Stangman]

Not sure there is a benefit between 30 and 60 over. I would think it would be better with a little extra meat in the cylinder walls and god forbid something happens theres room for another boring of the cylinders. How much extra horsepower does an additional 30 over give.

[Urgefor]

Depends on the horsepower per cubic inch, but a .030 over 428 block with a 4.25 stroker crank will be right at 462.  At .060 over just under 469 so we'll just call it a 7 cubic inch difference.  Assuming we have a build that produces 1.5 ponies per cube (2019 Blair Patrick FE build anyone?) naturally aspirated, 10.5 additional horsepower.  This is a super simplified comparison, but it gives a basic idea.

[blykins]

I'd much rather have the thickness and the ability to machine later on.  10 hp is too easy to get from other ways.  That's an air filter base change, or a carb spacer change, or an A/F ratio change.

[Barry_R]

Heck - you might get an extra 10HP from cylinder wall rigidity

[jayb]

I think the question was, would it be possible to go .060 over.  The original post says he has no plans to do that.

[fryedaddy]

i took a 30,000 original miles 428 engine to the machine shop for a rebuild.it came out of a t-bird.knew the owner of the car,it was a low stress engine.the crank did not need turned and the block did not need boring.bad news-my uncle who funded the build,had already bought .030  over pistons so the shop bored my block even though it did not need it.o well i guess thats at least one less over bore for the future of this block.you never know it might be bored to the max right now

[Joe-JDC]

I have a 428CJ "C" scratch numbers matching engine that I just bored to +.030" over, and did a fresh sonic test that has cylinder walls capable of +.065" overbore and still have at least .125" everywhere.  The block is dated 8G23 which should be a '68.5 dated engine.  I believe that those real CJs have decent cylinder wall thicknesses remaining if the owners used antifreeze in their engines from the beginning.  Joe-JDC

[428kidd]

David Garton owned the last production 68 1/2 mustang  . The production date on that car was 8G29.

[My427stang]

I have a 428CJ "C" scratch numbers matching engine that I just bored to +.030" over, and did a fresh sonic test that has cylinder walls capable of +.065" overbore and still have at least .125" everywhere.  The block is dated 8G23 which should be a '68.5 dated engine.  I believe that those real CJs have decent cylinder wall thicknesses remaining if the owners used antifreeze in their engines from the beginning.  Joe-JDC

I sonic check a few too and the C scratch is almost always head and shoulders over the early X, A, CI, and CX in thickness and consistency.  The later CI/CX can be as thick, but often inconsistent in core location, X and A tend to be a little thinner.  I agree with you though, if everyone would have used good antifreeze, things would be much easier.  I had one Mexican 302 casting that was thick for a Windsor, but rusted from the inside, sonic checked good, but I poured a little gas in the water jacket because I saw a shadow and it weeped.  Pitting can be bad

[blykins]

The pitting is what will bite you.  All the drill bit tests in the world won't tell you where the thin spots are.   And even a sonic test won't tell you everything.  I've ruined some good blocks before, even ones that tested thick, by getting greedy on the bore size.