Sonic test results and questions

[My427stang]

In the shop tech forum, you will see a question on my recent sonic tester purchase, I think I got it figured out this morning. I shaped the transducer a bit, and then did a drill bit test through a freeze plug, calculated the average cylinder wall thickness, measured that point, adjusted velocity to get close to a few check points, came out decent at the deck, china wall, and mathematically with my drill bit measurement. I also verified at a few other check points along the way to trust it a bit. Can't say I love this machine, but seems to do what it says it does.

Looking for opinions on what I ended up with. These are all minimum numbers, as any measurement in any direction or clock position was bigger, so rather than post everything, I am just posting the numbers I think are significant, anything not listed here was higher, .177 to well over .200 in some places. It's a 390 Ford block, clean inside and out, 4.08 bore with some run time.

Looking at drivers side bank, outward thrust side toward freeze plugs, I found my thinnest cylinders about 1.5 inches from the deck, all on one bank, passenger side was significantly better

5 - 0.126 6 - 0.134 7 - 0.118 8 - 0.134

If adjusted for a "worst case" torque plate hone to 4.09 (I mention worst case because I don't think all the cylinders will require the full .010 to get my clearance with a 4032 piston, but needed a comparison) I would end up at:

5 - 0.121 6 - 0.129 7 - 0.113 8 - 0.129

Every cylinder gets thicker as you go deeper, the passenger side of the block is thicker, and all dimensions around the block are thicker than those minimums.

Game plan is max 500 hp engine cammed for 5500-ish peak. Not a racer, street 4x4 truck, but planning a 4032 4.09 forged piston as tight in the bore I can safely go, with either a 1.0/1.0/2.0 ring pack, or potentially a 1.5/1.5/3.0 and want to make sure bore is stable.

Other dimensions. Deck height 10.160 squared to mains, 4.25 stroke, 6.70 rod, 1.33 CH, only about .200 of skirt comes out of the bottom of the cylinder at bottom of stroke. Max 10:1 compression

Thoughts? Specifically on the .113 number? Also, knowing a sonic checker seems to be a little voodoo on a round cylinder (or at least not as easily verifiable) versus a flat plate for me, if you like it, would you run 10% less than .113 if we added a WAG factor?

Thanks

[David Redszus]

Once upon a time (all fairy tales start that way including this one), we were considering sleeving a two stroke
snowmobile race engine. The OD of the sleeve was a bit larger than we liked and we became concerned about cylinder wall thickness.

I used a sonic thickness tester with mixed results. After obtaining various wall thickness numbers, we cut open a junk cylinder to validate the measurements. Some matched closely, some did not.

We determined that material density and temperature have will affect accuracy. The casting was neither uniform in size nor density. The day to day variations resulted from shop temperature changes when the furnace was shut down at night.

The bottom line was to purchase new cylinders and not take the chance that all the hand porting work would be compromised by a shifting sleeve. Your results may differ.

Yet I know of a machine shop that uses a sonic tester to determine the density of a material with a known thickness.
And they all lived happily forever.

[My427stang]

Once upon a time (all fairy tales start that way including this one), we were considering sleeving a two stroke
snowmobile race engine. The OD of the sleeve was a bit larger than we liked and we became concerned about cylinder wall thickness.

I used a sonic thickness tester with mixed results. After obtaining various wall thickness numbers, we cut open a junk cylinder to validate the measurements. Some matched closely, some did not.

We determined that material density and temperature have will affect accuracy. The casting was neither uniform in size nor density. The day to day variations resulted from shop temperature changes when the furnace was shut down at night.

The bottom line was to purchase new cylinders and not take the chance that all the hand porting work would be compromised by a shifting sleeve. Your results may differ.

Yet I know of a machine shop that uses a sonic tester to determine the density of a material with a known thickness.
And they all lived happily forever.

So the moral of the story is: Don't trust the block?

I have to tell you, if that is the intent, I could agree with that easily, because it seems pretty easy to get different numbers with a slight move of the hand. That being said, although density could likely change in a late 60s iron pour, temp was pretty stable for the duration of measuring, and the sonic check measurements matched the measurable "taper" as measured through the freeze plug hole.

Do I "trust" the method? I don't think so, but I don't distrust it either, based on the fact I was able to repeat and check my work a couple of different ways. Like anything else, looks like I need more data. I am going to go do a nice little 428 standard bore block using the same method and see what I come up with. At least that would increase my sample size to 2

[BILL-C]

We build FE engines pretty regularly, and those thickness readings are typical of an average block. I haven't had any cylinder wall failures at those thickness readings yet. To keep things in perspective, I sonic checked a 390 block that came in for a rebuild after it had already been bored .060 and worn out again.It was only .090 thick in one spot, yet apparently lived a very long life in a pickup truck without any issues. I talked customer into buying a replacement block because this one was going to need to go another .020 to clean up bore again. We had a block come in one time that was rebuilt to .040 oversize by another shop that had a cracked bore. Wall was only .035 thick at crack.

[ProPower engines]

I see those FE blocks quite often as well and I tell my customers that if the block is thin and most often they are after a heavy over bore like .040 or more that unless it is a numbers matching block find another one.
I repaired a matching 428 block a few years back with a sleeve kit from Darton. It was a bit of extra work to do all 8 holes but the customer wanted his original block saved and used.
While they are harder to get then a reg. 390 block but if you have a thin bore use the correct sleeve and be done with it.
They make some really nice sleeves that are very much stronger then the original cylinder was to start with.
I use the same style of sleeves on mopar 440 blocks that are a worn out .060 over bore back to std. that make in the range of 550 HP and in many years of doing so have had 0 problems with them.

[My427stang]

Thanks guys, I think I am going to use a different block. This one doesn't have a pedigree. I won't toss it, but I'll think about it's future

I ended up doing a std bore 428 industrial block yesterday afternoon and there was a noticeable difference in ease of sonic checking. I had the tool calibrated as I did, and every check figure came out exactly as measured and seemed that tool provided quicker and easier readings. That block was quite a bit thicker too.

Either I am getting better at it, or that block is slightly different material, because it sure went easy!

[PackardV8]

Yes, sonic testers are wonderful toys. They do give a reliable indication of wall thickness.

No, never rely on them, especially with this old junk. A fifty-year-old block has had who knows what run in the cooling system or left in the boneyard who knows how long. We've had blocks which are always good to +.125", open a hole at .060". It's impossible with a sonic tester to cover every square inch of every bore and that pit/corrosion could be hiding anywhere. What gives us nightmares is the weak spot hiding just underneath the shiny new bore, waiting to crack through under heat/combustion pressure/cooling system pressure.

Maybe, a high dollar build on an old block should have the block pressure tested after boring.