C6ME 390 block sonic check

[scott foxwell]

Just thought I'd share this for reference sake. I just sonic checked my standard bore C6ME block. This block passed the 7/32" "drill bit" test to be able to bore to 4.15.
Not.
You can see there is significant core shift fore and aft. Driver side especially. Top to bottom has a lot of nice material to work with. I may do a little offset boring but I'm feeling really safe at going .060 over and still having some good cylinder wall thickness. Planning on 4.11 bore, 3.98 stroke, 6.8 rod. I'll start a build thread when I get a little more progress.

Sorry for the huge pic...

[thatdarncat]

Actual 428 cylinder cores will show up around 12/64" when checking with a drill bit, 14/64" ( 7/32" ) is just a common 390, so no surprise on the results. 

[scott foxwell]

Actual 428 cylinder cores will show up around 12/64" when checking with a drill bit, 14/64" ( 7/32" ) is just a common 390, so no surprise on the results.

Was just going on this from Jim Dove using Allen wrenches.

SIZE



WRENCH SIZE
RESULTS

.375"
3/8"
No Good

.312"
5/16"
No Good

.281"
9/32"
4.080" Max

.218"
7/32"
4.160" Max

.187"
3/16"
4.18" Max (In a 406 or 428, Good Block)

.187"
3/16" (427)
4.293" (68 C8AZ-6010-G) .125''

.125"
1/8" (427)
4.310" (Marine Block & Some Early 427's)

[thatdarncat]

Actual 428 cylinder cores will show up around 12/64" when checking with a drill bit, 14/64" ( 7/32" ) is just a common 390, so no surprise on the results.

Was just going on this from Jim Dove using Allen wrenches.

SIZE



WRENCH SIZE
RESULTS

.375"
3/8"
No Good

.312"
5/16"
No Good

.281"
9/32"
4.080" Max

.218"
7/32"
4.160" Max

.187"
3/16"
4.18" Max (In a 406 or 428, Good Block)

.187"
3/16" (427)
4.293" (68 C8AZ-6010-G) .125''

.125"
1/8" (427)
4.310" (Marine Block & Some Early 427's)

The drill bit test is of course an arbitrary test someone came up with to basically help I.D. what kind of block you have found. As people have found out using it as a guide to over boring a FE block is a bad idea due to core shift, block abnormalities, etc. Although some of the info in that list is close, some is way off, and none should be used to bore a block. A 427 block cylinder gap will be around 7/64"-8/64", 428 block about 11/64"-13/64", 390 block about 14/64"-16/64".

[scott foxwell]

Kevin, that's exactly why I did the sonic check and why I'm posting this. 'Theoretically", if you could correct the core shift, these would go 4.15 just fine but this shows that the drill test is only a reference.

[FERoadster]

I've got an already  cross bolted C4 block that is currently at +060 and needs a clean up ,but a sonic check shows all  would be with a 4.13 bore @.120 thickness and the thinnest would be .090. So i'm going to sleeve that one.  This would not be a race block but for the low price I say why not?
Agressive street driving only.
What thoughts for my desicision.

Richard >>> FERoadster

[scott foxwell]

Will sleeving make the cylinder any thicker? Wouldn't you have to change the OD to do that? Maybe the sleeve is a better material? My two end cylinders (4 & will end up at .120 and .116 (depending on how accurate the sonic is)  but not on thrust surfaces. The thinnest parts will be at the top of the cylinder and that's where cylinder pressure is highest so it's not ideal...wish the thin part was at the bottom...then I wouldn't care a bit.

[Barry_R]

The drill bit test is a useful way of basic casting identification for a guy scouting a yard or a swap meet looking for a 390 or 428.  It does not help with wall thickness evaluation at all.  Take a quick look at the math.

With a 4.630 center to center distance, and a 4.050 base bore, you have a theoretical maximum of .580 between cylinders for the adjoining two wall thicknesses and the gap between them. That 7/32 measurement if accurate accounts for .219 of that, which is thus leaving a possibility of .361 total for the two walls to divvy up.  A "perfect" casting would therefor have adjoining cylinders with +/-.180 walls.

Sonic testers are reasonably accurate in the proper context.  They need to be calibrated to the block being inspected using a machined surface - the china wall area above the timing cover works well.  And useful as they are as a spot checking tool, they will not identify localized issues such as shallow areas or corrosion divots.

I guess this is a lengthy way of saying I still do not understand the reason for going to the 4.110 bore.  If the block will clean at 4.080 you will gain +/-8% in wall thickness.  In a marginal situation I think that would deliver an improvement in ring seal that would largely - if not totally - offset the gain in displacement or airflow.  You could crutch the thin walls with a short fill in the block, reducing the unsupported vertical span of the cylinder will definitely add rigidity.

Cylinder sleeves are made from better material.  They are  (or at least were) centrifugal castings from a ductile iron, stronger, less porous, and with inherently consistent wall thicknesses since they are machined on both inside and outside diameters.

[scott foxwell]

I guess this is a lengthy way of saying I still do not understand the reason for going to the 4.110 bore.  If the block will clean at 4.080 you will gain +/-8% in wall thickness.  In a marginal situation I think that would deliver an improvement in ring seal that would largely - if not totally - offset the gain in displacement or airflow.  You could crutch the thin walls with a short fill in the block, reducing the unsupported vertical span of the cylinder will definitely add rigidity.

I don't agree that the airflow gains from additional bore won't outweigh some loss in ring seal...if any at all. Not with two marginal side cyl walls that will still be >.120" thick. The rest are plenty thick to take advantage of more bore and maintain good ring seal. Plus, I may do some offset boring to help the situation. Besides, the engine I'm using this block for will probably make more power than the stock block can handle for very long. It'll all be moot other than for good discussion.

[jayb]

I love cylinder sleeves.  I have a 428  block with a sleeve in #5, that was blown out in 1981 when I overrevved and dropped an exhaust valve.  It was sleeved right away, and has been running fine ever since.  I probably have 50K miles and 20 years on it in my 68 Shelby.  I then used it for both versions of the 428CJ in the dyno mule testing in my book.  It is now at 0.040" over and is running fine in my 68 Mustang fastback.  As Barry said, sleeves are made of better material than the original cylinder wall, so a 0.090" thick sleeve is stronger than a 0.125" block wall.  Sleeves are wondeful, IMO.

However, you do not want to sleeve two adjacent bores in an FE block.  The deck area between the cylinders is not strong enough to hold after a sleeve is put in on each side, and will crack causing a coolant leak.  There are folks who have sleeved all 8 cylinders in an FE block, and they never last.

I think both Richard and Scott's blocks are good candidates for sleeves.  Peace of mind regarding block integrity is worth a lot, IMO..

[unclewill]

My 482 has 8 sleeves so we'll see how long it lasts - I hope the additional 427 deck thickness is sufficient to support the adjacent sleeves.  I also chose thin wall sleeves and used head studs to decrease stress on the deck.  I agree that sleeves are OK when installed properly.

[chris_r]

number one bore 4.05 div by two = 2.025 +back cyl .207 = 2.232           number two bore 4.05 div by two= 2.025+front of cyl .207 =2.232      number one bore 2.232+ number two bore 2.232= 4.464 +drill bit .219  = center to center or bore spacing of 4.683      check your calibration on sonic tester

[scott foxwell]

number one bore 4.05 div by two = 2.025 +back cyl .207 = 2.232           number two bore 4.05 div by two= 2.025+front of cyl .207 =2.232      number one bore 2.232+ number two bore 2.232= 4.464 +drill bit .219  = center to center or bore spacing of 4.683      check your calibration on sonic tester

Run the math on the center cylinders, driver side. That's where I did the drill bit test. Cylinders are probably 4.055+.
You don't have to divide the bore in half when doing centers.
Sonic tester cal is right on.
4.055+.151+.198+.219=4.623. That puts every one of those dimensions within .0015 of being perfect.

[chris_r]

Your not hearing what has been said. The same tester that gave the top , mid  gave you the bottom ?

[chris_r]

your bottom # are not possible