Over boring a 330FT block

[bsprowl]

The following is based on a 15/64 drill bit test on 330 FT block:                       
4.63 bore spacing.  Subtract the drill bit diameter, 0.219, leaves 4.411 inches.                     
Allowing (subtracting) for two 1/8th inch (0.125”) cylinder walls leaves 4.161.                       
This is just over a 0.030 over bored 428 cylinder.  The 428 has a 4.13 bore; with a 0.030 over bore the bore is 4.16.                       
So if there isn’t much core shift I should be able to bore this block to use 428 pistons.                     

Or am I mssing something?

[blykins]

Bob, I wouldn't even take time to mess with drill bits.  Find a local machinist/engine builder with a sonic tester and have it tested, and even then, keep your fingers crossed.

You can't see all the places behind the cylinders where it can be thin/pitted.

In addition, the cylinder wall thickness is paramount to ring seal.  You're better off with a thicker cylinder wall than a thinner one.

[bsprowl]

I agree about the thicker wall.  And the sonic check before boring.

I thought and 1/8th inch wall would be more than enough.  Probably use a 4.13 bore so it could be overbored later.

[frnkeore]

I have a late 330 block, with side ribs. I did the same test and found that there was a fairly big difference, between the top of the cylinder and the bottom.

The bottom (from memory of 3 years ago) was 3/16, while the top, under the deck, was 9/32. Also, my block doesn't have the third rib in the skirt.

[bsprowl]

My block is dated Jan 16 1970 and doesn't have the ribs. 

The drill bit barely goes in near the center and won't move up and down more than an inch. 

It has the reinforced mains.

[frnkeore]

As I remember, my block is a '72. I think they started the ribs close to '71.

With good sonic map readings, you should be good to at least 4.13.

[pbf777]

       A "sonic test" is nice, and yes, it does provide valuable information, but this can only provide an "impression", not an absolute value, of what one might get away with in the way of an over-bore capacity.  It's a "spot-check" operation, not an in-depth detailed study of the entire cylinder; and therefore there very well may be "anomalies" not realized in the testing effort. 

       I believe the best practice is to realize that the O.E.M. was not in the habit of proving excessive sums of material just so that someone down the road in a rebuilding process could 'punch' their "390" block out to the "428" bore size.  But, I might be inclined to believe that they did at times utilize the 428 water-jacket cores in some of the "390" bore intended blocks; the question to be answered would be "why"? 

       The first thoughts that come to mind might be, that this might be an acknowledgement from the O.E.M. that they had established that the cylinders "needed to be somewhat thicker" than as originally engineered; and this for an engine producing 'only' how much power?     

       Perhaps, the casting boxes were just getting tired, this resulting in excessive "core-shift" issues in the castings and an excessive sum of rejections; so someone said: we'll just substitute the "428" core which'll thicken-up the casting and allow it to absorb this problem.  Hey, that'd be cheaper than paying for all new casting boxes for an engine on it's last legs anyway!"?   

       Best possible scenario might be that the "390" water-jacket cores got damaged, so the "428" stuff was just substituted; but again, to offset the cost in the greater sums of casting material being utilized meant that there would be a cost savings in a reduction in rejections from cylinder wall thicknesses (somewhere) not meeting the minimum specification, even when the "core-shift" was great, the pouring was bad and the machining execution was sloppy!   

       So, your thinking "you" can go about making them thinner?     

       Scott.

       

[frnkeore]

When the FE car engine was introduce, it had a minimum cylinder wall thickness spec of .170 and recommend a max overbore of .060, cutting that down to .140.

I've studied wet sleeve engines and many of them have a .125 wall thickness so, that falls into the area that some (including me) recommend as a min wall thickness when boring a engine. That said, Jay has a dyno mule 427 block, that .060 or a bit under, in places.

The Ford FT block, that came out in '64, is a different matter, they are made with much thicker cores. I don't have the spec but, the CJ block has similar cores. It's my belief that that's where the CJ block was derived.

[blykins]

Let's be very clear.  Just because you can get away with something doesn't mean it's optimal. 

Scott, that's why in my response up above, I said to keep your fingers crossed, even after boring.  Back in 2006 I was trying to find a 390 block that would go to a 428 bore.  Sonic tested one.  It tested great in the spots I chose.  Started boring it, then bored a cylinder and ran into a bunch of pin holes where it was thin.  Sonic tested another one, it looked great.  Started boring it, got to a specific cylinder, and found thin spots in it as well. 

You know what would have worked?  4.080" LOL 

A sonic test is a good test, but you can't map every single spot in a cylinder.  There will be spots on the backside where there has been pitting.  You just don't know until you start machining.

Ring seal is paramount especially with modern thinner ring packs.  That's why with aftermarket blocks, such as a Dart/World/Ford Racing SBF block, even at a 4.185" bore size, the wall thicknesses sit at a .250" minimum.  When you're cylinder wall is flexing like a piece of cardboard, you're losing power.

[My427stang]

The following is based on a 15/64 drill bit test on 330 FT block:                       
4.63 bore spacing.  Subtract the drill bit diameter, 0.219, leaves 4.411 inches.                     
Allowing (subtracting) for two 1/8th inch (0.125”) cylinder walls leaves 4.161.                       
This is just over a 0.030 over bored 428 cylinder.  The 428 has a 4.13 bore; with a 0.030 over bore the bore is 4.16.                       
So if there isn’t much core shift I should be able to bore this block to use 428 pistons.                     

Or am I mssing something?

I agree with the others, drill bits might be a good idea to see if worth investigating further, but that's about it.  I don't even bother

You mentioned core shift, the only way to "see" it, is when you sonic check enough points to see show the entire pattern shifts on each bank, and each bank is generally different.  Usually, top bottom middle in every cylinder is enough to show the trend, but even then, it doesn't account for pitting, and certainly doesn't show the complete shape of a non-machined surface.

Nowadays, I try to do minimum bore and spend the money on a piston.  If that really is a thick block after sonic checking, I'd stop at 4.05 and build a snotty 390 or 437 at the biggest.

[frnkeore]

Nowadays, I try to do minimum bore and spend the money on a piston.  If that really is a thick block after sonic checking, I'd stop at 4.05 and build a snotty 390 or 437 at the biggest.

Ross, what do you do with CJ blocks. Since they have the same cores as the FT?

[428kidd]

Not all FT blocks have the same core. The later ones do have the triangle cooling jacket like the 428s. Early ones do not. The reverse 105 blocks have that also. Some FT do have sand scratches such as C, CX, and CI. I would look for those if trying for the best choice to do this, but still a gamble. It's my opinion and it's just that , that Ford deemed these blocks not usable for its production car line do to core shift and only bored them to FT bore sizes so to low rpm. I have no real proof of that other than Ford sonic checking 427 stuff to grade it for race, production car application, marine , and industrial.

[blykins]

We know that every CJ block will go to a 4.130" bore.  But will every FT block?