Same scale (new) same day

8-28-72 340 4.070 158#
2-19-71 318 4.070 122# was a running dirt track motor
5-7-70 340 4.070 159#
10-17-96360 4.040 175#
6-17-70 360 4.030 165# smallest distance between farthest apart bores
4-26-78 360 4.030 165#
1-2-97 360 4.000 179#
7-19-91 360 4.000 174# Roller has the thick pan rail also
8-30-73 318 3.910 165# Same casting as 122# block
9-19-96 318 3.910 177# Has thick pan rails
1-16-67 273 3.625 166#

I got all these blocks in my shop right now, weighed them tonight on new digital bathroom scale. They have freeze plugs, cam bearings, main caps and main bolts. If they did not have them for the weigh in I set a spare set on the block while on the scale.

All the magnum blocks have the thicker pan rails weather 318 or 360.

The space between the bores was measured with a flat screw driver through the freeze plug holes, not real scientific but it is what I had. The 340 blocks were both the tightest ones by far except the two center cylinders on them had more space than the tightest one on the early 360 block. The 273 was the worst.

LA pan rail till at least 78 and was changed some date between then and 91.

All the blocks I have in my possesion cast before 91 have this style where the pan bolts have extra meat cast around them so they don't leak where they go through the thin rail.

This is the 91 and newer style pan rail. Notice how the pan bolts go into actual meat and are not just "hanging out there" in a little added in boss.

Also anchors the base of the bores to a little more meat.

There are a few small gaps in the thick rail blocks but every single pan bolt is "anchored" to a main bulk head. Every main bulk head has some connection to the thicker part of the rail anchoring them to more meat. This should also keep the entire block from flexing as much in extreme builds and make bore last longer even though they may be a little thinner.

Also I am not a metallurgist but I can tell you the magnum block metal seems quite a bit harder when grinding for stroker clearance.

Now every one can tell me how crazy I am

Almost forgot, the magnum blocks from the biggest space to the smallest space (between bores) from all the blocks combined there was less variation than the best to worst of any single early block of any displacement.

I have a bunch of other engines in the shop also that I checked in this fashion and the pan rails, although they were not disassembled enough to include in the weigh in.

I like my magnum blocks also

So the first 318 on the list was .080 over? Was there a lot of lightening done on this block?

4.070 bore on a 318 would be a .160 over bore . That cuts a lil weight off. I have bored a few early year 318s in the past to 4.040 (stock 340). I always sonic test blocks before doing so. Interesting to see weight variables!

Good info! Thanks for the effort!

So how much more HP will the magnum block hold than the LA? 50hp? 300hp?

Probably going to depend on the exact block and sonic numbers... but if I had to guess I would think on average they could handle another 100hp. Of course the motors I build generally don't come close to the limit so it still boils down to roller cam for dirt cheap or possibly a little more bore. Right now I am building the early 360 block at 4.030 bore with a .590 solid flat tappet, w2 heads super light rotating parts and stock stroke.

My own personal motor is going in a 97 5.9 magnum block with full ported R/T heads, big hydraulic roller, and at least 410 cubes unless I can sell that kit, in that case I am going to get a BPE 4.25 stroker kit

Hello-o-o-o-o-o-o

4.25 BPE

Ron Silva built a 501" SB with a race block and a 4.5" (rifle drilled) stroke.

Rod angularity is gonna be pretty severe at 4.5" I don't think I'd try it with a stock block

But opinions vary.

I built a 4.25" stroke as a cruiser that I'll nail only on occasion. For a bracket car I for one will trade away more cubes in exchange for more RPM/Gear and go easier on the block.

Dad always used to say "Just because you CAN, doesn't (always) mean you SHOULD!"