Cylinder wall thickness is not the only concern on the OE LA blocks. High RPM and/or 550+ HP, bulkheads and block webbing become areas of potential issues also.

LOTS a fast stock block small blocks out there and I can't remember seeing or hearing of any block failures. And some of these guys are RPM crazy.

What's everyone's opinion on Magnum verses LA blocks regarding strength? Heard Magnums are a better ( stronger ) block?

Wait for HotRodDave.. he'll school you on the Magnum

The guys that preach this never provide any proof. 3-2-1.

Yep never showed any evidence for it.

https://board.moparts.org/ubbthreads/ubbt...tml#Post1711743

All you got to do is look at the pics I didn't post, the block weights I didn't post, the personal experience grinding on blocks I didn't post...

What? Weights? And guestimates that a magnum block can handle 100 more HP then LA blocks? Strange way to show proof.

How many cracked Magnum heads are out there? 1 in 4? 3?

Plenty of LA blocks running 600+ and living a long happy life.

Anyways.. it's all about prep.

There is extra meat where it counts, I posted pics. The iron is clearly harder, try grinding one block then the other. Cylinder walls though thinner on average are very much more consistant and the bad spots are not as bad as the older stuff and remember a chain is only as strong as it's weekest link, if you have one thin spot in a block with 1/2 inch thick bores it can wreck the entire thing. 9 out of 10 magnum heads are cracked... SO WHAT? How many does it cause a problem on? I never seen one and have worked with 100s of magnum powered trucks, if it was an issue you would see steam coming out the exhaust on most 92-03 dodge trucks. No stock head LA or Magnum makes enough power to bust any block (unless you get one with a thin spot of course) so who cares. Add on top of all that the 45 years of poor coolant maintnance corroding them up. I am not saying a LA block is a ticking time bomb but if you are really pushing the limits the mag block is stronger, how much I don't know but to deny it is stronger is foolish or in-experienced. As fer a 340 block, so what if you got .020 more clearance on 1/4 of the intake valve, .040 bore barely makes a measurable flow increase if any. Sure I would love to get a 4.25 siamese bore but for most heads out there it won't make any HP difference only more TQ but so will a dirt cheap roller cam. You can sell a 340 block buy a magnum, regrind the cam core bore and square deck it with the money.

I forgot about that other post. Thanks Dave. I am aware of your opinion on the Magnums, and your points are well taken IMO. Looking for any others that might chime in. Doesn't appear to be any big advantage ether way if you are making under 500 HP - except weight maybe?

Probably the only advantage under 600 hp is the cheap roller cam, I don't think the small weight difference matters in most builds.

According to race bulletin #8, July 1982:

"The early 360 ('71-'76) blocks are a special case. They use a 4.00" bore (340 was 4.04") but the block was made with the 340 water-jacket core. This means that these blocks can be bored to the same actual bore size as any 340 and have the same borewall thickness. This is NOT true of the newer 360's"

Basically there's enough "meat on the bone" to go to a 4.10" bore.

Cool.

I believe the "late" block began with 74. The casting numbers are different. Regardless, I wouldn't trust QC from the 70's and would have everything sonic checked for core shift, etc., before going crazy with one.

I know the 71-74's are 3418496 and use the 340 water-jackets. Maybe the 75-76 also. When did the start casting the 360 in MEXICO?

That quote is worthless. It's from the same source of the "thinwall 400s/440s" myth that was in every Mopar publication for years and years. The first I heard of this was in the very early '70s and back then it was considered gospel that the 496 block was the only 360 with the 340 core walls. As years went by it changed by, I think, wishful thinking.

RE: this quote, "all had thick walls ( around .200")".
Sorry, Charlie, the only place 0.200 is considered thick is in Moparland and some Ford circles.

Actually 0.200" is what's considered minimum for a major thrust in the rest of the old stuff. For Mopar engines if you can get 0.170" on a major thrust it's going to work. And the non-thrust parts of the block can go all the way to 0.120" and some won't even make that, and I mean virgin blocks! If you have 0.170" or more on all thrusts you go out and buy lottery tickets!

As for the thousands of 600hp 360s out there, I think they're all out racing those fabled 383 Hemis that Gramps had in his Road Runner. Put another way I don't believe it. If there are 100 360s making 600hp I'd be surprised.

If you had a 4.00" bore and 0.300" thick cylinder walls it'd be a Siamese block and you could go 0.200" over. It's being done with aftermarket smallblock chevy blocks right now. The largest area of concern is the head gasket between the cylinders.

R.

My 496 block

I have a 1971 360 block that has been run bored .060 over since the early 90's. and has many NOS passes on it.

Man I hope so. I have a block that is already .030 over and on its 3rd rebuild. Its gone 9.70's already but the block is worn out and needs bored. I picked up 2 sets of .060 over pistons that are standing by to be put to work.

Jason over at Shady Dell speed shop seems to think .060 is alright on a 360.

Agreed & I think the first number went from a (3) to a (4).

650 ponies here in my 360....been beating it for 3 years now....

1967 barracuda
1.30, 6.40 1/8 mile....