Wow! Lots of questions and.. whew! He we go. I’ll answer the high points with a thought at the end.
The 2 part main seal may be “Out Of Date” but still works well as one would only need to be careful in doing the job.
I like the LA bar for the rockers better myself. What I do like is the ability to use a cheaper Chevy rocker. The rocker girdle would be good for a race engine and not really needed for a street or street strip engine. Adding one would be a good plus. This I can’t argue, but is it really needed?
On over bores, IDK if the .040 is true. But it doesn’t really matter for two reasons IMO. One, the amount of overbore that is available is of very little HP gain as it only adds 5 cubic inches from the OEM 4.00 bore size. The benefits of a bigger bore are not really coming into play here. How much it can be bored out should be a fact finding four with a sonic checker. It has been said that 340’s are the best and thickest cylinder walls to bore out to a whopping 4.1 or better. I’ve had a few sonic checker that would and have failed at a .020. The machinists I worked with called the stock cylinder bore unacceptable even for a mild cam change. Then I have one that the machinist say we can go to 4.125, no problem!!!!
WTF? IDK!
Truly the bottom line is, a thicker cylinder wall is power!
Less flexing, no wobbling, great sealing…. That’s power buddy! Yea!
Making a block with blind holes requires more metal which adds weight. The Chrysler small block is heavy enough. The race block is even heavier. Adding blind holes with more metal… more weight. Less is better for racing but not at the expense of longevity. But I’m seeing blocks from the 70’s still in service in some not so light duty vehicles making good power. Must be that high nickel content exceeding other brands race blocks.
That also brings me to the advertised compression ratios. While the Magnum has a higher advertising ratio, how many people are actually trying to make some serious street steam with a 8.4-1 comp ratio with an engine that stopped being produced in the early 2000’s? The LA advertised ratio is actually lower, sometimes in the mid 7’s. BTDT & checked it out myself.
I don’t know if “ALL MAGNUM HEADS” eventually crack. Even if they do, the crack in the head doesn’t affect performance. Sometimes it affects about seal. Yes that affects performance I know. However, if you don’t know they’re cracked and the engine runs strong and you don’t remove the heads to check, how will you know that correct? You don’t you don’t! And you’ll never know until you physically check to see if they have cracks. LA heads crack as well. Do not before then to thinking they don’t.
All engines perform better with higher flowing heads, period! So if you took a stock magnum engine swapped out the top end for an Edelbrock RPM package and don’t touch the cam, the performance gain is marginal. Why? It’s the head flow amount at the low lives the cam provides coupled with the very very short duration and exceedingly wide centerline of the stock him it’s pathetic for performance. While the stock magnum engine is pretty good for what it is, taking the short block and giving it a better top and build and camshaft will wake it up, as it would with any engine. The half point of compression is a plus but still at 9 to 1, only mild cams will be entertained at that level.
I can’t think of a single person taking a 50 year old LA and expect a huge performance gain with just a top end swap. The bottom end on original stock (inside parts) LA engines for any use beyond a simple grocery getter is not going to be a good idea to use and this be rebuilt with the proper piston for the goal the owner is seeking.
My thought here is on your comparison making is not an accurate one and not debatable based on the age of an LA engine which is 99.9% probability of being simply worn out. While magnum engines can still be found in great shape.
Now a Magnum that has very low cylinder west and hood rings can still be found would be a good Candidate for a good street performance cam engine, a LA would not. At a 9.0-1 ratio for the Magnum, great street rail driver like power can be made. Also a wise person would add an overdrive trans.
