How large can a 413 block be safely bored?

Hi all,

I recently ran across the following statement, regarding 413 blocks, from an anonymous user on a different forum. I am wondering if anyone can verify this information, specifically boring it out to a stock 440 bore:

"These engines were produced up until about 1973. I have always found them to have standard 440 LY rods (1851535), and 6-bolt cranks. The blocks in these engines were actually originally supposed to be 426's, (you can find the casting number 2658836 on the top rear of the block, near the oil pressure sending unit) and they were, in fact, "under-bored" .070 to 413 size (4.180). I have sonic-checked many of these blocks, and the cylinder walls are much thicker. So much, in fact, that you can bore these to a stock 440 bore (4.320) and still end up with the same cylinder wall thickness as a regular factory 440. There is considerable additional webbing along the outside of the block walls (where the freeze plugs go). The main saddles, supports, and main caps, however, are completely identical to a standard 440."

As always, I appreciate any information.

Roger

Dunno about that, the info I've seen does not support the claim the 413 and 426 blocks have the same casting numbers.

Cap designed changed for 74 MY blocks. Main saddle designed changed early vs late as well.

413's have a interesting history, early pass car stuff vs later industrial/HD truck useage.

This question is easy to answer. Bottom line, you'll know how far pretty much ANY block can be bored once you have it sonic checked for wall thickness.

I've heard boring 413's to 426 bore diameter. 440 bore diameter seems a stretch.

Unless they used 440 molds for the late 413 you're not likely to be able to go to 440 bore

Unless it is a heavy duty truck block,boring to a 426 was not recommended by Chrysler.Also,the above mentioned 426 block is an industrial block,not a standard 426 casting.

Correct, there is just one 413 that shares a casting number with a 426 and it's an industrial engine, or it came in heavy duty trucks, meaning larger than a pickup truck. The chances of finding one are rather slim.

Here's the important point: The quote is referring ONLY to those blocks with that casting number. He is not talking about ANY OTHER 413 block.


Now that ultrasonic thickness testers are common, we are discovering how bad the Mopar blocks really were. It's a fact. Also, we're discovering that cylinder wall thicknesses could be all over the map in the same block.

IMHO the largest a 413 block could be bored to is 4.250. The blocks have such a low value that if one is bad you can always do another, although the price of boring another 8 holes may be more than the price of a sonic check.

R.

If indeed under bored(413) industrial, I would say it had thick walls. I got a 426 industrial block out of a crane, then had it bored .060 over. Guy who bored said way it sounded could have went way more than that, never heard one that solid, way before sonic checking, he had been boring engines for forty years and was amazed.

Thanks for the info, guys. I currently have a 413, but want to move up to a 440, and was just wondering about alternatives. Sounds like it would be less hassle just to look for a good 440 block, and go from there. Thanks again.

Roger