fakeyankee

OK Guys...Sorry to be a pain, but I need another lesson !!! It's to my understanding that the 4-bolt main motor is stronger than the 2-bolt type. Please explain why this is so, and exactly what it refers to. Also; Is there a way to tell which is which by just looking at the motor while it's still in the car ??? Forgive me if you think this is a lame question, but being a part of this group is like being in school without all the BS added in !!!!! You guys have taught me alot !!! Thanks !! Fakeyankee.

RB83L69

The difference is the number of bolts holding the center 3 main caps to the block.

You can't tell which ones are installed from outside of the motor, because all of the block castings that were equipped with 4-botl caps, also came with 2-bolt caps in other applications. It's jsut a matter of which caps were installed. The blocks themselves are the same.

The extra bolts stabilize the crank somewhat. They are mostly used it truck motors. Factory 4-bolt setups are inferior to aftermarket ones; for a high-perf application, it's better to start with a 2-bolt-equipped block, and equip it with better-quality caps with splayed bolts. Factory ones have all 4 bolts at 90°.

bredfearn

this was the EXACT answer i was looking for this morning too. awesome! thanks for your explaination RB83L69! :hail:

AJ_92RS

Here's a link I posted some pictures in to show the actual difference between 2 bolt and 4 bolt main caps.

https://www.thirdgen.org/techbb2/sho...hreadid=180386

fakeyankee

Great......I got it !!! Thanks ! Schools Out !!!!!

snakeskinner

that is the difference but in actuality, the factory 4-bolts are weaker. The extra two bolts are drilled into the thinnest point on the main webbing and actually weaken the block in that area. The strongest (without going aftermarket block) is a 2-bolt block with splayed 4-bolt caps installed.

rx7speed

crap I was hearing somewhere that the splayed bolt thing was a wives tale.... going to find that one again if I can

AJ_92RS

I do believe it's true, but primarily on a SB 400. The 350 doesn't seem to have that problem since the cylinders aren't siamesed together.

Although, I can't say I've ever heard of anyone actually breaking a 400 block because it had 4 bolt mains.

Have any of you?

Deemax

iTrader: (1)

Nope, never have. And IMO, to imply that factory 4 bolts are somehow "inferior" just because an aftermarket splayed-bolt cap is stronger gives the wrong impression. The difference is negligible unless you're turning upwards of 7,000 RPMs or pushing out 6,7, 800 HP+. For virtually any street or street/strip set up, the factory 4 bolt is more than adequate, and certainly far preferable to a 2 bolt.