I have been reading that the 4 bolt main SB 400s are not reccommended for build but they never really give a good reason into this. They just say that the 2 bolt main 400's are much stronger? What fails??

I wouldn't worry about it unless you're doing a radical race engine. The ultimate setup is to begin with a 2-bolt block & convert to 4-bolt. Pffft, my 35-year-old 4-bolt block that is now 408" is hummin' along just fine ;)

TEX

the 4 bolt main blocks are weaker because of the amount of metal they take out of the block and the caps for the extra 2 bolts per cap. this really shouldn't be a problem unless you are building a real serious race motor.

they are prone to over heating. they have alot of torque and are good motors.

So there should be no issues using a SCAT 9000 series bottom end for my 406 build up then?

that should work just fine for you.

they are only prone to overheating when not built properly or have an inadequate cooling system to begin with, which would overheat any motor.

Has anyone actually witnessed the failure of a 4 bolt motor? If so how did it fail, and how was it modified?

they are only prone to overheating when not built properly or have an inadequate cooling system to begin with, which would overheat any motor.

ive always wondered about that. i have a 400 going on about 5 years. never overheated it once and its been beat to heck... though it has a heavy cooling clutch, new radiator new water pump and new thermostat put in when i installed it out of paranoia

Has anyone actually witnessed the failure of a 4 bolt motor? If so how did it fail, and how was it modified?


The over heating issues and the 4-bolt-main block problems are 2 different issues.


400's can have heat problems due to the fact that the bores are 'siamesed'. That means that there is no water in between the cylinders. Which is also why 400's need the steam holes.

The 4-bolt block problems are due to the fact that when the factory did their 4-bolt block machining, the outer 2 bolts of the three main caps that actually have 4 bolts - they drilled and tapped the outer bolt holes 'thru' - or thery are very close if they haven't gone through. This means that the outer bolt holes have broken out into the bottoms of the cylinder bores. A hard-hitting 400 case that is a factory 4-bolt can start to crack from the bolt holes out into the bores.
Starting with a factory 2-bolt block and machining it for 'splayed' 4-bolt caps is a much stronger setup due to the materials of the main caps, due to the angle of the outer hardware, and due to the fact that the angled holes don't break into the bores.

The over heating issues and the 4-bolt-main block problems are 2 different issues.


400's can have heat problems due to the fact that the bores are 'siamesed'. That means that there is no water in between the cylinders. Which is also why 400's need the steam holes.

The 4-bolt block problems are due to the fact that when the factory did their 4-bolt block machining, the outer 2 bolts of the three main caps that actually have 4 bolts - they drilled and tapped the outer bolt holes 'thru' - or thery are very close if they haven't gone through. This means that the outer bolt holes have broken out into the bottoms of the cylinder bores. A hard-hitting 400 case that is a factory 4-bolt can start to crack from the bolt holes out into the bores.
Starting with a factory 2-bolt block and machining it for 'splayed' 4-bolt caps is a much stronger setup due to the materials of the main caps, due to the angle of the outer hardware, and due to the fact that the angled holes don't break into the bores.

Very well said.:grinpimp:

The over heating issues and the 4-bolt-main block problems are 2 different issues.


400's can have heat problems due to the fact that the bores are 'siamesed'. That means that there is no water in between the cylinders. Which is also why 400's need the steam holes.

The only 400's I have ever seen overheat (with an otherwise sound cooling system) were built with head gaskets that lacked the steam holes. This makes it virtually impossible to purge the air from the area around the upper cylinders. As long as the gaskets have steam holes, there isn't usually a problem.

The only 400's I have ever seen overheat (with an otherwise sound cooling system) were built with head gaskets that lacked the steam holes. This makes it virtually impossible to purge the air from the area around the upper cylinders. As long as the gaskets have steam holes, there isn't usually a problem.

Agreed.

The one REAL downside that I have ever been able to see with a 400 case is that the bores wear less evenly over time - more due to the short rods/long stroke than any heat issues - although I could guess that the localized material temperatures of the bores themselves could contribute to that situation also. Like visibly 'wavy' bores at teardown.

Agreed.

The one REAL downside that I have ever been able to see with a 400 case is that the bores wear less evenly over time - more due to the short rods/long stroke than any heat issues - although I could guess that the localized material temperatures of the bores themselves could contribute to that situation also. Like visibly 'wavy' bores at teardown.

Luckily, aftermarket pistons are available that let you run a longer rod :D