Not to rag on anyone but every single answer sounds like a answer read from a car mag. or repeated hear say.
The 4 bolt main has NOTHING to do with power so that one guy is WAY off.
The small block chevy engine has 5 main caps. The mains is what holds the crank in the block.
On a 2 bolt main block, all 5 main caps has 1 bolt per side (2 total) bolting cap to block.
On a 4 bolt main, the 3 center caps has 2 bolts per side (4 total) bolting the caps to block.
Everyone that DON’T know always says get a 4 bolt main, its stronger, etc etc. Pure BS
In the stock design, the main caps are gonna crack and break before the 2 bolts are gonna pull out of the block.
The idea of 4 bolts holding the crank in is great but GM goofed IMHO, If you look at the placement of the outter bolt holes on the 350, the outter bolts of the 4 are placed too close to the oil pan rail in a weak spot.
The 400 small block is even worse, the 4 bolt 400 is almost useless to performance builds
The best main setup is one that uses a billiet cap, and splayed 4 bolt main.
Now as far as stock blocks go.. A 2 bolt GM block with ARP studs in the mains will hold more RPM and power than a 4 bolt main with bolts ever will.
I’m running a studded 2 bolt block. 5 years daily driven, well over 200 1/4 mile passes, shifting at 6400 rpm, 505 HP, running 11.40’s at 118 mph
Truth be told don’t worry about the mains, main bolts.. Its the rod bolts and valve springs that lets go 1st in the small block chevy.
The ratio I have seen myself is 100 to 2.. 100 rod bolt or valve spring failures and 2 main cap/bolt failures
4 Bolt Main
There’s four bolts holding each of the caps on, which in turn holds the bearings/crankshaft. This increases the bottom end strength of the motor. If you’re sticking with a mild-to-mid-performance engine (making less than 350 hp and revving only to about 6000rpm), a two bolt block is perfectly fine, and even then, you can go with ARP fasteners to strengthen that block a little better. A four bolt first gen block can go pretty safely to 400hp and about 6500-7000 rpm. Of course these limits all depend on the quality of the machine work and engine build. I have about 300 hp on a 350 two bolt small block, and I’ve had no problems with it – same with my previous Camaro – both of them were 010 castings.
The 2 bolt block are just as usable to 400 hp, then you can have a two bolt drilled for splayed mains, which hold even better than a stock 4 bolt. so if i were given the choice i would get the 2 bolt. I have traded a few dummys in the past for a two bolt and extra parts/money.
Actually 4 bolt main caps were designed to keep the crankshaft from flexing. it doesnt take a rocket scientist to understand that a 4 bolt main is going to be more stable. but that doesnt make a 2 bolt main bad at all. ive seen plenty of 2 bolt main caps go well into the 500hp range
2 Bolt and 4 bolt refer to the main bearing cap in the center of the crankshaft. The 4 bolt is better for performance as far as able to handle more torque. They are also harder to find and of course more expensive because everybody wants them for racing or mudding.
I am kind of stumped I got this motor to install into a lifted Mud truck,and have always been told that the four bolt main bearing motors are the stronger of the 2 the guy I got this motor from was saying it had more ZINK in the metal WHat ever that does or does not do
It’s referring to main bearing caps on the crank shaft as to how many bolts per main bearing cap. Four bolt main bearing caps are stronger cause there is two more bolts on each cap.
it is in the bolts that hold the crankshaft and bearings so the 4 bolt is more durable if you wereto build it to produce more horsepower