I have an 86 Iroc that the previous owner swapped in a POS 350 that blew. Now I'm trying to swap it for a GM performance 350. My problem is that the original block is a two bolt and the new GM Crate has a four bolt. Will this still work or is there some kind of modification that i will need to do? and if so what do i need to do? i would love to hear from someone who may have done this same thing or something similar and how they did it and how it worked out. Thanks

 

The number of bolts refers to how many bolts hold down the main bearing caps inside the engine. There's nothing externally different between the two.

 

Right:

The 4-bolt thing makes no difference whatsoever to anything outside the oil pan. Everything bolts up (or doesn't, as the case may be) IDENTICALLY.

It also makes no difference whatsoever to the engine's durability, in a "high performance" (high RPM) application. That's not what it's designed for. While it doesn't really hurt anything, it doesn't do any particular good in applications like ours, either.

 

Here I happen to have everything laying around so I'll try to help you out.
A 2 bolt main is generally weaker than a 4 bolt main but a 2 bolt can be machined to be just as strong; if not stronger than a 4 bolt. 2-4 bolt main is referring to the amount of bolts in the main caps.

This is a 4 bolt main off my 454:


This is a 2 bolt main off my 350:


This is the same 350, but the center 3 mains have been splayed to 4 bolts:


Notice how the bolts are splayed from an angle.

 

jtrice02, first, welcome aboard thirdgen.org.

Now, what you need to look into:

Rear main seal type. Some 2-bolts and some 4-bolts are 2-piece rear main seal, while some 2-bolts and some 4-bolts are 1-piece rear main seal. The reason this is important is that the two different types of rear main seal cranks use different flexplates (or flywheels). So, you need to have the flexplate (or flywheel) that matches your new engine.

Dip stick location: Some 2-bolts and some 4-bolts had the dipstick on the driver side of the engine, while some 2-bolts and some 4-bolts had the dipstick on the passenger side of the engine. FWIW, all 3rd gens came from the factory with the dipstick on the passenger side, but since your engine has been replaced, and you're getting a crate engine (but haven't provided meaningful details about it), just be aware that driver side dipstick tubes and stock 3rd gen V8 exhaust manifolds don't play well together, and the two different types of engines use different oil pans. If your crate engine has the same dipstick location as your current engine, and/or your crate engine has a passenger side dipstick, and/or your crate engine comes with an oil pan and dipstick, and/or you're using headers, this won't matter, either.

Accessory mounting bolt holes: This is a function of the heads. Most heads these days are made with the accessory mounting bolt holes on the ends of the heads, but again, you haven't provided any meaningful details of the crate engine you are getting.

Basically, the fact that your current engine is 2-bolt main and your crate engine is 4-bolt main is moot. What may matter are the other little details (and which we can't really provide you meaningful information because you haven't provided us meaningful information about your crate engine).

But, fear not, we're here to help. We just need information you haven't provided yet.

 

heres some more info on the engine that i plan to get

Blueprint premium cast iron crankshaft (1 piece rear main seal)
Chevy heavy beam rods with 150,000 PSI bolts
Hypereutectic pistons; 9.5 to 1 Compression
Hastings Moly rings
Hydraulic flat tappet cam
Melling high volume oil pump
Heavy duty double roller timing set
4-bolt main block, 1 piece rear main seal
Passenger side dipstick
Square and parallel decked
Align honed main bearing bore

Thanks everyone for the help