i currently have a small block 350 2 main bolt. ill be rebuilding my block soon, should i stick with that one, or build up a 4 main bolt. whats the difference and which should i use

Hey Deluxechev,

Do a search on the forums here. I guess it depends on what you want the final rebuild to do as far as performance. If you want that 350 to push 500hp and turn at 7000rpm, definitely find a 4-bolt block. If you're just rebuilding it to drive everyday and hit the strip with once in a while, the one you have is perfectly fine and you'll save money by using the same block.

Like I said, check thru the forums.... you'll get a ton of opinions from those that know. A stock 4-bolt block won't be much different than a 2-bolt if you just want to squeeze 350hp and stay in the 6000rpm and below range. Above that, even a stock 4-bolt block could fail as quickly as a 2-bolt.

Racing at high RPM and squirting juice? 4-bolt properly prepped.
Driving everyday and hitting the strip on pump gas? 2-bolt is just fine.
Just my opinion.

Good luck with the rebuild!

Depends on what you plan for your engine, and what your budget is. A 2 bolt block should be plenty strong enough for a street performance application. If you plan on making serious power, using nitrous or a blower, now would be the time to upgrade to a 4 bolt if for nothing else than peace of mind.

If you're normally aspirated, not using NOS and under 500 horses, I say just use the two bolt block. Your money is better spent on some good aftermarket rods. Otherwise buy a set of splayed main caps and have your machine shop install them. It is the only way I'd strengthen the bottom end.

First off a 2-bolt main has 2 bolts holding the main caps to the block and a 4 bolt has 4.

Many claim that a 4 bolt is better because it has better clamping support. IMO factory 4-bolts are over rated, because the outside bolt holes are not angled(straight drilled and tapped)the added support is less than marginal. And the added holes to the block only weaken the clamping area.


Just curios if all these opinions are based on actual expierences or if it was read in a magazine?



I have a 421(sbc) 2-bolt w/stock caps that runs 9.98 w/150hp and 300hp(2 stage) shot of the "funny stuff" and have never had a problem(10 runs-4500m).
Also those blue oval boys have been runnin' 2-bolts for years and there timeslips are the same if not better!!!
I have had 4-bolts gernade under alot less stress. 98% of the time a factory 2-bolt will hold up to as much stress as a factory 4-bolt, if it is properly set-up.

Didn't mean to ramble, deluxechev- run what you have, you should be fine,a street/strip 450hp 2-bolt 350 are a dime a dozen......just make sure you find a competant machine shop!!!