2 bolt main vs 4 bolt main?

What are the pros and cons of each?

I've believed for a while that four bolts are better than two. Period.

But now I'm hearing otherwise. Can someone clarify?

4 bolt caps are good, but slayed 4 bolt caps using a 2 bolt block are stronger because the other bolts are angle tapped in a thicker part of the block

a studded 2 bolt blk is just as strong as a factory 4bolt blk.. a splayed 4bolt block is the best but unless you are really going to abuse the motor, high rpm, power adders, etc.. i would just stud the mains and go have fun!

Splayed caps and all the machine work and you are pretty close to Dart Little M territory. Personal opinion but if you are looking to get well north of 500HP you are time and money ahead with an aftermarket block. You can get GM Bowtie blocks in the $1600 range.

I agree with Big Dog and Ventura II,

Unless you're planning to really generate gobs of horsepower and high revolution's loads, you won't need all that extra support.

I have a 68 302-Camaro block in two-bolt version (perhaps a truck block:confused:) that I put through the paces at the track, and when I finally tore-it down, and I found very little scuffing of bearings or any other rotating damage.

And by the way, IMHO, balancing of the rotating components will probably give you added reliability on an engine build versus extra-support caps!

GerryLP:cool:

So, wishfully speaking for a second...

If I wanted 500 plus horsepower, a studded two bolt main would be the way to go? Or, are you telling me that I can drill some holes and put two more bolts in my block?

BTW, what's the difference in a "studded" block / two bolt main?

I can't comment on the first part of your question but to answer the "studded" question here goes. You replace the stock main bearing bolts with aftermarket main bearing studs and nuts, they are quite a bit stronger and won't stretch like the stock bolts could. I have been told by many engine builders that that's the way (studded two bolt) to go verses finding a four bolt block.

Okay, so what about boosted applications?

nothin wrong with a 2bolmain block, ive seen em turn althe way to about 6grand without blowin up, i was lucky enuff to find a 4blt that im puttin studs into...

Like every engine question, it really depends on what you plan on doing with the motor. If you plan on leaving it N/A and not reving it through the roof, it'll serve its purpose; However, if you're looking for a serious street/strip machine, then I'd suggest finding a 4-bolt main block and studding it.

It all boils down to expectation and longevity of the drivetrain.

I am with this guy>>>>ProchargedchevyI<<<< Good advice.

On the other had... and not to be accepted as a good thing in todays 4 bolt block availability. consider that the lowly 327 and 283 had nothing but 2 bolt mains..... and would ZING to the stratosphere.. (with good machine work) no studs, heavy TRW pistons, skinny stock rods... Stock bolts. but often failure at the most inopportune times.

and power levels were not what they are today... Just thought it was interesting.. thats all..

...consider that the lowly 327 and 283 had nothing but 2 bolt mains..... and would ZING to the stratosphere...

And this is a very good point, Veno.

You see, the lower displacement engines of yester-year (283's and 302's) had a shorter stroke on the crankshaft. (This is consistent with laws of inertia, really). These very same principles allows a ballerina to bring her arms closer to her body and spin faster.

So if Nox wants high end horsepower [(Torque X RPM)/5252] = Shaft-horsepower, a short stroke could be the answer. A very small amount of torque (say 200 lbs/ft) at 7,500 rpm will yield 285 Hp.

Heck, the early 1980's low-output V8 engines could give you 280 lbs/ft of torque, and on our example above that would give us nearly 400 Hp!:eek:

So a 2-studded main caps block will hold this just fine, but the kind of horsepower needed to get below the 12 seconds 1/4 mile, can reliably only be obtained with stout set-ups like 4-bolt mains, weight-momentum balancing below tenths of an once, and all the goodies you can afford. :D

My neighbor Dan could only break below the 10 second 1/4 mile with a nearly 1,600 Hp Hemi on his track 72 Cuda. To get into the 8's he'll need at least doubly that amount.

And it is never enough...you know:(

So when people say that "it depends on what you want", what they are really saying is "if you want to burn tires from stoplight-to-stoplight" then a 2-bolt main will do just fine. But "if you want to break below 12's in the 1/4 mile", you'll need a stout set-up or expect engine blow-ups.

GerryLP:cool:

every single chrysler engine is 2bolt mains, ever seen what a 426 max wedge on acki does? i know a guy buildin a 65 altered wheelbase playmouth, got one hell of a wedge motor in it, turns all the way to 9000rpm

I've believed for a while that four bolts are better than two. Period.

But now I'm hearing otherwise. Can someone clarify?

I believe its the 400 block where a 4-bolt can be weaker than the two bolt. On the 350 block, the 4-bolt is stronger. As said earlier, the splayed is best with either block

The 2 bolt caps v/s 4 bolt caps really have nothing to do with lower end strength. The keep the main caps from walking and shifting around under stress causing crank and bearing problems. Big Chevy's have the caps referenced into the block (there are like steps that the caps fit into), and other engines like Pontiacs use dowl pins to keep the caps in place, that's why alot of other engines don't need to go to 4 bolt caps. they have other maens of positive cap location. If you're going to rev this engine really high, have a heavy rotating assembly, or are adding artificial pressure tot he engine, than yes, use 4 bolt mains, for a street engine, just use studs in your 2 bolt block. As for studs v/s bolts, the bolts when being torques are twisting and pulling on the threads in the block, when you use studs you just pull on the stud, creating more accurate torque values and being much easier on the block. This creats a superior clamping force.