I am just wondering what the real diffrence is in a 2 bolt main vs.a 4 bolt main. It looks to me that there isn't any way to break or pull the bolts off at the block. So why did the machine shop take my 2 bolt and make it a 4 bolt?? I know I should have ask them but, I didn't wont to look real stupid face to face so I'll ask you, you cant see me. Lol!!!!!! Why is 4 better than 2 ??? Just wondering,Hawk
My little 67 SS 350 http://photos.yahoo.com/firefly_40440

While I'm not a ME, I am trying to get my degree in it and haven't taken the proper courses to correctly explain your question.

Basically, you have the load spread over the four bolts than the two. Also, the main cap and block webbing is larger, which can sustain higher loads.

I believe for a 400 block, a 2-bolt is prefferred because of the larger main journal size. The larger journal makes the webbing weaker in a 4-bolt block.

Somebody better chime in here and correct me if I'm wrong!

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Matt Jones
1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my UPDATED webpage at: http://www.geocities.com/compuboy007/ (Updated: 1/13/03)

There are two ways to go about a 4 bolt block. A factory 4 bolt is a good thing, but there are better ways to obtain more clamping load from the main caps themselves. If you were to take a 2 bolt block and make it into a four, specifically a 'splayed' 4 bolt register, the strength and the ability of the caps to hold the crank in the block is much greater.

A 2 bolt block has thicker main webs, which basically means there is more meat to them. That makes them choise for a 'splayed' configuration.

A 4 factory four bolt (parallel) is good too, although it does have some weakness'. The clamping load is only in one direction, which theoretically is not as strong as a 'splayed' four bolt. The parallel 4 bolt has been prone to cracking in between the bolts.

Simply, the answer to your question is that a 4 bolt, splayed or not, has the ability of providing a higher clamping load to retain the crankshaft in a performance application, with the better being the 'splayed' type register.

When you get to a certain 'level' of performance, the main caps can actually lift off the block register and change the bearing clearence by quite a bit. So the splayed design was figured to be the best to combat this phenomenom as its clamping force is in two directions. With the stock four bolt design the cap can still lift as the bolts only retain the crank in one direction.

Hope this provides some insight.

[This message has been edited by chicane67 (edited 01-14-2003).]

VS.... 4 bolt is said to be sturdier. But then I've read 2 bolt will let you know you there's a problem coming up sooner than a 4 bolt that is said to just cut loose when it breaks. A heck of a way to put it but it's the way I read it. So I'd figure for basic car use either is OK but for high performance 4 bolt is better... or at least you can figure it will take more torque.

Milodon has 4-bolt splayed kit for two-bolt blocks.

Comes with steel caps, bolts, and drill bushing for block. Block must be aligned-bored.

I have no problem with my two-bolt blocks at 6500 rpm, KNOCK ON WOOD!!! I could be running on borrowed time.



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Everett "OBJECTS IN THE MIRROR APPEAR QUICKLY UPON RAPID DECELERATION"

The best design to me is the two bolt with the horozontal bolts coming in from the sides. But this only can be this way if the block is a "Y" block, (i.e., deep skirted block), like the new LS1 or the old 427 Ford's.

I don't recall other's, but am sure there are at least a couple more blocks made this way....pdq67

Unless you are doing something very serious with your engine there is no reason the factory 2 bolt setup won't work just fine. When I say serious I mean like a bunch of juice or something to that effect. I have a friend with a 2 bolt long rod 427 that goes through the lights at 9200 RPM he has had no trouble with the 2 bolt block.

I wonder why they changed it to a 4 bolt without your knowing of it. Are you sure that's the block you took in?

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Robert Johnson

'69 getting better every day... (every pay day) (http://www.angelfire.com/ab7/tempcarpage)
350ci 700r4 (2000 stall) 3.55 posi A/C PS PDB

if 4 is better then 2 then 6 must be better then 4 http://www.camaros.net/forum/wink.gif

My new mustang cobra block has 6 bolts on the inside mains in a splayed configuration and it'll spin at 6800 rpm all day long.

-Marc

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69 Camaro* (http://sfcamaro.home.mindspring.com/web/camaro_front.jpg) 350/350TH (http://sfcamaro.home.mindspring.com/web/camaro_engine.jpg)
99 Explorer 5.0L (http://sfcamaro.home.mindspring.com/web/explorer.jpg)
01 Cobra 4.6L (http://sfcamaro.home.mindspring.com/web/cobra.jpg)

Here's a 6-bolt design - the Viper V-10 has 4 parallel bolts on each of its six main caps, plus two more horizontal cross-bolts on each one; the caps are recessed into the main webs, so the loads are equally distributed throughout each main web. You can see the six cross-bolts in this photo:
http://image1.villagephotos.com/pubimage.asp?id_=349603

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JohnZ
CRG
'69 Z28 Fathom Green

It has been known to be said that a 2 bolt block with studs is as strong as a stock 4 bolt with bolts.

The use of studs has definate advantages when considering clamping load.

And yes, most street engines will live just fine on 2 bolt, non-stud bottom end to 6000-6500 RPM without a hickup.

But spending the $38.00 on a stud kit is cheap.....but you will also should have the mains align honed. The way the fastner distributes the load, changes how the metal distorts under load. If you dont align hone you take the risk destroying the bearings and crank.

[This message has been edited by chicane67 (edited 01-15-2003).]

Thanks for the answers from everyone I was just wondering why they may have done that to my block. Im sure its my block because its a # matching car and I double checked it. Thanks everyone again, Hawk
My little 67 SS 350 http://photos.yahoo.com/firefly_40440

Don't the new LS1s have a 6 bolt main?

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Matt Jones
1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my UPDATED webpage at: http://www.geocities.com/compuboy007/ (Updated: 1/13/03)

Chicane,

I just tightened mine down in small steps, spinning my crank all along..

I think I did about 15, maybe 20 pounds first, then used a three pound Ford Tool and a block of hard wood to set my thrust bearing loading, front and back, then continued!!!

I do however recall peining my mains with a dull chisel, though to make double sure they registered tight, side to side... Just did a schosh, that's all...

Worked fine... pdq67

<BLOCKQUOTE>quote:</font><HR>Originally posted by Silver69Camaro:
Don't the new LS1s have a 6 bolt main?
<HR></BLOCKQUOTE>
YES! http://www.camaros.net/forum/biggrin.gif And LS6s

Speaking of Vipers - I have two of them.......Vindshield Vipers!

Ok BPOS, now SLOWLY...put..down...the beer and step away... http://www.camaros.net/forum/biggrin.gif


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Matt Jones
1969 Base Camaro
Vortec 355, Perf. RPM, Demon Carb., TH-400
All sheetmetal is NOS GM
See my UPDATED webpage at: http://www.geocities.com/compuboy007/ (Updated: 1/13/03)

Now that's funny!!

I've found that from 1980 to present, the 2 bolt main smallblock is STRONGER than the 4 bolt. I find less cracks in the main webs. My reasoning is that when gm re cast the blocks they made them lighter in 1980 and lighter still in 1986. Drilling an additional 4 7/16 inch holes in the main web did nothing to make the engines stronger.

I feel the same way on splayed bolts on 1980 and newer stuff. in my opinion a 2 bolt 010 block with splayed 4 bolt mains are the way to go. and an 010 2 bolt block is stronger than any 1980 to 98 4 bolt.

my .02
John