4 Bolt Straight vs 4 Bolt Splayed Theory

[Fox Slaughter]

There has been lots of debate on whether to go 4 bolt straight or 4 bolt splayed mains. Now keep in mind I am not an engineer, this is just my theory behind the two setups.

I personally prefer 4 bolt straight mains. Here is why.

If you toe a nail into a 2x4 it is not as strong as a nail that is nailed in normally. A factory block is not designed for splayed bolts but rather straight bolts. Now some people say a splayed main will distribute the clamping force into a different axis. This would be good if they was a vertical and lateral movement. Half of your crankshaft main journal sits in the block and the other half sits in the main caps. If you ask me there isn't a real way for the crank to walk laterally. I have read reports of LTx mains walking at over 700rwhp, that's over 800bhp, with a 2 bolt setup.

So now if you have 2 bolts providing clamping force now add two more bolts. If you ask me 4 bolts with hold way more horsepower then the block would possibly be able to handle.

People talk about that if the bolts are straight they will rip out because all the force is pulling on them. A splayed is less likely to break because its on another axis then the straight bolts. Well you aren't going to strip the threads or rip the bolt out of a hole, the bolts with just break in half. Now a bolt is designed to take stress along is axis. IE if the bolt is mount vertically then the bolt is designed to take stress vertically, not horizontally. If you were to apply pressure horizontally it will break way under its rating.

So you have a bolt that is say mounted at a 35 degree angle. It is going to take much less pressure to snap the bolt then a bolt that is being used as they are designed.

People will say mounting 4 bolts straight down or splayed depending on the block will tap the bolt into the weaker webbing. If you had 2 bolts into a weak webbing then yes this would be a problem, but when adding a 4 bolt setup you are only adding back up and distributing the pressure across multiple mounting points. Thus the material the bolt is mounted into is not taking as much stress as it would by itself.

I am not an engineer, this is my theory on the 4 bolt debate. Take it with a grain of salt. Ask your engine builder what he wishes to do.

[hoogiesngrinderz]

Shear VS tensil strength. Compare the red line to the green line, which would you think has a better sheer strength? Just a thought

[Fox Slaughter]

Shear strength is the object "sliding" and breaking. The Problem is with bolt being inside a hole it has no chance to "slide" or shear. Off ARPs website they state that the correct engaged thread depth must be obtained so a bolts shear strength surpasses the tensile strength of the bolt.

Also generally a bolts shear strength is about 60% that of its tensile strength.

.4375" ARP (7/16")

17780 Tensile Strength lbs
14280 Shear Strength lbs

http://www.rockcrawler.com/techrepor...ners/index.asp

[hoogiesngrinderz]

Just because a bolt is in a hold doesn't mean it cannot shear. Whether it applies to a main caps, not sure since half of the crank is "in" the block. Anything bolt that is angled on a shear line will have a much higher rating.

Toe nailing provides a stronger joint than face nailing, BTW.

[Fox Slaughter]

Take a something rigid such as a ruler or a tooth pick. Pull it along its axis. Bet you can't break it in two. Now take the object and hold it vertically and move your hands towards each other, it will break. Things are stronger along their axis. Take a carabiner, it is designed to be pulled along its spine which is its access. Side loading a carabiner greatly reduces its strength and it will break in half.


I also reword my last statement about a bolt shearing. Yes a bolt can shear in a hole with lateral force. I am talking about in a main cap sense. There really isn't any lateral force exerted on the main caps. Its a vertical force from the crankshaft trying to be 'pushed out of the block'.
sheartensile.png

"With direct shear joints the shank of the bolts sustain the shear force directly giving rise to a shear stress in the bolt. The shear strength of a steel fastener is about 0.6 times the tensile strength. This ratio is largely independent of the tensile strength. The shear plane should go through the unthreaded shank of a bolt if not than the root area of the thread must be used in the calculation. "

http://www.boltscience.com/pages/faq.htm#3

[hoogiesngrinderz]

Whoops, had my terms backwards. Face nailing is strongest, followed by toe nailing, then end nailing being the weakest. But the comparison is really like comparing apples to oranges. Grain, wood type, nail lengths, proper 30* toe nail, etc.


Keep in mind that any angular load is a result of a two forces
physics.png

[hoogiesngrinderz]

Then there are other factors to consider - cap walk, spreading out the forces into other parts of the block, so on and so forth. I'm interested in what people have to say about it.

The Camaro and the Bel Air both have 4 bolt. Not because I needed it, just happened that way

[Fox Slaughter]

Correct, yeah comparing wood and metal are two completely different animals haha. I was just reading that splayed mains usually are angled from 5 to 15 degrees. That is barely any degrees off a vertical sink.

Could I be wrong yes, but in my opinion there is no need to splay the block.

I mean a LSx block that will take over 2000hp is just a 6 bolt main. 4 vertical and 2 horizontal nothing splayed in them.



Are they for bolt splayed or just vertical .

[hoogiesngrinderz]

Just verticle - 1970 and 1991 truck blocks. The 70 is a flat tappet around 325hp and the 91 is a hydraulic roller around 425. Should be plenty for me. I hope.

[Fox Slaughter]

Horsepower is an addiction haha. I remember when I got my Camaro and I was like holy crap this is fast! (Stock) Now I am like jeez its like driving my cruise with 138hp. As Tim Allen and Jeremy Clarkson say "MORE POWER!"

This is why I like this forum. We can have a 'argument' well its more of a discussion of both sides, where as like Ls1Tech and stuff it would be, YOURE A ******* IDIOT ect.

[hoogiesngrinderz]

It actually caused me to get out my physics book and start reading it again.










Who the **** reads a college text book in their free time?! I've been going through my Calculus, C++, and XHTML/ASP books lately as well. Knowledge...gotta have it.

[Fox Slaughter]

I was reading into C+ for a while as I just recently dual booted my laptop for Windows 7 and Suse 12.1.

[hoogiesngrinderz]

I'm thinking about going that route as well, probably dual booting OS X Lion though. Windows 7 has been running slow lately - even with the SSD drive.


And after reading more about two bolt mains, it seems cap walk is the major killer. The caps get out of round and eats up crank bearings at high RPM and HP

[WMCCjames]

6 bolts FTW...end of discussion.

[DETROITMUSCLE]

This may be something else to consider as well, how many factory blocks come with splayed bolts? Ok how many aftermarket blocks? My assumption is not many and these are the types of companies with the money to properly test these types of things.