Thread: 4-bolt main or not

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a guy i used to work with had just quit a machine shop somewhere down in california where he used to build pro stock motors all the way down to street motors. the shop went out of business after 22 years. his explanation of 2 bolt vs. 4 bolt was this. why do you need to worry about it? the force during acelleration is projected UPWARDS only on decelleration does the crank and its energy go downwards.

Makes no sense to me whatsoever.

Originally Posted by gassersrule_196

a guy i used to work with had just quit a machine shop somewhere down in california where he used to build pro stock motors all the way down to street motors. the shop went out of business after 22 years. his explanation of 2 bolt vs. 4 bolt was this. why do you need to worry about it? the force during acelleration is projected UPWARDS only on decelleration does the crank and its energy go downwards.

I will try and remember this the next time I build a 15 to 1 engine on alky.
Where do you think all the force goes on an engine that has 15 to 1 for a comp. ratio and turns over 8,000?
That's right, the pistons and rods are trying like hell to push the crank right out of the bottom of the block.
This has to be one of the most asinine statements I have heard in a very long time.
Please don't believe everything you hear.

Originally Posted by gassersrule_196

a guy i used to work with had just quit a machine shop somewhere down in california where he used to build pro stock motors all the way down to street motors. the shop went out of business after 22 years. his explanation of 2 bolt vs. 4 bolt was this. why do you need to worry about it? the force during acelleration is projected UPWARDS only on decelleration does the crank and its energy go downwards.

Think he's confused, Scooter!!!! he could only (possibly) be referring to the torque created when you drop the hammer at the line on a solid mounted engine.... All those explosions in the cylinders create huge amounts of pressure that trys to rip the webs right out of the block!!!! That's how an engine makes power.....

I raced dirt modifieds for years and one of my best engines was a two bolt block that got splayed caps. It turned 8200 rpm with 525 hp and I ran over 30 shows on it before rebuild. I also ran alcohol for fuel. $7000.00 goes a little ways sometimes. Get an opinion from a machine shop that builds race engines not just reman stuff. You will likely be happier. just my .02

This argument can and will turn ugly in less than a heart beat. You all have hit the point of "downward thrust", etc. The 4 bolt main was designed as a misnomer. The weak spot was the bridge (arc) across the cap. Therefore, major block builders have beefed that area. The 4 bolt system as a straight through bolt was for keeping cap walk down to an absolute minumum. The bridge will still be your weakest link and needs the most amount of your building attention. The splayed version was found to be be most effective in controlling block fatigue and stress on rpm usage. It loads directionaly perportionate to the cylinder rather than "tug" away in an opposite state from the loaded arc of the crank. Rather than take my word for it, dig a little deeper into the geometry and load values of the webbing and it's supports (main caps) and see if I just fell out of my tree. My mentors from Dave Crower, Mike Troxel, Lee Beard, Robert Street, Bob Duvore, and others had to slap me around on this subject many years ago and I had to also learn the hard way of what can and will go wrong. 2 bolts live with proper geometry, Just don't try to make "King Kong " out of it. Know your limits and get wise to the money it's going to take to build "King Kong". Many race programs that are successful will be glad to answer questions in this area. Dig in and do some research, it's a lot of fun and very enlightening.

hey denny this is OT but was it you who posted some website that you can look up certain cars that were in movies or tv?

I heard that on a 2 bolt engine,replacing the factory bolts with studs finger tight and nuts is stronger than standard 2 bolt,and on a 4 bolt do the same to gain strength there too

I paid $400.00 to have my 350 block converted to a 4 bolt. Not bad because the block was free. It has Competition Products straight bolt caps.
Wayne.

Originally Posted by toolmantom

I heard that on a 2 bolt engine,replacing the factory bolts with studs finger tight and nuts is stronger than standard 2 bolt,and on a 4 bolt do the same to gain strength there too

Yes,ARP studs should be installed "finger tight" and then their own moly paste used on the threads or 30 weight oil and follow their torque specs.
I like to torque in five steps.

I heard form a guy, that the 400 2 bolt is better for more horsepower built-ups, then the 4-bolt. because of the placement of the 2 other caps, he says there in the wrong place, and didnt really do much more then a couple holes in the block?

IMO any block is better with the splayed caps then the straight bolts.... Never have had much trouble with 2 bolt blocks, not a lot of Ford 4 bolt stuff out there unless you want to buy new.... Unless I'm going with a blower or nitrous I usually don't worry about it, especially on a street engine with 9.5 or 10.0 compression. Good machine work, proper assembly, and cam and heads to make power at a reasonable RPM IMO is still far more important then how many bolts the caps have...... I mean heck, if it's just a cruiser, why pretend it's being built for Pro Stock????

ok, i must be thinking of number of caps....... on all sbc's there are four caps??? 2-bolt, 4-bolt means how many bolts there are holding them down??? or is 2-bolt, 4-bolt mean number of caps??

im still kinda of new to this, but, i have a 400, and i want to give it some more power, this same guy i was talking about in the thread above said he has built many 377's and there a really strong and powerfull engine, doesnt anyone know of some configurations that could be used on this, like cam specs, intake, heads specs?? i would like to keep the same bore, only because i think the engine was fairly fresh when i got it, just new rings, any one built one of these before???

We're talking about the number of bolts per cap, 2, 4, or 6...