2 or 4 bolt block

[cwilkie]

What is the difference between a 2 and 4 bolt block? Which is better or does it even matter?

Chance

[Joe67]

Here is a pic of a 4 bolt main block, 4 bolts hold on the main caps instead of 2. This is a stronger setup then a 2 bolt main setup.

[knsmodels]

Depends on your application. If you are just building a cruiser with occasional abuse (from the gas pedal... ) a two bolt main block is fine. If you are planning to be heavy on the abuse end you might want to use a 4 bolt block.......If you really want to abuse the motor at the track for instance I have been told a 2 bolt block converted to a 4 bolt is the strongest way to go......Hope this helps.....Paul

[panhandler62]

That about covers it. Always use a 4 bolt if money is not an issue but, for the rest of us, unless you are going for a serious build that will get serious use -- save the $$ and use a 2 bolt.

[arkracing]

Small Block 2 bolts are good to about 500 horspower if you put main studs in them.

BigBlock 2 bolts are good to about 650 horspower if you stud them.

There aren't many street applications that really need a 4 bolt main motor. A 1-ton truck that does alot of heavy towing or hauling may benefit from a 4-bolt.
most street driven trucks don't hook up the rear tires enought to merit the use of a 4-bolt main.

alot of people want the 4 for "assurance" or they just like to say "it's a 350 4-bolt main"

If you want a 700+ horsepower blown injected motor your going to use an aftermarket block or install splayed main caps anyway (the outside bolts in the above picture are angled out toward the oil pan walls)


I personally sell all my 4-bolt main motors to the guys who have to have one...and keep the 2's to myself besides if i ever build a motor that needs to be a 4-bolt you can rest assure it will be a World Products or Dart block.

j.m.h.o.

[cdowns]

4bolts overrated 2 is just fine for 90% of actual usage applications

[wolfthing2000]

Basicaly for the average Joe ,, all the 4-bolt is is something to brag and one up the other guys with .!!!

[junkyardjohn]

I ALWAYS USE 4 BOLT 350 BLOCKS WHEN I'M BUILDING AN ENGINE. MAYBE IT'S OVERKILL, BUT THEY COST EXACTLY THE SAME FOR A 4 BOLT CORE AS IT DOES FOR A 2 BOLT CORE, SO WHY NOT??? IT COSTS THE SAME (RIGHT TO THE PENNY) TO BUILD THEM. 4 BOLT 350 BLOCKS ARE NOT EXACTLY RARE, & IF ONE IS IFFY, OR NEEDS A SLEEVE..... I TOSS IT & GET ANOTHER ONE FOR $50 TO $70 AT ANY OF THE LOCAL BONE YARDS. JOHN

[FUNMUDDER]

I'd go four-bolt, too. Better to have toughness, even if you do just cruise around town. That way, when you see a ricer at a stoplight, you know you're ready

[HuggerCST]

arkracing is dead on the money. From my experience, (10 years circletrack racing), I have only seen one block ever fail, and it was a stock sb 400(about 500-550hp). It was a 2 bolt, but from what I hear, even the 4 bolt sb 400s are weak. If I had a choice between the 2 for an engine with less than 500 hp, I would simply pick the one with the least wear, and with the best casting. For a sb 350 above 500 hp, I would pick the 2 bolt, and add splayed caps, or go aftermarket.

[Joe67]

I guess it depends on how much you can spend on a motor and how you intend to drive it

[Dean]

You sure can't pick up a 4 bolt block for $50.00 at any junkyards around here.....I might need a road trip out west.

[arkracing]

just for referance around here in the Northeast: (it is obviuosly different out west since JYJ is getting them so cheap.... ....i'd buy a whole bunch of them out there for that kind of $$ and bring them back here and double it.

2-bolt bare blocks (at the machine shop) run about $50
4-bolt bare blocks (at the maching shop) run about $100-$125


but anyway it's really a matter of opinion..if you want it to say you got it...then go for it. if it doesn't matter to you then get whatever is the best core. if your racing it go after market or put splayed caps in a 2-bolt.

[junkyardjohn]

Originally Posted by 67c10step

I guess it depends on how much you can spend on a motor and how you intend to drive it

THATS MY POINT EXACTLY. THE COST IS THE SAME. SO UNLESS SOMEONE CAN CONVINCE ME THAT A TWO BOLT IS STRONGER THAN A FOUR BOLT MAIN, I GUESS I'LL CONTINUE TO USE EM. JOHN

[junkyardjohn]

Originally Posted by arkracing

just for referance around here in the Northeast: (it is obviuosly different out west since JYJ is getting them so cheap.... ....i'd buy a whole bunch of them out there for that kind of $$ and bring them back here and double it.

2-bolt bare blocks (at the machine shop) run about $50
4-bolt bare blocks (at the maching shop) run about $100-$125
.

MACHINE SHOPS ARE ABOUT TWICE AS HIGH PRICED AS JUNKYARDS. I COULD SPEND THAT MUCH OUT HERE IF I WANTED TO SHOP FOR CORES AT A MACHINE SHOP THAT I DON'T NORMALLY DEAL WITH TOO. BRING A BIG TRAILOR.... YOU'LL BE RICH...... RICH I TELL YA. JOHN

[arkracing]

Originally Posted by junkyardjohn

MACHINE SHOPS ARE ABOUT TWICE AS HIGH PRICED AS JUNKYARDS. I COULD SPEND THAT MUCH OUT HERE IF I WANTED TO SHOP FOR CORES AT A MACHINE SHOP THAT I DON'T NORMALLY DEAL WITH TOO. BRING A BIG TRAILOR.... YOU'LL BE RICH...... RICH I TELL YA. JOHN

i'll put about 20 of them in the back of my truck for that kind of $$$...looks like Dean will too.

Junkyards are pretty much picked clean here in the Northeast if it is a running motor they want $300-$500 for it and if you could find a bare block or core in a junkyard they run about $100-$150 your better off buying stuff out of the local classifieds. (4-bolts advertised as "rebuildable" anywhere between $150-$400 F...that)

Machine shops are about the easiest place and way to get blocks around here - Seems to be that everyone thinks motors are worth there weight in gold especially Big Blocks

[hilljob26]

im not sure,it also depends on if you are building a stroker or not,i would rather build a stroker out of a 2 bolt mainly beacuasee if it happens to come apart,you usually only have to get a new pan,and maybe,just maybe a rod,but a 4 bolt will stay together alot longer causing more damage to the bores of the engine,just my .02 but thats from my experience

[cdowns]

all the yards around here that i've gone to the smallblock chevy engines and most of the ford 9inch rears are pulled and sold wholesale to rebuilders long B-4 anyone has a chance to buy them

[pjmoreland]

I want to know why GM went to the trouble of putting 4-bolt mains on engines that only put out somewhere between 175 and 300 horse power. I have a 4-bolt main block sitting in my garage (3970010) that probably only had about 200 HP from the factory.

[Longhorn Man]

The 4 bolt verses 2 bolt is totally backwards if you are dealing with the 400 small block. The 2 bolt is stronger in that game.

[wolfthing2000]

I personaly went the machine shop route. 350 cleaned and magged for 150.00.. Now think about it: it will cost about that from a yard and then your teardown time and transportation, not to mention more money for clean and mag and then if it aint any good back to the yard again and try it one more time but this time you have to pay clean and mag again and hope that is a good one and if not:::::::::::::::::::::::::::::: Just call the machine shop and shop for a cleaned aND MAGGED BLOCK FOR YOUR BUILD.. wATCH OUT FOR THE YARDS.

[arkracing]

Originally Posted by pjmoreland

I want to know why GM went to the trouble of putting 4-bolt mains on engines that only put out somewhere between 175 and 300 horse power. I have a 4-bolt main block sitting in my garage (3970010) that probably only had about 200 HP from the factory.

they were mainly put in larger trucks 3/4 ton and up - because of the low gearing and the load that these trucks were pulling/hauling it put alot of tension on the crank. i've done a personal study and have found that 99% of the 350 4-bolt blocks have an 8" harmonic balancer from GM - the bigger the balancer the better the ability to control harmonic vibration of the crank.
these trucks also very rarely were expected to "break loose" - or spin the tires. there is alot less tension on a motor when it is spining freely than when it is "hooking up"

obviosly they came in other applications as well...maybe they had a batch of 4-bolts the day they did a run of the chevelles or whatever. I don't think GM thought out which motor when into the cars. but when it came to trucks most of them 3/4 + 1ton or larger ended up with a 4-bolt

that is just my own obversvation and thoughts on the subject. i could be completly wrong but i do know that most all the 4-bolt blocks have a 8" balancer...not all but 99% of the ones that i have seen neway

[edmonton72]

I know I was happy to find out when I pulled my pan off that my 350 has four bolt mains. Aren't 400 small blocks crappy anyways. My truck came with a 400 originally but I guess one of the previous owners put a 350 with for bolt mains so im happy about that. I think that motor has had work done to it, the cylinders are bored over .020. I can't wait until I get it back from the shop and start seeing some progress on my truck.

F.Y.I. - All the new Gen-III small blocks like the 4.8, 5.3, 6.0, LS-1, LS-2, etc. are six bolt mains.

[bowtie]

chance , the shop that built my 2 bolt main recommended the 2 bolt. They've been racing chevies since the 70's and have been racing Pro Mod for the last 10. As a matter of fact their going to Kansas to race this weekend and Spokane the following weekend.


arkracing
"I personally sell all my 4-bolt main motors to the guys who have to have one...and keep the 2's to myself besides if i ever build a motor that needs to be a 4-bolt you can rest assure it will be a World Products or Dart block."

[Mudder]

This is all good to hear. My 2 bolt 383 stroker is being assembled this week. It's getting studs.