Down toward the bottom of the page in this link,

http://www.montecarloss.com/SSThunder/SBCinfo.html

there is some good info concerning 2 bolt and 4 bolt mains, and the appropriate power levels for each. I can't vouch for it's accuracy, but it's better than taking a wild guess, I guess......
As long as we are on the subject, I have a question which I am sure the OP would also be interested in hearing the answer to. Is a 4 bolt main block less likely to need a line hone when doing a re-build?

Scott

 

It really depends on what you feel comfortable with.

I have read in print and on-line that a good 2-bolt main small-block can take 500hp if it has quality studs in it.

I would have to believe it also depends on the quality of the engine build. A 4-good bolt build might withstand some slight quality issues that would kill a 2-bolt build.

I do agree with the others that building and engine that can use the factory hydraulic roller setup is a great idea.

In the end, what others write won't mean much if your engine fails.

 

Here is something to think about:

No human being has ever looked down at a blown engine and uttered this phrase-" Awww, man!!! If only I had used a 2-bolt main block instead of a 4-bolt main block, this never would have happened!!!"


Scott

 

A cast or a hypereutectic or a forged piston all have their tolerances built in the piston based on what type they are. On a forged piston that will be run hard from the beginning, I may if I feel or the owner wishes hone an extra 5/10s in the hole. A 0.030 is a 0.030 regardless of the piston going into it. Some guys like a litle extra in a forged piston build.
It doesn't take a huge amount of run time before those numbers change anyway. Next teardown on an engine who is running and not making noise and run a bore gage down it and mic the piston and might be interesting to see what clearance most engines run on. Most are running from 0.020 or more and die from an contamination or oil issue. Many won't clean up at 0.030 but didn't die from a piston related issue. A little tight will kill one quick, a litttle loose will not.

 

Scottyp99, LOL that is so true. Many more spun rods than spun mains. Ford ran a bunch of hogh torque and high HP engines with two bolt main engines.

 

Ever look at the bottom of an LS motor? Granted, it's an aluminum block, but it has a skirt that comes down past the centerline of the crank, with cross-bolted 4 bolt mains, so basically 6 bolt mains. That bottom end ain't goin' nowhere!!! I think if you can get your hands on a 4 bolt block it's a good idea. Kinda like chicken soup when you have a cold. Will it help you get better? I don't know, but it can't hurt!


Scott

 

i looked into this and it worked out to be more expensive then buying a Dart SHP block.

check out Dart.

 

I hear a 2 bolt block with splayed main caps into a 4 bolt main is stronger than an original 4 bolt main block.
I have a 2 bolt waiting in the garage for just such an adventure.

 

So what kind of engine failure can be attributed to using a 2 bolt block versus a 4 bolt block? Remember, we're not talking about a high rpm race only engine.

The article that Scott linked to states the following (note the bolded text):

"Small blocks and HP recommendations

This is according to several sources, none which completely agree, so I used the lower values from several sources and rounded down to be safe...
2-bolt blocks with OEM main bolts are good to 400hp
2-bolt blocks with ARP main studs are good to 550hp ++High Nickel Blocks to 700hp 4-bolt blocks with OEM main bolts are good to 475hp
4-bolt blocks with ARP main studs are good to 700hp
OEM Blocks with Splayed 4-bolt main studs are good to over 950hp
Bowtie blocks with splayed 4-bolts main studs should handle over 1500+hp!

So essentially, a 2-bolt block w/ studs should handle anything a normally aspirated small block can produce. (assuming everything is in good shape and proper tolerances are closely followed)

Engine RPM plays even a larger factor in determining safe power limits for various block/cap combos.

OEM 2-bolt blocks are good to 6000 rpm.
2-bolts with ARP studs are good to 7000 rpm.
OEM 4-bolt blocks are good to 7200 rpm.
4-bolts with ARP studs are good up to 8500 rpm.
Bowtie or OEM 4-bolt Splayed Studs and cap are good for well over 8500 rpm.

-These figures were aquired from a Super Chevy magazine, Popular Hot Rodding,
and a couple local machine shops

In the Article, it stated that a 250hp engine that was spinning at 7500rpm exerted more loading force
on the Main-caps than a 550hp engine spinning at only 5500 rpm. This means power and RPM must be considered
when selecting how much beef you need in your bottom end.

The HP figures are good references, but the RPM limit of the motor is a better way to choose your block
according to the authors of the article."

 

All interesting points. What are the new Vette motors equipped with?

 

Why is that relevant?

 

Not real relevant. Just curious since most of them are pushing 400+ HP if I'm not mistaken.

 

Also not relevant, but I know of a supercharged 427 big block chevy making over 1000 hp with a 2 bolt block and ARP main studs.

 

Scotty noted this above, but the LS engines are incredibly stout in the main web, with a deep block and 6 bolts on every main bearing. Many believe for the LSx block (below) the limit is probably 2500+ HP


In the end, it's all about managing risk. Main bearings usually don't catastrophically fail - i.e. push a main cap out of the pan...the engine just chews up a main bearing. You have to make a call based on the dollar cost of the engine how much risk you're willing to take.

I remember some guy with one of the 95-97 Impala SS's that was drag racing with a cast-crank 383 and like a 250 shot on a 2-bolt main block with stock bolts. We all shook our head, waiting for the failure post - but it just kept cranking away.

 

I doubt there is any one who can predict when any engine or its parts will let go, with relationship to rpm's. If you took a survey of bolt related to grenaded motor, you could get an infinite number of different opinions. Reflecting to what Scotty said earlier.
If I had to gamble I'd bet that debris in the system and/or oil issues take out many more than the number of bolts. I think it's more that the more bolts there are the better it looks like it will fare.
If you run the two bolt and balance it well, if you're going to race it at higher rpms maybe over ballance a half gram, and check your clearances well, grind out all casting flash and clean the hell out of it, you'll be in good shape on a limited budget.
In a money don't matter budget, they still let go now and then, or engines wouldn't blow in NASCAR or at the strip.
The harder they get run the shorter the lifespan, kind of like people.

 

The failures typically come from the main cap shifting under load and associated atypical bearing wear. They don't go boom - they just start making metal.

I would take that article with a huge grain of salt, or maybe a whole salt lick I don't know the guy so I have no idea what his credibility is or sources are, but I sure wouldn't run a 950HP, 8,500 RPM stock GEN I block! There are just too many (comparatively) dirt cheap aftermarket blocks to even think about it. At that build level, we're talking about a $25K+ engine...$1500 or so for an aftermarket block is a very small part of that overall cost.

There's no "right" answer here - just a builder's assessment of risk vs. cost.

 

People used to make fun of Ford for their skirted mains, now GM has gotten there. I think the weight of the skirted mains may be why GM did without.

 

Billla's right, It's a ballance of cash to parts. Just about everybody comes in working on a budget and still sucks big air when the machine costs start to climb. It's like restoration when one increase in quality leads to the next. Next thing you know your budget went up in smoke.

 

I guess the ProMod and SuperStock pro classes should be moving towards the LSx block if it will handle the power for a 6 sec run, btw I was thinking of building a another motor how do you check the piston to wall clearance anyway ?

Two bolt block with ARP main studs will handle 550HP at least that's what I read, or someone told me...oh must be getting old I forgot about my old 406ci that made 550HP with 2 bolt ARP mains

6500RPM

 

I do it with a mic and bore gauge - how do you do it?