Thread: How much power will a 2 bolt block handle?

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My engine project is based in a 2 bolt block, and now i'm affraid about how much power will this block handle?

I'm sure you will have many advising you to use the four bolt, but when it first came out, the thinking was that for endurance engines, like in CanAm road racing, the two bolt was better, than the four bolt.

I guess the real question is, how much power are you going to make?

Originally posted by Alan76
My engine project is based in a 2 bolt block, and now i'm affraid about how much power will this block handle?

a 2 bolt block can handle alot more than you would expect.

for more strength you can buy a set of splayed 4 bolt main caps, and drill and tap the block. this would be much stronger than any factory stock 4 bolt block.

in a "chevy high performance" magazine they sprayed a junkyard 350 with NOS. and was able to get quite a bit of power from it before it blew. the crank didnt get hurt, only the stock cast pistons suffered the blow.

I would say the 2 bolt block can handle around 430 hp and under, but not with stock pistons and heads, would need some upgraded parts to prevent engine failure.

If you need to ask, you probably won't be making enough power to break a 2 bolt block.

HP has nothing to do with it. A two bolt block is stronger than a 4 bolt in the webbing. A four bolt was designed for extended running at above 7 grand. They were installed to keep the cap from walking. The thicker webbing in a 2 bolt is thicker and will handle more stress than a 4 bolt. Meaning it is "easier" to push the webbing out of a 4 bolt than a 2 bolt. If you want it stronger, Higher comp, ect, use a stud gurdle. It will keep the caps from walking and tie all journals together makeing all of them stronger. this is just my opi, i'm sure somebody will say i'm full of it but there it is. good luck robert

Originally posted by grunch
HP has nothing to do with it. A two bolt block is stronger than a 4 bolt in the webbing. A four bolt was designed for extended running at above 7 grand. They were installed to keep the cap from walking. The thicker webbing in a 2 bolt is thicker and will handle more stress than a 4 bolt. Meaning it is "easier" to push the webbing out of a 4 bolt than a 2 bolt. If you want it stronger, Higher comp, ect, use a stud gurdle. It will keep the caps from walking and tie all journals together makeing all of them stronger. this is just my opi, i'm sure somebody will say i'm full of it but there it is. good luck robert

I'm not going to doubt you. I have never heard that a 2 bolt block webbing is thicker than a 4 bolt. I have always thought they were cast from the same mold and was only machined differently.

you could be right, as I have never checked them myself.


and the 4 bolt block was develpoed to help with the stress of higher torque levels placed on the crankshaft and mains . most tow vehicles benifitted from the 4 bolt main blocks. and hp has everything to do with how much a block can handle. as everyone should know HP is a mathmatic formulation of torque/RPM's, to much torque at low rpms can destroy an engines internals. even bolts can only withstand so muct stress before they are stretched or broken. that is why I stated before a stock 2 bolt block can handle just a little over 400hp, and I should have included the torque of around 390 ft lbs at low rpms.

if you want high rpms and 450/450 hp,and torque. you will need to add the 4bolt splayed main caps. and use ARP bolts or studs. and when you spin an engine at higher than stock rpm's other things will need to be addressed as well, like oiling, bearings, valvetrain components, and ignition. no factory stock parts were made to go much beyond 6000 rpm's .

That is true of the 400's about the webbing, but there is no physical difference between a 2 bolt and 4 bolt 350 except for the 2 extra holes drilled for each cap. Any 2 bolt block can be converted to a 4 bolt by drilling the extra holes for the new caps. This is what most of the splayed cap blocks start out as.

They say a 2 bolt block is good to 500 hp if you use studs on the mains. Forgot where I read that. Ah now I remember it was a smallblock chevy book by Grumpy Jenkins.
I had a 2 bolt 400 block that I was going to go with but the darn thing had too much wear on the outside of the bores, actually found two 400 blocks with the same problem. Yes the 4 bolt 400 block is prone to stress cracking the main web area due to the material removed for the outer bolts on the caps. I ended up with a 4 bolt 400 block after all, haven't had any problems yet.

Thank you all, for your comments!!!

I did not fire the engine yet.
My engine is a 388 stroked with forged rotating parts, AFR heads, and i'm planing to run some nitrous. but i don't know if my main caps will survive to this power level! the only upgrade i had made was change the main bolts to ARP studs.
Since i can´t found good machine shops next to me, and main caps drilling are a delicate job, i preffer to not change the original main caps.
I will use this engine just for the street, but, once and while i will spray some nitrous.
How much power the two bolt main caps will handle?

A two bolt block is strong enough to handle anything under 450HP/450 ft.lbs. in the 6500 and below RPM range. The 4-bolt was designed for heavy towing to keep the crank from walking side to side at low rpm. I read of a test where a engine was built just to test a stock GM block. It had all forged internals and was put on a dyno. It was a 2-bolt main. The base HP was 512 @5800 and torque was 460 @4400. They started off with a 250 shot of N2O and did three pulls then increased to by 150hp shots doing three pulls each until at over 1200 HP the engine cracked down both sides in the lifter valley. No problem with the 2-bolt mains. If they were super weak, I think that would have been the first place to break.

I am by no way saying a 4-bolt is not a better block, just that a 2-bolt is not junk. If I built a 2-bolt over 350hp I would splay the three center mains just like the 2-bolt 400 blocks.

Originally posted by camaro_fever68
A two bolt block is strong enough to handle anything under 450HP/450 ft.lbs. in the 6500 and below RPM range. The 4-bolt was designed for heavy towing to keep the crank from walking side to side at low rpm. I read of a test where a engine was built just to test a stock GM block. It had all forged internals and was put on a dyno. It was a 2-bolt main. The base HP was 512 @5800 and torque was 460 @4400. They started off with a 250 shot of N2O and did three pulls then increased to by 150hp shots doing three pulls each until at over 1200 HP the engine cracked down both sides in the lifter valley. No problem with the 2-bolt mains. If they were super weak, I think that would have been the first place to break.

I am by no way saying a 4-bolt is not a better block, just that a 2-bolt is not junk. If I built a 2-bolt over 350hp I would splay the three center mains just like the 2-bolt 400 blocks.

that was the point I was trying to make, but it didnt come across as well as you have explained it. thanks

Originally posted by Alan76
My engine project is based in a 2 bolt block, and now i'm affraid about how much power will this block handle?

It also depends on the application.I.E. the shock load.If you are running around on the street with small tires, low stall speed I doubt 500 h.p. would break the block.Now if you had 450 h.p. in a tubbed car with 33/15/15 slicks,4 link or ladder bar's,5,500 stall and a trans. brake this would make me very nervous.We have run over 500 h.p. in a street car with a stud kit andnot had any problems.I have never seen anyone break a block ever in a street car.Now in a full on bracket car that is another story.

Thank you all!
I feel more confident about 2 bolt blocks!

just an example: My friend has an early 283 made into a 327. It is not dyno'd but works out to be about 400 hp. He can turn the motor up to 7500 rpm's with no problem. The reason I mention this is, this motor was just "thrown" together, nothing fancy, not even balanced! He's had it for years and still runs fine. To be honest, I'm surprised it still runs. That's why I like my chevy's, their tough little critters. Have fun.

A good block (2bolt with studs) will handle easily 500hp .
Thats a real 500hp motor like 10sec car. Most people over claim power and have never ever felt 500 hp,so you should be all set with 2bolt caps (except for all out racing).