4 bolt main 2 bolt main
Drifting
Joined: Aug 2009
Posts: 1,346
Likes: 160
From: new iberia la
The general rule of thumb is up to 400HP , a 2 Bolt Block is fine. After 400 HP ,4 Bolt is usually recommended ...If any kind of Power Adder is used, always go 4 Bolt . The 2 Bolt in your Stock L48 is more than enough ...
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
I have built 2 bolt engines up to 500hp and they are fine if studded.
The real killer is not HP but RPM.......and shock load if in a drag application. A Drag Car that "HITS" hard and revs high has the main webs moving around quite a bit.
A stock 4 bolt is not much help as the somewhat added strength is meaning less after 7000 rpm and about 600 ponies as the stock oiling system just will not sustain it.....the system can be modified....but at that point an aftermarket block is the viable option.
Actually a 2 bolt makes a better base to add splay caps to as the register is not cut as wide...and the outer holes are not drilled.
This kind stock block modification was the norm until the 90's...when Dart, World and GM all started making HP blocks....(The Dart and World have proprietary oiling....something for another time.)
Even the Bowtie block had to be drilled to allow proper oil volume.
For all intents and purposes....the only thing a 4 bolt GM block is good for is for restoration purposes....or conversations over Crown Royal with people who want to argue.
It is great if you have it...but not necessary!
Jebby
The real killer is not HP but RPM.......and shock load if in a drag application. A Drag Car that "HITS" hard and revs high has the main webs moving around quite a bit.
A stock 4 bolt is not much help as the somewhat added strength is meaning less after 7000 rpm and about 600 ponies as the stock oiling system just will not sustain it.....the system can be modified....but at that point an aftermarket block is the viable option.
Actually a 2 bolt makes a better base to add splay caps to as the register is not cut as wide...and the outer holes are not drilled.
This kind stock block modification was the norm until the 90's...when Dart, World and GM all started making HP blocks....(The Dart and World have proprietary oiling....something for another time.)
Even the Bowtie block had to be drilled to allow proper oil volume.
For all intents and purposes....the only thing a 4 bolt GM block is good for is for restoration purposes....or conversations over Crown Royal with people who want to argue.
It is great if you have it...but not necessary!
Jebby
Racer
Joined: Nov 2011
Posts: 261
Likes: 1
From: Montgomery TX
Instructor
Joined: Dec 2012
Posts: 107
Likes: 4
From: AZ
Most of the opinions here are a good rule of thumb, but I've seen blown alky BBC 2 bolt main last several years in a bracket dragster. It was a early 70's 1 ton pickup block that was ARP studded and freshened up several times a year. Your combo will really dictate when you need 4 bolt. I've got several friends that race jet boats with two bolt main 460 fords with factory main bolts and a girdle on the mains. They're pushing 900+hp naturally aspirated. But ford has huge main bolts compared to Chevy. Personally, I wouldn't go past 550-600hp on a 2 bolt main big block.
