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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
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| | | | Joined: Jan 2006 Posts: 42 Junior Member | | Junior Member Joined: Jan 2006 Posts: 42 | 3970010....302.....69....4...Z-28 Camaro 3970010....327.....69....2...Trucks and industrial 3970010....350...69-80...2 or 4 what do the numbers for "main cap bolts" mean? :confused: Any way to narrow this down? Please remember I am really new at this.  Thanks to all in advance!
jcf
| | | | | Joined: Feb 2002 Posts: 2,893 Socket Breaker | | Socket Breaker Joined: Feb 2002 Posts: 2,893 | main caps are metal straps/brackets on the bottom of the engine where the crankshaft is... and they have either 2 bolts per bracket or 4 bolts per bracket... for Hi-Po use the '4 bolt mains' as they are referred to are considered stronger and more desirable. some of the guys in the Hi-Po shop could prolly explain it better, with pictures.  I'm sure Wrenchbender Ret. can straighten me out if I'm wrong... -W | | | | | Joined: Apr 2005 Posts: 926 Shop Shark | | Shop Shark Joined: Apr 2005 Posts: 926 | Woogeroo is right about the 4 bolt main being stronger.You might want to keep in mind though that a "4 bolt main" engine will probably cost more to get,and that unless you subject your engine to very hard use or want to run it at more than 5,000 rpm,a "2 bolt main" engine will hold up just fine. The main things to do are to use a high volume oil pump,and the special drive shaft that is required with it,use a good timing chain and gear set,and call the tech line for whatevewr brand of camshaft you choose to use,and let the expert on the other end help you pick the right cam for your use. The right cam makes a bigger difference in the performance of your engine than any other mod you can make.
Also,if you have a "2 bolt main" block,you probably can run the "4 bolt main" bearing caps,but you have to have a machine shop drill and thread your block for the extra bolts,and you must then have the caps torqued down and the block line bored.(lotsa work and money for a little extra security)
This is probably more than you ever wanted to know,huh?
Speed | | | | | Joined: Jan 2006 Posts: 42 Junior Member | | Junior Member Joined: Jan 2006 Posts: 42 | printed it out, thanks again.
jcf
| | | | | Joined: Feb 2006 Posts: 117 Wrench Fetcher | | Wrench Fetcher Joined: Feb 2006 Posts: 117 | Just wanted to add that in the 400 sbc blocks, the opposite is true...2 bolt blocks are better due to the cylinders being so close together (siamesed) As long as you are not spinning the motor over 6krpm on a regular basis, it should hold up fine with cast parts. Anything over 6krpm (racetrack visits, nos, etc) and forged components are the only way to go. Dano 
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