Thread: question about 400 small block

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recently bought what i was told was an unmolested 4 bolt 400 short block. After disassembly i discovered that the block had been bored .040 over. Just wondering what the safest compression ratio and power output i should shoot for. I want as high as possible and still be on the streets. CR is not an issue as i work at a gas station that sells 112 octane leaded by the pump. i had originally planned on boring it .030 over with CR of 11.5-12 to 1. i plann on all roller valvetrain. Also are there any ways of strengthening a 70's factory block? any information is appreciated!

I think by I.D.'ing the block's casting numbers on the rear of the engine to see what you have is a good starting point.Here is a link for that:

www.mortec.com

After that to have the cylinders sonic checked is a good move and having it mag'ed.

Please keep us updated.

short fill with block rock

Originally Posted by pat mccarthy

short fill with block rock

Pat-that would stabilize the bores at the base for sure.The odd thing about these 400's is some have cooling problems and others don't.We know the bores on them move around quite a bit.Kind of a dumb design that GM created with those steam holes.Leaked down some and got a number of different %'s.We have seen filled blocks with the base is fine and the top was crack(thrust side that is).Really not intended as a hi-pro engine even through a number of guys have used then as such.

Originally Posted by 1gary

Pat-that would stabilize the bores at the base for sure.The odd thing about these 400's is some have cooling problems and others don't.We know the bores on them move around quite a bit.Kind of a dumb design that GM created with those steam holes.Leaked down some and got a number of different %'s.We have seen filled blocks with the base is fine and the top was crack(thrust side that is).Really not intended as a hi-pro engine even through a number of guys have used then as such.

well you can not have every thing now can you ? i know of 400s cracking thru head bolts holes as well on over bores i think it was a 060 over. he could all ways can sonic check it that would help as for heat short fill there maybe some heat soak but most of the heat is two inch s down from the deck better water pump alum heads better cooling all can help .thrust side if weak thin walls .bad rod angle. core shift. is going to help crack ahead of the block rock if heavy side load on bores. its that point its time to use a SHP dart block but he did not ask that

Pat,
Two yrs ago while I was at the Syr,NY Parts Peddler swap meet,I found a number of vendors selling "little M " blocks fully machined ready for assembly for only $1,200 bucks.Man those prices have dropped a ton.Not for nothing.

Is it not a good idea to sleve it Pat, if it's not a race motor?
Kurt

Originally Posted by vara4

Is it not a good idea to sleve it Pat, if it's not a race motor?
Kurt

i sleeved many race engine 1or 3 holes. i do not worry about sleeves in a well built block. in a stock block if you had the money you can sleeve all holes.i done race blocks were they were $$ to start with . with out sleeves pistons were going to end up to be off size customs were a smaller bore piston would be a shelf stocking piston with a ring set not hard to find but it gets $$ and better blocks can be found .less it a old engine that can not be found or a block thats was pickup very cheap your looking at about $100.a hole with a sleeve starts adding up

Got It Pat, It would be too much to spend on a wore out old block.
How much do those after market blocks go for?, I've never priced one.
Would you be ahead to buy one of those.
Kurt

I have a small block 400 with trans sitting in the garage. I have no use for it as i am a Ford guy at heart. Nothing against Chevy guys haha. I did pull it out of a 69 ford pickup(strange i know). Has 350 trans bolted to it. It ran a drove before i pulled it out. i was told the trans was fully rebuilt right before he drove the truck into a pole. And i looks as it has nice and clean almost new. He didnt say much about the motor except it was a 400 SBC like he was proud of it. If interested let me know. Ill take a few more pictures.

I have a 377 (400 block and 350 crank) putting out ~ 400 hp with zero problems. 6" rods, 10.5 CR. alum heads etc. Speed-O-Motive built my rotating assembly, and they do sonic check the 400 blocks first.

Russ