Technical 396 Chevy block with blocked water passage

Hey Guys,

New member here, so probably a dumb question.
Why do I see what appears to be blocked water passages at the front and rear deck of this 1966 396 engine block?
Thanks,
Kevin

 

Quick google search shows a 65-66 block in ebay that looks the same, must be normal.

 

The heads and gaskets are the same on both sides, so they have a coolant passage in the head at each end....but the block only has the passage at the rear, because you want the coolant to flow all the way to the back of the block, before heading up and forward through the head.

that's how all the Mark IV big blocks are.

this is the 396 in my shop right now....

 

I believe all the Mark IV blocks were that way...

 

Squirrel is always the quick draw!

 

Wow! I really appreciate the fast response; you guys are awesome.

As a follow-up topic, this is a 3902406 block, which is supposed to be a 396, but the block is bored to 4.320, which is like 0.195 overbore for a 396, or 0.070 overbore for a 427! I didn’t know you could overbore this much.

 

He is quick on the tree, and has the right answers! I'll just delete another post.

 

are the freeze plugs out of it? The test to see if it'll take the larger bore (4.25 or more) is that you can't stick a normal wood #2 pencil in between the cylinders, though a freeze plug hole. On the blocks that will not take the larger bore (like my 396), you can fit a pencil through them. This is because of the thickness of the cylinder walls.

 

That’s some awesome knowledge right there!

 

It sure is. Been playing with big blocks a long time and never heard of that. Guess I’ll throw out my ultra sound.

 

It's an old thing, I expect you can find it elsewhere on the internet. Of course you'd want to check the wall thickness with ultrasound, if you have a thin wall block that's punched out to the big bore size.

 

I like to go conservative with boring a 396. No more than .060" over for my liking. I'd rather make up for displacement with the stroke even if it means more expen$ive pistons.

 

According to internet lore, in 65-67, Chevy used the same casting for 396 and 427, and just bored the block according to which engine was desired. These are the blocks that pass the pencil test. Supposedly, these blocks can go 125 over to a 427 bore with no problem.
I have no personal experience; I’m just reporting what I’ve read in the past few days.

 

Well...the 396 that I posted a picture of the deck surface, fails the pencil test, it has a late 1965 casting date. It's already 60 over, so I was pretty interested in checking out that internet lore you're quoting. It's BS.

If your block is a 4 bolt main, then it might be the same as a 427 block.

 

Correct me if I'm wrong ;the 65 396 bore started at 4.093 and wasn't 4.125 from the factory until late 69 and 70. I don't know why the factory started with an unusual bore dia.

 

yup, 396 till the 1970 model, then it was a 402. And they called it a 396 still, unless you were ordering parts from the aftermarket, then it was a 4bbl 400. Not to be confused with the small block 2bbl 400

 

Yes, this block is 4 bolt main

 

Do the pencil check, please let us know.

 

Some good quick reference info presented above. In the end you still need to do an ultrasonic test before you decide whether to bore it or not. If you have one that the pencil goes in, thats a good quick indicator, but cores shift and bores aren't always in the center of the casting due to production variations. Measure twice cut once applies here too.

 

I think they were more likely to be called out as a 402 when used in trucks. Had a 402 w/ a Q-jet in a 3/4 ton Suburban years ago.

 

My grandfather had a ‘70 3/4 ton with “400” and I think an “8” as well on the fender badges. It was a BBC.

 

I thought the pencil test was a check for sagging boobs. Learn something new every day!

 

My pencil holder!

And a '70 BBC 402 pencil check.

 

Mine was a '72 Suburban (the last of the 3-doors!) but I don't remember it saying 400 or 402 or having any type of engine designation on the outside. But now that's been more than a few years ago . . . so . . .

 

Lol. This was in the early 70’s. My Grandparents were over and a guy stopped to see my dad. We were out front and he said “I bet that’s a small block” looking at the emblem, he popped the hood and said “I’ll be darn”.
If he hadn’t of noticed it I would never have this useless trivia in my head all these years

 

I have a 1968 bbc 396 bored out to 4.155 and have 454 990 heads what cam should I run and also what size pop up piston works best

 

^Just run your finger to the bottom of the cam chart and buy the biggest one. Huge domes on some cheap cast pistons and good to go!

 

but seriously.....

If you tell us all about what you're going to do with the engine, then we might be able to make useful suggestions.

 

I want my 1969 c10 long bed to haul ass when I smash the gas pedal..I'm mostly going to street race it ..with a 2500 stall converter in the 400 trans 3 speed