I've got a Aug '69 built 396/402 (still unsure which) that has .060 over pistons in it. The best I can tell with a cheap micrometer is a 4.125 inside bore. Does this help in translating whether this is a 396 or 402 block? I know the 402's started in '69 but not which month GM made the change. The block is a 3969854. Thanks in advance if anyone knows.

I think the 3969854 could have been a 68-72 396 or 402 depending on the bore size.

Standard bore on a 396 was ~4.094, while the standard bore on a 402 was ~4.125. The factory bored some of the 396's out .030, resulting in a 402 block. It sounds like you might have a 396 bore with .060 pistons = ~4.155 bore

Two letter engine code "should" be a 396, three letter engine code "should" be a 402.

Look at the code on the front right side of the deck.

Schurkey, where's the two or three letter engine code you are refering to? There's an F8? Bad Rat, the deck is clean, so it's either been shaved or no #'s there, if your talking about the area where the vin should be. I do have a vin behind the oil filter so it may not have been stamped on top. Anybody else have a vin in this location?

If you face the front of the car it's on the left front deck corner. That is unless the deck has been shaved enough to remove it.

I have the same engine, It's a 402 if the bore is
4.125.

Mine is bored 0.40. which makes is a 406. graemlins/thumbsup.gif

I picked up a digital micrometer and I'm getting 4.151-153 at the lip of each cylinder, probably 4.155 at the center. Crazyhorse what is the date code on your block and where is your vin number located on it? A .040 over 402 is the same as a .070 over 396 isn't it? They were the same block right? Not trying to confuse anyone but has any one gone .060 over with a 402, which would be a .090 over 396? :confused: This is not trying to be sarcastic in any way, just trying to get to the bottom of this so I know what my rebuild options will be prior to bringing the motor in. Thanks for your help.

I bored my 396 .090 over. I haven't started it yet. I'm still waiting on buy some new headers.

Hey, Crazyhorse - even better news, if you're .040 over, you actually have 410 c.i. graemlins/hurray.gif

Hey Bad Rat 414, what pistons and rings are you running and what year is your block? Brand and part # if you don't mind airing your secrets. ;) Any others out there feel free if you know of any. The pistons that are in the motor now are .060 over Speed Pro's, as Bad Rat was kind enough to point out in an earlier post.

If your at 4.155 and the pistons say .060 then you either have a .030 over 402 or a .060 over 396. The only difference in a 402 and a 396 is that they bored the 396 out .030 to make the 402. Speed Pro/TRW made pistons for both motors and so there is no way to tell just by the piston size (i.e. a .06 over 396 piston will fit fine in a .03 bored 402 but the piston part number will reference to a 396 bored .06 over and vis versa). Unfortunately the 3969854 block was used in late 69's and was a 396 but was also used all the way up until 72 as the 402. The only way to know for sure, since it's been bored, would be the engine code which doesn't appear to be on your block. The F8 your refering to is probably the casting date, if it's along the bellhouseing flange next to the casting number. It should have a third number (i.e. F=June 8=8th the last number would be the year) If that number is 9 it's probably a 396. If it's a 0,1,or 2 it's a 402. Hope all this makes since. :confused:

Trooper

Oh yes,
I bought a 396 block that was already .060 over and bored it to .070 over and put Speed Pro pistons in it made for a .040 over 402. Works like a charm. My machinist is very conservative and was nervous going .070 over but we had no problems. He said he has gone .090 over in the past with no problems but he has gone through the wall doing this once or twice. He showed me a block this happened to. It was sad. He also told me he has seen guys go .090 over and everything looks OK but they blow the wall out or it cracks when they get the motor running only to find out it was too thin. Don't mean to alarm you Fat Rat. I'm sure your will be fine. graemlins/thumbsup.gif smile.gif

Trooper

She's real fine my 4 1 0 :cool: tongue.gif

(Can I just say 409?) :D

396/402 will go .125 over...can you say 427?

This is why you have to sonic test a large bore 396/402, seems the 427 and 454 blocks could go 120 over bore with not to many problems...
(I would never go over 80)
also, sleeving is not un-common on the BBC.

When I bought the elky, the pistons were installed wrong on the driver side, Bent rods cracked pistons, and 4 cracked cylinders.

Anyway, the engine was sleeved and problem solved. (Matching Number Car)

Here's a concept, Take a 454 bore it to say 100
then install ceramic sleeves and ceramic coated pistons titainum rods ceramic bearings.......
.......Well maybe not.... graemlins/clonk.gif

Originally posted by Rapid Robert:
396/402 will go .125 over...can you say 427? =
Bob,
Most will, some won't.
Before I even knew what a sonic testor was & bored a lot of rats +125 for 427's & 482's,,, also put in a number of sleeves :D
I have a 66 396 4 bolt block right now that is .060 over & checks at .181" on the thrust side in a couple of cylinders.
Probably wouldn't want to go another .065 for anything serious.

OK Wolf... Just what would you be comfortable in
boring a 454?

Not sonic testing of corse. :(


I plan on a 454 build this summer... :D

Originally posted by Crazyhorse:
OK Wolf... Just what would you be comfortable in
boring a 454?

Not sonic testing of corse. :(


I plan on a 454 build this summer... :D =
If I am going over .060 I sonic test it. It is cheap, fast & just makes me feel warm & fuzzy all over when I know their is a bit of metal behind that nice shiny new bore :D
That said I have not had a rat that I would not use for most stuff at .080 including the one mentioned which would leave .170" (it is actually thinner on the non thrust side)
Chances are the above block would live at .125 over but it probably not make real good power in anything serious.
I have a two bolt 454 standard bore block that tests at .195 sitting here.
It would probably not be my first choice for .125" over :D
I would like .200" on the thrust side from about half way down on up but you ain't gonna get it on most blocks. I consider .150-160 as a minimum for performance.
Don't concern myself with the bottom being thin much, no load down there to speak of.

What are your thoughts on filling the block to the bottom of the pump ports?

Wouldn't this solve the thrust area weakness? or would this be a trade off for keeping it cool?

Depends on the use of the engine ;)
Filling will definitely help support the bores.
I don't like to fill a rat without an oil cooler for the street.
It covers up the main oil galley & you will see some pretty high oil temps.
A short fill won't really compromise cooling but filling to the bottom of the pump probably isn't the best plan for the street. :D

396/402 will go .125 over...can you say 427?
Rapid Robert,
What exactly are you referring to. A 427 doesn't use the same block casting as a 396/402. The 427 block was cast with thicker cylinder walls to accommodate the larger bore. You try to take a 396 .125 over and your treading on thin ice not to mention cylinder walls, if there are any left. Can you say resleeve

Trooper

Originally posted by 70ECam:
Hey Bad Rat 414, what pistons and rings are you running and what year is your block? Brand and part # if you don't mind airing your secrets. ;) Any others out there feel free if you know of any. The pistons that are in the motor now are .060 over Speed Pro's, as Bad Rat was kind enough to point out in an earlier post. My block is a 1969. The pistons are Speed Pro L2383F .060, I don't have the number on the rings right now. They are Speed Pro moly rings. I have a picture of the pistons on my web site.