Big Block Motor - Any Details?

[Joel T.]

Hi All...

I've got a big block Chevy motor which came out of a 1965 Vette which I picked up last summer. I was wondering if anyone could shed any light on what this really is...

Casting number is 3999290

Casting date is J 4 71

Pad T1007THB with no Vin# stamped

Pistons 2347P marked .030"

Near as I can figure this is a 402 replacement for the original 396. I have not pulled the pan but I assume this is a two bolt main set up.

Any ideas as to what the compression rating of the pistons is, or any other details, or what might be an appropriate application??

Thx, Joel

[Edward M.]

Re: Big Block Motor - Any Details?

Looks like a 1972 402 210hp, installed in a truck, 4 bbl carb.

[Joe L.]

Re: Big Block Motor - Any Details?

Joel-----

I don't think that the 3999290 block was ever originally manufactured with 4 bolt mains, so your assumption is probably correct. However, it can be rather easily CONVERTED to 4 bolt main configuration.

The pistons identified as "2347P" are stock type, Federal-Mogul/Sterling conventional cast pistons. With stock heads they will produce a compression ratio of right at 8.5:1. These are obviously for a .030" overbore, so the actual compression will be slightly higher than 8.5:1.

How did the motor run when you got it? Was there any problems with pre-ignition? With this kind of compression ratio there should not be, but big blocks have a great tendency to that condition, even at relatively low compression ratios.

[Joel T.]

Re: Big Block Motor - Any Details?

Joe,

Thanks for the information. I ran this motor in the car for only a short period of time and did not notice pre-ignition, but again the thing had a set of (after market) side pipes so I could not hear much other than the roar! It ran OK but not what you would expect from what was supposed to be a 425HP motor. It also had a set of oval port BB heads which I believe were from a later model 427/425 (3919840 B-18-9 casting date). What I am basically doing here is trying to figure out what to do with this motor... For the '65, I've found a correct block (resto) and a set of 208 heads with correct date codes so I have that covered. If this motor is worth some work I might look to find something (cheap) to put it in!!!

Regards,

Joel

[Mark #28455]

840 heads are worth some $

The block is nothing special but the heads are in demand by restorers for Corvettes, 375 HP 396's and COPO Camaros. The heads alone could bring $1000 or more a pair. Sell them and pick up a mid 1970's 454 core for about $400, then you have $600 to use on the rebuild. An oval port 454 will pull much harder than the 396 (especially with rectangular port heads). Just make sure you use a SHORT duration hydraulic cam.

Mark