Register now to get rid of these ads!

How to identify a 327

Discussion in 'The Hokey Ass Message Board' started by V8PunkRocket, Jan 16, 2007.

  1. Hey everyone,

    I'm looking at buying a 327 block I found for sale. The person selling it gave me the casting number, which is 3970010. According to, this engine could be a 302, a 327, or a 350. At first I was assuming that the 327 and 350 would have different cylinder bores, but I looked that up on the site and they both have 4.000" cylinder bores! (I don't know how accurate this website is, either)

    So, how would I tell if what I am getting is a 327, or just another 350? (I don't want a 350, I know small blocks are over-done as it is, but at least a 327 is slightly less common)

    I appreciate any info anyone has. Thanks!
  2. Orange54
    Joined: Mar 6, 2004
    Posts: 795

    from Missouri

    Is there a date stamping on the back of the block? Is there a stamping on the pad in front of where the passenger head goes?
  3. Tony
    Joined: Dec 3, 2002
    Posts: 7,286


    Being an 010 block, it's a large journal and should be of the '68 ( either 67 or 68 was the first year for the large journal..can't remember right now) and newer vintage.
    The only difference between the large journal 327 and 350's are the crank. Different stroke's per ci. They used the same block.

    If you can check the casting number on the crank itself, it will tell you which one it is.. that is if the pan is off obviously :)
    I have that same casting number mill in my 57 chevy. Mine was originally out of a 69 3/4 ton truck and is a 350.
  4. An intake casting number as well as the head numbers would aid in deciphering what it is. I think its more likely to end up being a 350 but there is a slim chance....
    Register now to get rid of these ads!

  5. Rand Man
    Joined: Aug 23, 2004
    Posts: 3,290

    Rand Man

    Is it just a block? The 3.25" crank is what makes it a 327. Your block could be built with a 3.48 crank and then it would be a 350. If you put in a 3.00 crank, then you have a 302. If you put in a 3.75" crank it becomes a 383 (with a .030 overbore).
  6. I learn new things every day! I will email the seller and ask if he can give me the crank casting number. Unfortunately, the engine is minus the heads and intake. I'll also ask about the date stamping. Thanks for the suggestions and information.
  7. Flatbush
    Joined: May 23, 2006
    Posts: 47


    68 was the first year for big journal,spin on filter and no vent in the rear of the block (for road draft tube or block mounted PCV) meaning you will have to vent it like any ol 350. Probably not the look you want. Big journal, 327 cranks are very, very rare.
  8. Fat Hack
    Joined: Nov 30, 2002
    Posts: 7,704

    Fat Hack
    from Detroit

    If it's in a "rat rod"...then it's automatically either a 327 or a 283!!!:D

    (Ha Ha...seriously, Tony said, the crank is what will give it away in a "0010" block)
  9. Geez I can get my hands on 2 68 Chevys both 327 4 barrel cars.... just have to tow them away. By that I mean dig them out of where they sank in the dirt!
  10. Gunny
    Joined: Feb 28, 2006
    Posts: 191


    the early 327 (the small jurnal jobbers) have the oil draft ( for pcv )casting in the rear behind the distributor hole..the later (large jurnal) was just like the 350 blocks ..hope this helps

    Attached Files:

    Joined: Nov 22, 2005
    Posts: 7,594

    from SIDNEY, NY

    If the heads are off, you can easily turn it over until a pistons is at BDC and measure the stroke.
  12. Model A Vette
    Joined: Mar 8, 2002
    Posts: 1,028

    Model A Vette

    If you want to make it a 327 you just use a 307 crank (same stroke as 327).
    That block was pretty common as you found out on Mortec's site.
    All the blocks with that casting number would have large journals, would have no cast in hole like Gunny's picture and spin-on filters.
    Can you get the number/letter code stamped on the pad in front of the pass head? That would help narrow down what it was originally.
  13. For those reading this and wondering "why bother, build a 350 and call it anything..." I can tell you from experience that a 327 has a smoother 'feel' to it, and revs slightly faster than a 350.
    I had a 327 in a '72 Camaro (it needed an engine, and I found a '68 327 out of a Caprice...), drove it both before (ratty 350) and after the swap, and liked the 327 better.
    Oh, yeah, the Camaro was a four speed car, too. The 327 felt REAL good with the muncie.

  14. That's because of the rod length to stoke ratio. The 327 is almost perfect.

    GM built the 350 using the same length rods and a longer stroke. This screwed up the ratio.

    To fix what GM screwed up, ya' need to put 6.0" rods in a 350. Then it'll behave better.

    The small journal 327 was probably the best V8 GM ever made. Most of the large journal 327's got cast cranks and ya' don't need the big bearing diameters.

    AND...........GM made the same screw up when they stroked the 427 to 454. Both use the same rods. 427 is quick reving. 454's are lazy.

    Ol' Smokey Yunick was an advocate of using the longest rods ya' can fit in an engine. Technically it makes sense.

  15. RacerRick
    Joined: May 16, 2005
    Posts: 2,749


    They are are not. They are just known as 307 cranks.

    Build it as a 350 if its a street engine and call it whatever you want. Much cheaper and torquier than a 327.
  16. '81 Exnihilator 327
    Joined: Jan 25, 2008
    Posts: 1

    '81 Exnihilator 327

    As mr. RacerRick said so dully, a 350 is much torquey-er.....but its a s simple as most of the others are saying, no one really prefers a 350 over a 327.....they rap up faster, the compression ratio(in relativitey to the motor) is much better, and they perform better, and they are sought after much more than a 350.
    rareity will make or break the trade/sale of any classic car part, so if you can get your hands on it, take it!
    Trust me youd rather find out for sure after youve bought it, than to find out it was a 327 after youve already lost it.....measure the stroke.....3.25"........bdc-->tdc!!!
  17. enjenjo
    Joined: Mar 2, 2001
    Posts: 2,370

    from swanton oh

    I have a fresh .010,.010 large journal 327 crank for sale.
  18. Joe Daddy
    Joined: Nov 21, 2007
    Posts: 232

    Joe Daddy

    From what i know, the cast# 3970010 is most popular as a 350 block. It came in production from 69-80. Also, but very rare, it can be a 302. In 69 the Z28 camaro had the same cast#. As far as i know the 327 never came with that #.
  19. silent rick
    Joined: Nov 7, 2002
    Posts: 3,431

    silent rick

    fuckin newbies bringing up year old posts, wtf?
  20. so..what would happen if you put 6" rods in a 327? i've got two of them. would you have to clearance the bottom of the cylinders? that number is very common. all i've ever seen it listed as is 302/350 no 327.
  21. Tony
    Joined: Dec 3, 2002
    Posts: 7,286


    This is copied off of Mortec's site which list's GM factory casting number's. You are right on the money about it being a comon casting number..

    3970010....302.....69....4...Z-28 Camaro
    3970010....327.....69....2...Trucks and industrial
    3970010....350...69-80...2 or 4

    As far as the 6" rod's on a 327 crank...good question..One i never gave any thought to myself..hmmm

  22. went back and looked my book does list as a possible 327 also. missed that somehow. i never thought about the rods either until this thread. seems to me a guy could have short stroke and big compression. with the right top end components this could be a real screamer in theory. are the rod journals the same diameter?
  23. Not2low
    Joined: Sep 5, 2007
    Posts: 83

    from Eaton,Ohio

    Depending on your needs and the cost of the 327 you are wanting you might think about building your own.All you need is a 307 and any 350 block with two piece rear main seal.Buy a set of 327 pistons and you are there.I just bought a complete 307 for $50.00, and I bet you have a buddy with a 350 block laying around.Food for thought for a low budget build.
  24. poncho62
    Joined: Nov 23, 2005
    Posts: 1,094


    If you want to find out what it "WAS"........(I take it there is no rotating assembly) need to look up the suffix code that is stamped into the pad in front of the passenger side head. It is 2 or 3 letters.........Look it up here.

Share This Page

Register now to get rid of these ads!


Copyright © 1995-2013 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.