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    Results 1 to 11 of 11
    1. #1
      Join Date
      Feb 2015
      Posts
      6
      Country Flag: Canada

      1970 GTO 400 Build

      Hello all,
      New to the site, just recently purchased a 1970 GTO and would like some advice on building a strong +/- 400HP engine. The car was originally ordered with a (L74)Ram Air III V8, unfortunately that is not what is currently in there. Currently has a 400 with a Holley intake, Carter AFB 8822, Heads are stamped "092". I just removed the engine yesterday, prior to that it ran well with no smoke, however, it did leak more oil on my floor then I care to describe. I did a compression test before removing engine and trans, all eight tested at +/-140psi. I am doing a Bore Scope early next week to see what I have going on inside.
      It is bolted up to a THM400 3spd auto and a 3.90 Posi rear end. Any suggestions on whether or not any of these parts are worth keeping in a decent configuration would be greatly appreciated.

    2. #2
      Join Date
      Apr 2013
      Posts
      120
      Country Flag: United States
      Without question talk with Cliff for your carburetor needs, no one better that I am aware of. http://www.cliffshighperformance.com/ As for intake manifold it would be very difficult to find a better intake for street and mild track use than a factory original intake for your GTO. Pontiac engineers did a fantastic job on their design and they are an excellent choice. Talk with Cliff and get his opinion as well. So get yourself a well tuned original Pontiac Quadrajet, a factory intake and if desired have your heads enhanced from one of the many Pontiac specific vendors, again talk w/ Cliff on who, what and where. I would steer you towards Dave Bischop at SD Perfomance, The Butlers in Tennessee, Kauffman in Ohio, etc. You have lots of options and certainly get over to the "Performance Years" Pontiac forum and ask all your questions there, the very best Pontiac specific forum on the net.

      Tim john---

    3. #3
      Join Date
      Jun 2006
      Location
      Katy,TX
      Posts
      1,678
      092 I pull up is a 66 389/421 head. If it is only 140 cranking either it has a big cam or something is amiss. My 8:1 400 ran 160 cranking. Those heads should put you at 10:1 or so depending on pistons. They are a closed chamber and not the best head either.You need to get the block casting number and code also to see what you really have there. Carb I pull up as a 625 cfm Carter. 65 and 66 389s etc used a Carter carb and had a dual plane manifold for that carb bolt pattern. 67 up they went to the Qjet.

      Is the intake the Holley single plane? If so on a smaller motor like a 400 you are also loosing some bottom end compared to a dual plane like the factory intake or the Performer(OK for a smaller motor like a 400) or Performer RPM.
      1978 Black Trans Am 455 Edelbrock heads [email protected] through mufflers on pump gas
      1981 Trans Am 400 stock type motor
      79 Camaro getting a 500" 695 hp IA2 Pontiac motor
      1965 GTO project car
      470ci/Chevy dual quad 409 604 HP 64 Impala SS project
      2004 Pulse Red GTO

    4. #4
      Join Date
      Feb 2015
      Posts
      6
      Country Flag: Canada
      Nice catch there, I just researched the casting number and code and something is amiss. What I have is a 1966 389, ouch. Casting number is 9778789 with code YC and a date code G116. Thanks for catching that, however now I am more unsure where to go with it. The Holley intake is a single plane and I cannot find a model number(it just has street dominator and firing order cast in it) to see what I have here. Is this block worth pursuing or am I throwing good money at bad?

    5. #5
      Join Date
      Mar 2011
      Location
      Ca
      Posts
      336
      Country Flag: United States
      what are your plans for the car, thats the first question that needs to be answered. if you're racing then the Holley is the intake you'll want, you'll also want to upgrade the heads in some form or another, if your just building something to cruise around with and have some good power on hand ditch the holley and get a dual plane intake, the carb you'll want to match up to the motors needs after you get your plans set, it'd be nice to know the cam specs and what youre doing for exhaust, everything needs to be added up to get you what you want. if you're cranking compression is as low as you stated you may have a pretty good cam in there already and that may not end up the best option for what you want to do, lots to think about and plan. don't just throw money at it and hope it runs, to many people do that and end up disappointed with the end result. a 389 with an actual 10 to 1 compression ration will not be hard to hit 400 hp, you need to spend in the right places and knowing whats already in place parts wise would be super helpful.

    6. #6
      Join Date
      Feb 2015
      Posts
      6
      Country Flag: Canada
      I am taking to a shop next week to do a bore scope, we can inspect the crank and cam then, I will at least know what I have and go from there. I will keep you posted. Thanks

    7. #7
      Join Date
      Jul 2013
      Location
      St Louis
      Posts
      213
      Country Flag: United States
      Check out this link for block ID http://www.pontiacstreetperformance....p/blockID.html. The year is always stamped by the distributor hole. 70=1970 block and they usually have the CID cast in the side.

      Pontiac Powered 72 GTO

    8. #8
      Join Date
      Jun 2006
      Location
      Katy,TX
      Posts
      1,678
      Holley intake is OK with a lot of massaging for a more race oriented motor, and larger motor.

      Any 65 and up intake will fit. 65 and 66 had an AFB Carter style carb , 67 up a Qjet. Pick one up if you keep it.

      389s can perform as well as a 400 but the heads are the kicker for performance. Sell it as a 66 389 to some restoration guy and build a 400 or 455 with 68 and up heads. What compression if you are going to use pump gas.
      1978 Black Trans Am 455 Edelbrock heads [email protected] through mufflers on pump gas
      1981 Trans Am 400 stock type motor
      79 Camaro getting a 500" 695 hp IA2 Pontiac motor
      1965 GTO project car
      470ci/Chevy dual quad 409 604 HP 64 Impala SS project
      2004 Pulse Red GTO

    9. #9
      Join Date
      Feb 2015
      Posts
      6
      Country Flag: Canada
      OK, I think I am back on track. I put the 389 off to the side for now.

      I found a 455 from a 1970 Grand Prix SJ. I just picked it up today. The guy I purchased engine and trans from was the original owner of the GP, he gave the car to his daughter and she smashed it up beyond repair a few years back so he pulled the engine and rebuilt it. It was wrapped in plastic in the back of his garage when I got there. Block code is "XF", heads are "64" with stock Qjet and stock exhaust manifolds. He did no performance upgrades when he did rebuild(he owned his mechanic shop before retiring so I am hoping that this engine is a strong starting point).
      What I am looking for is advice on upgrades before I tune and install. There is a guy not far from me that will dyno tune for me when I am at that stage.

      Thanks
      DW

    10. #10
      Join Date
      Feb 2005
      Location
      Waterloo, Ia
      Posts
      1,409
      That's a good starting point 455. This is the wrong place to ask the questions you are asking. Go here..... http://216.178.81.108/forums/

      That is performance years. Best Pontiac resource in the world. Go the the street section and be very specific about what you want. They will want to know how much compression you have so you might want to pull a cylinder head and identify your pistons, chamber size and how far down in the hole they are at TDC before you ask. Compression and cam selection is key to having a strong iron headed engine with 0 detonation.
      -Nick
      -1967 GTO I drive and race
      -Build threads:
      -http://forums.maxperformanceinc.com/forums/showthread.php?t=615847&page=23
      -https://www.pro-touring.com/showthre...project-thread


    11. #11
      Join Date
      Jun 2006
      Location
      Katy,TX
      Posts
      1,678
      Nick is right about the other site being a good one.
      That is a good 455 to start with but is a high CR. Heads have a smaller chamber for a 455 on pump gas. Lots of guys want them do you can turn them pretty easily. If you do keep them adding some slightly dished pistons and good rods would be a good upgrade. Then in the future you could always go with 72cc aluminum heads since you have a dish.

      Some guys will tell you you can run 10:1+ on pump gas with iron heads -ONLY if the tune cam selection is all perfect. Most of thos eguys also never test with race gas to see the motor does pick up showing it was probably detonating and they couldn't hear it.

      1978 Black Trans Am 455 Edelbrock heads [email protected] through mufflers on pump gas
      1981 Trans Am 400 stock type motor
      79 Camaro getting a 500" 695 hp IA2 Pontiac motor
      1965 GTO project car
      470ci/Chevy dual quad 409 604 HP 64 Impala SS project
      2004 Pulse Red GTO






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