Pontiac 400??

Discussion in 'High Performance Modifications' started by NYH1, Nov 26, 2010.

  1. NYH1

    NYH1 Veteran Member

    1,512
    0
    Feb 27, 2010
    Central New York
    I know this is a Camaro site, but the Firebirds and Trans Ams are sister cars to our cars. So here go's.

    Can a Pontiac 400 with 6X heads setup properly make around 400 HP with good torque for street use with the right compression, good hydraulic flat tappet cam, RPM type intake and 750/800 cfm carb, full length headers and a 2 1/2" full length dual exhaust system?

    Thanks, NYH1! :bowtie:
     
  2. Kamikaze

    Kamikaze Veteran Member Lifetime Gold Member

    Most definitely!

    Where you are at used to be a hotbed of Pontiac performance! You need to research Nunzi Romano. He was the Pontiac genius in the 60's-80's and some of his performance works produced insane Poncho power!

    More parts are available today for Pontiacs but good basic hot rodding will yield great torque and horsepower that rivals Big Block Chevy power
     
  3. z28rod

    z28rod Veteran Member

    4,473
    0
    Apr 30, 2009
    hopewell junction,ny
    yes if done up correctly.
     
  4. warped

    warped Veteran Member Lifetime Gold Member

    Nunzi romano -- I haven't heard that name in 30 years. Check him out here:

    www.nunzi-pontiac-expert.com
     
  5. 455 Formula

    455 Formula Veteran Member

    1,421
    0
    Dec 8, 2009
    Fresno, California
    NYH1,

    Pontiacs are my specialty....my 413 CID Pontiac street-motor devloped 433 HP @ 5500 451 lbs/ft of TQ @ 4800 with 6X-4 heads, 9.00:1 compression, custom-ground Ultradyne .491"/.510" - 231°/235° @ .050" - 110.5° LSA hydraulic flat tappet camshaft, Performer RPM Intake, 800 cfm Q-Jet, 1-3/4" headers and full 2-1/2" exhaust. Ultradyne has done all of my custom grinds for years and their work is excellent.

    This is a very simple engine to build. I did a lot to this engine that wouldn't be necessary for the average street engine, but that's just how I build things.

    This engine is based on a 1970 4-Bolt Main block bored .060" over to a 4.181" finished bore size. The stock 'N' crankshaft was retained as was the stock 3.75" stroke length. The CID works out to be 411.9 and I refer to this motor as my '413' for discussion purposes.

    The block is zero-decked (about .017" overall) to bring the piston crowns level with the deck. Speed Pro Hypereutectic Flat Top Pistons are used (L2262F) with Total Seal Gapless Rings. With the 85cc chambers of the 6X-4 head and a .039" gasket, the static compression ratio (SCR) works out to about 9.30:1.

    [​IMG]

    To begin with, I install screw-in galley plugs up front in place of the stock press-in plugs and polish all of the casting flash out of the oil passages. I also enlarge the tiny 3/8" oil feed in the block out to 5/8" and polish/enlarge the passage all the way from the pump to the filter housing. The oil pump is also matched to the opening in the block.

    [​IMG]

    This is a critical, often overlooked area of mismatch and oil flow restriction in a Pontiac. Shown below is the stock oil hole for comparison.

    [​IMG]

    I use a grooved camshaft thrust plate, that is highly polished and is fitted along with a 9-keyway timing set with a bronze thrust washer. This improves oiling and reduces thrust wear on the face of the #1 camshaft journal and camshaft gear.

    [​IMG]

    The 6X-4 heads use the stock diameter 2.110" intake valve and were fitted with the larger 1.770" exhaust valve. The heads were ported and fully poished to 241 cfm intake @ .600" and 212 cfm exhaust @ .600" lift respectively.

    [​IMG]

    [​IMG]

    Crower #68405 dual valve springs are a 100% bolt-on and provide about 115 lbs seated @ 1.700" and roughly 285 lbs @ .500" net valve lift. The 6X-4's have screw-in studs and guideplate from the factory, so nothing is needed in this area. The stock pushrods are also hardened, so they can be used as well.

    The block and heads are drilled between the center cylinders, as was the early 421's, to provide additional cooling into the center exhaust port section of the heads. This is very easy to do, as most Pontiac head gaskets all have this hole.

    [​IMG]

    Since Pontiacs use oil, draining back out of the right rear orner of the RH cylinder head to lubricate the distributor gear, I drill a .030" hole in the galley plug right in front of the gear. This gives the gear pressurized oiling.

    The engine that the local Chevy guys really hate is my 9.50:1 Pontiac 350, cleverly disguised as the original 455 that came in my 1975 Formula.

    [​IMG]

    This is a basically stock, 1975 350 short-block with factory flat-top pistons. The heads are 1966 421 (092 castings) with 1.920” intakes and 1.660” exhaust valves. The heads have been fitted with ½” screw-in studs, replaceable valve guides and the spring pockets were cut to accept Crower 68405 dual springs @ 1.700” installed height.

    [​IMG]

    The camshaft is another one of my creations and features .466”/.467” (actual) – 220°/226° @ .050” on a 111.5° LSA.

    [​IMG]

    The intake is a simple Edlebrock Performer, the only aluminum intake that will fit under the Ram Air Hood, with a 800cfm Q-jet featuring .070” air bleeds, .039” idle tube restrictions, .056” idle channel restrictions, a 7 in/Hg power piston spring. .074” main jets with .045” metering rods. The secondary side features .029” metering rods and a ‘G’ hanger.

    The ignition is handled by a stock GM HEI with a zero-resistance carbon button between the coil and rotor, which replaces the stock carbon button, which has a whopping 9kΩ. This is one of the big limitations in the HEI unit as far as ignition output goes and a source of elevated coil temperatures. You just don't need that kind of resistance, especially with resistor wires and plugs!

    The timing specification is 20° BTDC at 800 rpm with 16° of mechanical advance and a Crane adjustable vacuum advance set to provide 8° of advance for 44° total advance.

    Headers are 1-3/4” primary Heddmans with full length, 2.50” mandrel-bent Flowmaster exhaust with a 42585 crossflow muffler.

    Corrected HP and TQ output was 373 HP @ 5650 rpm and 397 lbs/ft of TQ @ 4200 rpm.

    For dyno testing, 92 octane pump gas was used with #2 heat range Autolite AR72 Racing Plugs gapped at .045" respectively and open exhaust. When the AC R46SZ plugs, gapped at .080" were used, HP and TQ levels remained unchanged, but the engine starts faster, had better throttle response and a smoother idle with reduced exhaust emissions.

    I hope this information is helpful...
     
    Last edited: Nov 26, 2010
  6. 455 Formula

    455 Formula Veteran Member

    1,421
    0
    Dec 8, 2009
    Fresno, California
    One of the weak areas of any Pontiac V8 is the cast connecting rods. Shown below is a stock (cast) Pontiac rod on the left and a 5140 forging on the right.

    [​IMG]

    It is important to note that I always use a 5140 I-Beam Rod (at a minimum)in all Pontiacs to replace the factory cast steel rods.

    [​IMG]

    These feature 7/16" ARP Wave-Loc Bolts and torque to 75 lbs/ft. They are good insurance at less than $250.00 a set.

    [​IMG]

    Very good rods...

    [​IMG]
     
  7. NYH1

    NYH1 Veteran Member

    1,512
    0
    Feb 27, 2010
    Central New York
    Thanks guys. My friend swapped out a 400 Pontiac and installed a GMPP 454 HO Crate Motor for one of his customers GTO's. The 400 wasn't original so the guy didn't want to rebuild it. He wanted a bolt in crate motor instead. My friend has the 400 Pontiac and it's just sitting in his shop. I figured if he's not going to do anything with it and wanted to get rid of it, I might be interested in hanging on to it for a future build.

    I like Firebird's and Trans Am's even GTO's, Lemans, Tempest, and Ventura's. Not that I'd do anything with it anytime soon. But if it'll make around 400 HP with good street torque on pump gas, that's got me written all over it.

    How does the 400 compare to the 455? Can the 400 be stroked? Or is it better to stay with the stock stroke in a 400?

    Thanks again guys! ;)
     
  8. 455 Formula

    455 Formula Veteran Member

    1,421
    0
    Dec 8, 2009
    Fresno, California
    Stick with the 400.

    Yes, you can use a 421 crank (4.00" stroke) in a 400 and make a 440 or a 455 crank (4.210" stroke) and make a 462, but the 400 is hard to beat and is a very stout performer.

    A 440 or a 455 will make more torque, but requires clearancing the oil pan rails with a die grinder and custom pistons.

    Here is something to chew on....

    I recently took a bone stock, USED junkyard 400 with unported 6X-4 heads with the stock (1.660") exhaust valves and installed one of my Ultradyne 231°/235° @ .050" - 110.5° LSA hydraulic camshafts in it. That's only about an 8.50:1 compression motor. With a tuned Q-Jet and headers it made 380 HP through the mufflers.

    That's 380HP from a nothing junkyard motor with used rings, guides, bearings and unported heads....
     
    Last edited: Nov 26, 2010

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