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Pontiac Motor/Tranny in '70 Blazer

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by T HAUS, Sep 5, 2001.

  1. T HAUS

    T HAUS Newbie

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    Pontiac Motor/Tranny in \'70 Blazer

    Has anyone had the experience of putting a Pontiac motor/tranny in a GM 4X4?
    I had a Pontiac 400 with a TH400 tranny attached, given to me a few yrs back. I had the motor rebuilt to put in my GTO, but have since sold the Goat. The motor has Ram Air III heads on it and a midrange cam. I think it will perform great. These Pontiac motors put out some awesome torque.
    I've talked with a local tranny guy and he said all I need to do is swap out the tailshaft in my TH400 with one that matches the input gear in my transfer case.
    Just wondering if anyone had done this and what info you might have.
     
  2. BluThndr71JMMY

    BluThndr71JMMY 1/2 ton status

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    Re: Pontiac Motor/Tranny in \'70 Blazer

    A buddy of mine had a C/10, '78 stepside with that lashup installed: a Pontiac 400 and a TH350 or 400. The engine worked well in there. Cheers for GM engineering compatability. He had problems with the body work, however -- Pass side door had to be caulked shut. The door hinge support pillar was rusted (in AZ!). Also the hood was bent in the middle. Not to mention the sidemounted gas tank. I like the older New Breed trucks -- '67/'72 -- solid sheet metal, no frills, just Tough Trucks.So I think your Pontiac 400 would probably fit fine in a '70 Blazer. Is it a small block or a big block? I don't know Pontiacs that well. But both the SBC and BBC have been successfully installed in 1stGen K/5s.
     
  3. Roostr84

    Roostr84 1/2 ton status

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    Re: Pontiac Motor/Tranny in \'70 Blazer

    The older pontiac motors are neither small or bigblock. they are the same externally as far as i know. I dont believe they had a "Small block" until the 301 smogger.

    Chris =)

    I think the exhaust fumes have finally gotten to me!!
     
  4. T HAUS

    T HAUS Newbie

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    Re: Pontiac Motor/Tranny in \'70 Blazer

    Roostr is right. All the Pontiac motors used the same block, just changed the bore, stroke, etc. If you've ever seen the inside of a Chevy motor, wait till you look at the guts of a Pontiac. This one has huge mains (4 bolt too) and a monster crank. They were truly built for power. I had to have it bored .30.
    My Blazer is a basket case as far as the body goes. Prev owners must have let it sit for a LONG time without a top on it. The door hinges are rusted away from the pillars. Both sides of the floorboards are gone, even the windshield frame is rusted thru. Just got a '72 Blazer front end installed under it this past weekend, so I've got disc brakes now. Going to put the rearend under today.
    Gotta run. I hear some fine thread rusted U-bolts calling my name. ( I hope the cheeter bar is cooled off....)
     
  5. bitchin4x4

    bitchin4x4 1/2 ton status

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    Re: Pontiac Motor/Tranny in \'70 Blazer

    I believe the 455 was a bigger block though.

    If it ain't broke, break it!
     
  6. Steve_Chin

    Steve_Chin 1/2 ton status

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    Re: Pontiac Motor/Tranny in \'70 Blazer

    All Pontiac blocks (including the 301) share the same bore spacing. The tall-deck engines (326-455) all have identical external dimensions. The main distinctions are main journal size (326-400 blocks have a 3" main journal diameter, 421-455 blocks have a 3.250" main journal diameter) and deck height (the lightweight 301/265 have a shorter deck height than the 326-455 family). There have been a LOT of different pulley/bracket setups over the years that varied not only by model year, but by chassis.

    I was planning on putting one of my spare Pontiac 455s into my Blazer, but I decided against it when I couldn't find a bellhousing for my transmission (NV4500) and also figured that the stock clutch linkage wouldn't work (no secondary boss for the block side pivot stud). With an automatic, it'd be an easy swap. Since you have a TH400, I would suggest changing the input gear on the NP205 to the 32 spline female setup (this requires machining the case for a larger input bearing). You can then pretty much bolt the TH400 directly to the NP205 (I have never done a TH350 to TH400 swap on a GM 4x4, so I am not positive, but from what I've read, those are the mods necessary to do the swap, perhaps someone else here has done it). For the engine, I would suggest that you keep all of the pulleys and accessories off of the donor car and swap them in with the engine.

    What year 400 and what year/casting number heads do you have? Since you have a 4-bolt block, I'd guess it's a '68-'70 400 block. 400 Ram Air engines used the #48 (1969) or #12 (1970) heads. Both heads have 72cc combustion chambers and 2.11"/1.77" valves with pretty decent ports (could be cleaned up for better performance without hurting low-lift flow). What are the cam specifications? What intake will you be running?
     
  7. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Re: Pontiac Motor/Tranny in \'70 Blazer

    So could a 326 be turned into a 400?

    Rene

    <font color=green>Dyslexics of the world...UNTIE!</font color=green>
     
  8. T HAUS

    T HAUS Newbie

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    Re: Pontiac Motor/Tranny in \'70 Blazer

    Steve,
    It's been 3 yrs since I had the motor rebuilt. I had a local machinist do the block and head work and he was the one who told me about the Ram Air heads. Just by running casting numbers thru an old motor spec book, it came back as a late 60's-early 70's motor. I had the motor and tranny given to me, so I have no idea what it was in. There's a slim possibility that it was a GTO motor, but I doubt it. The motor still had the "ball" on the back/side of the block for the clutch linkage, so who knows???
    A "gear head" friend of mine ordered the pistons and cam for it. He's a drag man and had never messed much with 4x4, so he went a little mild on the cam. All I know is that the cam is Wolverine cam and it is a 260 series. I have forgotten the intake and exhaust specs on it.
    I haven't purchased an intake yet. I'm just in the process of getting the motor/tranny put in to determine if we need to move/modify motor mounts. I'll then check for clearance for headers and go from there on a intake/carb combo.
    As for the t/c, you described the mods for a New Process t/c, but the one I have is a Dana/Spicer. I haven't been able to pin down exactly what model it is, but I'm guessing a model 20?? I had a local tranny guy give me a tailshaft to put in the TH400, but it's not the right one.
    I'll check the cast numbers on the heads and let you know.

    Thanks a ton for the input.
     
  9. Blazer1970

    Blazer1970 1/2 ton status

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    Re: Pontiac Motor/Tranny in \'70 Blazer

    I don't think you will ever be able to adapt the model 20 t-case to your TH400. You should start looking for an NP205 to use. You will need a 205 with the 32 spline female input, and the adapter for the TH400 trans.

    Tim

    70 Blazer CST 4X4 350 SM465 NP205
    87 Burb 4X4 350
    01 GMC 2500HD 4X4 Duramax/Allison
     
  10. DesertDueler

    DesertDueler 1/2 ton status

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    Re: Pontiac Motor/Tranny in \'70 Blazer

    Let me know where you are getting motor mounts. I have two 400s laying around in my garage. You know in case I blow the one in firebird, and the other one for another just in case. I figure it would work better in a truck though.

    86 Jimmy 4"lift 35"MTRs Other cars 69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  11. Steve_Chin

    Steve_Chin 1/2 ton status

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    Re: Pontiac Motor/Tranny in \'70 Blazer

    No, a 326 cannot be turned into a 400 because the OD of the cylinder walls is smaller than on a 400. I suppose one could be wet-sleeved and then turned into a 400 (or bigger) that way, but that's an expensive proposition.

    The coolest thing going right now (it's expensive) is to put the new stroker crankshaft the Jim Butler has for the 400 blocks, bore 0.060", and make a 468 out of the thing. It uses custom pistons and BBC 6.8" rods for a reasonable R/S ratio.
     
  12. Steve_Chin

    Steve_Chin 1/2 ton status

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    Re: Pontiac Motor/Tranny in \'70 Blazer

    As was said before, the New Process 205 is the way to go with the TH400.

    A 400 should make decent power and torque. Check the head casting numbers (on the two center exhaust ports or on the exhaust port that's on the left, depending on what year and model the heads are), the casting date (above and to the left of the center exhaust ports). Also check the two letter engine code (stamped into the front of the block below the passenger side cylinder head) and casting date (near the distributor hole in the back of the valley). The casting dates are standard GM in that they're a letter followed by three numbers. Those pieces of information should yield pretty much what original engine combination you had and in what year model car they were supposed to be installed.
     

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