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Mmmm....781 Heads w/Big Valves - Greg72's 496BBC Build Thread

Discussion in 'The Garage' started by Greg72, Mar 21, 2007.

  1. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Fresh valves (so Manley!) installed to check displacement for my 496BBC buildup...

    All credit goes to 4X4HIGH for performing the work, and spec'ing out the proper parts. :thumb: At this point, we know what style piston to order to keep the C.R. in the 9.25:1 to 9.5:1 range.

    [​IMG]

    :usaflag:
     
    Last edited: Apr 11, 2007
  2. thatK30guy

    thatK30guy 1 ton status Premium Member

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    Very nice!

    Wheres the shop Scott works at? Name, too?
     
  3. thatK30guy

    thatK30guy 1 ton status Premium Member

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    Oh, BTW, are you doing a "build up thread" like the others on this site? I'd like to follow along with your engine build up.
     
  4. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Fremont Machine in Fremont, CA. He is co-owner of the shop.

    I don't really have a buildup thread per se, but I do have a couple of photos of the 454 teardown in my gallery pages in the Suburban gallery folder:

    http://www.norcalbigdawgs.net/Gallery/album95


    We've been waiting to find out how many cc's the heads were, so that we could order a stroker kit with the correct piston for the compression ratio we want (not too high). Lots of fresh parts will be showing up in the coming weeks, and I'm sure Scott will take photos as he goes along......if he does, I'll repost them in my gallery.
     
  5. tarussell

    tarussell 1/2 ton status

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    Very nice !
    NEVRENUF and I used 781's and big valves in a roller BBC and it had a fantastic power band. Mid range torque was most impressive!

    Please keep the photos coming - it is always nice to follow along a well thought out motor build .

    Tom
     
  6. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Yeah......Scott and I were playing with some numbers in CamQuest6 and this motor puts out something like 590 Lb/Ft of torque the way it's getting built (mild roller cam, moderate C.R.) It's going to have to serve as my tow rig so I didn't want to give up low end TQ for a large peak HP number.

    I still haven't decided if it's getting a 6-speed manual, or some sort of O.D. slushbox.... :thinking:
     
  7. 76zimmer

    76zimmer Flyin Rat Premium Member GMOTM Winner

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    mmmm 496. looks like that'll be fun. Keep posting with pics and progress. You got me interested.:bow:
     
  8. mofugly13

    mofugly13 1 ton bucket of rust Premium Member

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    I am planning on building something similar, a 496 with 781's w/ big valves and mild porting. I want something that will last a long time as long as I take care of it, nothing too hot. So, what pistons are you using? Bored over any? Cast or forged crank? Rods? Should I just look in your other thread????
     
  9. thatK30guy

    thatK30guy 1 ton status Premium Member

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    Whats so great about the 781 heads? And 049's, too (if thats the right number)?

    If it were me, I'd spend the money on some Merlins.
     
  10. mofugly13

    mofugly13 1 ton bucket of rust Premium Member

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    Best flowing open chamber stock heads made. Merlins are what, around a grand or so? I haven't added up the cost differences between the two by the time everything is said and done, but I bet Greg has an idea......


    Greg, what's up with the different valves in different chambers? Manley vs. stock? For checking chamber volume?
     
  11. thatK30guy

    thatK30guy 1 ton status Premium Member

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    Merlins are around $1700, assembled, for a pair.
     
  12. mofugly13

    mofugly13 1 ton bucket of rust Premium Member

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    WHOA! I got some rebuildable 781's on the way for $140, shipped. I dont think the machine work, valves, springs and whatnot will come even near that. But hey, I could be wrong as well.....
     
  13. bowtiepower00

    bowtiepower00 1/2 ton status

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    Merlins are good heads, but are overpriced, IMO. For that kind of money you can get better flowing aluminum heads from a couple of other manufacturers. I bet if you flowed Greg's 781's they would be close to if not better flowing than the Merlins, depending on the amount of work done to them.

    Greg- have you considered a NV4500? You're going to have enough torque that you're not going to need 6 gears. It also weighs a lot less and is much smaller than the NV5600. I would not consider the ZF 6-speed. They are fragile poor shifting junk. The 4500 shifts like a dream, and won't suck up all of the power that a slushbox will. If you're going auto, I would look into a TH400/ GV unit. It's not going to run much more than a 4L80e, will not involve any electronics, and will allow you to split gears. It should also be bulletproof. The 80e is a good choice too, and if you're able to find everything in a yard, maybe the most affordable way to go. I would not run an 80e w/o going through it, however.
     
  14. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    The different sized valves are so i could compare stock chamber and valves against the stock chamber with the large valves. As you can see, just by installing the large valves the CC's drop by 3cc's. I now need to surface the head and re-check the CC's again but i'm already guessing i'll end up about 115cc's. Once i have done this THEN i'll know what piston it's going to take to achieve about 9.3:1 CR to make it a friendly tow rig engine and also friendly with pump gas.
     
  15. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    To answer a few questions:

    Wes,

    Didn't spend much time thinking about aftermarket heads for this one. This is supposed to be a more "budget" oriented build (don't forget I just finished paying for a 502BBC buildup so I'm still recovering!).... this one gets the best "bang for the buck" mods to keep the costs under control. The only reason I'm going with a stroker crank is because the stock crank spun at least 2 rod bearings, so reconditioning it would cost more than a NEW stroker crank.....that made it a no-brainer. I'll go with a roller cam to free up some extra power too (cost / HP is pretty good on that one also).

    BTP,

    I haven't really thought about the NV4500 mostly because I have heard it can be a costly swap....I guess the same is true for any slushbox that uses a GV overdrive unit (last I checked their kit was $2500 + the cost of the tranny). I like the idea of 6 automatic gears, but AFAIK it won't shift in and out of OD between shifts without user intervention (1st - 1st OD - 2nd - 2nd OD - 3rd - 3rd OD).????

    I wasn't thinking about a ZF 6-speed either.....I already picked up a Viper T56 trans, so I was thinking about just using that since it's "free"....I will need to convert to a 3-pedal assy, and deal with some other conversion issues, and I'm not 100% sure I want to manually shift the 'Burb since it has such a relaxed, heavy-cruiser vibe already. Being able to just drop it into Drive and go is still pretty tempting. Maybe a more conventional 4L80E with a standalone controller??? (Still seems like at least $3000 though...) :thinking:

    Anyway....that's the info. I've gotten away with towing a 7500Lb trailer with a 350SBC long enough, so it's finally time to get serious.
     
  16. tarussell

    tarussell 1/2 ton status

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    I agree that the 781/049 GM castings are a great bang for the buck option compared to after market ovals. In an application such as a tow rig with part throttle driving they should be damn nice as far as throttle response and driving under load.

    The Viper T56 is stout but it ain't rated to tow anything under load. It has a fair input torque rating but that is also because it is meant to be in a light weight passenger/race car not a work truck.

    Anyway , it all sounds good - I always enjoy reading about your projects and build-ups.

    Tom
     
  17. SUBFAN

    SUBFAN 1/2 ton status

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    Yes definately keep us posted on the buildup. The parts used, head flow numbers, length of rods, and dyno results would be great too....(If that was in the plans.)

    Looking around the net, there is not much information on 496 builds, and I think more than a few of us are interested in reading a guide. Thanks for being the 'Guinea Pig!' :D
     
  18. bowtiepower00

    bowtiepower00 1/2 ton status

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    In your situation, you may just want to consider a trusty old TH400 and some tall rear gears (3.31 or 3.42). You would avoid quite a bit of cost and complexity. Your rig is 2WD, right? The GV could always be added later, if you decided you needed one. If it makes any difference, I think the 2wd NV4500's are quite a bit easier to find, and cheaper, than the 4wd units, but the swap will take a fair amount of time and money.
     
  19. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Greg, i've heard recently that GV now offers some sort of automatic feature for splitting gears. :thumb:
     
  20. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Yep, it's 2WD....

    I'll look into the TH400 and tall gears option, I know that I'll have plenty of torque but I was still unsure about whether I could afford to throw away so much leverage with those "freeway flyer" gears and still effectively pull a load :thinking:

    As far as the engine build is concerned, one of the interesting things I've learned is that some of the stroker kits come with a rod that is something like .125" longer than stock, which isn't done for rod ratio as much as it is to keep the piston skirt away from the crank counterweights when the piston reaches the bottom of the stroke....???

    I'll post up whatever I learn, but if you really want to know specific details we are all going to have to pester Scott for those, since he's going to be the one closest to the actual parts and assembly.

    :usaflag:
     

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