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Rebuild a 454 w/781 heads.... or take it to 496? HP/TQ estimates??

Discussion in 'The Garage' started by Greg72, Jan 12, 2007.

  1. Greg72

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

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    The subject line says it all:

    Complete 454 w/781 heads.

    I can rebuild it with some larger valves, or stroke it (also with the larger valves) to 496. The plan is to run it with the Holley Commander 900 TBI for easier tuning and smooth throttle response.

    The 496 is going to be a more expensive build (Duh!) so I'd like to understand what the expected benefit would be HP/TQ vs. doing a basic rebuild on the 454. Anyone got Desktop Dyno numbers for either, or both of these??? I'm willing to run premium fuel (91 Octane) so I can tolerate a bit more compression than a "junk fuel" 87-octane motor buildup would allow.

    I don't really want to get into swapping heads for aluminum ones....by the time I buy new heads and a complete stroker kit, I'm in WAAAY to deep in the $$$$$. So the constraint is that I will use the existing heads and block, but almost everything else is negotiable... :deal:



    This is for the '72 Suburban....will serve double-duty as my tow rig, and for general terrorizing of the local Civics and Scoobys. (...maybe)


    :usaflag:
     
  2. jays68yak

    jays68yak 1/2 ton status

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    Umm what happened to the 502? Or is this going into the rig for sure?
     
  3. Greg72

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

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    502 is going into the K5... :saweet:

    Back on topic......
     
  4. jays68yak

    jays68yak 1/2 ton status

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    Ok yeah 496 duh.
     
  5. HarryH3

    HarryH3 1 ton status Author

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    Having experienced what happens when you add stroke to a 350 (making a 383), I can only imagine how awesome it would be to do the same with a Fo Fiddy Fo! :cool1: Go for the longer lever arm! :)
     
  6. SkysTheLimit

    SkysTheLimit 1/2 ton status

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    I'm an amatuer with Desktop Dyno but according to it stroking it to 496, all else stock will net you a bunch of grunt down low and a few hp centered at 3500 rpm.

    496 is ~500 lbft & 275hp
    454 is ~430 lbft & 260hp

    Thats with a bunch of the defaults. I'm sure the numbers would vary greatly depending on airflow and whatnot.
     
  7. Greg72

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

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    Thanks.....I'm trying to do the same thing in DD2000. I know there MUST be sites out there with updated .flw files for the 781 heads, but I haven't found them yet. Obviously, the head flow numbers need to be accurate for the output values to be even close to correct.

    :thinking:
     
  8. iwaxmyjimmy

    iwaxmyjimmy College web wheeler Premium Member

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    portmatch them heads, by the stroker kit and get a decent cam and call it done. u need something reliable and a big stroker can do that w/o boring it over b/c then u start making the cyl walls thin and thats cooling problems. i would deff set it up for a wide band to get the tune just right,and maybe even some dyno time.
     
  9. bigblock72

    bigblock72 1/2 ton status Premium Member GMOTM Winner

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    A 454 with mildly ported 781s w/ 2.19" & 1.88" valves, a cam with .530ish lift and 220ish (@.050") duration and 9:1 compression, Performer RPM air gap intake etc. will make 440 horse and 500+ ft. lbs. torque on a mild tune. Add about 40 horse and 50 ft. lbs. with a 496. Add another 30 points or so if you go with a hydraulic roller.
     
  10. iwaxmyjimmy

    iwaxmyjimmy College web wheeler Premium Member

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    where are them numbers in the power band?
     
  11. Greg72

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

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    I'm wondering the same thing too.....I'll be the 496 hits it's peak torque a lot lower and I'll also bet that there's more TQ "under the curve" than the 454.
     
  12. bigblock72

    bigblock72 1/2 ton status Premium Member GMOTM Winner

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    Peak torque on the 454 is around 4000, 496 is about 3800. Peak horsepower is 5300 on both, and time to shift by 5500. The small 220 duration cam shuts things down early, you could probably go up another 6-8 degrees on duration and a little more lift could bring even more torque and horsepower with no losses on the 496.
     
  13. iwaxmyjimmy

    iwaxmyjimmy College web wheeler Premium Member

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    thats kinda high for a tow rig. thats deff one bad thing about some really free flowing heads, power is always kinda high in the RPM range.
     
  14. thatK30guy

    thatK30guy 1 ton status Premium Member

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    Do the 496 and buy some Merlin heads. That combo should rock.
     
  15. bowtiepower00

    bowtiepower00 1/2 ton status

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    I think this all depends on a few things. Lets look at it this way, check out Ohio Crank, they make killer rotating assy's. You're looking at about a grand for a solid 496 bottom end, assuming you don't plan on Nitrous or a large blower in the future. On the other hand, how much work are you going to do to those heads? Stock, they are OK. Modified they are signifigantly better, but still wayyyy behind an aftermarket casting- nobody says you have to go aluminum, but I would. The difference in heads is going to make more power than the extra cubes, and use less gas. I would spend the money on aftermarket heads, and reuse the stock 454 rotating assy, perhaps with ARP hardware. Throw in a nice hydraulic cam, and if you need more power down the road step up to a roller cam.

    A 454-468 with a set of as-cast AFR ovals, Edelbrock/ GM ovals, World Iron ovals, or even mildly worked GM vortec BBC heads would make good power. With a good FI friendly cam and the Holley EFI, I think you'll have more than enough power- and if you have OD, you'll probably be capable of decent economy too (for a BBC.)

    OTOH, you could go the 496 route, and add heads later if you still need em. I would keep in 87 octane friendly, just to be safe. 9:1 with iron, 9.5 with aluminum. FWIW, the latest Hot Rod has a 496 buildup in it that makes 700HP on pump gas. It's a little more radical than what you'd want for a towrig, but still makes 500 lb+ torque everywhere.

    I'd just be afraid that all those cubes would drink lots of gas. Even the 454SS guys with OD are having trouble breaking 10MPG with big cubes.

    Maybe you don't care how much gas it drinks. At any rate, heads and cam are where the power is at, I don't see any reason to make the same or less power with more cubes. When you add the price of decent headwork and a new rotating assy, you're probably getting close to a set of heads. It doesn't really matter where the power is at when you're talking about built BBC's, and you can always regear, etc., to put the power where you need it.
     
  16. thatK30guy

    thatK30guy 1 ton status Premium Member

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    Agreed. I still recommend Merlins!
     
  17. Greg72

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

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    This is really good food for thought.....

    At first, I was annoyed by what looked like a "buy better heads" response....but what you appear to be saying is to spend the money on heads INSTEAD of the stroker kit..??

    Clever idea if the power is really going to come that way (and it sounds like it will). My thought process was to do a roller cam conversion on the block, add a stroker kit and enlarge the stock "781" castings with the 2.19/1.88 valve combo. I haven't added all those costs up yet.... do you really think that I'll be at equal costs by simplifying the build and leaving it as a 4.00" stroke (maybe punch it to 468 though?)

    Ideally, I'd like the thing to put down maybe 550Lb/Ft of torque....600 would be insanely great. I don't need/want numbers beyond that....and wouldn't want to pay for the fuel needed to feed it!! :D

    Keep in mind, I only get 7MPG now....so it's not going to take much in the way of "economy" to impress me. 10MPG would be phenomenal....


    Thanks for the insights.... you always seem to have good advice on this stuff when I ask. :bow:


     
  18. bowtiepower00

    bowtiepower00 1/2 ton status

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    I think, powerwise, that a 496 with worked 781's and a roller cam and a 454-468 with good oval ports and a flat tappet cam will put out similar numbers, depending on how much head work is done to the 781's.

    The Hot Rod 496 I refered to earlier used a Comp 292 Solid Roller, AFR 305 as-cast rectangles, and a Super Victor/ 850 Squarebore. It made 500+ torque across the board, 572 avg, and over 600 at 5K. It also made 700HP at 6500 and wasn't done.

    That's with AS-CAST, not CNC AFR's. The CNC AFR's will make even more power. I know that's apples to oranges, but a set of good ovals and a nice FI friendly hydraulic roller will make loads of torque- even on a 454-468. If you're not going to be putting lots of miles on it and don't mind running the valves once a year (or less), you could always run a solid roller. The thought of running a lower compression truck pull motor on the street is very appealing to me. The Iron Merlins also flow well and cost a bit less.

    The weight savings on a BBC with aluminum heads is significant. Every bit helps.

    I'd make some calls to some head manufacturers and cam manufacturers and see what they say. I'm sure they've got some dyno numbers somewhere for what you're looking for, or at the least can give you some recomendations.

    Lots of guys are looking for 781's. When you add up what you can get for them with what you'll spend to build them, you'll be close to a set of aftermarket castings. If you throw in the added expense of a roller cam you'll definately be close, if not over.

    I would see what you can get for the 781's. Put this money toward the build. When you look at the price difference between a flat tappet cam and roller cam, it's $400+. You could always start with a flat tappet.

    You may be able to build a flat tappet, aftermarket head 496 for the same price after you sell the heads.
     
  19. thatK30guy

    thatK30guy 1 ton status Premium Member

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    And final food for thought.......

    Buy some Merlins, Greg!!!
     
  20. Ned Kelly

    Ned Kelly 1/2 ton status Premium Member

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    I agree, if you can burn 87 octane fuel that is a bonus. Maybe calculate how much power difference there would be between a 87 octane setup vs a 91 octane setup. The slight gain ( I don't know, maybe it will be significant?) may not be worth the expense of premium fuel. Factor in how many miles you expect to drive a year and see what the cost difference in fuel will be for 87 vs 91.

    I know two fellows who went with the 91 ocatane builds and later wished they didn't. Again, depends on what you pocket can swallow and how many miles you expect to drive per year.
     

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