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Thread: Vortec 8100

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    Default Vortec 8100

    My father and I are building up a 1981 Buick Century I stumbled across. The old 301 is knocking hard (probably a spun bearing) and the trans has trouble engaging reverse (has always been that way) so we plan on replacing the engine, tranny, and rear end with whatever we stumble across and is affordable because this is just something we want to put together so we can spend some time in the shop, hone our skills and just put in some father/son time.

    We were both thinking we would like to put in a Chevy big-block and tranny from a three-quarter ton. An acquaintance of mine has a totaled off 2002 GMC Sierra with a 8100 Vortec with less than 75 000km on it and if the price is not astronomic I think it would be an ideal motor because isn’t it is essentially a larger updated 454 with fuel injection and other improvements?. We are thinking of sticking that in front of a 4L80E and then to the first three-quarter ton rear end we can find.

    This car will mostly be seeing the highway and cruising the streets as a bit of a sleeper but it is unlikely that it will ever make a real pass down the quarter. We want a nice blend of power, reliability and stealthiness and that is why we’re looking at newer stock fuel injected v-8's as opposed to an old big block with a lopey cam and long tubes. We are both very capable of assembling, machining, or building anything in our shop and we do have mechanical knowledge, just it pertains to farm equipment and large trucks not so much cars.

    Do any of you guys have advice for us? Will the engine fit between the frame rails and under the hood(we will have to move the old A/C unit)? Is it worth spending the extra money for a modern big block and transmission or would it be better to go with an older v-8 and tranny but opt for a gear vender and tall gears to maintain milage? Any suggestions or insight would be greatly appreciated. Thank you in advance.




    Cliff-notes-

    Thinking about putting a 2002 GMC 8100 and 4L80E into a 81 Buick century, need advice and insight.

  2. #2
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    No need to go through the complications of a fuel injection swap, especially with a newer motor. Get an older big block from a truck at any yard, throw a H/C/I pack on it and call it a day. You'll have a 500hp motor for 3g's or less. As far as fitament; the Buick Century isnt exactly the hot-rodder's choice vehicle, but from what I can tell, it came with a SBC, which uses nearly the exact same mounts as a BBC so mounting to the frame shouldnt be too difficult. But putting a BB into any car opens up a whole new can of worms with all the extra weight, getting headers to fit, fitting the motor itself, etc. Im a SB guy....always have been. Give me a SB w/ its cheap parts, simplicity, and weight savings any day. But the choice is up to you.

    Oh, and what is in there now?

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    The 8.1 is not a motor that you would want to modify, I sugest you get a 454 and do what Monte said.


    Monte: Edited for pointing out my ignorance
    Last edited by Monte; 02-23-2006 at 12:40 PM.

  4. #4

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    It has the old 4.9 (301) in it now; I think its the same as the ones used in the turbo trans-ams of the 1980's less the turbo of course. I'm not sure which tranny but its a 3-speed auto. I was planning on leaving the 8.1 stock because it did have decent power (345bhp, 445lb-ft or something) and i knew there wasn't tons of parts available but I do think a SBC would be a wiser choice.

    We do have our hearts set on fuel injection though and an auto that can handle the highway; would it be worth looking for a running gear from a modern 3/4 ton? It's just that up here there are few part shops and almost no sports cars to get parts from so GM trucks are our best option for engines and trannys. If not a motor from these do you have any sugestions?

    Thanks for all the help.

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    Trannies from modern trucks are not geared for performance AFAIK. 700's can be built to handle lots of power, but I dont know how one would stand up to punishment from a BBC. Best bet would be a Turbo350 or 400 and a gear vendor unit if the budget allows. My friend has one in his Monte, and it is great, rated to 1200hp I believe as well.

  6. #6

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    Thanks Monte, do you know what kinds of trucks i could find those in? Or where they ever put in full sized cars (we seriously only have beaters like that around)? Do you suggest a certain rear end?

    By the way, your car looks great. I'm a fan of V-8 G-bodies, you never really hear about them because of their v-6 brothers.

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    The 350 and 400 are the most common transmissions evar. Any v-8 GM w/ a 3-speed is most likly a 350. Any high torque engine or truck should have a 400.

    For rear ends, the 8.5in I think is the best rear made. The ring gear is only a 1/4in shorter than a 12bolt with a lighter/smaller housing that is nearly as strong. A stock 8.5 from a GN is good to low 11's. Upgraded axles/carrier/gears will give you a rear end far superior to a stock 12 bolt with a substantial weight savings.

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