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  1. #1

    Default 5.7 L Vortec L31 Torque Monster Build Suggestions.

    I will be getting a 96 Z71 in Feb. of 2012, been doing some research on the motor and it appears that Chevy set it up to tow from the factory. 250-350 HP at 4600 RPM and 430-450 lb-ft at 2800 RPM stock!!!!!!!!!!!! WOW!!!!!!!!!!!!!!! Was looking to redo the motor to get around 600 lb-ft in the lower RPM range. Initial thoughts are flat top pistons, machining block and heads, balancing crank, upgraded valvetrain (including cam and valvesprings, longer rods and possibly bigger RA ratio), bigger injectors, and a programmer. If this sounds good to you guys gimme a thumbs up, if you guys would do anything different (or more ) please let me know. I do not have a lot of experience with the computer controlled Vortec Motors so that is why I am asking the forums.
    2002 Silverado K1500HD (NEW!!!!!!!)
    1999 S-10 Blazer
    1990 K1500 5-spd TBI 350.
    2001 Monte Carlo SS Pace Car

  2. #2
    Legend
    TRPLXL2's Avatar
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    If you go with a mild cam depending on the specs, you could have problems with the knock sensor/s. On my Lt1 it is common to go to an aftermarket knock sensor, as the stock one will pick up the lope of the cam as a knock. Might want to check into this to see if it applies to your motor, my knock sensor was inside the ECM case so It might be different.

  3. #3

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    The L31 Vortec 350 that was installed in all GM half ton trucks (Pick-ups, Tahoes, Suburbans, Vans) put out 255 hp and 330 lb-ft. Whoever told you 430-450 ftlb of torque was off by 100 lb-ft. 600 lb-ft is possible but very expensive with a small block. If you want the motor to live a long life plan on adding a forged crank and rods, and I'd talk to an experienced builder about the strength of the factory block.
    Last edited by Boonduff; 11-08-2011 at 11:18 PM.

    97 Chevrolet Suburban K1500 5.7L
    78 GMC High Sierra K1500
    Fat, drunk, and stupid is no way to go thru life.

  4. #4
    Legend

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    The 383E- drop in GM performance stroker replacement for the L31 makes 340hp 435 lb ft.
    I don't think a 350 gasoline motor can make 600lb ft wihtout some sort of boost or nitrous oxide.
    Without a supercharger of N2O you just can't put enough mixture in the cylinder
    Big torque like that requires lots of displacement-or boost
    Charlie
    PS Even those 14/1 compression Nascar motors don't make anything like 600 lb ft-they make big power-700 hp- by running double the RPMS-9000 or so-I doubt they make more than 450lb ft
    6.7 liter Turbo diesels make 600-700 lb ft-BUT they have 18/1 compression and more importantly 15 psi OF BOOST- so they can stuff double the mixture in a cylinder that a normally aspirated spark motor can.
    Aiming for numbers like GMs 383E is probably the best you can do Torque wise- you can make more than 340 hp by using a cam that gives torque farther up the RPM range- like other said- you will need a stouter- forged- crank and connecting rods if you plan to make power at 7000 RPMs or so-redline on most 350's is about 5500 RPMs or so
    The little 302 from years ago made power at 7000 RPMs or so but it had a 3" stroke-so it could rev higher-fancy heads also
    Last edited by phoebeisis; 11-09-2011 at 07:24 AM.
    1998 suburban-
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    199500 miles
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  5. #5

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    Ouch. You don't need all that crap. Honest. Not on a pickup truck, pal.

    A camshaft change is all you need. You have some good heads on it already. If you have money burning a hole in your pocket, contact a local shop that does engine work on street rods and other custom work, and ask them if Edelbrock makes a Performer head that will work with your motor and fuel system. I have them on my truck, and with the right builder and the right rocker assemblies, and the right cam, you will have all the power you will ever need.

    Only other thing I would add: quality headers, and a larger diameter exhaust (custom is best).

    Get it worked on at a shop that tunes on a dynomometer with a laptop. That way you can have them do a "before" and "after" dyno run to show you the difference.
    1994 Chevy K2500 Silverado, 454 (modified), original owner.
    And other vehicles and toys.

    "...If you can meet with triumph and disaster
    And treat those two imposters just the same;
    ...you'll be a Man, my son!" Rudyard Kipling

  6. #6
    Jr. Engineer McMahan's Avatar
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    If you have enough money I would do a engine swap. Get a LQ9 and put a maggie on top of it and a built tranny and a good set of gears and you wont be let down

    2005 Silverado SS
    Color matched AEM CAI,Magnaflow mufflers,cat delete,true dual 2.75" stainless mandrel bent exhaust,Circle D 300K stall,Transgo shift kit,Corvette servos,Detroit Tru-trac,SLP 160* T-stat,Taylor 10.4mm red wires,Comp cams 228R,903 springs,12" cross drilled and slotted rotors,WHEATLEY tuned!!!! Boss 313 22X9.5,Toyo proxes II 305/45/22,

  7. #7

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    I agree with phoebeisis, go with the GMPerformance HT383E crate motor part # 17800393. Its a direct bolt-in and has a 24month/50,000 mile warranty.
    :cool:

    2005 Chevy Silverado Z71 Crew Cab
    6" Skyjacker lift w/Edlebrock dual front remote resoviour shocks, single rear remote. Rancho skid-plate.
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    Banks CAI intake, ported throttlebody, JBA coated headers, over-sized Magnaflow cats, Magnaflow cat back exhaust, Diablo tuned
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