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Thread: OBS to LSx conversion

  1. #1
    Join Date
    Nov 2003
    Denton Texas
    Starting this to answer as many questions as I can in one place. I am trying to compile the most complete list of what to do to complete a conversion as I possibly can. I am only a man so don't blame me if I forget something. I will work on this slowly as time allows. Let me know if I forget something. Drinking lots of beer just goes without being said.

    A good read to start your education...

    Gen III GM Small Block: Engine Builder


    How to Build High-Performance Chevy LS1/LS6 V-8s by Will Handzel. Publisher Cartechbooks.com ISBN 1-884089-84-4
    HPBooks CHEVY LS1/LS6 PERFORMANCE by Christopher P. Endres. Publisher Penguin.com ISBN 1-55788-407-2
    Another document good to have if you can get it is the ASE 16013.00-2 for GEN III V8 Specialized Engine Repair. This is a document for remanufacturing a GEN III engine.

    A good read if you want to do a stroker... http://www.gmhightechperformance.com/tech/...s1_engine_build

    Removal of OBS engine...

    Be environmentally friendly and have your a/c evacuated and reclaimed if you have freon or 134a in your system. Most places will do it for free, they keep the gas and re-use it. That pays for the labor of reclaiming it.

    Remove OBS engine and transmission as one piece...
    Step 1 is to set the parking brake.
    Step 2 is to have the battery disconnected. I prefer to remove it from the vehicle to prevent shorts. Don't set it on concrete for too long unless you just want to buy a new battery.
    Remove exhaust system from factory exhaust manifolds.
    Cut/sawzall the exhaust off behind the OBS catalytic convertor(s). Do not discard, old cats are valuable. Take them to the recycler to recover some funds.
    Remove air intake system.
    Drain all fluids(coolant, transmission fluid and oil). Leave old oil filter in place.
    Remove all electrical connections from old engine. Go ahead and label them if you know where they came from. You will be re-using the coolant temp, oil pressure, starter, alternator and a/c wiring.
    Remove upper and lower radiator hoses. Feel free to cut them off because you won't be re-using them.
    Remove the top half of the radiator shroud.
    Remove the radiator fan by unbolting it from the water pump.
    Remove the lower radiator shroud.
    Remove transmission cooler lines. It's going to get messy here. Be prepared.
    Remove engine cooler lines if equipped. Again, messy.
    Remove the radiator.
    Remove the heater core hoses by cutting them off at the firewall, you'll replace them with new hose the correct length when the new engine goes in.
    Disconnect the throttle linkage and remove the cable from the bracket. If you have throttle body injection you will have to totally remove the cable from the firewall and accelerator pedal. This will be replaced later with an S10, NBS or Fbody throttle cable. This list will be updated later as others let me know what cables they used.
    Remove the cruise control cable from the throttle linkage. A longer one will be required if you had TBI.
    Remove the brake booster vacuum hose from the intake manifold if you have one.
    Remove power steering hoses and drain fluid (save the return line,it's the one with a light weight hose clamp on it, you may use it again in your conversion)
    Remove a/c low pressure hose from accumulator canister on firewall and disconnect high pressure line at condensor behind front grill. Disconnect the hose assembly from the compressor and save for later. Whomever builds your a/c lines may need the connections.
    Remove starter and power leads(main power battery lead and the purple solenoid signal lead). You should be able to reach them from the top side under the passenger side exhaust manifold, if not remove the manifold. If you don't like that option you can crawl up under the truck and unbolt the starter and then disconnect the two wires.
    Remove alternator lead if you haven't done that already.
    Remove and save oil pressure and water temperature sending unit.
    If you have a returnless fuel rail, cut the fuel line just behind the old fuel filter and cut the return line at just about the same location. Unbolt any bracket and hanger for the fuel lines going towards the front of the truck.
    If you have a return type fuel rail, two connections, do not cut the fuel lines, disconnect them at the throttle body and disconnect any mounts than hold the lines to the engine and transmission.
    Remove speedometer cable if equipped. Disconnect speedometer sensor otherwise.
    Remove all transmission wiring such as the main connector on passenger side above the oil pan on 4L60E vehicles.
    Remove gear shift selector wiring on passenger side if you have it.
    The transmission cooler lines will come out with the engine and transmission.
    Unbolt the transmission mount from the crossmember and unbolt the crossmember from the frame.
    Disconnect the shift cable or selector rod from the transmission.
    If you have a manual transmission you'll have to remove the shift handle, shift boot cover, shifter filler panel and finally unbolt the top loader shifter from the transmission. Next you need to remove the hydraulic line from clutch slave cylinder or remove the slave cylinder from the trans.
    Optionally, you can now remove the drive shaft.
    Remove the engine mount bolts. There is one on each mount using 5/8 bolt heads and 11/16 nuts.

    The assembly should be ready to come out about now. Time to remove the hood because you are going to need the room.
    Hopefully you have an engine hoist and chain available about now. A load leveler comes in handy too when removing both parts at once. A couple buddies would be helpful, too. Go easy on the beer drinking at this time because it's easy to get hurt.

    You'll need to put a jack under the tail of the transmission to get the mount stud out of the crossmember hole. Use the factory engine lift brackets if you have them, otherwise bolt your chains to the cylinder head at the passenger side rear and the other end can go on the driver side some place that has a 3/8" or larger bolt hole. The engine will be heavy so use good quality bolts with a minimum of 10.8 metric reading or 6 points on the head SAE.

    If you have already removed the driveshaft, I like to take a heavy freezer bag and slip it on the transmission tailhousing and then electrical tape it on really tightly to prevent making a big mess. An old slip yoke or plastic plug works good but I don't have either.

    Time to hoist the engine out. If you don't have a leveler, one of the buddies will have to maintain weight on the transmission to angle the engine assembly upwards to clear the radiator core support.

    Good luck, have fun. All the easy stuff is over, now it's time to use your brains and max out your credit cards.
    Last edited by RedHeartbeat; 04-21-2009 at 08:26 AM.
    See my truck data in the "My Garage" section here... http://www.ls1truck.com/forums/my-ga...tml#post191709

  2. #2
    Join Date
    Nov 2003
    Denton Texas
    A good read... http://www.hotrodlane.cc/PDFFILES/Lisa%20Tahoe.pdf

    Items needed...

    Everyone that doesn't have a late model Vortec V8 engine (pre 1996)...
    Walbro 255lph in-tank fuel pump or AC Delco EP-381. The Walbro I buy is for the Buick Grand Nationals.

    Racetronix.com sells a nice fuel pump hot wire kit for the conversion that I like to use to make sure there is plenty of amperage feeding the pump... RXG7-FPKG

    Replace fuel pump with high pressure pump...
    I find it much easier if you remove all the hoses, electrical connections and have the fuel pump assembly in hand away from the vehicle.

    Removing the bed is the easiest way IMO.
    Remove the retainer ring holding the pump and fuel level sensor by rotating it counter-clockwise. Disconnect the old pump by first removing the in-tank fuel filter sock, disconnect the electrical connection from the pump and pull the pump sideways to dislodge it from the hose. Remove and discard factory rubber hose connector that was connected between the pump and the feed tube..

    Install the new pump...
    If your pump came with new wiring connectors that are different from your factory wiring or your old wires are brittle or cracked, it's time to solder in the new connector or use red crimp connectors to join old with new. Be sure to cut one wire at least 1/2" longer than the other so that the connections won't have an opportunity to short to one-another.
    DO NOT reuse the rubber hose that came with your factory OBS pump, it won't handle the pressure and WILL eventually blow out or leak and you WILL be doing it again. Use the hose that came with the Walbro kit or fuel injection quality hose or braided stainless hose that is rated for at least 60 pounds of fuel pressure. I use the hose from the kit and I buy the hose clamps that have smooth bands with a bolt through it. I prefer not to use the worm type clamp because it damages the outside of the hose. After you install the pump in the pump assembly, install the new in-tank sock type filter. DO NOT attempt to re-use the old one you removed from your old pump. Buy a new one if you didn't get one with your pump.
    Re-install pump assembly into tank. If you had to remove a bunch of black butyl sealer around the fuel pump retainer ring, be sure you get some from your auto part store or GM to seal the tank back or else you WILL leak fuel when filling or when you have close to a full tank of fuel. Lock the fuel pump assembly back into the tank by turning the retainer ring clockwise until it stops. While you are at this point check all the electrical connections and grounds. Plug your pump electrical connector back in and reconnect all hoses you removed.

    This section is if you will be using a single inlet fuel rail. A return style rail will use the old style filter and return line.

    Corvette fuel filter commonly used in OBS conversions if you are doing a returnless type fuel rail install....



    Wix 33737 PlanetAutoParts $37.93
    GM 10299146
    Purolator F55493
    Hastings GF336
    GKI GF1822

    Connectors required to hook to the filter...
    Dorman PNs

    3/8" female connector DOR-800-121 Midway Auto Supply Online Shopping $7.36 (2 required)
    5/16" female connector DOR-800-120 Midway Auto Supply Online Shopping $7.36 (1 required)
    3/8" x 12" double ended male connector DOR-800-155 Midway Auto Supply Online Shopping $9.57 (1 required)

    This looks helpful, too...http://www.ls1truck.com/forums/238259-post16.html

    If you go with braided -6 hose you will need Russell hose connectors 640850 (3/8 fuel rail to -6 male AN) and 640860 (5/16 fuel rail to -6 male AN).

    Remove the factory fuel filter by cutting the tube with a tube cutter, not a saw, immediately behind the OBS fuel filter.

    Cut the return line in about the same location and bend it slightly downward to make a new slip-on connection. You can now remove all the fuel lines forward of this point going to the OBS engine. Do not remove the smallest tube(evap/charcoal canister).

    Install the Corvette fuel filter...
    You'll need fuel injection quality fuel hose to connect the Dorman quick connects to the old steel fuel lines. I cut both the pressure and return lines about 2" before the factory filter location. Use the rubber fuel injection hose to connect to the new filter. Use 2 hose clamps on each end of the new connections. It's best if you use the hose clamps that have a smooth stainless steel liner to protect the hose. You'll need about 6 feet of hose to connect from the filter to the fuel rail if you have an extended cab. The outlet side of the filter will require the male fitting be cut to about 4"-6" long from one end and then push it into the fuel hose and double-clamp it.
    Last edited by RedHeartbeat; 03-21-2009 at 12:36 PM.
    See my truck data in the "My Garage" section here... http://www.ls1truck.com/forums/my-ga...tml#post191709

  3. #3
    Join Date
    Nov 2003
    Denton Texas
    V6 to V8 engine mount conversion...

    Hooker now makes some really nice engine adapter mounts and are available through Jegs and Summit. Hooker 12611 - Hooker Headers LS1 Engine Swap Headers - JEGS

    I've heard of guys actually turning their adapter plates around backwards (triangular section of mount pointing towards transmission) to mount the GENIII engine into a V6 frame. I prefer to convert the frame to V8 mounts.

    Parts needed...
    Buy these part to fit your year model truck.
    V8 frame mounted rubber engine mounts that bolt to the crossmember(pre-1999)
    V8 engine mount cups that bolt to the side of the engine block (pre-1999) 15719194 (thanks Brian1987)

    If you were unfortunate enough to have the V6 engine before, now you get to have some fun!

    To make your frame V8 style you have to remove the V6 engine mounts/pedestals. You should remove the lower control arms from the spindle and unbolt/remove them from the frame along with the coil springs to reach the bolts inside the crossmember.

    Once you have unbolted the factory V6 mounts from the frame, it's time to install the new V8 engine isolator mounts. Bolt the new rubber isolated engine mounts to the holes in the crossmember. You'll have two holes at the bottom and one at the top of the mount. Use the bolts from the V6 mounts. Once you have the conversion to V8 mounts done you can replace the coil springs and lower control arms.

    It's a great time to replace the stock coils with lowering coils or to cut a full round off of them to lower the front about 2.5".
    Last edited by RedHeartbeat; 03-12-2009 at 07:25 PM.
    See my truck data in the "My Garage" section here... http://www.ls1truck.com/forums/my-ga...tml#post191709

  4. #4
    Join Date
    Dec 2006
    You are the man, I was wondering why there was not some kind of sticky on a gen III to an obs truck, It seems like enough people have done this or are planning this by now. Kinda like me I am doing one and planning one at the same time. That's ok because my buddys ls1 swap will be a learning experence for my 6.0 build/swap.

    I guess what better place to ask questions now. What are some header choices (if any) for the gen 3's in to an obs 93 truck?

  5. #5
    Join Date
    Nov 2003
    Denton Texas
    Site sponsor Schoenfeld now mass produces headers for our conversion for under $300! Nice price for painted long tubes.

    Site member NITROUS now is developing some long tube OBS to GENIII headers. Contact him for status and pricing.

    There are no long tube header options at this time, other than custom build it yourself types. Street and Performance (Welcome to Street and Performance) makes some mid-length headers that some of the guys on here are running. They look nice. Check out Nitrous and MotoXLifer's trucks, they have them. Other than S&P, you're only other choice that I know of is custom built. Most guys run the stock exhuast manifolds. The Fbody manifolds work the best in my opinion.

    Here are the ones I built from a set of big block truck headers and GM exhaust flanges...

    Last edited by RedHeartbeat; 03-12-2009 at 07:26 PM.
    See my truck data in the "My Garage" section here... http://www.ls1truck.com/forums/my-ga...tml#post191709

  6. #6
    Join Date
    Dec 2006
    Saginaw, Texas
    this has become my new favorite thread... since i have a 91 that i wil be converting to either an ls1 5.7 out of an fbody or an ls2 6.0 from a gto... awesome information...
    I am gonna be a new Daddy...

    Drive it like you live hard and fast....
    '91 rcsb, 4.3 V6, 700R4 trans swap, 4/6 drop rolling on 18's, roll pan, 2" cowl hood, electric fan, TBI injector spacer, K&N filter replacement, flowmaster muffler...

    [Today 08:09 AM] ChevyLee: dale would make a awesome dad in law too

  7. #7
    Join Date
    Jun 2006
    The Socialist Union of Canada
    Kick ass. Great job Red.

  8. #8
    Join Date
    Nov 2003
    Denton Texas
    Time to prepare the engine for installation...

    If you don't have a wiring harness, time to order one now. There are many suppliers of engine wiring harnesses. From looking around all over the internet I have to agree that the Nelson Performance - Performance without Sacrificing Drivabilityharness is the best value around. When you order your harness be sure to know where you want to locate your PCM. The factory PCM is located behind the glove box. A good place to locate the PCM is on the passenger fender well. Take a measurement from the center of the firewall and then follow the routing you want to run the wires all the way to the PCM location. Give John and Allen that measurement so that they can make the wires long enough for your needs. Let them know if you have removed any smog devices and they can delete them from your new harness. They will need to know if you have a cable or electronic throttle body.

    If you have a stock factory wiring harness that you want to try to convert, you will have to work out the wiring. Pink wires are typically switched 12V supply, red wires are 12v constant, dark blue and dark green control the electric fans. The fan leads provide a ground for relays. Below is a post I did years ago on LS1Tech.com and someone quoted my post in their conversion topic. There is a lot of good information there.

    LS1Tech conversions

    Bolt your engine adapter mounts to the block with the triangular portion towards the front of the engine using the supplied hardware. Do not put a bolt in the bottom forward hole, that hole will be used to mount the engine mount receiver cup. You may need some of the stock engine mount bolts to complete the installation. Some adapter plates use metric bolts and others use SAE bolts so be sure you have the correct thread pitch, don't cross-thread them by accident. If they get hard to turn try a different style bolt. Metric bolts have a number such as 10.8 on the top and SAE will have lines, 3 or 6 typically. Time to bolt on the engine mount/receiver "cups". The cups should have three holes to bolt them to the adapter plates. The bottom one will use a metric bolt, the two top ones you will have to check to make sure if they are metric or SAE. One thing I do to help the cups sit best on the adapters is to either to flatten or remove the raised section that mates to the adapter plates. If I don't have a torch to heat the detent area I take a hole saw close to the same size and drill it out and then grind off the rest of the raised section. If you don't do this the distance between the engine mount cup holes will be much greater than the distance between the frame mounts. You can verify this by measuring the distance between the mount holes on the frame and then using two plumb bobs or weighted strings hanging down from the mount holes on the engine. Most times I still find myself having the coax the mounts a bit during the install. Some people will slot the holes on the crossmember to allow a little adjustability of the mounts. You'll need to slot the holes about 1/2" on all six holes to do this. You'll also want to take off or leave off(if you converted from a V6) the lower control arms until the engine is installed so you can tighten the rubber isolator mount bolts after the engine is installed. Be sure to have all six nuts and bolt installed loosely before dropping the engine in if you're going to attempt this method.

    Remove any exhaust parts beyond the manifolds, any pipes or convertors that may have come with your take-out assembly.

    If you are going to reuse the transmission cooler lines from the LS1, leave them on because they are tough to install later, just watch that you don't crush them on the mounts when installing the engine.

    Remove all radiator and heater hoses remnants from the original vehicle. It's much easier to do it now.

    DO NOT install your new oil filter yet. If you bump it into something and dent it in the least bit while installing the engine you have to pull it off and throw it away. Want to know how I know? A dented filter cost me a rotating assembly when debris bypassed the filter because it was dented and oil was able to flow around the filter rather than through it.

    When you have the engine installed, a common issue is the alignment of the holes in the mounts to the engine mounting cups that are bolted to the block/adapters. The holes are usually off by about 1/4". What I do is get one bolt in on the driver side and then put my hoist chain to a bolt hole on the driver side and lift just a bit to put a load on the rubber mount. That will give you the alignment for the passenger side hole. Just play around with it for a little bit and all will line up fine.
    Last edited by RedHeartbeat; 11-21-2007 at 10:23 PM.
    See my truck data in the "My Garage" section here... http://www.ls1truck.com/forums/my-ga...tml#post191709

  9. #9
    Join Date
    Dec 2006
    I was just reading through this topic again. there is a lot of good info here. this should be a sticky

  10. #10
    Join Date
    Jun 2006
    The Socialist Union of Canada
    <div class='quotetop'>QUOTE(s10mods &#064; Jan 6 2007, 04&#58;06 PM) [snapback]78539[/snapback]</div>
    I was just reading through this topic again. there is a lot of good info here. this should be a sticky
    +1 on that.

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