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C5 LGM Longtube Header Install

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Table of contents

- Tools/Supplies needed
- Preface
- Part 1: Removal of stock H-pipe
- Part 2: Removal of stock manifolds
- Part 3: Installation of the LG longtube headers
- Part 4: Installation of Xpipe/Cats
- Part 5: AIR Pipe conversion ('97-'00 year models only)
- Part 6: Finishing up
Tools Needed:
  • Set of metric sockets, deep and normal (from 8mm to 15mm is good)
  • Set of Metric wrenches (8mm, 10mm, 13mm, 15mm, 18mm, 19mm)
  • Metric "Gear" wrenches (not absolutely necessary, but REALLY handy)
  • 7/8" open ended wrench (for 02 sensors)
  • Pliers
  • Flathead screwdriver
  • Various Extensions, 1", 3" and 6"
  • Torque Wrench
  • Rhino Ramps (or other brand of car ramps)
  • 4 jackstands, 2 of which need to be able to support a vehicle 20" in the air
  • A floor jack with the ability to lift up to 20", or blocks of wood to extend the reach
  • Optional: Fuel line disconnect tool (may be needed for 97-00 year model cars)
  • Optional: 1" open ended wrench, or adjustable crescent wrench (needed for 97-00 cars)
  • Parts/supplies you will need:
  • LGM header package, available from LG Motorsports
  • Optional: 2 O2 Simulators (if not using custom programming)

  • Optional: 2 hpipe to catback gaskets (2x GMPN 10276792)
  • Optional: 2 O2 sensor SIMMS if not using cats
  • Optional: GM Metal exhaust manifold gaskets (2x GMPN 12558573)

  • Tube of Anti-seize
  • Tube of dielectric grease
  • Preface:

    One of the most common big power mods done to these cars is headers. That's for a few reasons.
    • The price for performance is good.
    • The sound will be changed quite a bit (especially without cats), in what most consider a good way.
    • They can be installed by mildly skilled do it yourselfers at home. The motor stays together and many dealers will still warranty the engine with aftermarket headers.

    Pictures of the parts:

    The complete LGM Pro Longtube Headers, with optional Random Tech metal matrix catalytic converters. The kit includes:
    • Left and Right stainless headers, with 32" Primaries and race style merge collectors
    • X-pipe
    • X-pipe to catback pipes
    • All necessary clamps
    • Exhaust manifold gaskets
    • AIR tube gaskets
    • Adapters to connect rear O2 sensors to front O2 harness
    • 2001+ style AIR tube (included for 97-2000 installs only)
    • Optional: Random Tech metal matrix catalytic converters.

    Part 1: Removal of stock H-pipe:

    Time to complete: 0.5 - 1 hour

    First things first, get your car up in the air. What I do is drive the front end into Rhino ramps (black plastic ramps available at walmart or various other places), make sure the wheels are pointing straight ahead, block off the front wheels so they don't roll, then jack the rear up by the center of the rear crossmember and place 2 jack stands under the crossmember. Throw a light under the car, and we're ready to begin!
    Get underneath the car with a deep 15mm socket wrench and some WD-40 or equivalent. You should see where your H-pipe mounts to the exhaust manifold. Spray down the 3 nuts on the studs coming out of the manifold with WD-40, and then try to break the 3 nuts free. Initially they may be tough to break free but should come loose with some effort. KEEP THESE NUTS as you'll need them later on to install the rear pipes on the LGM header setup.

    While you are under here, follow the wire off of the O2 sensor until you see an electrical weatherpack connector. Disconnect this connector. Look for the wire coming from the REAR o2 sensor as well, and unplug it too. The connector will be right next to the one for the front O2 sensor.

    Repeat for the other side of the car.
    Now go to the rear section of your stock Hpipe and find where it connects to the muffler pipes. Unbolt these 4 15mm bolts, and the muffler/exhaust tips should sorta droop down. Keep these 15mm bolts as you'll need to reuse them for the LG's.
    The H-pipe is now supported by 4 bolts. 2 in the front, mounted to the bottom of the motor, and 2 in the rear mounted to some springs hanging from the torque tube/tranny.

    First, remove the 2 supporting 15mm bolts. Keep these as you'll need to re-use them for the LG's. Keep the front of the hpipe either supported by a helper, or put a box or a jack stand under it.
    Now, unbolt the rear two supporting bolts that hold the exhaust springs to the exhaust. These 2 are 13mm bolts. Keep these too.
    That's it! Now you've got the hpipe/cat assembly totally free. It should look something like this.

    Use a 7/8" open ended wrench and remove the 2 O2 sensors and set them aside. These will become your front (and only) O2 sensors with the LGM Longtube setup.

    Part 2: Removal of stock manifolds

    Time to complete: 0.5 - 1 hour

    Pop the hood, disconnect the battery, and pull off your fuel rail covers.
    On each side of the engine, there is a metal AIR tube bolted onto the exhaust manifold. Each is held onto the exhaust by 2 10mm bolts. Remove them. On the drivers side, the AIR tube immediately connects to a rubber hose. Using a flathead screwdriver, undo the plastic clamp on the rubber hose and remove the AIR tube totally from the engine bay. On the passenger side, this will not be possible.

    While on the passenger side of the car, using a 10mm wrench to unbolt the oil dipstick tube from the exhaust manifold and with a firm tug, pull the dipstick tube up and out of the engine bay. Don't lose the dipstick bolt.
    Now disconnect all 8 plugwires from the coilpacks. Try not to pull on the wire, but instead pull on the boot that connects to the coil. Do the same for the spark plug end of the wires and set all 8 wires aside. Next, disconnect the wiring harness that goes to the coilpacks. Its a large white weatherpack connector, labeled in the photo.

    Next we need to remove the coil packs from each valvecover. On 97-98 LS1's, each coil pack is bolted to the valve cover separately. On 99+ year models, all the coil packs are on a bracket and the bracket is then mounted to the valvecover. Depending on your year, either unbolt all the coil packs individually (97-98), or unbolt the 5 10mm double-ended bolts (using a deep socket) and remove the coil bracket with coils still attached. On 99+ year model cars, there may or may not be a bracket mounted to the backmost bolt. If there is, undo the nut and pry the bracket off with a big flathead screwdriver, and then unbolt the final bolt to remove the coilpack rail.
    Next we need to loosen the drive belt so we can remove the alternator. Loosen the belt tensioner using a 15mm wrench and slide the belt off the alternator, leaving the rest of the belt in place as much as possible in the engine bay (it will stay in place on all the other pulleys if you are careful).
    Disconnect the wiring plug on the backside of the alternator, and using a 13mm socket unbolt the thick cable bolted to the back (WARNING: this cable is HOT (12 volts) unless you have disconected the battery. Make SURE you disconnect the battery before attempting this)

    Now, unbolt the alternator. There are 2 15mm long bolts holding it onto the alternator bracket. Remove them, pry the alternator out of the bracket at the top (it's tight),and then rock the alternator back and forth to wiggle it out of the bottom of the bracket.
    Now lets remove the exhaust manifolds themselves. On each manifold there are 6 10mm bolts holding them to the head. I recommend undoing the backmost bolt first, and leaving one of the middle bolts until the end. Once all 6 on one side are done, the exhaust manifold should be able to be pulled out from the top. Make SURE you disconnected the O2 wire mentioned in the earlier steps before you go pulling the manifold out, as the o2 sensor is still screwed into the manifold.

    Repeat for the other side of the car.

    Part 3: Installation of the LG longtube headers

    Time to complete: 0.5 - 1 hour

    Now its time to slide the headers in. The method I use in this document will be to install the drivers side from the bottom, and the passengers side from the top.

    If you don't have the car up very high, now is the time to jack the car up in the front and rear as high as you safely can. You're going to need somewhere between 18 and 20" in the front to get the headers in from the bottom. I had to use wood under the jack to get enough lift on the vehicle, and used large jackstands.
    With the car in the air, we can now clear the path for the drivers side header. The only thing we'll need to disconnect is the metal ground strap and the black wire that are bolted to the block.
    Now slide the drivers side header up from the bottom. Its going to take a while to figure out how it goes in, but it will go. There is a block of metal that sticks out on the back of the engine, which the rear most section of the header will have a hard time getting past. It may help to put a jack with a block of wood under the bellhousing and jack the motor up only SLIGHTLY, about a 1/2" for some extra clearance.

    There will also be a clutch line fitting that will be somewhat in the way, but it can be pushed up and into a small indentation to allow the header to pass by.
    Here's to prove it is possible, and a photo to show just how high the car needed to be. The tape measure reads about 19".
    Now that the header is up in the engine bay, we can start the bolts and install the gasket. Rather than using the gaskets that came in the LGM header kit, I bought OEM style gaskets from GM. If you have a helper, it would be best for them to hold the header up while you try and get the gasket/bolts all lined up and started. If you DON'T have a helper, the way I do things by myself is as follows:

    First, with no gasket in place, start one of the center bolts, and just turn the bolt in 5-7 turns. This will hold the header up in place.

    Now with the header in place, figure out the gasket orientation and line up the front most hole in the gasket with the front most bolt hole in the header flange, and start that bolt (use antisieze on this bolt).

    With the front bolt started, now remove the middle bolt and swing the gasket down into place, and start another bolt of your choice (again, remember to use antisieze on all 6 headerbolts).

    Now the gasket and header are held into place, and you can finish starting the remaining 4 bolts. Be sure to leave all 6 bolts loose...5-7 turns should be enough for now.
    On the passengers side, we'll need to remove the valve cover. On 99+ year model cars, there are 4 8mm centerbolts that hold it on. Unbolt them, disconnect any hoses going to the valve cover, remove the valvecover.
    With the valvecover removed, try and slide the passengers header in. If it seems to get stuck, or just doesn't want to go in, get under the car and see what is going on. You *may* find that you need to unbolt the starter due to the metal tab on the header hitting the starter. If so, read the next step for instructions.

    Optional: if the header hits the starter

    If the header seems to be hitting the starter, don't worry. The starter is only held on with 2 bolts, as shown in the photo. Just unbolt both bolts, and tilt the starter up an inch or two. With the starter lifted up, the header should slide right past with no issues. Once the header tab has slipped past the starter, bolt the starter back into place. The bolts should be torqued to 37 lb/ft.
    That's it! With the header in place, you can now install the gasket and start all 6 bolts, making sure to leave them loose again like we did on the drivers side.
    With both headers held loosely in place, we can now get the bellhousing/header mounting bolts started. Loosen the 2 15mm mounting bolts on the bracket so that it can be moved around freely on the bellhousing. Then, using the 2 15mm bolts removed earlier, bolt through the tabs on the LG headers into the bracket. Only hand thread these in 5-7 turns again, as we want to keep everything loose right now.

    Congrats! The hardest part is behind you.

    Part 4: Installation of Xpipe/Cats

    Time to complete: 0.5 - 1 hour

    Find your old REAR o2 sensors, which should have a square connector on them, and plug in the provided adapters.
    Install O2 sensors using a 7/8" wrench.

    Once the sensors are in tight, the most important part of the whole job needs to be done...the O2 sensor wire routing. The way I routed mine is over to the back of the heatshields, under the metal, and through the metal clips, just like the stock wires were run. Once you get the wires up into the engine bay, you may find that you have to move the computer side of the connector down some to reach. Once you are from behind the heatshield, use some zipties to tie the wires to anything you can find to hold them away from the headers. There may not be anything to tie them to on the passengers side, so careful tucking and routing will be essential.

    The most important thing is to make absolutly sure the wire going from the drivers side header plugs into the drivers side wiring harness, and the passenger side sensor goes back towards the passengers side. With the way the O2 sensors are pointed and angled, its very easy to get confused and plug them in on the wrong side.
    Before we slide the Xpipe section in place, you need to visualize how it will be oriented. The cut edges going towards the front of the car. One rear leg of the xpipe will be longer, and this should be on the drivers side.

    On the front 2 pipes of the Xpipe, loosely place 2 band clamps on them with the bolts pointing down, and towards the outside. Now slide the X-pipe in place onto the 2 header collectors. Since we left the headers really loose, it should be pretty easy to get the Xpipe to slide on. Push it forward enough onto the header collectors so that you can no longer see through the cracks into the pipe, and then position the clamps so they are over the cuts in the pipes and hand tighten them down just enough so that they stay in place.

    You can now go back into the engine bay and tighten all 12 header bolts, and torque them to 18 lb/ft. Then tighten the 4 exhaust/bellhousing bolts under the car to 37 lb/ft, or just snug them down good.
    With the headers tightened and the Xpipe in place, all that is missing is the rear pipes. If you are going to be using cats, and the cats don't have slits in them like the rest of your pipes, you are going to need to cut slits in them to ensure a proper seal.

    On the side marked INLET, cut 2 thin slits about 3/4" to 1". You can do this using a grinder with a cutoff wheel, a dremmel, a hacksaw, or various other methods.
    If you don't have a one piece rear pipe (ie, you have cats, or a swappable offroad/cat setup) you now need to assemble the rear pipes as shown. All cuts in pipes will be towards the front of the car, and all clamp bolts will be facing downwards, towards the INSIDE of the car. The cats are staggered a couple of inches so that the clamps will fit without hitting each other.

    The shorter of the 2 pipes will be the drivers side.
    You can now slide the rear pipes in place and start the rear catback flange bolts, making sure there is a gasket in place. You should be able to reuse your stock gaskets, or you can optionally install new ones (part #'s at the top of the install). You'll need to re-use 4 of the 6 nuts from your stock manifold studs, and re-use the 2 bolts from the catback flange (they used to just thread into your old H-pipe).

    Next, install the 2 13mm exhaust suspension bolts that hold the exhaust up.

    Finally, Tighten the 4 (or 2 on some setups) clamps down, again making sure that you can't see light through the cuts and that the bolts are angled up enough so that they wont cause a ground clearance issue. Go back to the front 2 clamps and tighten those down good now as well.

    Part 5: AIR Pipe conversion ('97-'00 year models only)

    Time to complete: 1 hour

    Now if you have a 1997 - 2000 model C5, you are probably noticing a slight problem. The passengers side AIR tube does not match up with the port on the header! For some reason in 2001, GM decided to change it, and LGM decided to make the headers one way, and one way only to keep costs down and inventory availability the same for all cars so he used the new style.

    Included in the LGM header kit, there should be included a new style AIR pipe. The part number is 12561494. We'll need to swap this pipe in place.
    The AIR pipe is a solid metal pipe, and it runs behind the motor, so the only way to get it outta there is to remove the intake manifold. This is not a difficult, nor necessarily time consuming process, so don't worry. To remove the intake, we need to do the following:
    • Unplug any wires going to the throttle body and MAF and IAT sensor. Unplug the red electrical plug that sits on the drivers side of the intake manifold, near where the coils were.
    • Pushing in the metal retaining clips on each injector, unplug the plug going to all 8 injectors.
    • Using pliers to loosen the hose clamp, pull the large black rubber hose off the brake booster nozzle.
    • Using a flathead screwdriver, loosen the clamp where the air bridge meets up to the throttle body, and slide the air bridge off. You may need to loosen whatever air intake system you have on your car to do this.
    • On the passenger side, pull the PCV hose out of the rubber receptor in the neck of the intake manifold. Also remove the short rubber hose that goes to the throttle body.
    • On the drivers side, press the light gray clip on the plastic hose going to the neck of the intake manifold and push/pull on the connection until it comes off.
    • Using a fuel line disconnect tool, disconnect the braided metal line going to the intake manifold. If you do not have a fuel line disconnect tool, you can leave this line connected.
    • Once all wires and hoses are out of the way, unbolt the 10 bolts going into the top of the manifold, and totally remove the front 8. The rear 2 will not be able to be removed due to the cowl.
    Now, you can pick the manifold up some, and while holding the rear 2 bolts up some so they don't get caught on the heads, try to slide the intake manifold forward 4". Now look on the back of the intake manifold and you'll see an electrical connector and a tiny black hose. Disconnect those. Look for anything else tethering the intake to the car (aside from possibly the braided fuel line), and continue to carefully move the intake manifold forward and out of the way as much as you can. You may have to help guide the rubber brake booster hose through the mess of wires to keep it from pulling on them.
    Now that the intake is out of the way, we can more easily get to the AIR tube. Before we can unbolt it and remove it, follow the air tube from the drivers side to the firewall, and you'll feel or see where the rubber hose meets up with a metal pipe. You'll need to pull this rubber hose off the metal pipe (the metal pipe is the pipe we're about to remove).

    Finally, there will be one bolt holding the AIR tube to the back of the drivers side head, via a small metal bracket that is part of the pipe. Loosen that bolt and the pipe bracket will slide up and off the bolt. You can now remove the air pipe from the car! Whew!
    With the pipe off the car, we can now swap the black check valve from the old pipe to the new pipe. Using adjustable pliers, or large open ended wrenches, (7/8" and 1" I believe), unscrew the check valve and transfer it to the new pipe.

    Install the new pipe, and test fit it on the AIR flange on the passenger's header to make sure it fits properly. If it does not, you may need to pull it back out and bend the air pipe a little to fit. Once it fits, bolt it to the back of the drivers side head, and hook up the rubber hose you disconnected previously to the pipe. Now you can start the 2 10mm bolts into the AIR flange on the passengers header making sure to use antisieze on the bolts, and a new AIR gasket (included in LGM kit).
    Here's what it'll look like with the new pipe installed.

    Now reinstall the manifold:
    • Slide manifold back in place, making sure to hold the rear 2 bolts up in place so they don't catch on the head. Before seating it fully in, remember to reconnect the small vacuum line and electrical connector on the back.
    • Slide the large rubber brake booster hose back onto the brake booster nozzle, and position hose clamp properly.
    • Reinstall the remaining 8 bolts and torque them to 4 lb/ft starting from the center and working your way out, then do a second pass at 8lb/ft. Due to rubber gaskets sealing the intake, overtorquing these bolts is a bad idea!
    • If you disconnected the fuel line, reconnect it now.
    • On the drivers side, press the light gray clip on the plastic hose going to the neck of the intake manifold and push on the connector to reinstall.
    • On the passenger side, reinsert the PCV hose into of the rubber receptor in the neck of the intake manifold. Also reinstall the short rubber hose that goes to the throttle body.
    • Slide your air filter/intake setup back onto the throttlebody, and tighten the clamp with a screwdriver.
    • Re-plug in any remaining hoses and wires, like the 8 injector plugs, MAF, IAT, TPS, ThrottleBody, red fuel vapor, etc.

    Finally, reinstall the oil dipstick tube if you haven't already. If you use a flashlight and look at just the right angle, you should be able to barely see the hole in the engine where the dipstick will be inserting into. Press it in firmly, and reinstall the retainer bolt to hold it to the header.

    Part 6: Finishing up

    Time to complete: 0.5 - 1 hour

    Now we need to do the final re-assembly of all the odds and ends. Here's a checklist:

    • Reinstall the alternator, and reconnect the power cable at the back, as well as the weatherpack connector.
    • Reinstall belt, using a 15mm wrench on the tensioner. To do this, I usually route the belt onto all pulleys except for the water pump, then push on the tensioner, and slide the belt up onto the waterpump pulley.
    • Reinstall valvecovers. On centerbolt valvecovers, you can torque them to 9 lb/ft.
    • Reinstall spark plugs, making sure to put a dab of antisieze on the threads. I use NGK TR-55's with the out-of-the-box gap.
    • Reinstall coil packs, and reconnect the spark plug wires, making sure to put a dab of dielectric grease on the connector tip of the spark plug before pressing the wire on.
    • Reinstall drivers air tube, making sure to use a new AIR tube gasket (included in LGM kit) and antisieze on the 10mm bolts.
    • Finally doublecheck all hoses, wires, etc, and re-tighten the exhaust bolts both in the engine bay, and under the car.
    • Doublecheck O2 wires for proper clearance from the header pipes
    • Carefully lower car back down on the ground. NOBODY should be under the car while it is being lowered. If you had the car high up in the air, it may be safest to lower the front half way, then lower the back, then lower the front the rest, then finish lowering the back. I have seen cars fall off of seemingly perfectly situated jackstands when lowering cars too far in one go.
    • Reconnect the battery! You will need to put the key in, turn it to the ON position, and then hold down the lock and unlock buttons on your fob until the car honks at you. This will "synch" the fob up to your car again after the battery has been disconnected.
    That is it! Its time to fire the car up and see how she goes! When you first fire it up, it is perfectly normal to see a fair amount of smoke coming from the engine bay. This is grease and dirt burning off the pipes.

    To burn the grease from machining from the inside of the pipes, take the car out for a spin and feel free to put the pedal down. There is no break-in period for headers, so have fun! After a few heat cycles, you'll want to get back under the car and check your wires and retighten all exhaust bolts.

    Frequently Asked Questions

    1) Do I need O2 Simms?

    Yes, or you will need to have the O2 sensors turned off via tuning. LGM headers do not have rear o2 sensor bungs, so even if you wanted to run rear sensors, you couldn't.

    2) My car sounds like it has a louder ticking after the install?

    This could be a few things. It could be an exhaust leak on an AIR tube flange or at a primary on the header gasket. BUT.....most likely, it is normal. Longtube headers typically use a much thinner (and higher quality) metal than stock, thus exhaust pulses and exhaust valve noises are transferred much more efficiently now, making for quite a racket.

    3) My car runs really poorly after the header install

    The first thing to check for is crossed o2 wires. It is very common for people to plug the passengers side O2 sensor into the drivers side, or vice versa, due to the way the o2 sensors are angled. Do not be confused, the drivers side sensor MUST plug into the drivers side harness.

    If that is correct, get a scan tool and watch the o2 sensor values, or read the codes from the DIC and look them up (or have someone look them up for you). Sometimes codes will be thrown soon after install due to the oil inside the headers from machining getting onto the o2 sensors. A good spirited drive will burn this grease off and clean the O2's, then you can reset the codes and see if they come back.

    4) Will this system make my car louder?

    Yes. The LGM system will add a fair amount of volume to the exhaust note, but nothing extreme if you have a good quiet catback (like an OEM Z06 catback), and use the catalytic converters. The off-road setup may be unbearable for many with "straight through" mufflers instead of proper mufflers, but it really just all comes down to each individuals threshold and preference for how they want their car to sound. Before ever modifying your exhaust, see if you can find locals with various setups and listen to them first. Ride around in their car for a few minutes and see just how much noise you are willing to put up with.

    All content provided on this site is to be used as a suggestion only. Any damage to the vehicle or injury resulting from usage of these materials is 100% the users responsibility. Use of a professional mechanic is suggested if you do not feel comfortable with the instructions. Reproduction of any photography, work or otherwise herein is expressly prohibited without written permission from the publisher
    2004 - jmX - All Rights Reserved.