Engine Guides / LS Engines

LS4 5.3L FWD Engine Upgrade Guide: Expert Advice for LS4 Mods to Maximize Performance

[Editor’s Note: No offense to the LS4 intended, but the most notable thing about it is that it’s usually the worst-possible choice for an LS engine swap project because it’s designed specifically for front-wheel drive (lovingly called “wrong-wheel drive” by some) cars, so if that’s why you’re here, save yourself the time and hassle and choose a different LS or LS-based Vortec engine for your build. We are growing our collection of LS engine upgrade guides, courtesy of our LS-expert friends at Summit Racing. If you already possess an LS4 engine or LS4-powered car and are looking for tips to add more performance capabilities, you’re in the right place. For a primer on the entire LS engine universe, read LS Engines 101: An Introductory Overview of the Gen III/IV LS Engine Family.]

Intro to LS4 FWD Engines

The LS4 is unique in the LS engine family because it was a transverse-mounted engine used only in front-wheel drive (FWD) cars from 2005-09, namely the Pontiac Grand Prix GXP, the Chevy Monte Carlo SS and Impala SS, and the Buick LaCrosse Super.

While the LS4 is likely a poor choice for an engine-swap project, it’s not out of the question that you own one of these likable V8-powered vehicles, and want to add a little giddy-up to that sideways 5.3-liter.

We can help with that.

To make this engine work for those FWD cars, GM made several major modifications to the engine:

  • The engine was mounted in a transverse position, using unique motor mounts.
  • The intake manifold was smaller than other LS manifolds and reversed, placing the throttle body over the flexplate. It also had a unique (small) 4-bolt throttle body pattern.
  • The engine used a metric, 60-degree, Chevrolet V6 bellhousing. The engine shaved about 3mm off the flexplate side and 10mm off the crank snout, and featured a unique timing cover.
  • The starter was mounted on the transmission—not the engine block.
  • The timing cover, crankshaft, and accessory drive were all modified to fit in a FWD engine bay.

[Every engine spec you’ll need can be found here: LS4 Engine Specs: Performance, Bore & Stroke, Cylinder Heads, Cam Specs & More.]

How to Get More Power From Your LS4

The LS4 is a bad choice for an engine swap, but it can be improved when used in a FWD car or mid-engine kit car swap.

For the rest of this article, good fabrication skills and probably more research will be required.

Upgrading the LS4 Intake Manifold and Throttle Body

The LS4 has a smaller throttle body and intake manifold than other LS engines.

The intakes were necked down behind the throttle body to clear the oil pressure sender. As a result, a larger throttle body doesn’t offer big gains.

It’s possible to upgrade to an aftermarket intake manifold. However, be prepared modify the following components to make it fit:

  • PCV is on the wrong side
  • EGR
  • Valley cover—use a non-PCV cover and delete AFM
  • MAP sensor
  • Oil pressure sender
  • Injector pigtail adapters
  • Alternator bracket
  • The underside of the intake manifold (if you’re trying to keep AFM active)
  • A throttle body and/or adapter

WARNING: Throttle bodies came with either silver or brass blades during this time period. They differed in rotation and pinouts between different models. The LS4 had a unique brass blade and smaller 4-bolt pattern (as used in V6 models). Further, the airflow tables and ETC scaler may require work by your tuner to get proper throttle response after an install.

Upgrading the LS4 Camshaft and Valvetrain

You will need to drop the entire engine cradle to do a cam swap, but that’s more cost-effective per horsepower than an intake swap.

Keep in mind that going bigger than about 220 degrees of intake duration (at 0.050 in.) is pushing it with the stock intake and torque converter.

The 2005-2006 models came with the 3-bolt cams with a 1X-single pole to match the 24X reluctor and E40 ECU. Halfway through 2007 however, it changed to a single-bolt 4X-4 pole gear to match the 58X reluctor and E67 ECM. The cam is also a few degrees bigger than the early cam.

GM switched to a spring-loaded timing chain tensioner in 2007+. If you’re performing a cam swap, going back to the 2005-06 wedge-shaped plastic guide adds reliability.

Don’t forget to pick up a spring kit to match your new camshaft. Titanium retainers are also available and will reduce valve float at high rpm.

The trunnion bearings in the stock rocker arms are a known weak point. A trunnion upgrade kit should be installed whenever you upgrade the valvetrain.

The LS4 was equipped with Active Fuel Management (AFM). It’s good for gas mileage, but not for performance. If the valvetrain is in good condition, an AFM disabler plugs into the OBD-II port and will turn it off.

When upgrading the camshaft, an AFM delete kit is strongly recommended. These kits replace the AFM components with standard parts. It also becomes easier to fit an LS6 intake or aftermarket LS2 manifold. A smooth, non-PCV / non-AFM valley cover won’t interfere with underside of the manifold. You may need to modify the oil pressure sender bung to avoid the throttle flange area.

Upgrading LS4 Cylinder Heads

The cathedral port cylinder heads are based on the LS6 heads and make good power. You can mill them about 0.030 in. for more compression. They can also be CNC-ported for better airflow.

There are a few aftermarket LS4 heads available. The heads will flow better than stock and have thicker decks to maintain a proper head gasket seal.

Upgrade the LS4’s 4T65E Transmission Before Adding Power

The 4T65E wasn’t made to handle a lot of horsepower beyond stock output.

There are transmission builders that specialize in the 4T65E who can build it to withstand 400-450whp.

Once you have the transmission equipped to handle more power, a single-nozzle nitrous kit is adjustable and allows you to sneak up on the limits of the drivetrain.

We found examples of advanced fabricators building turbocharged LS4 engines, so it’s not impossible if you have the knowledge and resources to add significant power to an LS4-powered FWD vehicle, but adding that much power will require a number of potentially expensive and labor-intensive upgrades and reinforcements elsewhere.

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  1. Daniel Wilson says:

    Hello Brian Nutter,

    WOW !!! The things we do in our quest for higher performance seems to have no boundaries. In the situation you described for the LS4 In the ‘04 and later Grand Prix, that quest could turn into a major headache real fast. I guess the saying “where there’s a will, there’s a way” might be appropriate.

    I’ve often thought “I shoulda bought a V-8” while using what’s available to increase the performance of my ‘02 Grand Prix GTP, Supercharged 3.8 V-6 (code 1), but fortunately the aftermarket does offer a few choice components to make the task a little easier.

    I also have the 4T65E transmission which, with normal maintenance and Mobil 1 Synthetic ATF, has handled increased torque and Drag Strip abuse very well. A good source of performance parts for the 3.8 V-6, including hardcore internals for the 4T65E is ZZ Performance. They also offer upgrades for the LS including the LS4 featured in your nicely detailed article.

    But I still think about how I shoulda, coulda, woulda bought a V-8 but I dropped the ball. HEY….THE SUN WAS IN MY EYES !
    And the beat goes on…..

    • I just bought a backup supercharged 3800 for my gtp and also coulda woulda shoulda got an ls4 dropout. I want the v8. I know its s front wheel drive (98 gtp) but i love driving the car the big mirrors the hud and alot of glass and i go into snow and mud alot with this car and it handles it well. I really want the v8 but in this car and i think i can do it if i do the dropout and the dash and exhaust (pretty much the whole car).

      • Mikel Brooks says:

        I have a 05 Pontiac Grand Prix GXP for sale..I take good care of this car…191k miles on it. Rebuilt transmission from Chance Transmission that have over 3,000 miles on it. Brand new lifters. Car goes through a ton of oil changes but I don’t care…car nice powerful n fast. I wanted to place Magnaflow on it like I did the V6 3800 but not at this time. Cars color is Spiral Metallic…nice.Leather interior, no rips or tears… Contact me a brooksm49mb@gmail.com if interested.

  2. Pingback: LS Engines 101: An Introductory Overview of the Gen III/IV LS Engine Family - OnAllCylinders

  3. Ive personally done a ls4 engine swap, though not the most powerful of choice it has been a relative dream to work with. My pontiac montana seems quite pleased with it’s new power plant oh and I strongly recommend adding an lsd differential makes a world of a difference

  4. Hi, I have a Buick Lacrosse super that I am trying to find aftermarket parts for but all the speed tuners and specialty automotive builders have no support for the lacrosse as they say my ecu files are different from its sister cars the impala ss, gxp, and monte ss. Any hints as to where I can go to find a tuner? Thanks.

    • I have a super and was having the same issue with Handheld tuners like diablo….my two options were dyno tuning or HP
      Tuner 93oct tuner file … I went with the basic tune….This turn of DoD, rev limiter and firm up trans shift points

      • Glad to see other Super owners here! I need to upgrade the crappy stock transmission soon before I do anything to mine (I have cold air, doesn’t help much without other mods tho)
        Shame it sounds like tuning is pretty limited…

    • I need a cam shaft positioning sensor for my 2005 Chevy impala ss but it’s discounted any idea wat I can do to get her running

  5. Saved Burrow says:

    What is the fireing order for 2000 ford truck 5.4 engine

  6. Jeffrey Hendry says:

    I have a 2006 Impala SS and the transmission does not shift into 4th gear OD until I hit about 50 mph. I was trying to find out how I can get it to up shift into 4th gear OD at 45 MPH as the majority of the roads where I live are posted at 40 MPH. My transmission is rarely shifts into 4th gear and I drive around in 3rd gear most of the time. Are there can electronic tuners or other modifications I could do to get the transmission to up shift into 4th OD at a lower speed than 50 mph? Thanks.

  7. Hey bub I have a 08 impala ss with 70k it runs like a monster but I hate the 4cyl mode bs I know u said dyno tune but I don’t have access to one which one would u recommend for turning that of n getting a more power? I was looking at diablo there r so many choices please help theodinsonx@gmail.com

    • just a headsup unpluging the oil preasure sensor (behind the throttle body) will kick out 4cyl mode! iv had my (06’impala ss) unplugged for 2yrs and is way better! and stays in 8cycl. mode

  8. I want to put an LS4 with active fuel management (Displacement on demand ) WORKING into a S2000 Honda as I live in Europe but work in the USA so after the conversion in the USA I will ship it home. Fuel in Bulgaria is Over $6 a gallon. My shop in the USA I am sure can figure out how to adapt a 6 speed T56 the problem would be the starter?



  9. my tranny went on my 2007 monte carlo…can i still swap it with a 4t65e hd from a GXP? the gear ratios are a bit different 2.93 for gxp and 3.96 for monte does it matter???

    • If your MC has a V8, then yes. They use the same trans. Everything is the same. Both have a 2.93 fdr. (3.29 diff with 37/33 chain sprocket).

      If your MC is a V6, then this is not a practicle swap. The starter on the V6 is bolted to the lower engine block and the trans has a spot down low for it there. The V8 has the starter mounted on the trans bell housing near the top. The V8’s have a fdr of 2.93. The V6 cars had either a 2.86(3.5l) or 3.29(3.91) for 2007. I am not sure where you get 3.96 from, but the factory never had such a ratio.

  10. Shot in the dark but would an 02 lincoln continental be a candidate? 4.6l v8

  11. Dillon Jackson says:

    Hey im very curious on where to find headers and the best chip for my 08 impala ss and im looking for a little bit more bite in the performance i guess it is sort of a daily but would like to take it down the track once in awile

    • Paul Jennings says:

      Dillon, better late than never, eh? If you’re in the U.S. then I know of 2 companies that manufacture headers for the 5.3L LS4. KOOK and DOUG THORLEY. Check CarID.com

  12. Brian Nutter says:

    Dillon, in my research I didn’t see that headers were available any longer without going custom built. As for tuning, we’re a fan of taking it someone local with a chassis dyno and uses HP Tuners. They can tune the engine AND adjust the transmission shift points etc.

  13. It’s good to see that these cars are still of interest to some. My ’05 GXP has sat for over a year since the trans shelled out for the 3rd time. I should have gone with one from TEP the first time, but didn’t know any better. The first time was under warranty, the second time I thought ‘surely this will be the last time’, and this last time was just out of warranty. Since I decided to go back to school, my interest in the car comes and goes. I have the money but not the time to put into this thing. I guess I’m looking for encouragement to dive into it or someone to offer to take it off my hands. Good luck to everyone in their LS4 endeavors.

  14. I have a 2000 Cadillac devile ….. looking to remove n* and replace it with the fwd 5.3 can anyone give a heads up on what I’m getting into

    • Tony Whitesel says:

      I’m here for similar information. I have an ’86 Coupe Deville with the 4.1 Cadillac V8. The car is almost immaculate and am thinking I would like to do an LS4 swap sometime in the future. I am curious as yo how difficult this is going to be?

  15. David Hill says:

    Can’t find any info on the wiring harness.. need to stand alone it. But no one has posted anything..

  16. I have a fully built 2007 Gxp with the LS4 pushing a little over 450hp was wondering where do I go about finding more stuff to upgrade the trans I cannot find hardly anything. Thanks! Add me on Snapchat to see the car. >>> dillonkerner

  17. Dennis Proulx says:

    Hi… I have an ’06 Impala SS, and am looking for a cam positioning sensor… They have all vanished! GM has discontinued them… Did I miss something? Is there an upgrade that deleted these somehow? Help? Car is running like crap! Thanks in advance! Den

  18. I wanna drop a ls4 in an 06 charger any tipz?

  19. Hi. I just bought a 2006 GXP in excellent condition except it has a blown transmission. I live in Ottawa Ontario. Any suggestions on where to get a transmission?

  20. 08 5.3l impala harmonic bouncer went out could that mess up the old pump?

  21. Pingback: 2002 Monte Carlo Engine Diagram – Wiring Diagrams Image Free

  22. Estevan Gutierrez says:

    Have no fear yall!! Heres a very good Transmission upgrade.


    Monster makes high performance transmissions that are reliable. So hope this helps everyone here.

    • Estevan Gutierrez says:

      Monster also custom builds Transmissions. Yes that’s expensive but well worth the trouble. Give em a call and see what they can do.

  23. Charles Williams says:

    I have a 2006 impala ss 5.3L that i need to do an engine swap on. What year 5.3l engines can i use use or they all the same ?

  24. Jamell Ethen Osgood says:

    the ls4 is useless for most swaps, but not if your planning a longitudinal awd swap like in a Mitsubishi 3000gt. I that would actually be a great starting point.

  25. Hey there, I’m looking for info on the LS4. I want to swap one into a smaller car but keep the FWD application. I’m curious if anyone has actual dimension measurements of the LS4, I can’t find those anywhere.

    Also, how are people going with a manual trans with this engine? I understand the main trans is an auto, I want to have a manual shift to go with the LS4, is that even possible?

    • George Willever says:

      I have a 1999 vw beatle with a 2008 Chevy engine and drive mounted in the rear of it , I’m selling if you might be interested I’ll send you a pic

  26. I have a 2008 LaCrosse Super. Nothing has ever been done to it and it has 83k on it. I can tell the tranny is not in the best shape as it slips occasionally in first gear.

    When the time comes, or even sooner, I want to improve upon the factory transmission. Do any of you have any suggestions.

    P.S. I love the car. It is Ruby Red with the brown interior and power roof. When I have the cash, I also want to find one of the 139 2009 LaCrosse Supers also. They are out there…


  27. Thomas Owens says:

    Will the LS4 fit into a 98 Deville? Everyone knows the Northstar engines are not the best and the LS a lot more reliable. My question is will it work and if so, what parts would be needed?

  28. Can I ls4 swap my 06 Malibu ss ? It has the 3.9l v6 in it

  29. john snelling says:

    have stock ls4 in 3 wheeler mounted tranverse in rear lookin for a seperate blower [belt driven] since iam not running a ps pump or compressor have made brackets to support pullys to replace them the area OF THE PS PUMP SHOULD GIVE ENOUGH ROOM QUESTION 1 WHAT SIZE BLOWER DO I NEED ,2 ANY FUEL [INGECTORS] DO I NEED 3 JUST WANT TO RAISE THE HP NO MORE THAN 100 FOR NOW ,ONLY WEIGHS AROUND 2000 LBS

  30. Dawson Young says:

    I am currently building a single turbo ls4 build and I’m looking for anywhere between 700-1000hp and I was wondering if a stock 4T65E could hold the power or if I should look into a built 4T65E or if there are any swap options that I could look into. If anyone has any suggestions it would be very appreciated!

  31. I won’t to put a super charger on pontiac Grand Prix gxp

  32. Carlos blue says:

    If i have the ecu and pcu and wiring harness that goes with a 24x fwd 5.3 how can i make it work in my 08 impala ss

  33. is the car in the picture a Pontiac GTO.

  34. Chris Jainnini says:

    I have a 2007 Monte Carlo ss and everything seems to be a hassle to upgrade it, why and where are these cars at anymore? It seems like I’m the only shmuck with one.

  35. Pingback: LS4 Engine Specs: Performance, Bore & Stroke, Cylinder Heads, Cam Specs & More

  36. Tryna see wat kit should I buy in order to rebuild the motor in my 2008 impala SS

  37. Matthew L Gullett says:

    Okay, crazy idea. I just picked up an ’87 Cadillac Allante and am considering an LS4 swap. The HT4100 is a great boat anchor, but at 170hp, even a 3800 v6 would be an upgrade. There seems to be enough room under the hood, so your thoughts? I know other upgrades would also be needed, like suspension (whjch also sucks).

  38. Alan Ordonez says:

    Hey , i own a 2007 chevy impala LTZ and would like to swap my 3.9 with 5.3 of the same year . I looked all over but i cant get a solid answer. Will the transmission from the ss fit perfectly in my ltz ? Is it as easy as it seems for this swap to be? Im ready to spend money for the whole ss drivetrain because my current transmission is seeing its last miles. Someone please help

  39. greeeeeeetings eeeeeeeeeearthlings! i am a owner of a 96 monte carlo ls and i am pondering on adding more stooopid juice/horse power! may someone enlighten me on this matter at hand cause im clueless…
    with my sincerest regards live and direct from california republic port of los angeles – harbor area 310!

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