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Our Newsletter

3500 Swap

The LX9 3500 Swap has become one of our biggest selling products to anyone with the 3100 or 3400 engine. Due to the sheer volume of customers wanting detailed answers of exactly what is involved in the swap, and the countess amount of time I spend walking each of these customers and potential customers through every step, I’ve decided to post a page on the website outlining everything you need to know before taking on a 3500 Swap. Until now, I have never posted instructions on how to do a swap because of the liability involved. I didn’t want to persuade people who have no business working on cars to pick up a wrench and start going to town just because they have a step-by-step guide in front of them. So with that in mind, I am writing this as a guide to inform customers about the 3500 engine, its benefits, and how to use our swap kit to install the 3500 engine into various vehicles properly.  I can say without a doubt that myself and those who work at my shop have done more 3500 swaps than anyone else out there. It’s possible we’ve done more of these swaps than anyone else combined. Therefor I consider myself the foremost expert on the subject. I’m not stating this to blow my own horn, but to assure you that when it comes to the 3500 swap, I know my stuff. The advice and instruction below is my opinion, and the opinon of others may differ, but I stick by everything I say. That being said, Milzy Motorsports is not liable for the result of any mistake made by an individual attempting to work on their car without the proper expertise and/or equipment. Work on your vehicle at your own risk.

Why a 3500 Swap?

If you’ve called or e-mailed me asking how to get better performance out of your 3100 or 3400 car, or for advice on what mods to do while you are fixing some problems with the engine, chances are within the first 5 minutes, I’ve brought up the idea of swapping in a 3500. There are a number of reasons why a 3500 is better than your current engine…

  1. Power - The 3500 makes 201 hp at the crank, which is 26 more hp than a 3400, and 41 more than pre-2000 3100 engine. It makes this extra power due to its increase in displacement, its increase in compression ratio, a 65mm throttle body from the factory, and also improved cylinder heads which mostly improve airflow during the “mid-range lifts” which corresponds to more power under the hp curve, making the engine more responsive and more efficient at making power. Please note that the 201hp is based off of the 3500 having a 65mm throttle body. Since it is electronic aka “drive-by-wire”, it cannot be used on a 3100/3400 vehicle using the vehicle’s current pcm. If you remove the oem 65mm tb and install a smaller one, the power will be reduced. Also keep in mind depending on our vehicle, the stock pcm can hold back the 3500 from making its full power, so we highly suggest one of our PCM tunes before or during your swap.
  2. Reliability - In developing the 3500, the engineers who designed the new engine improved on all the bad things about the 3400 and 3100 engines, namely the tolerancing of the engine and the gasket problems which plagued the 3100 and 3400 engines. Unlike every 3100 and 3400 out there, the 3500 is no longer afflicted with every single engine having intake gasket issues or with the constant ticking whether that be “piston slap” or “lifter tick” that the other 3x00’s are known for. The intake gaskets also now include side valley gaskets much like a 3800 has, which eliminates the need to have a whole tube of RTV sitting around when you take the lower intake off.
  3. Strength - One of the other improvements the 3500 received was the use of what are called “powdered metal” connecting rods. This is a new process of making connecting rods which allows the rods to be much stronger than their predecessors. In fact, they are as strong if not stronger than many of the aftermarket forged rods. These new rods are made in one piece (cap and all), and then cracked open. The LS1 engines and its variants use the same process, as do the series III 3800 supercharged and nonsupercharged engines. I know it’s apples and oranges, but I helped a friend build a rear wheel drive firebird 3800 with two gt35r turbos, which made 870 whp at 28 psi and ran 8.80 at 156 in the ¼ mile. The bottom end of this engine consisted of a stock 3800 crankshaft, L32 stock rods (series III powedered metal rods), aftermarket forged pistons, and ARP hardware, and the engine not only never failed, but after my friend sold the car, and they sold it, and they sold it, etc, about 5 owners later the car ended up back at my shop last year for a tune-up … 400+ passes later, we replaced the valvesprings, welded some cracks in the headers, and sent it back on its way. I’m going to get some people calling BS here, but due to the ridiculous drivetrain loss of the 350 turbo hyrdromatic trans behind that monster 3800, we estimate crank hp figures in excess of 1200 hp, all being transferred to the crank with those OEM rods. Although this is a different application, it just goes to show the potential of the strength of these new type of connecting rods. Another huge benefit to those who want to build an all-out monster 3500 is the fact that a fair portion of the 3500’s even have forged crankshafts. In other words if you buy one of these forged crank engines, all you have to do is get some aftermarket pistons and some ARP hardware, and you’ll have all the parts you need to build a strong bottom end for one hell of a boosted 3500.
  4. Ease of Swap - In conjunction with our 3500 swap kit, the 3500 is essentially a direct bolt-in replacement for the 3100 and 3400 engine. Our kit allows you to use your vehicles current engine harness and computer to run the newer engine. This is mostly due to the fact that the 3500 is simply an updated version of the 3400, with improvements in strength and performance, but essentially functioning in the same way. Most of the engine sensors transfer right over to the 3500, and the kit takes care of the ones that don’t. The LX9 is a much easier swap than say a LZ4 3500 or LZ9 3900, both of which are very similar to eachother, but use variable valve timing, or more accurately variable cam timing, which makes it a much more complicated and costly swap to pull off.
  5. Efficiency - This pretty much goes for anything performance wise, not just 3500 swaps, but anytime you increase performance in an engine by increasing the efficiency of how the engine moves air into and out of the engine, this is also going to have a positive effect on the efficiency of the engine with respect to fuel consumption. In less complicated words, you’re going to get more gas mileage by making your engine more powerful. This may seem counter-intuitive, but the reason is because you’ll need less throttle position and rpm to achieve the same acceleration to a given speed compared to what the lower powered engine would need to create the same effect. Now it’s probably not going to be a huge difference in mpg, especially if you find yourself hitting the skinny pedal more often to enjoy the new 3500’s power, but there should be a noticeable gain in economy. Please note that if you go wide-open-throttle all the time, you’re economy will definitely go down, because horsepower is proportionate to fuel consumption, so the more power you make, the more fuel your car will consume at wide-open.
  6. Cost - So we’ve got more power, more reliability, stronger parts, and more efficiency … this 3500 swap can’t be cheap … or can it? The 3500 engines are actually more affordable than a comparable 3100 or 3400. Every single 3100 ad 3400 out there needs the intake gaskets replaced if they haven’t been already (and some still do if they took it to the wrong person and/or used cheap gaskets), and many of these vehicles are left this way long enough for the problems to become worse. Maybe the owner didn’t realize the gaskets are leaking, maybe they didn’t have the money at the time … whatever the case, the problem is only going to get worse, the car overheats more, and inevitably results in one of the following failures … blown headgaskets, spun bearing, broken camshaft due to excessive friction (turns out water isn’t such a great lubricant), etc. Many 3100’s and 3400’s fail and then need replaced, so the junkyards and recycling yards are constantly selling them, and their value has gone up and up because everyone wants a good low mileage engine, and they just keep getting older and older. It’s supply and demand. There is a higher demand, and the supply is low for good low mileage engines, so the price can only go up. Meanwhile you have the LX9 3500 engine. It only was offered in vehicles a short couple of years. It does not have near the failure rate of the 3100 and 3400, therfor the yards do not sell them often. Demand is low, and so is the price. In general a 30-60k 3500 engine will typically sell for around the same money as a 80-100k 3100 or 3400.


What vehicles can a 3500 be swapped into?

Any vehicle currently powered by a 3100 or 3400 engine can easily have a 3500 swapped into it, and run off the factory engine control system (along with our swap kit). Most of our customers have vehicles like Monte Carlos, Impala, Malibus, Grand Prix’s, Grand Ams, Aleros, Berettas, Cutlass’s, etc, but you can also swap 3500’s into minivans like the Venture/Montana/Silhouette, and crossovers like the Aztek, Rendezvous, and others. On top of all these, any vehicle with a 2.8L or 3.1L multiport engine can also be swapped to a 3500, and can technically run off the factory ECU, although we highly recommend either tuning the ECU and getting bigger injectors because 17lb/hr and 3500’s don’t mix, OR do an OBD2 conversion which will put you into a much more reliable and tunable setup. If that’s not enough applications, lets say you have a grand am base model, and you can’t stand the 4 cylinder engine and you’re tired of buying ignition control modules for your quad 4, well if you use the components for the V6 version of your car minus the engine, you can then do the same 3500 swap as your V6 cousins. This applies to any vehicle which has an option for a 3100/3400 during that bodystyle, or possibly even across bodystyles of the same chassis, depending on application.


How do you do a 3500 Swap into a 3100 or 3400-powered vehicle?

First let start with the contents of the swap kit …

  • External Crank Trigger Kit- This is the most crucial piece of the swap kit. Without it, the 3500 won’t run on the 3100/3400 pcm. The kit is designed to replicate the reluctor wheel on the crankshaft of the 3100/3400 engine, and place this new wheel on the face of the harmonic balancer, and then relocate the old crank sensor that used to read this wheel on the crank in the block to the new position at the front (timing cover side) of the engine.
  • Throttle Body Adapter - This allows you to bolt your cable-driven throttle body to the 3500 upper intake. Any of the throttle bodies we offer for the 3100 ad 3400 engines will bolt to the 3500 using this adapter. There are options for 52mm (stock 3100), 56mm (stock 3400), 59mm (bored out 3400), 65mm billet, and 68mm billet throttle bodies. The 68 mm is the biggest throttle body we make for these engines, and will fit the 3500 engine with minimal porting. We include a 65mm throttle body with the kit standard, but if you order a 68mm throttle body at the same time, we include a 68mm throttle body adapter instead.
  • Coil Pack Adapters - These little brackets allow you to bolt your current coil pack/ignition control module assembly to the 3500 engine.
  • MAP Adapter Pigtail -This allows you to plug the connector from your old MAP (Manifold Absolute Pressure) sensor into the 3500’s MAP sensor located on the intake manifold, allowing for a cleaner install than using the old 3x00 MAP sensor with the new engine.
  • ECT Sensor Extension - This allows you to plug your current ECT (Engine Coolant Temperature) sensor connector into the 3500’s ECT sensor which is located in the rear cylinder head instead of the lower intake manifold. The 3500 has a 2-pin ECT sensor like most of the 3100/3400 cars out there. If you have a vehicle with a 3-pin sensor from the factory, we have a solution for this as well. We make a 3-pin sensor that will replace the 2-pin sensor in the 300’s rear cylinder head, and then we have a matching 3-pin ECT extension to go with it.
  • Oil Level Bypass - The 3500 engine does not have an oil level sensor in the bottom of the oil pan, and most 3100/3400 cars do. This Bypass plugs into the stock harness to delete the oil level sensor and keep the Low Oil light from turning on. Please note this will mean you don’t have a low oil monitor anymore. If this is a feature you need to have, you can use your old oil pan, but it isn’t a direct fit. One bolt is out of place where it bolts to the engine, and some of the bosses for the 10mm x 1.50 bolts on the oil pan are not in the same locations, so we advise checking fitment of all your brackets before you go that route.
  • Differential Bracket - Since the bosses for the differential bracket on the back of the 3500 are in a different location compared to where they were on your 3100/3400, we provide this new differential bracket to attach your new 3500 engine to your current transmission. We offer them for both the 4t65e/4t60e transmissions as well as the 4t45e. If you don’t know what those are, don’t worry, just order the kit for your car, and we’ll take care of the rest.
  • AC Spacer/Modified Dogbone Bracket - The bosses on the 3500 engine for the AC compressor protrude out of the bock more than they do on the 3100/3400, so we offer this short AC Spacer to keep your AC compressor mounted in the proper position. N-body vehicles like Grand Ams, Aleros, Malibus, etc will use the AC Spacer, but the W-body cars like Grand Prix’s, Monte Carlos, Impalas, and also the minivans and other similar vehicles use one big bracket to be the AC spacer and to hold the passenger side dogbone to the engine, so on these applications, we provide a modified dogbone bracket that has been machine down to make up for the difference in thickness.
  • Camshaft Position Sensor - If you have a vehicle that is 2000 or newer, you don’t need a new one, but cars using a computer from 1994-1999 will need to use this cam sensor to read the newer style reluctor on the 3500’s cam, and be able to plug into their current harness. 2000-2002 vehicles will need to install their current cam sensor into the 3500 engine. 2003+ cars can just use the 3500’s sensor and directly plug in.


Basic tips for doing the swap/pulling stock engine

  • Always start by disconnecting negative post on battery and tuck it out of the way (or remove battery if you are worried about dropping a tool across the posts)
  • If you have an N-body (4th digit in VIN if you don’t know), DO NOT REMOVE FUEL LINES FROM THE FUEL RAIL. This will cause them to leak, and you’ll need new o-rings. Replacements from GM cost upwards of $30. Instead unbolt fuel rail from lower intake, and once you’ve got crossover pipe off, you can fold the fuel rails over towards the driver’s side with the fuel lines still attached. This also means you should remove the upper intake before you pull the engine, and also install the new engine without an upper intake or fuel rails. If you have a W-body, use the quick disconnects, they are easy to get to.
  • Also if you have an N-body, removing your driver’s side fan makes it much easier to get the front trans mount off. Hopefully your fans are bolted in and you can remove it. If your fans are riveted in, have fun. You’ll need to leave them in and work around them.
  • Drain the coolant out of the engine before you pull it, it’s a lot less messy. There is a 9/16” drain plug to the top right of the oil filter. Reinstall the plug before you pull the engine. Also a good idea to wait to do all the stuff underneath the car before you do this, but before you remove coolant hoses.
  • If you have an N-body, do not remove the tube from the top of the thermostat neck. Simply remove the two bolts holding the t-stat neck to the lower intake, and disconnect the rubber tube that slides onto that tube on the passenger side.
  • Also if you have an N-body, be aware that your belt runs around your engine mount, and therefor you need to remove the mount to remove the belt from the vehicle. This mount holds your engine up, so you need to use a jack with a wood block on it to support the engine when you take the mount off. Since you also need to remove the mount to get to the power steering pump bolts, we recommend waiting until you are in the process of removing the power steering pump and the fuel rails before removing the mount. Also make sure you’ve already done everything underneath the car that you need to do before you do this. After that, you can leave the mount off and engine supported by jack until you roll in the cherry picker and pull the engine out the top. I guess that brings us to the next tip which to me is obvious, but some people may think differently …
  • If you are only pulling the engine, and have an N-body or W-body, PULL THE ENGINE OUT THE TOP, DO NOT DROP THE CRADLE. If you have a mini-van, you’re on your own, have fun. If you have a W-body and want to pull the engine and trans … pull them both out the top. If you have an N-body and want to pull the engine and trans, you will need to either pull one then the other out the top, or drop the cradle. I would still recommend pulling them out the top unless you have a lift and good tools.
  • Before removing bell-housing bolts, remove all torque converter bolts, as well as the bolts from the diff bracket into the engine block and oil pan (3 total). Also don’t forget about the rear bellhousing bolt on the backside of the rearward ear on the bellhousing flange of the engine. Want to guess why we always call this one the “Bitch Bolt”?
  • Keep the lift point on the chain about 6-8” above the engine or less, and you should clear the hood easier. You should not have to pull the hood to remove the engine. If you chain it too tight though, you’ll bend the brackets.
  • Do not disconnect AC lines, leave them attached. It’s a felony to vent that nasty stuff to atmosphere, and you’ll have to pay to fill it back up, just leave the lines intact.
  • Do not remove your radiator. (sorry if this is obvious, but it wouldn’t be in here if I haven’t seen it happen)


Parts Transfer/Engine Assembly before installing 3500

  1. Remove harmonic balancers off both of the 3400 and 3500 engines, remove 3400 24x crank sensor (behind harmonic balancer), and install the sensor on the 3500 timing cover. Don’t forget the brackets for the crank sensor. Using Ultra Black or GM Assembly Adhesive RTV, put a bead of RTV on the keyway groove on the back of the 3400 harmonic balancer, and slide onto the 3500 crank, making sure the keyway is lined up. Using a large socket placed where the crank bolt would go, use a hammer to drive the balancer on far enough that you get enough thread engagement on the crank bolt to begin using the bolt to drive the balancer on the rest of the way. You should have a minimum of ½” thread engagement before using the bolt. Now using the stock crank bolt, finish installing the balancer by either using an impact, or by using a ratchet and having someone hold the flexplate still using a prybar in the teeth of the flexplate. Once the balancer is fully installed, now remove the stock bolt, and install the wheel for the External Crank Trigger along with the new longer bolt that comes with the trigger kit. Torque the bolt using the stock torque specs.
  2. Remove 3500 coil packs, throttle body, upper intake, fuel lines, fuel rail/injectors assembly, as well as any motor mounts or brackets attached to the back of the block or the bottom of the oil pan.
  3. Run a 12mm x 1.75 tap into the two holes on the block to the left of the harmonic balancer, where the crank trigger bracket will attach. Do not install the bracket yet, this will be one of the last things you’ll put on the engine before it runs. Also run a 10mm x 1.50 tap into the holes on the engine where the diff bracket attaches. If you don’t know which two will be used, run the tap through all 4.
  4. Remove the front and rear exhaust manifolds from both engines, transfer 3400 ones to the 3500. You can re-use the stock gaskets from the 3400 if they come off in one piece, otherwise install new ones.
  5. Remove 3500 alternator bracket and engine pull bracket from rear head. You can install the 3400 ones now if you want, but I always do this when the engine is in the vehicle.
  6. Remove any extra pulleys on the 3500 timing cover that do not correspond to a pulley used on your current engine’s serpentine belt setup. If you have an N-body you’ll need to transfer over your front engine mount to the 3500. If you have a w-body, you may need to transfer over your tensioner. If you have a 3500 with a “Roush” plate on the timing cover, it’s usually best to remove it. Remove any bolts holding the plate on, and use a small screwdriver to pry the plate off. Then use brake-clean or some other solvent to remove any left-over residue. Now re-install the bolts and torque to spec.
  7. Now it’s time for the Cam Sensor. If you have a 2003 or newer car, skip to the next step because you don’t have to do anything. If you have a 1999 or earlier car, your swap kit will include a new cam sensor, just remove the stock 3500 one and replace with the one we supply you in the kit. If you have a 2000-2002 car, you’ll need to reuse your old sensor. This is where it gets tricky because the 3400 cam sensor is tough to remove. The easiest way to ensure keeping it in one piece is to remove the timing cover, which gives you a lot more room to get in there with a small screwdriver. If you want to try to get it out without removing the timing cover, it is possible, but much harder to do. The trick is to get it to rotate first, then pry it out gently. If you try to pry to hard, it can break very easily, and then you need a new sensor, so do yourself a favor and remove the timing cover.
  8. Remove 3500 thermostat neck, install whatever t-stat you want to use, and install 3400 t-stat neck.
  9. Remove 3500 oil filter and then oil filter adapter bracket and gasket. Using a 10mm allen socket, remove threaded piece from oil filter adapter bracket, and install into the block. Now re-install the 3500 oil filter on the block. We will change this for a new one later, but installing a used one for now prevents damaging the new one during the engine install.
  10. Remove 3500 knock sensors front and rear, transfer single 3400 knock sensor to 3500 just above oil filter.
  11. Check oil pressure sender on 3500 to see if pin-out matches your old one. If it doesn’t match, transfer the old one over to the 3500.
  12. If you have a W-body, and want to install your fuel rails now instead of later, scroll down and follow the procedure below. If you have an N-body, wait until after the engine is in and power steering pump installed.
  13. The 3500 upper intake has a raised section near the bolt next to the alternator where there may or may not be a vacuum nipple facing out of the back of the raised section. If yours does not have this, you’ll need to drill and tap the flat face of the raised section for 1/8” npt, and install a barbed brass fitting. We recommend a 3/16” barb for most cars, or a ¼” barb for those cars using a vacuum controlled transmission like a 4t60e.
  14. It’s not a bad idea to run a 10mm x 1.50 tap into the holes on the block and oil pan where the AC Compressor bolts to, which could save you time later when you go to bolt that on.
  15. Install Oil Level Bypass pigtail onto oil level sensor connector on the vehicle, and zip-tie to the adjacent harness laying against the transmission.
  16. Once finished, your 3500 should look just like the 3400 you removed.


Tips for the rest of the swap

  • Everything should go back together in the reverse order that it came off. It’s important to keep the same sequence so you don’t put something on before you are supposed to. Also it’s a good idea not to tighten any bolts for a particular part until you have all the bolts for that part started in the threads.
  • From this point on, you need to pay attention to torque specs, torque sequences, sealants, and lubes for any of the bolts you put back on. In general, any bolt holding an engine part to another one that has a gasket between them should get torqued according to the proper sequence and torque specs. You should torque the lower intake 3 times at the max torque value. Timing cover bolts get Teflon paste, toque converter bolts get red Loctite, exhaust manifold studs get antiseize, etc. Any bolt or fitting that had sealant on it from the factory, should get new sealant when you put it together.
  • One of the first things you can do after dropping in the new engine and tightening all the bellhousing bolts is to bolt on the AC Compressor,using the new AC Spacer. Some customers report they have trouble with fitment of the AC compressor with their 3500. If you find you’re having trouble getting the bolts to start properly, follow these steps …
    1. Loosen up all the bolts, try to start bolts
    2. If that doesn’t work, try installing the old AC Spacer, see if that helps at all.
    3. If you still have no luck, drill each of the three holes out on the AC compressor about 1/16” over the stock size, and repeat step 1. This is a last-resort fix. I have never had to do this in all the swaps I’ve done, but if it gives you a lot of trouble, this will fix the problem.
  • Remove the old differential bracket(s) if you haven’t done so already. Install the new Differential Bracket using the old bolts. Make sure you start all bolts, and turn them by hand all the way down before tightening any of them. Then tighten the transmission ones, then tighten the two into the block last. The lower section of the differential bracket that attaches to the oil pan is not necessary.
  • After you’ve installed the power steering pump, but before installing the crossover pipe, now it’s time to install the 3400 fuel rails, injectors, and injector harness onto the 3500. This is something a lot of people have trouble with, but if you follow this procedure, you can install the upper intake without major interference problems with the 3400 fuel pressure regulator.
    1. Lube up the injector o-rings, we use Sil-glyde for this.
    2. Remove fuel rail brackets, reinstall them in the same locations, but above the harness instead of below. This keeps the upper intake from smashing the harness. Leave the bolts for these brackets almost all the way tight, but backed off just enough to be loose, so the brackets can oscillate around on the fuel rail horizontally, but have no vertical movement.
    3. Temporarily install 3400 fuel rail on 3500 lower intake with bracket bolts loose. Install bolts holding brackets to lower intake also loose as in the step above. Install 3500 upper to test-fit. Upper should fit right up against fuel pressure regulator, all bolt holes should line up, and upper intake should be flat against mating flange on lower intake. If this all checks out, remove upper intake, and then remove fuel rails being carefully to keep them in exactly the position they were in before, then tighten the bracket bolts to the fuel rail in that position, and reinstall. Check fitment of upper one more time.
    4. If that checks out, now it’s time to do a fuel pressure test. This isn’t to test the actual pressure, but to verify there are no fuel leaks before installing the upper intake. First off, by now the starter should be fully installed and wires connected, and the grounds should be installed to the bellhousing bolts. The alternator can be off, just make sure to cover the big power wire going to it. Now temporarily hook up fuel injector harness, and turn the key forward listening for the fuel pump to run, and then turn it back off once it stops. Repeat this about 5 more times, and look for leaks. If there are no leaks, keep putting it together.
  • Now is a good time to hook up the ECT extension. Just plug the extension into the 3500’s ECT sensor in the rear cylinder head on the driver’s side, and then route the pigtail under the fuel rail and over to the stock ECT connector and plug it in.
  • Once you’ve installed the upper intake, and have removed the two throttle body studs, you can now install the Throttle Body Adapter. If you are using one of our billet throttle bodies, just bolt them right on to the adapter using the o-rings. If you are using a stock throttle body, you’ll need to cut a gap in the throttle body to match up with the gap in the back of the throttle body for the IAC (Idle Air Control) port. You will also need to cut the o-ring that overlaps in this section as well so it does not block the IAC pathway. If you have a 2000+ car and wish to use the stock throttle body, your throttle body does not have the IAC port attached to the throttle bore, so you’ll need to open up a channel between the two to connect them. We use a Bridgeport mill for this which works great. You can either try to modify it yourself using whatever tools you have, or you can buy a throttle body for a pre-2000 3400. You may have to transfer the linkage from yours into the new one if you do this. We also sell stock throttle bodies for $20 on the site. Anyways once you have the necessary IAC port connected to the throttle body bore area in the back of the throttle body, cut the outer o-ring on the adapter right where the IAC “tunnel” overlaps it. Then we recommend coating the mating surface of the throttle body with Permatex High-Temp Sensor-Safe Orange RTV.   It needs to be this specific one so it doesn’t mess up any sensors. Because the throttle body adapter makes the throttle body stick out about ¾” further than it did from the factory, we highly recommend buying one of our Modified Heater Tubes to make it a nice clean install. It is technically possible to use the stock heater tube, but the little bypass tubes connected to the throttle body will be very prone to failure from the extreme angles they have to be positioned in.
  • Once you’re ready to bolt on the throttle cable bracket, it’s good to have an extra set of hands because this can be tricky. Using the provided spacers that came with your throttle body adapter, place the bolts through the bracket and then the spacers, and then move the bracket into position to line up with the corresponding holes on the throttle body adapter, and start both bolts, then tighten both bolts. Now the bottom hole on the throttle bracket by the bottom front edge of the throttle body, should be close to where it needs to be, but not quite lined up. All you have to do is bend that leg of the bracket down enough to start that bolt. A small pry bar or large screwdriver usually works well. You can add a hammer if needed, just be careful not to damage the throttle body, especially if billet.
  • Once you’re ready for the coil packs, it’s now time for the Coil Pack Adapter Brackets. Install the longer bolt through the adapter bracket and into the lower intake, leaving it loose. Repeat for the other side. Now install your coil packs/ICM assembly on top of the studs in the back, and then overtop the adapter brackets. Line up the brackets with the holes, and install the 2 remaining bolts, then tighten all the bolts. Don’t forget the two nuts on the back of the coilpacks.
  • With the coilpacks installed, now you can install the MAP Adapter Pigtail. Plug the pigtail into the 3400 MAP connector which is routed between the upper and lower intake manifold. Route the pigtail under the coil packs to the passenger side, and loop it up and over to the MAP sensor on the 3500 upper intake, and plug it in.
  • Once you’ve installed all your accessories and the serpentine belt, you can now install the rest of the External Crank Trigger Kit. Remove the rear crank sensor out of the back of your 3400 block, and install on the crank trigger bracket, and tighten the small screw. Please note the washers supplied with the crank trigger bracket go BETWEEN THE BRACKET AND THE BLOCK. Next install the crank sensor bracket onto the block of the 3500 to the left of the harmonic balancer, leaving the bolts barely snugged, but the bracket moveable. Using a feeler gauge, set the gap between the end of the crank sensor and the reluctor wheel to .020”. Hold the bracket tightly in this position, and tighten the mounting bolts. Check gap again. If the gap opened up while torquing, you aren’t holding it tight enough, so try removing the feeler gauge (setting the gap to 0), and tighten again. If you end up around .020”, that will work just fine. Now take the ~3ft long pigtail for the old crank sensor, and plug it into the relocated sensor. Then route the pigtail away from the belts, between the power steering lines and the firewall, and then up and over to the ICM (Ignition Control Module), and plug it in.
  • The last little modification you’ll need to do is to make the new vacuum lines. Locate the vacuum nipple located on the top of the 3500 upper intake, in the raised section near the alternator. Run vacuum line from there to the area near the fuel pressure regulator. For a clean install, we recommend routing this vacuum hose under the coilpacks, around the corner of the engine, and then overtop of the neck of the upper intake to plug into the fuel pressure regulator. Many vehicles have a vacuum line in the wiring harness that used to plug into the upper intake. This is for the HVAC functions in the car, and needs to be hooked up for these to function. All you have to do is T this into the hose leading to the fuel pressure regulator. Also vehicles with a vacuum modulated transmission like a 4t60e will need to plumb the vacuum hose into the vacuum modulator on the front of the transmission. Without this, the transmission will not be able to shift.

Once you finish buttoning everything up, fill her up with fluids, and get the coolant system bled, now it’s time to enjoy that new 3500 engine! Hopefully this guide made things a little easier.




Recommended Modifications

We recommend the following modifications for anyone doing the swap, in order to help the 3500 engine be as powerful and efficient right out of the box.

  • PCM Tune - Most of the OBD2 vehicles you would swap a 3500 into have a torque limit of 208 ft-lbs, which means right out of the box, the stock pcm is literally limiting you from achieving even the stock power levels that the 3500 engine is rated at. Our Standard PCM tune not only eliminates that restriction, but also gives you more power, much more responsive and predictable transmission settings, even settings to keep the engine running cooler, among other benefits.
  • Throttle body - In our opinion, you should atleast install a 65mm throttle body right off the bat, and while it may sound extreme, the 68mm throttle body is the one we always recommend people go with. The 3500 upper requires only minimal porting to be able to match up to a 68mm. If you buy a 68mm tb and 3500 from us at the same time, we do the modification for free.
  • 2.5" downpipe - It's the most restrictive part of the stock exhaust system, replacing the stock downpipe with one of our 2.5" ones just opens up the exhaust so the engine can breathe a lot better. It is also a knock-reducing mod. You can choose with or without cat depending on your preferences and your state's requirements.
  • Modified Heater Tube - the billet throttle bodies do not have accomodations for the coolant bypass, but even if you install a stock throttle body that does when you do your 3500 swap, the stock heater tube does not fit very well since the throttle body will be sticking out further from its usual location. We highly recommend our modified heater tube to allow you to have an easier swap, better fit, and a better look, while also eliminating the power-robbing problems of the stock heater tube.
  • 180 T-stat - Chances are if you are doing a 3500 swap, you probably already have this knock-reducing mod, but if you don't, it's a great thing to do while the engine is out to keep your engine temps down and your knock retard in check.
  • Colder spark plugs - Another great knock-reducing mod, we recommend one heat-range colder (like Autolite 605's), and reducing gap to .050".
  • EGR Delete - If you don't have to worry about emissions testing, removing the EGR will help performance by keeping the intake charge much cleaner and cooler, while making your engine bay less cluttered and easier to work on.
  • Injectors - If your car came with a 2.8L or 3.1L multiport engine, I would not even think about doing the swap without changing injectors, because the stock ones are 17lbs, which means the injectors would be maxed on even a stock 3500. If your car is a 1999 or earlier 3100/3400 car, it came with 19lb injectors, which are still on the small side. The stock injectors can barely flow enough for a stock 3500 (although the duty cycle would be higher than ideal), but the more mods you do, the closer and closer you get to their max. If you do all the mods on this list, the 19's will be absolutely maxed. Since they share the same injector connectors, the best option for this application would be to get our 36lb injector kit, which would give you ample room to grow. Unless you went boost, and added a substantial amount of power, you're not even getting close to their limit. You could install our stage 3 heads and cam package, headers, 68tb, etc and still be under the ideal limit of those injectors(70% of max), which means they could last a long long time. If you have a 2000+, your car came with 22.5lb injectors. With a stock 3500, the 22.5's are right at the limit of that 70% figure, and with one equipped with the above list of mods, injector size is starting to become a problem. If you want to do the suggested mods, and then nothing else, the 28lbers would probably be the way to go. If you plan on going further, you can't go wrong with the 36's. When you change your injector size, these new flow ratings will need to be programmed into the pcm.


Frequently Asked Questions about the 3500 Swap

  • Can I use a 3400 (or 3100) upper intake with a 3500?

            Yes. Any 3400 upper can be bolted to the 3500, as well as 2000+ 3100 upper intakes. 1999 and earlier 3100's that had the small port intake manifold (12 bolt instead of 6) will not work. If you use a 3100 or 3400 upper for your 3500 swap, you do not need the throttle body adapter, coil pack adapters, or MAP adapter pigtail.


  • Is there a disadvantage to using a 3100/3400 upper intake?

            Yes. The 3100 and 3400 intakes have a 58mm inlet from the factory, and can be ported to 65, but no larger. So you can bolt a 59mm throttle body to a stock intake, or a 65 to a modded one, but that's it. Meanwhile with a 3500 upper you can go right to a 65mm throttle body, and with minimal porting to a 68mm. This combined with the fact that the 3500 intake is a better design is the reason we'd suggest using the 3500 upper unless for some reason you would want to hide the fact you're doing a 3500 for whatever reason by dressing it down to look like a 3100 or 3400. We do this sometimes for people who want their engine to look stock when you open the hood, and refer to them as a "Sneaky Pete" 3500.

  • How long does a 3500 swap take someone to do themselves?

            Tough question, highly depends on skill level and tools available. Somewhere between 5-40 hrs?

  • Do I have to buy your swap kit to do the 3500 swap?

            It is possible to do the swap without buying the kit. The kit was just designed to take all the guess-work out of the equation of what parts are needed, to make the electrical conversion a simple plug-and-play operation, and to make the swap much easier to do and more visually appealing. Some of the components in the 3500 swap kit are absolutely crucial, and you won't be able to do it without them. Some of the components can be eliminated by re-using the upper intake off your old engine, as mentioned above. The rest are just to make the install a much easier job. Three of the components are electrical connector plug-ins.   Could you wire these in yourself? Yes, but if you don't wire things up properly, this can create major problems, possibly even an engine fire. What is your time, and your car's safety worth?

  • How do I make the EGR work on a 3500?

            If you have a 2000+ 3100 or 3400, you can just use your current EGR valve and tube. If you have a 1996-1999 car, and are using a 3500 upper intake, you need an EGR valve and tube from a 2000+ 3400.  If you have a 1994-1995 car and don't want to do an OBD2 swap, you'll need one of our EGR adapters to bolt your current EGR to the 3500 upper intake.

  • How do I make the EVAP work on a 3500?

            Hopefully your 3500 came with a good evap solenoid, because they are usually broken, but all you need to do is hook up the line that came from the gas tank forward into the stock solenoid, and hook it into the 3500 one instead. To do this, you need to cut the stock tube in a good location (we usually cut it near the brake booster), and then hook the other end into the evap, and then bridge the two together with some rubber hose. Don't use vacuum line for this, just has to be something rated for fuel. If you have a 1999 or earlier car, you'll also likely have to extend your evap connector to get it to reach to the new location. If there is enough interest in this, we can possibly add this as an optional part for the swap kit.

  • Will the car pass emissions/state inspection after the swap?

            This is basically two questions, 1) Is the swap legal to do? 2) Will the 3500 negatively affect emissions testing? It's always a good idea to check your state's guidelines on this, but to the best of my knowledge, the 3500 is completely legal to swap into your car. You have to retain all the emission equipment. Using your current catalytic converter, 3400 egr, and 3500 evap is perfectly fine. Some states (California comes to mind) require paperwork to be able to legally have the 3500 engine installed. The other thing that may give you trouble in the states that require the california emissions versions of the 3100/3400 engines, the 3500 engine to my knowledge did not have a california emissions version with machined ports into the cylinders as its predecessors, but I think if you could show proof of this, you should be fine. (For example, if you bought the engine out of a California-legal car and it did not have the "california emissions" plumbing from the factory, then provide proof of purchase, and you should be good). So will it pass emissions testing? Requirements vary from state to state, but you either have a visual inspection only, or you have a visual inspection in combination with a "sniffer" test, where they measure the chemical content of your exhaust with your car on a dyno. The 3500 will pass the visual inspection as long as you have all the emissions parts installed. The 3500 should also be fully capable of passing the exhaust test as long as the gaskets are in good shape, and as long as there is no problem with any of the parts that stayed on your vehicle from the previous setup, including the parts that were transferred to the 3500 engine. If all the gaskets and sensors are in good condition, the 3500 will have no problem passing the emission test, even with some mods.