DOHC Swap: A Basic Guide for Newbies

So you want to swap an Evo DOHC head onto your Eclipse/Galant/Stratus/Sebring.

First let me begin by saying if you have a 3.0L V6, turn back now. This may seem obvious, but many are blissfully unaware that a four-cylinder head will only work on a four-cylinder engine block. So no, you cannot DOHC-swap a V6. Do not fret; there are other swaps you can try out. Just search around on Club3G.

Perhaps you're reading this because you heard an Evo engine (called the 4G63) will bolt right in to replace your 4G64. Or perhaps that a DSM engine (90-99 Eclipse turbo) will bolt right in (spoiler alert: It won't). Well, there's good news and bad news. The bad news is that you'll have a lot of tuning and a small bit of fabrication to swap in an Evo 4G63 that will really run up your budget. It's not exactly just "drop in". And have you checked how much an Evo engine goes for? They don't exactly just sit around at any old junkyard, either. Even if you do turn your car into a two-door Evo and build it just like an Evo, with all that power you'll still be channeling it to just the front wheels. It won't be an issue of having enough power; your problems will start to be trying to keep your tires planted to the ground. Might as well just buy an Evo at that point and save yourself the headache.

The good news is that you don't have to swap a whole Evo engine: The head itself is enough to reap 90% of the benefits! The 4G64 engine in your Eclipse/Galant/etc is a 2.4L four-cylinder. The 4G63 engine in the Evo 8/9 is a 2.0L four-cylinder. That .4L difference in size comes from the pistons being a little bigger and travelling a little further. Other than that, the bottom ends are virtually identical. It's nearly a matter of pulling your SOHC head off and throwing an Evo one on.

Not entirely though. Why would you want to swap to a DOHC head to begin with? What are the benefits? It doesn't make installing a turbo any easier - all 4G6x exhaust manifolds are interchangeable, meaning you can bolt an Evo 8 or DSM turbo manifold right up to your engine whether it has a SOHC head or DOHC head swap. So what gives? Well it turns out the SOHC head's setup is a weak point in the 4G64 engine. For obvious reasons, Mitsubishi didn't design this engine to make oodles of top-end power, because that design (this is before MIVEC was popular, of course) would've sacrificed low-end torque. Low-end torque translates to good driveability and fuel economy. That's what your average customer buying the Eclipse in 2003 wanted - not an extra 30hp he's never going to use or would never want the 16-year-old daughter he's buying it for to ever use. They liked the looks of the car. A bit of fuel economy and smooth driving is a bonus. So for engineering purposes, the intake manifold was designed with long, narrow runners and a camshaft designed for low-end breathing. Ever peg the throttle on your 4G64 and see how much steam it loses after, say, 4000 RPMs? That's my point. The better the engine breathes through head design, intake manifold design and camshaft design, the higher up the peak torque moves in the powerband. This also means a higher peak horsepower and ability to rev higher.

"So a DOHC head will let me rev higher and only give a few horsepower?!" Yes and no. See, when you do the head swap, you'll need a lot of parts such as an Evo intake manifold, cams and throttle body. These alone are a huge upgrade to help with that airflow problem you had with the stock SOHC setup. And yes, if you turbocharged your engine and do the head swap, the results will compound on each other. It will let you feel the real results of a turbocharger. At say, 10PSI a SOHC head could only flow, say, 200 CFM of air (these are made up numbers). On the other hand, if the turbo is still set to run at 10PSI but you throw on a DOHC head that can flow 250 CFM of air, you'll be getting 25% more air for the same boost. Any seller page for a cold air intake on eBay will tell you, more air (plus fuel to compensate) means more power. These principles apply whether or not you have a turbo, but point is head swap = good, turbo = better both = best.

Additionally, there is no difference in difficulty to install a turbocharger whether or not you have a DOHC head. The tune will be different sure, but the physical parts such as the turbo manifold bolt on the exact same way as they do on a SOHC head.

What about just the head on its own? And what if you just build the SOHC to flow better? That's where you run into problems... There's a term car enthusiasts use called "aftermarket support". It refers to the amount of parts manufacturers make for a given engine. So an Evo, on which you can upgrade the cams, pistons, clutch, head bolts, intake manifold, timing belt, shifter bushings, intercooler, etc., has better aftermarket support than a Nissan Maxima which you could only get intakes and maybe some expensive exhausts for (again - this is all for argument's sake, I'm sure they sell more than that for Maximas). The SOHC head? Little to no aftermarket. At all. RPW, an overseas company, can grind you a new cam for a pretty penny. You might even be able to find somebody to make you a custom intake manifold that might or might not fit. But that's about it. And even then you'll be spending thousands to try to polish a turd. Why not just swap to a head that you can upgrade the cams, springs, valves, cam gears, intake manifold, throttle body, etc., for all around? The more aftermarket support there is, the cheaper prices are because of the higher competition. So for example, RPW makes the only aftermarket 4G64 cam grinds for $550+, and that's just a regrind, not a whole new cam. Brian Crower sells a whole new set of 4G63 cams - intake and exhaust - for $450/pair. They're so common that I picked up a used set for under $200.

Okay, so you're convinced you want to do a head swap! Well not so fast, there's a huge glaring thing in the way of most 3G owners: Budget. Let's face it, you didn't get a 3G because you could afford a 2015 Evo and just preferred the looks of the decade-old Eclipse. So how much are we looking at here? Well Evo heads are not cheap. Sure some people can scoop up a deal here or there but on a lucky day expect no less than $500. A quick gander on eBay showed rebuilt heads going in the low-$1000 range, not including core charge (meaning you send in your stock Evo head that you don't have). And naturally junkyards generally don't hold Evos for very long, if at all. Your best bet is to either bite the bullet and pay big bucks or search the internet like a scavenger, day in and day out. (try EvolutionM.net)

But wait, there's more!

You can go home today with a junkyard cylinder head for the low, low price of just (about) $100!

Yeah, as it turns out Mitsubishi and Hyundai were getting it on behind Chrysler's back. When Chrysler found out about the secret affair, she threw a fit and filed for divorce, leaving Mitsubishi all alone with the DSM factory, which he promptly turned into a man cave named MMNA.

I joke; Chrysler had nothing to do with it. But back when Hyundai/Kia were still getting off the ground, Mitsubishi gave them a little help. One of the most glaring examples of this was an engine called the "G4JS". It was one of many examples of Hyundai using Mitsubishi casts to make their own engines. This one was found in 98-04 Sonatas, 00-05 Optimas and 00-06 Santa Fes. It was a four-cylinder that looked remarkably similar to the 4G63 found in the Evo. And as it turns out, it is. And it's everywhere. There are five or six at my local yard alone. I pulled one from a yard I'm friendly with for $80, and probably could've gone as low as $60. I can't see a u-pull-it asking more than $150 for one of these under any circumstances. Evo 8 cams bolt right in. So does the intake manifold. It fits right onto your 4G64 block. An EvolutionM.net member named Live4Redline even documented a build where he swapped one into an Evo, calling it the "De-Evolution".

So what's the differences between this and an Evo head? Not many. For one, the thermostat housing is different so you need that with the head. The cam sensor housing is different too. And most pressingly is the valve cover, so don't expect to throw an Evo valve cover on and fool anybody, because it won't bolt on. It still looks cool either way. And yes, the G4JS head flows the same amount (if not more due to the extra bore meaning less shrouding around the valves) as a 4G63 head, and has a similar compression ratio. No need to touch the pistons in your 4G64 or anything, just mount it onto a stock bottom end.

Now back to budgeting: Assuming you get a cheap head from a G4JS-powered Hyundai/Kia, how much can you expect to spend? Well it depends how far you want to go and what deals you can find. Want to use stock injectors, stock Evo cams, stock valvetrain, bare minimum and skip out on most maintenance? I could see if done for $600 or less.

This is HIGHLY DISCOURAGED. Do your basic maintenance while you're in there and DO NOT cheap out. And that price is assuming you do all the work yourself, not paying a shop. There's question number two: Do you have the experience/skill to do this job yourself? If you can do a timing belt, head gasket and are confident that you know how wiring works, go right on ahead. Keep in mind a timing belt is a dangerous job - you CAN bend valves and have to tear apart the motor all over again if you get it wrong. You can do this entire job with hand tools. Just be aware that there are portions you WILL need a shop to do. You WILL need to take the junkyard head to a machine shop, buy new valve stem seals and have the shop install them. If this is the case, you SHOULD have them grind the valves and hot tank the head to clean it of all oil and carbon buildup and make sure the valves seal right, thus improving compression and with it, efficiency. If you plan on running anything more than a stock Evo 8 camshaft setup, you should upgrade the springs. You WILL need to resurface the head before reinstalling it. This all adds up, because unless you have a lathe or pay for a valvetrain disassembly tool, you'll need a professional here. And assembling valvetrain is a pretty tedious task for a first-time. Don't worry - machine shops are everywhere and you'll be glad in the end when your head looks like a brand-spankin-new 4G63 head. I paid over $100 for resurfacing and valve stem seal installation/valve lapping alone. That's not a professional grind nor does it include a hot tank or port job. Being that I didn't get the valves done properly the first time, I had to buy myself a tool ($60) to pull a few valves and redo them myself. And no, a $10 AutoZone tool will NOT work on this head. In fact, most valve spring compressors on the market don't fit. Do it right the first time or do it twice.

What else do I recommend? ARP head studs are a nice upgrade and make the installation slightly easier, as they allow you to line up the head and gasket when installing. Any head studs that work for an Evo 8 will work on the 4G64 and they give you a little more peace of mind as to how well your head gasket seals. Speaking of which, get a nice MLS head gasket. Of course like I said, DO your maintenance. Head gasket and timing belt are non-negotiable. Get a head gasket that fits your 4G64 Eclipse. Get a timing belt for an Evo 8. Get a tensioner pulley, idler pulley and hydraulic tensioner for your Eclipse. Get a water pump for your Eclipse. Clean the surface of your block while the head is off. Clean the piston crowns cause it makes them look pretty. An oil change and coolant refill is obviously required here. Cams are nice to upgrade, adjustable cam gears are good (note you NEED at least one adjustable cam gear to make the timing belt fit properly on your new head), an intake manifold like an OBX or Skunk2 is an okay ugrade, and you can get an Evo 8 fuel rail/FPR for cheap used. If you want to go turbo eventually, get a set of STI injectors with new seals and get your car tuned when it's done. This all adds up, but this is doing it the right way.

All in all, expect to spend well over $1000 in parts alone. I'd say closer to $2000 if you pay average price for everything and get a lot of things new. Expect a lot more for labor if you get it done by a shop. Think about how much a head gasket job would cost at a shop, and think how much a timing belt job would cost. Add those two up and tack on a couple hundred extra for good measure. I personally start my pricing at $3000 for a turn-key head swap on 4G64s (this is including parts). Expect to have problems. You need to do wiring work: Extend the cam position sensor wiring, repin the throttle position sensor and possibly extend the coolant temperature sensor wiring. I extended my crank position sensor harness and ignition coil harnesses because I tucked them away. It'll get messy. You'll need to know how to properly diagnose sensors if something goes wrong otherwise you'll have a paperweight in your driveway that you'll be paying me hundreds to diagnose and fix the electrical problems. Fortunately if you have a good understanding of this stuff, the service manual is free on Tearstone.com and gives you all the readings and specs you'll need. If you saved up just enough, expect the budget to run out just as you need a part. If you need to finish it tomorrow, expect thunder and hail. Long story short, prepare for the worst. You shouldn't be deliberately doing a heart transplant on your daily driver without backup means of transportation. I'm not liable if you thought you could get it done in a weekend but it goes bad and you can't get to work on Monday.

So no, it isn't an easy task. But it's not a crazy hard one either. If you're keeping it naturally aspirated with no turbo plans, just keep the stock injectors. If you just want a little more pep with no loss of driveability, keep stock Evo cams.

By the way, unless you make a custom throttle body flange, say good-bye to cruise control. You can also use an Outlander 4G64 throttle body as well if you can find one.

As for the tuning, you can indeed run a stock ECU on a head swap. FlashBlueRS pioneered this swap a while ago and gave the opinion that it not only ran well on stock ECU, but also had more top-end than his SOHC with a cam and adjustable cam gear. Still, get a tune. Tunes always bring out the best potential in everything.

By the way, theoretically an Evo 9 head would work as well. Personally I haven't seen a 3G with an Evo 9 head swap, but assuming you figure out a way to control the MIVEC solenoid, it will theoretically work the same. That's the only major difference between the Evo 8/9 is the addition of MIVEC (variable valve timing only - not lift) on the intake cam. I wouldn't personally say that it's worth the added cost of getting an Evo 9 head myself.

So, you have the money, have a car to drive to AutoZone to pick up odds and ends, have a machine shop queued up and understand the benefits you will get versus the cost? Well, I've compiled below a short list of parts (off the top of my head - many may be missing) with short comments and my approximate price. These may be off, I'm not going out to look up the price of every single part, these are all rough estimates, especially for used parts (which go for as much as the seller wants for them). I could be missing a few odds and ends; Google for a complete list, I'm just going off of what I used myself (having personally deleted EGR and Evap in the process). Things such as valve cover bolts should come intuitively. Better to grab more stuff and have all you need than not grab enough and have to take a second trip.

DOHC cylinder head - $100 for a G4JS at a yard, much, much more for an Evo head purchased online. Should come with valve cover, camshaft caps, thermostat housing, water pipe (connects thermostat housing to water pump), cam sensor housing, ignition coils (you can use these; you don't need Evo coils!!) and all bolts.
Evo 8 cams ~ $100 used, upgrades start around 268/268 profiles. Don't recommend anything higher than 272/272 for daily driving personally, although others have made it work. Used aftermarket cams usually start around $200. New aftermarket cams usually start around $400+.
Evo 8 valvetrain - No idea used. I can't see anything more than $100 for used springs/retainers if I had to take an educated guess. If you're not going over 272s, you don't need to upgrade, just. Otherwise $200+ for new springs, valves and retainers.
Evo 8 throttle position sensor - $60. An overlooked part that you can usually only find in whole-car partouts or buying OEM. Don't get a cheap replica on eBay. You need this part.
Evo 8 intake manifold/throttle body ~ $150 would be a fair price for the both of them. Upgraded throttle bodies are both expensive and unnecessary (Boombas, a legit brand, go for $400+). The stock manifold is fine too but aftermarkets range from ~$300 ported stockers to $800 AMS top-of-the-line manifolds. The only reason the Hyundai/Kia manifold doesn't work is that it's pretty close to the firewall. The MAP sensor is on the back of the manifold, which means it will hit the firewall, and the throttle body nicks it as well. So you could use it from the Hyundai if you want to go HAM(mer) on the firewall; it has successfully been done before.
Evo 8 adjustable cam gear(s) ~ $50($100). Okay, this one varies. In all fairness I found a set of two Helix gears for $80. A set of used HKS gears can go for near $200, and brand new HKS gears for over $400. I could expect to find one singular used cheap-brand gear for below $50 easily.
Evo 8 cam reluctor and bolt - $20. Pretty much dealer-only. This bolts into the end of your exhaust cam for the cam sensor to read. You NEED the bolt too. The Evo reluctor doesn't sit properly in the Hyundai cams, hence why you need Evo cams. You can get the reluctor machined to fit Hyundai cams if you want.
Evo 8 cam gear bolts - $10. Also need two of these, dealer-specific, don't cheap out with Lowe's bolts or something, these loosening and falling out = blown engine.
Evo 8 fuel rail and FPR - $40-$50. I highly recommend even if you're keeping stock injectors. Can sometimes find for cheaper on EvolutionM.
Powdercoating valve cover (optional) - up to $100. For that pretty engine bay look.
Timing belt components - $100. Again rough estimate, get some decent brand belt, water pump and pulleys at least. Again, while some have proven the early-90's Galant DOHC timing belt works fine, I recommend the Evo 8 belt out of personal experience.
ARP head studs ~ $100, I don't know how much they go for new, I got a BNIB set for $60. Not too shabby. Don't recommend a used set because after being torqued down for a bit they stretch slightly. Again optional, you can use normal head bolts too.
Gaskets - $100+. Intake manifold gasket, valve cover gasket, head gasket, thermostat housing gasket, thermostat gasket (oh grab a new thermostat too for like $5 at AutoZone, too), exhaust manifold gasket, throttle body gasket. Cam seals too.
Radiator hoses - $20? This is a tough one because the hoses must be customized for the most part. You can cut the stock lower radiator hose and use it for a new upper radiator hose. As for the new lower... Use your imagination. Grab a wire hangar, bend it to shape and cut it to the right length and bring it to the parts counter guy.
Extra odds and ends ~ $20. By this I mean extra vacuum hoses and bolts. You might be missing an intake manifold bolt, maybe a thermostat housing bolt, maybe a nut for the exhaust manifold studs. A tube of RTV helps when installing the outer cam caps so they don't drip oil. Point is, expect to pick up some of these.
Spark plugs - $10. Just change them.

A cold air intake and exhaust header are good supporting mods to do with this in the meantime if you don't plan on going turbocharged. If all is done properly, you SHOULDN'T get any check engine lights. The ECU sees normal signals, normal values and fires the injectors/spark plugs the same way it did before. If you do get a CEL, my first bet would be on a vacuum leak, meaning air is getting sucked in somewhere after your MAF sensor, such as on the intake manifold or through the seals on the throttle body. If you have no leak but have a rich/lean code, try getting tuned to properly adjust your fuel trims and check again. If you do remove your pre-cat you might get a catalyst code. I didn't when I removed my stock exhaust manifold way back when I was naturally aspirated, but all experiences vary, so who knows.

If the engine won't start up after all this, follow the checklist:

1) Is it turning over? If not, your battery may have died.
2) Did it turn over and make a huge clunk and seize? Check your timing and make sure it all lines up at top-dead center. Is it off pretty far? Congratulations! Pull that head off, buy some new valves and start all over!!

If it's turning over, check the three things needed for an engine to run: Fuel, spark and compression.

Spark: Easiest to check. Buy an inline spark tester at AutoZone. It plugs in between your spark plug boot and onto the spark plug itself. Turn the engine over. If it blinks, you're good. Do not necessarily trust a test light. I had no spark according to a test light yet an inline tester told me otherwise. You can also hold the spark plug in the boot on the engine so it is grounded, and see if it sparks visually. This didn't work for me for some reason, possibly a grounding issue. Test on all cylinders.

Fuel: Initial way to check is to put your ear up to the injectors as the engine turns over. You should hear ticking sounds in each one as they open and close to spray fuel. Attaching an inline fuel pressure gauge will make sure you have fuel pressure (meaning your pump is working). A noid light, which is pretty much a test light that plugs into your injector clips, will blink if the injectors are firing as you turn the engine over. Test on all cylinders. Additional ghetto test is to let the engine sit for a while without the key in, pull the back seat and have somebody turn the key to the "on" position. You can hear the fuel pump momentarily whine as it primes the system with pressure. Even more so if it's a Walbro 255. Those things are pretty loud.

Compression: Easiest way is to listen to the engine as it turns over. As it turns over, you'll hear the starter slow down as it fights each compression stroke in the engine. If the starter slows down three times in a row then quickly speeds through a fourth time, you're missing compression on one cylinder. YouTube "sound of engine with no compression". If that doesn't help, get a compression tester from your local auto store. It screws into the spark plug holes and as you turn the engine over, you'll get pressure built up.

If all this is good, you'll need to check two harder things: PROPER AMOUNT of fuel and PROPER TIMING of spark. Make sure the cam reluctor is properly set up, with the small tab above the exhaust side when the engine is at top-dead center (TDC). Make sure the wiring is good and check voltages as per the service manual. Make sure the ignition coils are plugged in right, as well as the spark plug wires. Make sure the TPS was repinned properly. Pull the spark plugs and spray them with brake kleen, because after getting too doused with fuel from no-starts they get "fouled" and can't fire properly anymore, even in normal conditions. Check your ECU conditions when the key is on if you have EvoScan and a cable to connect to your ECU. This will tell you what your ECU is seeing. For example, if your ECU says the coolant is below freezing and it's a warm, sunny day, your coolant temp sensor might be unplugged. This would cause the engine to run too rich.

Also, there's two coolant temp sensors. One big one used by the ECU which threads into the thermostat housing (coolant temp sensor) and one small one which has nowhere to go on the new thermostat housing (coolant temp sender). The sender just tells your coolant gauge how hot it is. Some recommend an inline adapter from eBay. I tried it, and as a result my hose kept bursting and stranding me. I had to go through gallons of coolant per week from what I lost. If you really need it, I recommend tapping the back of the thermostat housing on the flat surface of the freeze plug. Just get a nice nut/washer on the other side that will seal under intense heat. The reason most Hyundai/Kias have no place for this is that they use one sensor for both applications. Certain later years do have a thread for a separate sender, so keep your eye out to avoid the trouble.

As far as I can see, I don't think I'm missing much. Of course this isn't a comprehensive guide and each job will vary based on what parts you use/your end goal/your budget. A good write-up exists on Club3G but you have to use your own automotive expertise on a lot of it. It's not bad; there's really not a lot any normal mechanic couldn't figure out on his own, and most of the stuff you need to know I told you above. You can make some non-essential (to engine life anyway) parts work with some imagination. For example, some people say to use an Evo dipstick and throttle cable, I made the stock ones work just fine.

Contact me for any further details.

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