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Derek Beland's guide to adding turbochargers to Chrysler 2.2 / 2.5 TBI engines

Neither Allpar nor Derek Beland takes any responsibility for the results of your actions or for the results of following the steps or advice presented below. Some of these may shorten the lifespan of your car and/or its components.

[Webmaster note:] You can also "simply" swap in ALL the pieces from a turbo car - engine, computer, fuel pump, new fuel lines, etc., etc. - into your car - but if you do, we strongly suggest you also grab the turbo car's heavy-duty suspension parts and brakes!

Every TBI owner has considered it... turbo guys sneer at you and you're sick to death of the phrase "just get a turbo". Seeing everyone talking about their latest quarter-mile time on the lists and wishing you could muster something better than a 17.0... With as many Chrysler turbo cars rotting away in the junkyard as there are, it should be easy to score some cheap parts and convert your car to a turbo engine... shouldn't it?

This page is an attempt to explore the necessary steps required to do this conversion. One thing it is not is a complete recipe, I simply wanted to make you aware of the magnitude of the task and get you thinking the right kinds of things while doing it. One thing to bear in mind - I've never done it myself. I mean, I own both a TBI (throttle-body fuel injection) and a T2 (intercooled turbo) car, but that's not the same as spending the weekend breaking your knuckles doing the wrenching to make this work. I'm very much open to corrections and additions by people that have done this swap or are just more knowledgeable than I am. Most of this will apply to a carb -> turbo conversion, but you'll have to figure that out for yourself. V6 to turbo... well, I don't even want to go there.

I'll tell you straight up - it's not for the faint of heart. If you're not intimately familiar with these cars or are not an experienced wrencher I wouldn't even try it on a daily driver. If you have a project car that you can afford to have downtime on, great - because you likely will. It will probably take 2-4 days just to do the physical work and you have to expect at least a few more to chase down all of the bugs that you just know are going to show up. Worst case scenario is that you spend months doing the swap and end up with a badly-running car that won't pass emissions and has no balls.

This doc assumes a certain amount of familiarity with engines and general mechanics. If I had stopped to explain all of the terms used here this doc would be even longer than it already is. I strongly urge you to look up any mystery terms as you encounter them. 

A lot of the following obstacles can be overcome by simply getting a turbo longblock from the junkyard, but we'll go over the details anyway.

The exhaust valves in a turbo head are made of a tougher material than TBI valves that will take the heat better. If you try and use TBI valves with a turbo car, they will likely fail after a short time. The intake valves should be OK. Note that unless you know the history of a valve it can be hard to tell a turbo valve from a non-turbo. Any valve that has a T on it will be turbo, but they don't always have the T. We compared notes on the FMP mailing list one day and sometimes the T was on the intake, sometimes the exhaust. G/bathtub/445 head valves are a different length than swirl/782 valves and can't be interchanged.

TBI cams and turbo cams have different specs. A lot of people swear the 88 TBI cam is a good upgrade for a turbo car with rollers, so if that's your model year, you're in luck. You can probably get away with using the TBI cam in a turbo car, but what the performance and idle will be like will depend on the year of the cam. Turbo heads use a higher-rated valve spring. You may get away with using the TBI springs for a while, but if they're tired they will allow valve float which will destroy the cam over time (pits on the lobes). Beware any cam stamped with "OSJ" or having green paint on it, and the head it comes from. OSJ stands for "oversized journals" and it means that the diameter of the cam journals is bored bigger than standard. You can't mix OSJ cams and regular heads and vice versa.

The distributors in turbo and TBI cars are different. Turbo distributors have a window in one of the blades on the shutter wheel that TBI distributors do not. The window tells the computer where in the cycle the engine is and the computer determines which bank of injectors to fire. Make sure it matches the year of the computer you intend to use, 86+ distributors are different from earlier years and will not work with an older computer. Beware of mid-year changes if dealing with 85-86 hardware. Relating to the window in the shutter, turbo cars also use a different hall effect pickup - it has two plugs where the TBI sensor has only one.

The oil pressure sensor on my TBI car screws right into the hole for the oil gallery. There is no sending hex with feed holes in it like there is on my turbo car. The turbo will need an oil supply line added to this source, so you will likely require the sending hex and sensors from a turbo car.

You need the complete intake, throttle body, fuel rail and injectors from a turbo car. If you are using a T2 computer with a T1 intake, you need to drill and tap the boss on the front of the intake for the Intake Air Temperature sensor.

The airbox and intake hoses will be totally different between the two cars. You require the complete intake system and mounting brackets from a turbo car, or you can go straight to the cone filter setup that a lot of turbo owners use. Remember though you have to do something with the PCV system that normally hooks to the airbox. Add a filter, catchcan or a hose to the ground with steel wool in it, something. Do NOT plug the PCV system or restrict the flow of gasses out of the motor in any way. This will cause crankcase pressure to rise, which will inhibit oil draining out of the turbo (because of the back-pressure). If the oil can't drain it has to go somewhere and it will squeeze past the seals in the turbo into either the intake or exhaust. Instant Spy-Hunter smoke screen!

Some engines use lightweight rods that will not take the punishment a turbo car can dish out. They will break at some point, perhaps scoring a cylinder wall, ruining your block (and day). They really need to be swapped for beefier turbo units.

The pistons in a TBI car create a higher compression ratio than a turbo car requires. TBIs are typically 9:1 or 9.5:1, and turbo cars are around 8:1 or 8.5:1. You can run a modest amount of boost on a 9.5:1 motor, but you'd have to be careful to avoid detonation which will also destroy your motor and the fueling of any of the turbo computers will be way off. You really need a set of turbo pistons to get the right compression ratio. If you're changing pistons, then much bigger issues come into play... replacing the rings, condition of the bores, etc. You might be able to lower the compression ratio using a G-head in place of a swirl head. The chambers are bigger, which will lower the CR. 

If you intend on running more than about 9-10 psi of boost you will require an intercooler, especially if using a small Mitsubishi turbo. Not using an intercooler will be asking for detonation problems, although some people get away with it for a while. Mounting an IC means either sourcing a stock T2 unit, or fabricating something. If you use a T2 unit you will need to replace the radiator, fan, and possibly rad hoses with T2-specific versions. This makes room for the IC which is mounted next to the radiator on a stock system. If you want to put something other than stock in, forget using the stock airbox setup and plan to do the cone-filter intake thing. It might still be a good idea to switch to a T2 radiator, because it provides a clear space to run pipes to a front mounted intercooler (see my page elsewhere on the site for pictures). It can still be done with a TBI/T1 rad however.

The turbo will require a coolant feed line to come from the thermostat housing of the head, and a return line plumbed to the back of the block just under the power steering pump. Both fittings should be there, but you will need to remove the plugs and they may be reluctant to come out. Take it to a machine shop if they start to look stubborn, don't use a torch on an aluminum cylinder head. I wouldn't suggest reusing the lines from the turbo donor car, I would purchase new ones. It's vitally important to replace the oil feed to turbo line. Any particles you shake loose while plumbing the lines that get into the turbo bearing can kill it in a hurry. If you bought a good used turbo that didn't smoke and it starts to smoke not long after getting the car running, you probably got junk in the bearings while installing. 

Non-turbo blocks do not have an oil-drainback hose fitting, so you will have to remove the oil pan and braze a fitting onto it. Be sure to put it above the level of the oil.

Turbo cars have a heat shield between the turbo and the firewall. It may not be strictly necessary but I would grab it anyway.

If your starter doesn't have a heat shield you definately need to add one before installing a turbo. Without it your starter will probably croak in six months. The turbo sits 4-5 inches away from the starter and gets up to 1500F regularly. Get some Thermo-Tec wrap and wire ties at least.

Exhaust

Turbo cars use a different exhaust manifold. You could take your TBI manifold and weld the turbo flange onto it, but that requires a whole raft of other modifications which we won't get into here. Suffice it to say you need a turbo manifold and as far as I know, they're all the same (except for T3). Turbo manifolds from log intake motors may need to be notched to clear the intake runner if using a late model T1-T2 intake. You should be able to transfer your O2 sensor from the TBI manifold to the turbo. Replace it with a new Mopar sensor if you can afford it.

Turbo cars use a different downpipe connection. You will have to cut off and weld on the downpipe from a turbo car onto your exhaust system. Use a new donut and spring-bolt kit.

The stock exhaust on a TBI car is more restrictive than what comes on a turbo car. You can still use it, but it will cut into your power heavily. You should at least swap on the exhaust from a turbo car, or better yet get a nice 3" manderel-bent system from one of the net vendors or a local exhaust shop. Expensive, but worth every penny.

Of course... (drumroll) you need a turbo. You need something that has a Chrysler-pattern exhaust flange if you intend to use a stock manifold. You can choose from an early Garrett T1, a Mitsubishi turbo or a Garrett T2 turbo. The latter are a bit hard to find cheap or in yards, but people are often selling them on the lists and they're your best bet for performance. Early Garrett T1 turbos can be converted to T2s by way of an adapter that is available from several vendors. Mitsus are however plentiful and cheap, spoolup is instantaneous, just don't expect to get more than about 16-17psi of boost out of them, and you better have an intercooler to do that. Turbos from 89 and up will have the larger 2.5" swingvalve housing, vs the 2.25" of earlier years, so look for those if you can. Note, a mitsu turbo will not fit if your engine has the bulky pre-86 starter. You will have to switch to a later model starter.

Be cautious what turbo you buy. Building your turbo conversion, then having to turn around and replace the turbo a month after putting it on the road would be a definate bummer. Older turbos are frequently tired turbos waiting to croak. If you have the money to spare, get a rebuilt unit. If not, try to find out the history of the turbo. Did it smoke? Is there any play in the shaft? Does the shaft spin freely? Does it feel like the blades are in contact with the compressor housing? Is there any damage visible on the compressor or turbine blades from foreign objects? Does the wastegate can still work? Is there any oil visible inside the swingvalve housing or the compressor outlet?

Electronics

Here's the real bugger - you need to change computers. You can't have a TBI computer reprogrammed, because they don't have all the hardware necessary to drive a turbo car, and forget soldering anything onto it. You need a turbo computer, preferably from a car of the same model-year as yours. Obtaining the same year computer will make your wiring job a lot easier. It should match the displacement of the car (2.2 vs 2.5), and it would be preferable to get a computer from a car with the same type of transmission (AT [automatic] vs MT [manual]). While the ATs in our cars are not computer controlled, there are still some subtle differences in the programming of the computers (trust me, I have the code). I suspect the main differences are to support smooth shifts for the autos [power is reduced during shifts to smooth shifts and prolong transmission life, and tip-in is reduced for the manuals to avoid sudden jerks; idle speed is probably also faster on the automatics due to fluid drag]. Sure any computer will probably work, but drivability may be affected very slightly. Get the right one if you can.

It's probably best to source a complete wiring harness from a turbo car. Trying to graft the necessary circuits onto a TBI harness would be a nightmare to say the least, and you should be able to get a harness easy enough from any yard. If using a T2 computer, try to get a T2 harness of the same year, or you can graft the IAT circuit onto a T1 harness with a bit of work.

You need the solenoids and MAP sensor from a turbo car. The TBI MAP sensor has a range of only 1 atmosphere or 1 "bar" (barometric unit). A turbo MAP sensor can read 1 bar of vacuum and 1 bar of boost. If you plan to let the computer control boost, you need the wastegate solenoid from a turbo car. Right next to it will be the baro-read solenoid, which allows the computer to read the atmostpheric pressure so it can adjust to the altitude you're living/driving at. An alternative to letting the computer control boost is a grainger valve. The valve allows you to set the boost level by mechanical means, but you should probably use a resistor in place of the wastegate solenoid, or just hook it up but don't bother running the vacuum line to it. The computer will generate a code and perhaps enter limp-in mode if you don't do something to keep it happy.

The firewall wiring on two cars where the only difference between them is that one has a turbo and the other does not will likely be identical. However different platforms of the same model year can have different pinouts and connectors. There will definately be differences if using a model year computer different than your cars. It's possible you will have to do some cutting and splicing with a connector pinout to make things compatible, however most of the wires are signal-compatible. Obtain the pinouts for the firewall connector of both your car and the donor car and compare. If you're getting parts from a junkyard car, make sure to write down the VIN so you can look up the specifications later if you need to.

Your TBI will not have a boost gauge, you need to add one. A stock boost gauge from a turbo car should be easy to install, or you can go aftermarket. I also recommend putting in an Air/Fuel ratio gauge as well, you may need it during the debugging phase. EGT gauge is handy as well if you can afford it and have time. Might as well add it while you have the motor apart.

Note that if going to a Logic Module setup that the power module is different than the TBI unit.

Note that an 88- T1 is a 2.2 with 27pph injectors, but an 89+ T1 is a 2.5 with 33pph injectors. Don't get them confused when shopping for parts. If a list member says "Yeah, I can sell you some injectors from a T1", make sure to ask which year.

88 and 89 Turbo computers will interchange. In fact, the electronics from both years is very similar. The only notable difference I can think of is that the oxygen sensor in 88 was 3-wire, and 4-wire in 89. There are conversion kits available to upgrade to 4-wire if you need to (I recommend it). 

Vacuum Harness

The vacuum harness of a turbo car is completely different than a TBI cars harness. If you can get a turbo  harness complete that's a step in the right direction. Otherwise you need a bunch of check valves, different sizes of T-connector, some different-sized orifaces (the plastic kind), worm gear clamps, and a box of several different sizes of vacuum hose that can withstand boost.

Parts of the stock vacuum harness from a turbo car will probably disintegrate on you anyway. They were made of hard plastic that over time becomes extremely brittle because they're sitting on a manifold that sees 200F regularly. No, I don't know what they were thinking either. So no matter what you will probably have to rebuild at least part of your harness.

Make sure you have access to a vacuum diagram for the appropriate model-year engine you are working with. www.thedodgegarage.com has some of them online. If you have a donor car, it's right under the hood. I think Haynes books have them too, and the FSM definately does. Best thing you can do as ask someone local to you with a turbo car of roughly the same year to come over for an afternoon and use his car for reference while you hook it up. 

If you have to worry about visual inspections, then you'll have to make sure you hook up the vapor canister to the vapor line from the gas tank, connect the solenoid, and connect the can to the nipple on the throttle body. If you have to do EGR, then you need to mount, wire and plumb vacuum to the EGR solenoid, plus all the crap between the exhaust and the intake. The PCV system connects to the airbox and the intake manifold. Don't forget the check valve.

Fuel

The injectors will need to be matched to the type of computer you use. 2.2 vs 2.5, T1 vs T2, etc. Different engine packages used different sized injectors. T2 and 2.5 cars used the same injector. Don't try to use injectors from a non-Chrysler engine unless you're positive they're compatible. Chrsylers use a peak-and-hold injector (2 ohm), and many others use saturated injectors (12-14 ohm). If you don't know what those terms mean, stick with stock Chrysler stuff.

You will have to cut the TBI fuel lines and find a way to attach them to the turbo fuel rail, hopefully only fuel injection hose and some clamps are needed. I seem to recall some of the turbo fuel pressure regulators requiring a screw-in connector, might have to get creative there. [Be careful given the higher pressure of turbo engines, see below]

You need to replace your fuel pump with a turbo unit. Newer TBIs ran at 39 psi fuel pressure (vs 15 psi for older TBIs), and you might get away with using the stock pump for a while at 55 psi + boost. I'd be deathly afraid it would overheat and pack it in while you were under boost which could spell the end of your new motor. Get a proper V6/turbo pump and install it with a fresh fuel filter. Hopefully you don't have to drop the fuel tank, cause you'll probably have to cut and replace the straps. Never done it myself but I understand it's hard.

Transmission

You can use any transmission with the turbo motor of course, but there's a question of durability that sooner or later will probably need to be addressed. Non-turbo cars didn't get the 555 and 568 trannies, they got the weaker ones that were more than strong enough to withstand the "punishment" a TBI motor can dish out. Now you're increasing the power, but not changing the rated power levels for the transmission. What do you think will eventually happen? 523 trannies are rumored to be tough little buggers, so if you have a newer TBI you might be lucky for a while.

There's the question of gearing. TBI cars, not having the power of their turbo cousins, tended to be geared higher. If you add a turbo engine to the mix, you may end up having traction problems because of the tall gears. Most turbo racers gear down to help with this, which also benefits the top end. 92+ 523s have a 3.77 final drive, and a 3.3 first gear, which is taller than even earlier 523s or older TBIs. Burnout city!

The clutch in your MT car was most definately not designed to handle the power a turbo engine will want to put through it. It will slip and be burned out in no time flat. You need to upgrade to at least a stock turbo clutch and pressure plate or if you can afford to look to the future, something better than stock.

Most TBI flywheels have the small clutch pattern and the turbo clutch won't fit, so you'll need to source a turbo flywheel. However I do know some TBI minivans used the turbo flywheels, I'm not sure if the 2.5 TBI car application used a turbo flywheel or not. Check your flywheel type before buying anything. I believe the 523 flywheel has both TBI and turbo patterns.

Misc

Do you have to upgrade the brakes? No. Should you? Well that's debateable. I find the four wheel discs on the Shelby stop that heavier car FAR better than the disc/drums of the TBI car. Drum brakes work great - when they're adjusted properly. The problem is that they go out of adjustment easily, the "automatic" adjuster gets full of crap and jams, etc. Any sensible person who adds power to their vehicle also increases the stopping capability to match - it's just plain common sense. It could save your life, or the life of someone else.

Suspension is another area that doesn't strictly need attention, yet should get some. Turbo cars came with bigger sway bars and stiffer shocks for a reason. If your new-found power inspires you to do hard cornering in your turbo hotrod, you need to take care of business and make sure that your tires stay where they belong - glued to the road. Use your judgement here and err on the side of caution. [There's also the issue of torque steer!]

Beware of hack jobs done on donor vehicles. It's not uncommon for people to do stupid things like replace a turbo head with a TBI head, use the wrong head gasket, replace the computer with the wrong model or year, the list goes on. Buy your parts from a trusted source, and make sure they won't give you a hard time if you find out later that it's a frankenstein POS you can't use. Buying a running car in a private sale is no guarantee that you'll get the right parts either. These are 20 year old cars, and chances are any car that ends up in the junkyard has had one major repair in its lifetime. Given their low resale value, people aren't usually willing to do these repairs "right." Gary Donovan has lots of information on how to identify various parts, I suggest you use his online reference to help verify that you have the right stuff.

The good news is - the battery tray can stay RIGHT where it is. :)

If after all that you're still going to do this, I would try and locate a complete turbo car from which to source all of the parts you'll need (which as you've seen are quite a few more than maybe you first thought), and a local expert to help you debug it when you're done if you can't do it yourself.

The best routes to go are (in order):

  1. Buy a turbo car
  2. Buy a complete wreck of a turbo car and park it in your driveway next to the TBI
  3. Buy everything you can off of a turbo wreck in the yard, and make them promise not to crush it in case you have to come back
  4. Go broke buying the parts individually from list members and EBayers.

Good luck!

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