Now we get to the best part: making more power! Here you'll find lots of great information about souping up your turbocharged Dodge Caravan or Plymouth Voyager. We'll give you a general overview of upgrades to perform, recommend in what order they be performed, and list specific how-to pages where appropriate. Be sure to also check out the performance tips page; it will make a number of small but important recommendations that impact your van's performance.
Now that you own a turbo minivan, the very first thing to do is to bring it up to proper operating condition. This means performing a complete tune-up, verifying perfect alignment of the timing belt, adding fresh oil (preferably Mobil 1) and filter, making sure the cooling system is functioning well (flush the system and/or replace the radiator if needed) and so on. If your van is not in tip-top shape you have no business trying to squeeze more power out of it--don't come crying to us when you blow it up!
Now that the van is ready to go, we need to do something else: install a quality boost gauge and an air/fuel gauge. You have some choice in the former (I prefer AutoMeter's Phantom series myself) but the latter should be a Cyberdyne gauge or one from Dawes Devices. Or both. Another important gauge would be an EGT, but they're not very practical to install unless you're already tearing into the engine; if you do need to open your van for any reason, I highly suggest you add an EGT while you're at it.
As with most turbocharged vehicles, the first logical upgrade is the exhaust system. Despite any myths you may have heard, turbos need no downstream backpressure to operate properly. The more you uncork your exhaust, the quicker the turbo will spool and the faster you will go! I suggest thinking about what your ultimate performance goals might be, then go straight for the throw-down exhaust system up front. This way you'll never have to upgrade twice.
As far as a catalyst is concerned, Products For Power make inexpensive ones that flow very well. And on the muffler front, the Dynomax UltraFlo bullet muffer (sometimes called a Race Magnum) is the best flowing muffler available on planet Earth. Each of these are available in 2.5" and 3" sizes; you can buy them from Don's Hot Rod Shop in AZ--call 1-800-888-8892.
Which exact size should you go for? Depends on your turbo. If you intend to never upgrade and want to retain your stock Mitsubishi turbo, 2.5" exhaust pipe is all you'll need. If you want to go to a larger turbo, though, go straight for the 3" pipe.
No matter which size you use, be sure to install mandrel bends! If you cannot find a shop in your area with a mandrel bender--and you probably won't--just order pre-bent aluminized pieces from JC Whitney. (Don's Hot Rod Shop sells ones which are not aluminized; go with JCW and your system will look nicer longer.) Then carry all your parts to a welder and have the system assembled under your van. You will need four 45^ bends plus two 90^ bends; starting from the turbo you need a 45^ to follow the bottom of the body, then you'll have the cat and the muffler, then a 90^ to get to the perimeter, another 90^ to turn toward the rear, two 45^ bends to get up close to the body of the van, and a final 45^ bend to use as a tailpipe.
Tip: for added stealth, leave the tailipe tucked up behind the bumper; cut it off just where it would begin to drop into view. This way your killer exhaust system won't be visible to cars behind you!
After your exhaust system is complete, the next logical step is to ditch the horrible stock boost control setup. As you've learned by now thanks to your boost gauge, the factory does a sneaky thing: the computer uses two-stage boost output. Below 4000 RPM you are limited to a mere 5 psi of boost; at higher revs the boost will increase until it tapers off around 10 psi. No good. Eliminate the wastegate solenoid vacuum tubing and switch to manual control! (I strongly recommend a brass pressure relief valve, aka the "Grainger valve"). Not only will a Grainger valve allow you to run higher boost, it'll also cause your turbo to spool much more quickly--the first time you nail the throttle you'll be a believer. For the time being, your target boost output is 13 psi. Be sure to increase boost gradually, reading your plugs (and your air/fuel gauge) along to way to make sure all is well. Also, remember to leave the wastegate solenoid plugged in! This will prevent the check engine light from coming on.
Now that your turbo can make 13 psi just off idle (the little Mitsu turbo spools very quickly) it'll feel like you gained 50 HP! By now you will have chopped nearly two full seconds off your stock van's quarter mile time; fart-tipped VTEC Civics will now become specs in your rear-view mirror.
By now you've learned that boost is your best friend. More boost is the pathway to more power, yes, but now we've got a problem: heat. The higher your boost output the hotter the air is when it exits the turbo. This hot air is bad for a lot of reasons, and 13 psi is about as high as we want to go before we do something about it. What to we do? We add an intercooler!
Now it's time to do some serious soul searching and decide how wild you want to go with your van. All things being equal, you want to run the biggest, best intercooler you can lay your hands on. The PowerStroke intercooler (seen above) is a popular choice, but it requires removal of the A/C system and actually doesn't perform as well as you'd expect. If you don't want to sacrifice your cold air, you'll need to go with something smaller--a Volvo intercooler can fit (though it performs even worse than the PowerStroke unit), as could a custom dual-core setup using two stock Dodge intercoolers (which would easily outperform the PowerStroke). Whatever you decide, don't forget to add a blow off valve!
When you intercool, now will be the time to ditch your stock airbox and upgrade to a K&N cone filter. Be sure to mount the cone where it can draw in cool outside air--do not place it underhood in the engine bay! Also, it's time to swap to a cooler 180^ thermostat if you haven't yet done so.
Now that we've got an excellent intercooler it is safe to turn up the boost. There is one final obstacle, though: the engine computer. It cannot deliver the fuel required to run more than 14 psi of boost, and it'll cut the spark if you try. Is there any way to cope? You bet! We either install a grainger valve to pneumatically prevent the MAP sensor from 'seeing' more than 14 psi or else add a 4.3v zener diode to electronically limit the MAP sensor's output voltage so the computer won't know there is more than 14 psi. Either way works fine; read about both methods and decide which you want to do.
There is one very important word of warning here, and I cannot stress it enough: from now on whenever you are at 14+ pounds of boost the computer will not provide sufficent fuel and you'll have to manually add more. If you fool the MAP without adding fuel at high boost, your air/fuel mixture will go lean and you will destroy your engine. You have lots of options for adding fuel; I prefer to run +40% injectors with an adjustable rate of gain regulator but I've also successfully used extra (cold-start) injectors. Do whatever makes you comfortable.
Now that the MAP sensor has been blinded and you've got fuel to support higher boost pressure, it's time to run those higher pressures! Depending on your specific turbo's health, you ought to be able to generate anywhere from 17 to 20 pounds of boost on this stock (Mitsubishi TE04H 13c) unit. The trick to not ruining things is to gradually increase your boost level, only one pound at a time. With each increase be sure to monitor your air/fuel gauge, then read your plugs for final word on the matter. If they say all is well, go up one more pound and repeat. (If you've not already done so, you should now install colder spark plugs, specifically Champion RN9YCs.) Feel free to increase the boost output up to the limit of your particular turbo, provided your fuel supply is sufficient and there is no detonation.
Those of you who are more educated in the ways of turbocharging may ask, "isn't this much boost bad for the turbo?" Well, sorta. I will not enter a discussion of thermodynamics here, but will just say this: every turbo is designed to operate within a certain range (or speed). As you keep increasing boost output you move outside this range--the turbo must spin faster and faster to produce the desired power. This is called overspinning the turbo and it can shorten your turbo's lifespan. With proper care and maintenance (regular oil & filter changes with an exclusive diet of Mobil 1, no hot shutdowns, no boost on cold engine) the net effect is very small. Many of us have overspun our turbos for years with no ill effects. And besides, you'll be upgrading your turbo anyway!
Once you unplug your wastegate actuator and run maximum boost, you'll clear the quarter mile three full seconds quicker than stock and you'll be experiencing serious traction problems at green lights. Further, drivers of near-stock Mustang GTs and Camaro Z28s will start freaking out as you show them your taillights. You may need to schedule plastic surgery to remove the evil, sadistic grin from your face.
After running with your stock turbo at max boost, you'll be itching to install a larger turbo. But before we do so, there's something else we ought to do: lower the compression ratio. Why do we want to do this? The big reason is to reduce the chance of detonation, which can kill your engine in an instant. Another key reason is because we can make more power more reliably with lower compresson and higher boost than we can with higher compression and lower boost. In short, it's just better this way.
Before you get worried about the difficulty and expense in altering your compression, let me assure you: it's easy and cheap to do. You see, Mopar made two different cylinder heads for their turbo engines. The earlier style (used in 84 and 85) is called the G-head or the bathtub head; the style used from 86 onward is the swirl head. The swirl head has a smaller combustion chamber than the G-head, so different pistons were engineered for the newer engines to maintain an approximate 8.1:1 compression ratio with the new head. But if you take a G-head and swap it onto your 86+ shortblock, voila! You've just lowered your compression ratio a bit. How's that for easy?
Be advised the stock head on your van is crossdrilled, meaning there are a few extra tiny holes drilled to allow for extra cooling. Putting a non-crossdrilled head onto a crossdrilled block isn't a major problem, but you can have your G-head drilled to match... and I do suggest you have it done. After all, more power = more heat = greater cooling need, right? Also, understand that not all cylinder heads were created equal: turbo heads had some better goodies (hardened exhaust valves, etc) which the naturally aspirated heads didn't get. If you go junkyarding for a G-head, be sure your donor engine was turbocharged!
Another benefit to a lower compression ratio is the ability to run 25 psi on pump premium fuel. Not needing jet gas for day to day use can sure help reduce your overall fuel bill, plus it's kinda fun to brag about. For maximum safety during severe flogging sessions, some guys will still add one gallon of race gas to their vans while at the drag strip. If you want a little extra insurance, go ahead.
If you plan to go hog nuts wild with the boost, you might want to also install a copper head shim. Fel-Pro makes one that is .020" thick and it's crossdrilled, part number 9296SP (available at AutoZone for around $16). If you do opt for a shim, I suggest you not go thicker than this--you'll ruin the quench characteristics of the engine. (If you don't know what quench is, don't worry; just trust me--don't go stuffing thick shims in there.)
Now that the compression ratio dilemma has been solved it's time for a larger turbo. (TIP: perform step #7 at the same time as #6 and you'll only need to remove your cylinder head once.) You have many options ranging from a good used Garrett T03 off a TurboII Dodge car up to a custom $1000 hybrid turbo built to your design. Which is the right way to go? That's something only you--and maybe your wallet--can decide. But even on a budget, the Garrett T03 is a nice upgrade; the stock Mitsubishi TE04H turbo has a reputation among the FWD Dodge crowd, but it isn't pretty. To quote Gary Donovan:
"For performance use I cannot recommend a stock Mitsubishi turbo AT ALL! It has a much smaller compressor, the shaft bearings are a third the size of a Garretts and the exhaust housing is a major restriction! The backpressure at high boost levels must be obscene, the picture [below] shows the difference in exhaust housing passage sizes. The mitsu's is about the size of ONE 2.5L exhaust port!"
It's easy to see that the Garrett T03 exhaust housing flows much better than the little Mitsubishi. The compressor on the Garrett is also noticeably larger, and this will allow us to run more boost for more power. See the difference yourself:
If you want to upgrade to the Garrett, be advised you'll need to install a different coolant supply line, oil feed line, and oil return tube. The turbo itself bolts right to your van's exhaust manifold, though, so overall the swap is an easy one.
What if you're thinking about something more exotic? Maybe a Super60, or perhaps a hybrid? Gary Donovan has a great page which discusses many ideas related to running truly large turbos--it's worth the read!
So now that you've got your larger turbo installed, always remember to keep an eye on your fuel supply and only up the boost one pound at a time.
By now you're left with one main question: how far can you go? That depends how you build your engine. As delivered from Mopar, the bone stock 2.5L turbo shortblock can handle 25 psi without breaking a sweat. With a good intercooler and a proper air/fuel ratio, some guys manage 28 psi without component failure. But usually by 30 psi the stock cast pistons begin to reveal their weaknesses... and a few other odd problems rear their ugly heads as well. So if you don't want to spend money on exotic parts, I'd say 25-28 psi is the theoretical ceiling for your boost pressure. But don't despair--28 psi plus a pair of slicks can net you handfuls of 12-second timeslips.