Mopar 2.2 and 2.5 TBI Power Upgrades
Neither Allpar nor any of the contributors take 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.
The TBI engine is essentially any 2.2 or 2.5 with a single fuel injector. These engines were used on many cars, minivans, and light trucks. The computers and the engines underwent many changes as the years went on.
Turbocharged engines had multiple-port fuel injection (each cylinder had its own injector), but the TBI models had only one, which is less efficient. David Zepeda pointed out that in Mexico, the 2.5 was given multiple port injection, boosting power.
Modifications to Chrysler/Dodge/Plymouth 2.2 and 2.5 liter TBI engines
There isn't much you can do to increase performance a TBI engine, and the following modifications may not affect your performance too much. Adding a turbocharger is rather extreme but works, as does selling the car and buying a turbo model.
The 2.2/2.5 TBI engines were competitive when they were made. These engines have nice low-end torque for four-cylinders but have issues with breathing and fuel supplies.
by Edward Kelly
For substantial money you could have the head ported, with port matching of the manifolds. Back cutting the valves and 3-angle valve job will both help the head flow better especially at low valve lift. The valve guides are probably worn, you can have them replaced or spiraled to bring them back into tolerance; new valve guides will last longer. Spiraling is cheaper.
Porting is probably the most costly intervention. Shaving the head to up the compression ratio would also increase hp. If you shave it too much you will need to run an oversized timing belt tensioner or an undersized belt (both sold by Mopar Performance). You may also need to run higher octane fuel. If you decide you don't like the increase compression, you can get a copper shim gasket (Felpro makes one) to move the compression back to stock.
Degreeing the cam will also help.
by Derek Beland
The problem with tweaking TBIs is that very few changes are individually noticeable. Most mods you can make will yield an increase in power that is a factor of the baseline power from the factory. Since factory power is around 93-100 hp, gains come in 2-5hp increases. Some ideas are:
The expensive/time consuming stuff:
This assumes of course that your engine is in top running shape. A compression test might be wise, and potentially a ring-job. These mods may cause you to run lean so you will ned to get an air fuel meter when you start.
There are differences between the later model TBIs and early ones. My stock fuel pressure is 39 psi, so I'm sure the injector is a different flow rate as well. My head has the "TS" stamp on it, which Gary's website says indicates a turbo head - but this one is definitely the original. Perhaps flow is better. I know the intake manifolds for later models are slightly different. There was a TSB about hard starting that indicated the manifold could be switched to a later revision to cure the problem.
Most people have to mod what they have. I don't think it's unreasonable to think you can get another 20-30hp out of the motor, with a reasonable budget.
I like my MSD6A ignition system. The cars pulls to redline at a steady speed, vs running out of steam at the higher RPMs. I have my car set up so that I can bypass the MSD and run straight to the coil, and there is a small but noticeable difference. Is it worth the $200 price tag? That's subjective. You need to mate it with a Blaster 2 coil.
Lots of people say they've had problems with the MSD breaking down. I had one Blaster coil die on me, an interior connection snapped off. Because my coil is mounted on the thermostat and thus subject to a lot of vibration, I switched to the "High Vibration" version (filled solid with resin) and haven't had a problem since. I've had the MSD setup in the car going on five years now, 3.5 on the new coil. I mounted the MSD with rubber isolators, so maybe these people were screwing them down solid to the frames/fenders and they got shaken to death?
Timothy Pindell
I took my Daytona to the Nationals for a few passes. The car is now capable of mid 17s with a good reaction time. Here's what I did to mine:
I shifted at 6200 (indicated) rpm. It was still pulling, but not much.
This illustrates my belief that you can't get much out of a TBI unless you get radical. It's got a bit more than what it had when it left the factory, but not as much as the turbo guys get for the same effort. Don't teach a TBI to go real fast. It wastes your time, and annoys the engine.
Summary of low-buck approach
David Reynolds wrote: "the best performance you can get from a 2.2L TBI car is to be had by (in order of expense):
I have done all of this to my Sundance, and I have very good drivability for a 2.2 non-turbo. I am also using a Comp Cams camshaft, but I'm not convinced it makes a big difference over the stock cam. For an '87 or earlier slider cam, though, you may want to consider switching to an '88 or later roller cam. Switching cams is actually a fairly easy thing to do yourself, and you can usually get a used one pretty cheap.
Note that the changes I made to my Sundance require 93+ octane and raised fuel pressure to keep it from knocking. I raised the fuel pressure by squeezing the regulator in a vise (a la Gus) a little at a time, then testing to see if the knocking improved.
All of this taken together has given me a strong power band between about 2000-3400 rpm, which is great for my city driving to and from work. It has next to no top end, though.
2.2 / 2.5 TBI breathing
Exhaust
Dan Stern wrote: A Magnaflow (similar to an Ultra-Flo) muffler and low-restriction catalyst perceptibly helped.
Bradley Miller suggested: "Daytona/Laser mufflers will fit our cars. Stock pipe is 1 7/8". Lambros Race Engineering has an adjustable fuel pressure regulator that will allow for fixing lean conditions. They also have different gear ratios (provided you don't mind losing top end) and they have different pulleys. This will spin the accessories a little slower to reduce parasitic horsepower losses. The exhaust helped with the sound of the car and the mid-range pull. I've now got 2 1/4" pipe all the way back to a Walker Super Turbo muffler. You can step down on the accelerator and really get a good shove in the pants without the car downshifting. In the upper RPM bands it doesn't really help too much."
Derek Beland wrote:
Jerry Adams warned:
Intake manifold
Dan Stern said there was an updated intake manifold to solve the long crank time on cold starting. Joe Pfeiffer also suggested replacing the intake. Vincent Cheng described reworking the intake manifold:
Bradley Miller said:
Martin Rempel wrote:
Before my turbo van I had a 89 Spirit TBI. One of the things I did was pick up a throttle body (TB) off of a wrecked car and had it bored out. There is not a whole lot of material to bore out. There are two very small vacuum ports that are in the bowl area. These tend to open up as you bore it out. I had a larger throttle plate made and had the TB on the car for a while. It made some difference but not much. I still have the bored out bottom half of the TB if you want it. The throttle plate I made was not quite big enough so my idle went up about 2-300 rpm. According to Gary Donovan, the major problem is the intake. Check out his site for more insight. He recently completed the TBI database. www.thedodgegarage.com
Ignition
The general consensus is that the stock ignition system works well enough for most purposes - unless you really hot-rod the engine, which as you noticed we do not recommend (given the effectiveness of a turbo-swap).
Mike King wrote that overgapping the spark plugs to .040", rather than the stock .035", helped in power. This had also come up in the EEK mailing list several years ago. The consensus was that Chrysler tended to be conservative in plug gap - other makers have larger gaps. Mike said that the power boost was stronger when coupled with midgrade gas. Note that this increases the strain on the ignition system, but that others have reported no problems.
Transmissions
Dan Stern wrote: Most of the TBI cars came with a final-drive ratio of 2.78. This is great for cruising at 75 mph all day, but around-town the engine is working below its torque peak and straining against the low-stall torque converter together with the high final drive ratio. This is also why early Slant-6/auto Darts feel peppy, while later cars feel "mushy" and slow --the early A-bodies have 3.23 or 2.93 gearing, while the later cars have 2.76s (and even later cars got 2.45s and 2.26s!). There was also a 3.22 ratio available for this A413 3 speed auto used with the 2.2 and 2.5 engines.
Sensors and stuff
Some advise a lower-temperature thermostat (e.g. 180 degree) - this is fine if you want to pollute more and lower your gas mileage, but is not really a sensible way to run your car. The engine was designed to have a certain amount of heat.
Fuel injection
Herb DaSilva: "If you start to get lean, get in touch with some of the companies that specialize in fuel injectors and get an 8% or 10% oversize injector. The stock computer will be able to handle it." (This is if you make other power modifications which cause the stock injector to be unable to handle the load.) Conversion to multiple port fuel injection is generally considered more trouble than swapping in a turbo engine.
Bradley_W._Miller wrote: "we have the little blue bottle. (NOS) The ultimate equalizer. A system runs under $400, depending on where you get it. An extra 50-75 hp is about the safe limits, with stock parts. You just have to be careful to keep adequate fuel pressure and not to use it at too low of an RPM. Dropping 2 seconds off your ET with one of these is no problem."
Manifolds
Stefan Mullikan wrote: Pierce Manifolds sells the side draft Weber kits [that fit the 2.2 and 2.5 engines[ as well as the manifolds for our 2.2/2.5 motors. The complete side draft Weber kit from Pierce is $823.20. The side draft Weber manifolds, is $293.24 They can be reached at:
Pierce Manifolds
321 Kishmura Dr.
Gilroy, CA 95020
1-800-874-3728
Camshafts and balance shafts
Taking out the balance shafts from the 2.5 engine is said to provide a very small power gain at the expense of smooth idling.
Gus Thomas wrote: The rumor of increased performance from disconnecting the balance shafts in the 2.5 engine is the result of a tech article by a Chrysler engineer a few years ago. It was re-written by Gary Donovan last year, and put in the SDAC newsletter. He said that 14 HP is gained at 6,000 rpm. How long are you at 6,000 rpm? For less than 1/10 of one percent of your engine's life? You're sure not gonna feel that 14 HP much!
Because frictional losses increase as the square of the increase of rpm, at 3,000 rpm (a real-world everyday rpm) you only gain 3.74 hp (the square root of 14). That's difficult to feel in the seat of your pants. I do it anyway (remove them) because I get slightly better gas mileage, don't whip up the oil as much, and get a little edge when I am at 6,000 rpm at the track. When you're heading into the 11s with a 2,770 lb Acclaim, you need every bit of free help.
åHerb DaSilva suggested that 2.5 owners get a Mopar Performance cam and getting underdrive pulleys from LRE (Lambros) or others.
Bradley W. Miller wrote:
Neither Allpar nor any of the contributors take 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.
The TBI engine is essentially any 2.2 or 2.5 with a single fuel injector. These engines were used on many cars, minivans, and light trucks. The computers and the engines underwent many changes as the years went on.
Turbocharged engines had multiple-port fuel injection (each cylinder had its own injector), but the TBI models had only one, which is less efficient. David Zepeda pointed out that in Mexico, the 2.5 was given multiple port injection, boosting power.
Modifications to Chrysler/Dodge/Plymouth 2.2 and 2.5 liter TBI engines
There isn't much you can do to increase performance a TBI engine, and the following modifications may not affect your performance too much. Adding a turbocharger is rather extreme but works, as does selling the car and buying a turbo model.
The 2.2/2.5 TBI engines were competitive when they were made. These engines have nice low-end torque for four-cylinders but have issues with breathing and fuel supplies.
|
For substantial money you could have the head ported, with port matching of the manifolds. Back cutting the valves and 3-angle valve job will both help the head flow better especially at low valve lift. The valve guides are probably worn, you can have them replaced or spiraled to bring them back into tolerance; new valve guides will last longer. Spiraling is cheaper.
Porting is probably the most costly intervention. Shaving the head to up the compression ratio would also increase hp. If you shave it too much you will need to run an oversized timing belt tensioner or an undersized belt (both sold by Mopar Performance). You may also need to run higher octane fuel. If you decide you don't like the increase compression, you can get a copper shim gasket (Felpro makes one) to move the compression back to stock.
Degreeing the cam will also help.
by Derek Beland
The problem with tweaking TBIs is that very few changes are individually noticeable. Most mods you can make will yield an increase in power that is a factor of the baseline power from the factory. Since factory power is around 93-100 hp, gains come in 2-5hp increases. Some ideas are:
- advance ignition timing to 15 degrees
- play with cam timing via offset keys
- remove intake elbow
- remove heated air flap in airbox inlet (this will hurt drivability and emissions)
- hotter coil, wider plug gap
- remove coolant lines to throttle body (the latter may hurt drivability)
- bore out throttle body
- modify the butterfly (shave shaft, shorten screws, knife edge leading side)
The expensive/time consuming stuff:
- ported head
- bigger valves
- convert to carbs (may be against the law or cause emissions test failure; may hurt gas mileage; may hurt drivability)
- shave head to raise compression
This assumes of course that your engine is in top running shape. A compression test might be wise, and potentially a ring-job. These mods may cause you to run lean so you will ned to get an air fuel meter when you start.
There are differences between the later model TBIs and early ones. My stock fuel pressure is 39 psi, so I'm sure the injector is a different flow rate as well. My head has the "TS" stamp on it, which Gary's website says indicates a turbo head - but this one is definitely the original. Perhaps flow is better. I know the intake manifolds for later models are slightly different. There was a TSB about hard starting that indicated the manifold could be switched to a later revision to cure the problem.
Most people have to mod what they have. I don't think it's unreasonable to think you can get another 20-30hp out of the motor, with a reasonable budget.
I like my MSD6A ignition system. The cars pulls to redline at a steady speed, vs running out of steam at the higher RPMs. I have my car set up so that I can bypass the MSD and run straight to the coil, and there is a small but noticeable difference. Is it worth the $200 price tag? That's subjective. You need to mate it with a Blaster 2 coil.
Lots of people say they've had problems with the MSD breaking down. I had one Blaster coil die on me, an interior connection snapped off. Because my coil is mounted on the thermostat and thus subject to a lot of vibration, I switched to the "High Vibration" version (filled solid with resin) and haven't had a problem since. I've had the MSD setup in the car going on five years now, 3.5 on the new coil. I mounted the MSD with rubber isolators, so maybe these people were screwing them down solid to the frames/fenders and they got shaken to death?
Timothy Pindell
I took my Daytona to the Nationals for a few passes. The car is now capable of mid 17s with a good reaction time. Here's what I did to mine:
- Mopar Performance camshaft P4529320 252/252 duration, 36 overlap, 108 centerline, (uses factory .430 lift)
- Cam installed "straight up" with the help of the offset keys
- Accell super coil, .05 gap on the Champions
- Ignition timing set to 15 advance
- Fuel pressure raised to 15.5 psi (it idles poorly)
- Removed rear seat, spare, jack
- 2 gallons fuel
- Removed AC and PS belts
- Rear tires to 55 psi, fronts to 35
- Removed air filter, left the box
- Dynomax muffler/ 2.25 exhaust from the manifold/ no catalytic converter (it's rather loud with a straight-pipe edge to it)
I shifted at 6200 (indicated) rpm. It was still pulling, but not much.
This illustrates my belief that you can't get much out of a TBI unless you get radical. It's got a bit more than what it had when it left the factory, but not as much as the turbo guys get for the same effort. Don't teach a TBI to go real fast. It wastes your time, and annoys the engine.
Summary of low-buck approach
David Reynolds wrote: "the best performance you can get from a 2.2L TBI car is to be had by (in order of expense):
- advancing ignition timing to 14-15 degrees (free)
- K&N drop-in filter ($35)
- 2.25" exhaust (around $100)
- raise compression *a little* by shaving the head and/or block (expensive)
I have done all of this to my Sundance, and I have very good drivability for a 2.2 non-turbo. I am also using a Comp Cams camshaft, but I'm not convinced it makes a big difference over the stock cam. For an '87 or earlier slider cam, though, you may want to consider switching to an '88 or later roller cam. Switching cams is actually a fairly easy thing to do yourself, and you can usually get a used one pretty cheap.
Note that the changes I made to my Sundance require 93+ octane and raised fuel pressure to keep it from knocking. I raised the fuel pressure by squeezing the regulator in a vise (a la Gus) a little at a time, then testing to see if the knocking improved.
All of this taken together has given me a strong power band between about 2000-3400 rpm, which is great for my city driving to and from work. It has next to no top end, though.
2.2 / 2.5 TBI breathing
Exhaust
Dan Stern wrote: A Magnaflow (similar to an Ultra-Flo) muffler and low-restriction catalyst perceptibly helped.
Bradley Miller suggested: "Daytona/Laser mufflers will fit our cars. Stock pipe is 1 7/8". Lambros Race Engineering has an adjustable fuel pressure regulator that will allow for fixing lean conditions. They also have different gear ratios (provided you don't mind losing top end) and they have different pulleys. This will spin the accessories a little slower to reduce parasitic horsepower losses. The exhaust helped with the sound of the car and the mid-range pull. I've now got 2 1/4" pipe all the way back to a Walker Super Turbo muffler. You can step down on the accelerator and really get a good shove in the pants without the car downshifting. In the upper RPM bands it doesn't really help too much."
Derek Beland wrote:
Muffler replacement instructions, tips, and stories
Jerry Adams warned:
Bradley Miller wrote: "I did all the bolt-ons I could within reason on my Duster and didn't see any neglible improvements. Going from 100 to 110 hp in a 2900 lb. car . . . well you get the picture."
Intake manifold
Dan Stern said there was an updated intake manifold to solve the long crank time on cold starting. Joe Pfeiffer also suggested replacing the intake. Vincent Cheng described reworking the intake manifold:
Air filters and related stuff
Bradley Miller said:
- Between the headlight and the battery there will be a little plastic "bucket" that's supposed to keep snow/debris from going up the intake hose to the air cleaner. Pull this off. Smooth pipe from the airbox to the air duct by the battery will also help. Do not remove the hose. This hose pulls air across the drive transistors for the injector. Without this hose, you WILL burn out the transistors. [Note: one EEK! member took off the hose but added a fan to blow air onto the transistors. Others, including Gus McMahon, have been running for years without it, and suggested that the airflow was probably only needed in desert areas or during extreme heat. Jeff Chojnacki wrote that he has been doing without computer cooling since 1989.]
Cut a hole (about 3" dia.) in back of air box. This is supposed to give you a little bit more low end torque. Make sure to put a mesh up there to keep large objects out of the air box. OR - Change the airbox altogether. (Webmaster's warning: cutting the hole in the back of the air box will delay warming, especially in cold weather, because it bypasses the stove. The best way to do this would be to have a control, like a manual choke, where you can shut it off or turn it on from inside the car; if you like electrical stuff you might even be able to fit a solenoid in there somehow. I do not suggest cutting the straight hole for most people who live in "normal" climates. Those who are in very hot climates, e.g. South America, may be able to get away with it more easily. A cold engine has lower fuel economy and power, higher emissions, and shorter life).
Martin Rempel wrote:
Before my turbo van I had a 89 Spirit TBI. One of the things I did was pick up a throttle body (TB) off of a wrecked car and had it bored out. There is not a whole lot of material to bore out. There are two very small vacuum ports that are in the bowl area. These tend to open up as you bore it out. I had a larger throttle plate made and had the TB on the car for a while. It made some difference but not much. I still have the bored out bottom half of the TB if you want it. The throttle plate I made was not quite big enough so my idle went up about 2-300 rpm. According to Gary Donovan, the major problem is the intake. Check out his site for more insight. He recently completed the TBI database. www.thedodgegarage.com
Ignition
The general consensus is that the stock ignition system works well enough for most purposes - unless you really hot-rod the engine, which as you noticed we do not recommend (given the effectiveness of a turbo-swap).
Mike King wrote that overgapping the spark plugs to .040", rather than the stock .035", helped in power. This had also come up in the EEK mailing list several years ago. The consensus was that Chrysler tended to be conservative in plug gap - other makers have larger gaps. Mike said that the power boost was stronger when coupled with midgrade gas. Note that this increases the strain on the ignition system, but that others have reported no problems.
Transmissions
Dan Stern wrote: Most of the TBI cars came with a final-drive ratio of 2.78. This is great for cruising at 75 mph all day, but around-town the engine is working below its torque peak and straining against the low-stall torque converter together with the high final drive ratio. This is also why early Slant-6/auto Darts feel peppy, while later cars feel "mushy" and slow --the early A-bodies have 3.23 or 2.93 gearing, while the later cars have 2.76s (and even later cars got 2.45s and 2.26s!). There was also a 3.22 ratio available for this A413 3 speed auto used with the 2.2 and 2.5 engines.
Sensors and stuff
Some advise a lower-temperature thermostat (e.g. 180 degree) - this is fine if you want to pollute more and lower your gas mileage, but is not really a sensible way to run your car. The engine was designed to have a certain amount of heat.
Fuel injection
Herb DaSilva: "If you start to get lean, get in touch with some of the companies that specialize in fuel injectors and get an 8% or 10% oversize injector. The stock computer will be able to handle it." (This is if you make other power modifications which cause the stock injector to be unable to handle the load.) Conversion to multiple port fuel injection is generally considered more trouble than swapping in a turbo engine.
Bradley_W._Miller wrote: "we have the little blue bottle. (NOS) The ultimate equalizer. A system runs under $400, depending on where you get it. An extra 50-75 hp is about the safe limits, with stock parts. You just have to be careful to keep adequate fuel pressure and not to use it at too low of an RPM. Dropping 2 seconds off your ET with one of these is no problem."
Manifolds
Stefan Mullikan wrote: Pierce Manifolds sells the side draft Weber kits [that fit the 2.2 and 2.5 engines[ as well as the manifolds for our 2.2/2.5 motors. The complete side draft Weber kit from Pierce is $823.20. The side draft Weber manifolds, is $293.24 They can be reached at:
Pierce Manifolds
321 Kishmura Dr.
Gilroy, CA 95020
1-800-874-3728
Camshafts and balance shafts
Taking out the balance shafts from the 2.5 engine is said to provide a very small power gain at the expense of smooth idling.
Gus Thomas wrote: The rumor of increased performance from disconnecting the balance shafts in the 2.5 engine is the result of a tech article by a Chrysler engineer a few years ago. It was re-written by Gary Donovan last year, and put in the SDAC newsletter. He said that 14 HP is gained at 6,000 rpm. How long are you at 6,000 rpm? For less than 1/10 of one percent of your engine's life? You're sure not gonna feel that 14 HP much!
Because frictional losses increase as the square of the increase of rpm, at 3,000 rpm (a real-world everyday rpm) you only gain 3.74 hp (the square root of 14). That's difficult to feel in the seat of your pants. I do it anyway (remove them) because I get slightly better gas mileage, don't whip up the oil as much, and get a little edge when I am at 6,000 rpm at the track. When you're heading into the 11s with a 2,770 lb Acclaim, you need every bit of free help.
åHerb DaSilva suggested that 2.5 owners get a Mopar Performance cam and getting underdrive pulleys from LRE (Lambros) or others.
Bradley W. Miller wrote:
John Basol wrote:
High Energy