fast1.8sohcDSM
This is Kalani's FAQ he posted on DSMTalk, and I thought this would be perfect here, so don't think I wrote it, the credit goes to him:
ginsu417
New DSMtalker
Registered: Sep 2001
Location: Hawaii
Car: 90 Eclipse GS 1.8 Turbo
Turbo 4G37 FAQ (post #1)
- Wake-up Call -
It is not only possible, it's already been done. And I must have heard this a million times...
"But why would you want to do that when you can just sell your car and buy a turbo 4G63 like mine?".
Well @#$% you. I like my car. When's the last time you threw a timing belt and just slid another one on and drove along on your merry way? How much time does your car spend with its hood open? Can you change a clutch in 4 hours?
I'm going to be painfully honest. My motor has been smacked around a lot. It's been driven hard, run out of water, run out of oil, neglected, thrown 2 timing belts, and it just keeps coming back like that ugly chick you got drunk and had a 1 night stand with from the club. I could almost weld the hood shut.
New pistons? Machine work? Everything in the my motor is the same piece it was from the factory. No grinding, no boring, no replacement pistons, valves or rods. Just a standard set of rings, bearings and seals after 140K miles and all that abuse.
Reliability. Part for part, he 4G37 IS more reliable than a 4G63 of the same year. So before I get started, I'm going to be forthcoming with this - if you RACE a turbo 1.8, you defeat the entire purpose of having one, so if you want to race, buy a 4G63T to abuse, and leave some spare parts for us enthusiasts.
- My Research -
After I bought my 4G37, I was looking for ways to improve its performance. In the past 4 years, I must have gone through 9 passes at the local scrap yards in search of matching DOHC heads, and turbo options. After extensive research, many calls to Mitsubishi, Chrysler, part stores, supply warehouses, JDM scrap yards and a few psychiatrists, I was able to scrape together some parts to build a turbo 4G37.
The 84-87 turbo dodge colt and 84-87 turbo mitsubishi mirage came with a turbocharged inline 4-cylinder 4G32 motor. (some 1987s were sold as 1988s and came with that motor as well, depending on where you're from, but that's a shakey area, so I'm going to say '87 since that's when they stopped making them). The sister motor, the JDM G37B, was internally the same motor, but with a larger bore, giving it a displacement of 1.8L. Both of these motors have a lot in common with the 4G37 in your eclipse. In fact, if you wanted to, you coould just bolt one in your eclipse, but I wouldn't recommend it. Back to our history lesson.
For 1988, mitsubishi redesigned the motor, giving it a better flowing head, domed pistons, a dome-top combustion chamber and a few other goodies, prepped it for fuel injection and called it the 4G37. The manifolds from a turbo 4G32 bolt right up. The 4G32 turbo motor took a TC03-9A turbo. If you want to use this manifold, you'll want to have an adapter plate made to bolt up a different turbo. Preferrably a Garrett T3/T4. I was in the process of doing this when I came across a custom manifold (a one-off made by a local shop) for sale on a local board, and decided it would be easier to go that route.
Depending on what turbo and intercooler you buy, you may be able to use intake piping made for the 2.0. The throttle body elbow won't bolt up, but you can find silicone elbows to take its place. Exhaust work will have to be custom. If you lower the compression ratio, you should be able to get at least 15 lbs of boost in there without a problem. As with any turbo conversion, tuning is no longer an option. It's a requirement.
- P r e p -
First thing you need to do is improve the volumetric efficiency of your motor. The 1.8 has a volumetric efficiency of 78%. Meaning that when your piston reaches the botttom of its intake stroke, the air in it is at 78% of atmospheric pressure. DOHC motors run around 85-95% efficiency from the factory. You'll top out around there without sacraficing much driveability if you do it right.
Don't let the turbo 2.0 folks fool you. The 4G37 is choked, starved and chained to the ground from the factory. Simple mods like a 2.5" exhaust system will net much larger performance gains (HP/Liter)than they would on a 4G63. If you don't have a 2.5" system, get one before you go turbo - and a high-flow (or hollowed out) 2.5" cat (unless you plan to just cut it off when you convert to turbo).
Perform the free airbox mod on vfaq.com and remove the silencer. If you haven't replaced the capacitors in your ECU, do it. Unlike the 2.0, the 4G37 still uses distributor ignition. So if your ECU craps out under boost, you may still have ignition and go lean and detonate.
I strongly recommend an engine rebuild at this point, and installing a double head gasket to lower compression. I'm sure people will tell you to just buy different pistons. A head gasket is 15 bucks. The geometry of the combustion chamber, including the domes on the pistons was designed by professionals to keep the charge as cool as possible and keep detonation to a minimum. To lower the compression rate with different pistons, you'd need different shaped piston tops, which aren't going to work the way the thermodynamics engineers designed that combustion chamber to work. Don't go messing with factory engineering, unless you know what you're doing. Double head gasket will get you around 8-8.2:1 depending on the manufacturer.
- P a r t s -
* 4G32 Turbo manifold - This is off the 84-87 turbo mirage or colt. Should be about 40-50 bucks. They're difficult to find, but if you look hard enough you can get your hands on one. It bolts to a TC09A turbo, so you'll need to have it modified or have an adapter plate made to take a different turbo. You'll also want to have it ported and matched to your exhaust ports, because it's way small. The closer you can match the manifold to the exhaust port, the better.
If you can't find a manifold or you can't find someone to make an adapter plate for you, you'll need to have a manifold made. Mine was custom made out of cast iron tubing by a company which is no longer in business. It's more expensive than the 4G32 manifold, but then you don't have to port or modify it.
* Turbo of your choice - Perferrably a garrett. Mitsubishi turbos are great, but not that great. And they're a pain in the ass to pipe. You'd need to run oil and water lines and work with whatever angle the compressor housing happens to open up with. Garrett turbos are more flexible, and you can rotate the compressor housing to suit your angle needs and ease piping pains. Garrett turbos also have thrust bearings from hell and have proven more reliable than the Mitsubishi units.
Unfortunately, I didn't design my setup with "best-fit turbo" in mind. I bought a turbo that was capable of pushing the HP target I wanted and had a compressor map that I thought I could fulfill the air requirements for, and I set out to build my motor to reach that potential. It will be different depending on your exhaust manifold and the modifications to your motor. My exhaust manifold has much larger runners than a 4G32 manifold, and thus a larger turbo was in order.
You'll want a turbo capable of pushing the amount of air your motor will digest but not so big where it takes 5 minutes to spool. A T3-45 trim will work well, but every motor is different. I've heard of a lot of people opting for T28s in thier 1.8s, so that may be a good option as well. You're welcome to try your own combination. There's a java tool at
Ray Hall Turbocharging - Java turbocharger flow map calculator
Bore and stroke are in inches 3.173 x 3.385, use 78% for the VE on a stock motor. Higher after mods. There's common values for intercooler and compressor efficiency on the page. Best match on a compressor map is when your RPM/Boost points are just under the surge limit.
* Wastegate - External is better, but internal is fine. If you don't plan to run a ridiculous amount of boost, and your turbo isn't the size of a peanut (like a T-25) then an internal gate should work just fine. Keep in mind, your motor is not flowing as much as a 4G63T and at a lower RPM (although that can be changed). If you choose an external gate, you'll need to have your manifold machined to accept it. That means grinding down a section and welding in a flange for it - make sure there's room in your engine bay for it (in that location). You don't want to be removing the PS pump or anything to accomodate it.
* Intercooler - Stock one, front mount, doesn't matter. The stock IC will work fine for what you're doing. Your motor won't flow nearly as much as a 4G63 motor because it's smaller and doesn't rev as high. I had a supra MKIV sidemount (way overkill) and lag was horendous. It has since been removed in favor of my "top secret" setup, which is closer to the size of the stock one, only higher flowing. That's all I can tell you about it until it hits the magazines.
* Piping - If you're using the stock intercooler, an aftermarket upper intercooler pipe for the 2.0 MAY work. The upper part that bolts onto the throttle body won't match up but you can get a turbo elbow that will fill the gap. With a little innovative thinking and some turbo couplings you can get an aftermarket upper IC pipe in there without a problem. Don't use the stock one. Aftermarket ones start at about 120.
The lower pipe, you can either have fabricated or use a length of aircraft grade hose. Make sure it's the tough stuff, not radiator pipe. It needs to have that hard treated surface that's heat resistant. It feels almost like canvas. Radiator pipe will just melt and peices of melted rubber will get sucked into your intercooler, where they will dry and clog up the core. Same with the turbo inlet pipe.
* BOV - I can't stress this enough. Stock 1G BOV, or one that routes back to the turbo inlet. Or you'll wonder why you're being left behind. If you vent your BOV to the atmosphere, you're upsetting the air/fuel mixture a LOT. Especially on a 1.8 - enough to drown the motor between shifts. You're also allowing your turbo to spin down. Routing it back to the turbo inlet will keep your turbo in a spool until you open the throttle again. And while ricers with thier loud coughing BOVs drown in turbo lag, you'll see your boost gauge jump from zero, right back to full boost after a shift.
* Fuel Pressure Regulator - You need a rising rate fuel pressure regulator. Don't use the one off the 4G63. That motor has a computer that's designed to accomodate boost. You don't. A rising rate regulator will raise the fuel pressure 1 psi for every psi of boost until the return end of the fuel rail is completely capped and your motor is consuming every drop of fuel the pump is pushing. If you need help hooking it up, let me know. This is only, of course, until you can afford a SAFC and a lot of fuel upgrades.
- C u s t o m W o r k -
* Downpipe. Someone needs to build a downpipe for you. If you're looking to make it easier for them, I'd recommend you get a turbo with an O2 housing. Mine didn't come with the O2 sensor housing, so I had my pipe welded to a custom flange that bolted directly to the turbine outlet. My Exhaust work from the turbo back cost me about $650 in parts and labor, which is about right for custom work here. Where you are, things will be different.
* Oil lines. Use braided steel oil lines. They sell them at hot rod shops. I tapped my oil feed off the place the oil pressure sender screws into. Just screw in a T-fitting behind the pressure sender. The oil return will depend on your turbo. You will need to drill, tap or weld an elbow onto your oil pan for the oil return. If you use an oil cooler, hook it up to the oil return from the turbo. That's where the oil is going to be its hottest. We want it at about operating temperature. Nothing below.
All turbo couplings and oil lines should be sheilded hoses. They aren't available over the counter at most auto part stores, and can be found at performance shops or aircraft supply shops.
No injector or computer mods are necessary for low boost. What is low boost? Subjective. Depends on your motor, ambient temps, etc.
Anything else you want to know, email it.
- Kalani
ginsu417
New DSMtalker
Registered: Sep 2001
Location: Hawaii
Car: 90 Eclipse GS 1.8 Turbo
Turbo 4G37 FAQ (post #1)
- Wake-up Call -
It is not only possible, it's already been done. And I must have heard this a million times...
"But why would you want to do that when you can just sell your car and buy a turbo 4G63 like mine?".
Well @#$% you. I like my car. When's the last time you threw a timing belt and just slid another one on and drove along on your merry way? How much time does your car spend with its hood open? Can you change a clutch in 4 hours?
I'm going to be painfully honest. My motor has been smacked around a lot. It's been driven hard, run out of water, run out of oil, neglected, thrown 2 timing belts, and it just keeps coming back like that ugly chick you got drunk and had a 1 night stand with from the club. I could almost weld the hood shut.
New pistons? Machine work? Everything in the my motor is the same piece it was from the factory. No grinding, no boring, no replacement pistons, valves or rods. Just a standard set of rings, bearings and seals after 140K miles and all that abuse.
Reliability. Part for part, he 4G37 IS more reliable than a 4G63 of the same year. So before I get started, I'm going to be forthcoming with this - if you RACE a turbo 1.8, you defeat the entire purpose of having one, so if you want to race, buy a 4G63T to abuse, and leave some spare parts for us enthusiasts.
- My Research -
After I bought my 4G37, I was looking for ways to improve its performance. In the past 4 years, I must have gone through 9 passes at the local scrap yards in search of matching DOHC heads, and turbo options. After extensive research, many calls to Mitsubishi, Chrysler, part stores, supply warehouses, JDM scrap yards and a few psychiatrists, I was able to scrape together some parts to build a turbo 4G37.
The 84-87 turbo dodge colt and 84-87 turbo mitsubishi mirage came with a turbocharged inline 4-cylinder 4G32 motor. (some 1987s were sold as 1988s and came with that motor as well, depending on where you're from, but that's a shakey area, so I'm going to say '87 since that's when they stopped making them). The sister motor, the JDM G37B, was internally the same motor, but with a larger bore, giving it a displacement of 1.8L. Both of these motors have a lot in common with the 4G37 in your eclipse. In fact, if you wanted to, you coould just bolt one in your eclipse, but I wouldn't recommend it. Back to our history lesson.
For 1988, mitsubishi redesigned the motor, giving it a better flowing head, domed pistons, a dome-top combustion chamber and a few other goodies, prepped it for fuel injection and called it the 4G37. The manifolds from a turbo 4G32 bolt right up. The 4G32 turbo motor took a TC03-9A turbo. If you want to use this manifold, you'll want to have an adapter plate made to bolt up a different turbo. Preferrably a Garrett T3/T4. I was in the process of doing this when I came across a custom manifold (a one-off made by a local shop) for sale on a local board, and decided it would be easier to go that route.
Depending on what turbo and intercooler you buy, you may be able to use intake piping made for the 2.0. The throttle body elbow won't bolt up, but you can find silicone elbows to take its place. Exhaust work will have to be custom. If you lower the compression ratio, you should be able to get at least 15 lbs of boost in there without a problem. As with any turbo conversion, tuning is no longer an option. It's a requirement.
- P r e p -
First thing you need to do is improve the volumetric efficiency of your motor. The 1.8 has a volumetric efficiency of 78%. Meaning that when your piston reaches the botttom of its intake stroke, the air in it is at 78% of atmospheric pressure. DOHC motors run around 85-95% efficiency from the factory. You'll top out around there without sacraficing much driveability if you do it right.
Don't let the turbo 2.0 folks fool you. The 4G37 is choked, starved and chained to the ground from the factory. Simple mods like a 2.5" exhaust system will net much larger performance gains (HP/Liter)than they would on a 4G63. If you don't have a 2.5" system, get one before you go turbo - and a high-flow (or hollowed out) 2.5" cat (unless you plan to just cut it off when you convert to turbo).
Perform the free airbox mod on vfaq.com and remove the silencer. If you haven't replaced the capacitors in your ECU, do it. Unlike the 2.0, the 4G37 still uses distributor ignition. So if your ECU craps out under boost, you may still have ignition and go lean and detonate.
I strongly recommend an engine rebuild at this point, and installing a double head gasket to lower compression. I'm sure people will tell you to just buy different pistons. A head gasket is 15 bucks. The geometry of the combustion chamber, including the domes on the pistons was designed by professionals to keep the charge as cool as possible and keep detonation to a minimum. To lower the compression rate with different pistons, you'd need different shaped piston tops, which aren't going to work the way the thermodynamics engineers designed that combustion chamber to work. Don't go messing with factory engineering, unless you know what you're doing. Double head gasket will get you around 8-8.2:1 depending on the manufacturer.
- P a r t s -
* 4G32 Turbo manifold - This is off the 84-87 turbo mirage or colt. Should be about 40-50 bucks. They're difficult to find, but if you look hard enough you can get your hands on one. It bolts to a TC09A turbo, so you'll need to have it modified or have an adapter plate made to take a different turbo. You'll also want to have it ported and matched to your exhaust ports, because it's way small. The closer you can match the manifold to the exhaust port, the better.
If you can't find a manifold or you can't find someone to make an adapter plate for you, you'll need to have a manifold made. Mine was custom made out of cast iron tubing by a company which is no longer in business. It's more expensive than the 4G32 manifold, but then you don't have to port or modify it.
* Turbo of your choice - Perferrably a garrett. Mitsubishi turbos are great, but not that great. And they're a pain in the ass to pipe. You'd need to run oil and water lines and work with whatever angle the compressor housing happens to open up with. Garrett turbos are more flexible, and you can rotate the compressor housing to suit your angle needs and ease piping pains. Garrett turbos also have thrust bearings from hell and have proven more reliable than the Mitsubishi units.
Unfortunately, I didn't design my setup with "best-fit turbo" in mind. I bought a turbo that was capable of pushing the HP target I wanted and had a compressor map that I thought I could fulfill the air requirements for, and I set out to build my motor to reach that potential. It will be different depending on your exhaust manifold and the modifications to your motor. My exhaust manifold has much larger runners than a 4G32 manifold, and thus a larger turbo was in order.
You'll want a turbo capable of pushing the amount of air your motor will digest but not so big where it takes 5 minutes to spool. A T3-45 trim will work well, but every motor is different. I've heard of a lot of people opting for T28s in thier 1.8s, so that may be a good option as well. You're welcome to try your own combination. There's a java tool at
Ray Hall Turbocharging - Java turbocharger flow map calculator
Bore and stroke are in inches 3.173 x 3.385, use 78% for the VE on a stock motor. Higher after mods. There's common values for intercooler and compressor efficiency on the page. Best match on a compressor map is when your RPM/Boost points are just under the surge limit.
* Wastegate - External is better, but internal is fine. If you don't plan to run a ridiculous amount of boost, and your turbo isn't the size of a peanut (like a T-25) then an internal gate should work just fine. Keep in mind, your motor is not flowing as much as a 4G63T and at a lower RPM (although that can be changed). If you choose an external gate, you'll need to have your manifold machined to accept it. That means grinding down a section and welding in a flange for it - make sure there's room in your engine bay for it (in that location). You don't want to be removing the PS pump or anything to accomodate it.
* Intercooler - Stock one, front mount, doesn't matter. The stock IC will work fine for what you're doing. Your motor won't flow nearly as much as a 4G63 motor because it's smaller and doesn't rev as high. I had a supra MKIV sidemount (way overkill) and lag was horendous. It has since been removed in favor of my "top secret" setup, which is closer to the size of the stock one, only higher flowing. That's all I can tell you about it until it hits the magazines.
* Piping - If you're using the stock intercooler, an aftermarket upper intercooler pipe for the 2.0 MAY work. The upper part that bolts onto the throttle body won't match up but you can get a turbo elbow that will fill the gap. With a little innovative thinking and some turbo couplings you can get an aftermarket upper IC pipe in there without a problem. Don't use the stock one. Aftermarket ones start at about 120.
The lower pipe, you can either have fabricated or use a length of aircraft grade hose. Make sure it's the tough stuff, not radiator pipe. It needs to have that hard treated surface that's heat resistant. It feels almost like canvas. Radiator pipe will just melt and peices of melted rubber will get sucked into your intercooler, where they will dry and clog up the core. Same with the turbo inlet pipe.
* BOV - I can't stress this enough. Stock 1G BOV, or one that routes back to the turbo inlet. Or you'll wonder why you're being left behind. If you vent your BOV to the atmosphere, you're upsetting the air/fuel mixture a LOT. Especially on a 1.8 - enough to drown the motor between shifts. You're also allowing your turbo to spin down. Routing it back to the turbo inlet will keep your turbo in a spool until you open the throttle again. And while ricers with thier loud coughing BOVs drown in turbo lag, you'll see your boost gauge jump from zero, right back to full boost after a shift.
* Fuel Pressure Regulator - You need a rising rate fuel pressure regulator. Don't use the one off the 4G63. That motor has a computer that's designed to accomodate boost. You don't. A rising rate regulator will raise the fuel pressure 1 psi for every psi of boost until the return end of the fuel rail is completely capped and your motor is consuming every drop of fuel the pump is pushing. If you need help hooking it up, let me know. This is only, of course, until you can afford a SAFC and a lot of fuel upgrades.
- C u s t o m W o r k -
* Downpipe. Someone needs to build a downpipe for you. If you're looking to make it easier for them, I'd recommend you get a turbo with an O2 housing. Mine didn't come with the O2 sensor housing, so I had my pipe welded to a custom flange that bolted directly to the turbine outlet. My Exhaust work from the turbo back cost me about $650 in parts and labor, which is about right for custom work here. Where you are, things will be different.
* Oil lines. Use braided steel oil lines. They sell them at hot rod shops. I tapped my oil feed off the place the oil pressure sender screws into. Just screw in a T-fitting behind the pressure sender. The oil return will depend on your turbo. You will need to drill, tap or weld an elbow onto your oil pan for the oil return. If you use an oil cooler, hook it up to the oil return from the turbo. That's where the oil is going to be its hottest. We want it at about operating temperature. Nothing below.
All turbo couplings and oil lines should be sheilded hoses. They aren't available over the counter at most auto part stores, and can be found at performance shops or aircraft supply shops.
No injector or computer mods are necessary for low boost. What is low boost? Subjective. Depends on your motor, ambient temps, etc.
Anything else you want to know, email it.
- Kalani
...my 1.8 succed butt...
