Ok, With the increase in questions reaguarding the 1.8L recently, I felt it was in the forum's best interest to have a 1.8L FAQ (We have one for ever other engine, why not this one?) I am going to try to go as detailed in this as possible.
I am going to start this off with what seems to be the most popular question regaurding the 4G37 (1.8L) engine.
1.) What can I do to increase my performance???
To be blunt, there is really only one option to make this engine fast. Turbo. Now mind you, this option is NOT for the faint of heart. It requires A LOT of custom work, researching, time, and most of all, cursing. I will go into more detail with this in another section but for now, let me give you some links to basic bolt-ons that will help a little (And I stress the term "little".)
A.)
Cat-back Exhaust System - The building block for all performance on any car. The very first performance mod you should do. We have all heard of this in one way or another. Weather it's driving down the street only to hear the cry of a "pissed off bumblebee", or learning about it in your college's Fluid Dynamics course. Whatever the reason, you NEED this no matter what your goals are. However, with this said, the type of exhaust you choose will vary depending on your goals and setup choice. The first thing you are going to need is a performance muffler. There is a WIDE variety of these out here, but how do you know which ones actually work? Well, to answer your question, There aren't many. The ones that are pretty popular in the DSM scene tend to be as follows: Magnaflow, Megan Racing, Apexi N1, HKS Ti, Tsudo and off the top of my head that about covers it. I am sure there are more, but the best advice I can give you is simply try to stay away from knock-offs, whether it be from Ebay or elsewhere. The next exhaust piece you are going to want is a high-flow cat (Catalytic Converter.) Again, there are many, many brands of these but the two that people tend to trust most are Magnaflow, and Megan Racing. Both are relatively cheap. The last piece of the cat-back system is the piping. This piece (or pieces if you will) is a VERY touchy subject. The size of pipe you want/need is COMPLETELY dependent on your goals and setup. To simplify things for the sake of this write-up, I will give you two choices. If you plan on staying Naturally aspirated (Non-turbo for the acronym challenged), then I highly suggest going with 2.5" piping. Any more and you will be loosing a lot of back pressure. You need this. If you are going turbo, the I would suggest 3", but if you don't plan on much power, then 2.5" is fine.
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Exhaust Manifold (Header) - Ok, before I go into this I want to make something clear. It is NOT headers!! a 4 cylinder car only has ONE manifold, thus it is called a HEADER!! I get VERY upset when people say this wrong. Why? I have no idea. At any rate, it is far more politically correct to say Exhaust manifold or simply, manifold anyway, so please do us all a favor and try to expand your vocabulary pallet and use this term instead. Now that my rant is finished, on to the point at hand. After much searching and research I have come to a rather unfortunate conclusion. These are rare, very, VERY rare. Your best bet as to getting a manifold that actually does something besides make your engine bay look like 50Cent's teeth, is to have one custom made. The best design for our motors is, hands-down, a tubular design. RP Fabrications (http://www.rpfabrications.com/) makes a very nice affordable manifold. Check them out. Your only other option is to just find an exhaust shop that can mandrel bend pipe and have them make you a tubular manifold using 1.5" pipe for runners. Don't ask me for a price, since it will be different with each shop.
C)
Intake OK. First a little lesson in the types of intakes. There are two major types, short ram intakes (SRI) and cold air intakes (CAI). Theoretically the latter of the two SHOULD make more power due to the fact that colder air yields to better combustion, however the reality of this subject is not too compliant with theory. In small engines it doesn't make enough of a difference to matter. THE BEST intake I have found for the 4G37 is made by a company called Cosmo Racing. It only costs 99.75 USD + shipping and fits nicely.
http://cosmoracing.com/productinfo.asp?cid=131&pid=394D)
Spark Plugs - NGK. 'Nuff said. Go to your local parts store and pick up a set. Not too expensive. Also, the only ones that are available pre-gapped are the BRP6ES-11's, however, if you wish to go colder there are some BRP7ES-11's from other motors that will fit, but they will require you to gap them yourself, however, that is rather easy.
E)
Spark plug wires - Honestly, there really aren't any "performance" plug wires out there. The best advice Ic an give you is to head over to
http://www.sparkplugs.com/ and grab a set of NGK wires. They are pretty much OEM replacement, but NGK have been proven over and over on many different motors and are hands down the best brand out there.
That about covers bolt-ons. I know it isn't much, but do you see now why your only real choice is to boost?
The next part off this section is internal mods. These are probably the hardest mods to do if you do them yourself, however, they are crucial for a turbo build, and will give you some decent gains in a N/A build.
A)
Bore - The factory bore of the 4G37 is 80.5942mm (80.6mm), if you bore this out a bit, you can force some extra ponies out of your block. the MAX I would bore it out is .060 over but even that is pushing it. Any more than that and you will be seeing coolant jackets.
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Forged Pistons - There really are no forged pistons for the 1.8L. However, there are a couple options. Ross and Weisco are both reputable names in the DSM world and both of them are so gracious as to offer a custom piston option. If you give them the specs you want they will fab them up and send them to your door for the small fee of 495 USD. Go ahead, send them a thank you e-mail. You know you want to. Before you go ordering though, I should probably inform you on what you are looking for. If you are going N/A you want some higher compression pistons. If I was truly building a Solid N/A motor and had absolutely NO plans to EVER go turbo, I would probably go with 10:1 or 11:1 pistons. This will allow for hbetter volumetric efficiency and net some decent hp and torque gains. Also note that if you decided to bore your cylinders then you will need to take that into account when ordering. If you plan on going turbo, best bet is anywhere form 8:1 to 9:1. The higher the compression ration, the more power will be output, however, the higher comp ratio, the harder it is to tune and the mores tress is put on your internals.
C)
Stroke - No, this is not what your grandfather suffers after being scared, this is the distance the piston travels in the cylinder. The factory stroke of the 4G37 is 86mm. Aside from a custom made crankshaft (Since there are none available for the 4G37) there is really no way of changing this.
D)
Connecting Rods - The 4G37 rods are actually pretty strong. from the factory, the rods are said to support 300whp, however, if you still want to upgrade, the only real option is to have them custom made. Pauter does some very nice custom rods, but they are rather expensive (~850 USD). Unless you are goin' all out and not leaving a single component untouched, there is no reason that the factory rods won't suffice, however, even if you decide upon this option, I would still recommend getting some new Eagle OEM spec rods. You never know how much life is actually left on your stock rods.
E)
Camshaft -
http://www.importperformanceparts.net/impo...mitsu-cams.html Schneider is the ONLY company that makes camshafts for the 4G37, and event these are simply regrinds. Since, ideally, when it comes to cams you want some that will work all the way to the red line plus a little over the red line, the best option they have is the 3000-7000rpm option. However, this really depends on your personal preference.
F)
Valves/Valve Springs/Retainers - Whenever you go with a different grind cam, it is standard practice to upgrade your valves, springs, and retainers, as well. To my knowledge there are no aftermarket valvetrain components other than camshafts that are supplied for the 4g37, so your only option here is to go custom... again. There are three different materials used in these components:
I) Titanium - This is the best, hands down, however, it is also the most expensive. These are VERY lightweight, thus allowing you to safely rev much higher than you would be able to with other materials.
II) Stainless Steel (SS) - SS is VERY durable, and least prone to breaking, however, because they are SS, they are rather heavy compared to other materials, thus limiting your rev capabilities.
III) Steel - This is what most factory components are made from. it is not as lightweight as titanium, but at the same time it is not as heavy as SS, however, it is also the least durable of all materials.
G)
Port/Polished Head - Since, from the factory, the VE of the 4G37 is only 78% (compared to the 4G63's ~89%), your main focus should be getting this as close to 100% as possible. Something that REALLY helps is porting and polishing the head. the factory size of the intake/exhaust passages of the 4G37's head is 1.25". Most enthusiasts choose to port them out to 1.5" for increased airflow.
H)
Knife-Edged Crankshaft - Since odds are your motor has many miles on it, when rebuilding the motor, you should MAKE SURE to have your crankshaft knife-edged. this will smooth out all of the nicks and scratches on it and make it flawless again, which will help performance a bit and keep your motor running nicely. More of a maintenance mod than a performance mod.
I)
Head Studs - A common practice on ANY built motor is to replace the factory head bolts with aftermarket head studs. Most of you are probably;y asking, "WTF is the difference?", well the difference is this, when you torque down head bolts they expand, thus rendering them useless if you ever remove the head again, meaning you will have to buy new ones. Head studs are stronger and do not expand upon torquing, meaning they will last you forever. The best brand out there is ARP. However, no brands make them for the 4G37, let alone one as prestigious as ARP. There is, however, an alternative. If you drill/tap the holes on the head/block to accommodate for the size of the ARP head studs for the 4G63, you can use them. Just make sure you only drill 3/4" down as the studs are shorter for the 4G63 than the 4G37.
-All rights to this guide belong exclusively to Jon Bonazza. All unauthorized use or reproduction is punishable by law.
4g37(1.8l) Faq Ver. 3.0, READ ME!
Mar 14 2009, 11:10 AM
