Engine Discussion (also a little bit of hybrid talk).

[EJ22D]

EJ20: This engine was stuffed into every mainstream Subaru car since 1989. This 2.0L engine comes in both DOHC and SOHC, open and closed decks, as well as being available in turbocharged and N/A formats. It has a 92mm bore and a 75mm stroke. This is the first engine of the EJ family to be produced by Subaru. It has proven to be a very durable engine in some variants, and temperamental in others. A good engine overall. The crankshaft and rods in these engines are forged.

EJ22: This engine comes in a few variants and was also stuffed into almost every mainstream car that Subaru produced in the 90's. Only TWO variants came turbocharged with closed deck blocks (EJ22T and EJ22G, which is a bored out EJ20G closed deck RA block). The rest, designated with "E" or "1, 2, 3" as the fifth digit, were all naturally aspirated engines. They all had a 96.7mm bore and a 75mm stroke, as they shared crank and rods with the EJ20 series. They are 2.2L. This engine series is known as one of the toughest to ever come out of Subaru.

EJ25: This engine is the overstroked/overbored variant of the EJ20 yet literally so different that it can be considered it's own machine. They had a 99.5mm bore and a 79mm stroke. The crankshaft and rods used were totally different from the EJ20's, the crank being heavier. This engine never came in a closed deck format. It DID come in DOHC/SOHC, turbocharged/naturally aspirated, and open/semi-closed deck formats. This engine was either REALLY good or REALLY bad, as it is known to develop horrific bearing and piston clearances over time, as well as blown head gaskets, which can create more trouble than one is willing to spend to fix.

[EJ22D]

Now that the basics are out of the way, let's talk. There are many builders out there who are stuck on a specific engine. Here, I will be speaking stock engines, hybrids, and the pros and cons. First off, when one speaks of an upgrade, jumping from an EJ20 to an EJ25 is NOT always the answer for more power. Same goes for having DOHC. These engines are like legos, as most on this forum already know. That being said, let's talk about stock engines first.

Stock engines: These are the engines that are untouched, meaning no head or internal swap. You can usually upgrade these engines to get the most out of them and they almost always perform really well...until they reach their powerband limits and no matter what you do, you cannot exceed them, as they will only do what they can within engine design. If you are going to mod a stock engine, you need to be aware of those limits and know that even if you use stronger internals, that engine will continue to respond a certain way, even with more power.

Hybrid engines: This is the ONLY WAY to exceed a stock engine's powerband limitations. An example of a hybrid built engine would be EJ20 crank/EJ25 block/EJ22 head or EJ20 head/EJ22 block/EJ25 crank. If you know what to do to make your hybrid perform the way you want it to, then you can build a whole new kind of hybrid that has the pluses and minuses of stock engines, or just purely pluses, which can be a hard thing to accomplish, depending on what parts you decide to use in your hybrid build. Done correctly, your hybrid build will be an amazing machine that will last a long time. Done incorrectly, your hybrid will last anywhere from 10 seconds to 10 months. Again, hybrids are just that, engines that use a mixture of parts that help it all come together and become better than their original engines.

[EJ22D]

EJ20/EJ22 vs EJ25:
There is usually a lot of debating on which engine is "better" to use for a build. Well, let's start with the EJ22, which is pretty much an overbored EJ20. These blocks have internals which are capable of turning the same high rpm as EJ20s, although they have a bigger bore, which means they can make more power turning the same rpm as an EJ20 and respond even faster, as the crank weight remains the same (the crank is shared with EJ20). Now, lets start with the EJ25. The EJ25 is NOT capable of turning the same rpm as the EJ20/EJ22 and though it can produce more low end TQ, because of the crank's longer stroke and heavier weight, it requires more air/fuel/spark to produce power.

Example, if one were to build an EJ22 with DOHC heads and pit it against an EJ25 DOHC, it would lose out in a power struggle, by a lot less than one would think, but it would win in an area of smoothness and overall operation. The EJ25 crank is known to create vibration at high rpm, causing imbalance, which the EJ22 crank does not. Also, since it takes more air/fuel/spark to run the EJ25, it would also lose out on efficiency to the EJ22, since not nearly as much energy is needed to run or spin the EJ22 up to high rpm. But, this doesn't mean that the EJ25 is out of luck. Not by a long shot. Because the internals are beefier, it will exceed an EJ22, slightly or greatly, depending on build goals.

When built properly for power, an EJ25 can turn high rpm and produce great power, provided that the internals are balanced and fortified for the targeted rpm/power goals. The one thing that the EJ25 will never have over the EJ20/EJ22 is cylinder wall strength. If it is not sleeved, had the deck pinned or closed, then the EJ25 cylinder walls will be weaker than the EJ20/EJ22's, due to them being slimmer and less rigid. Yes, 2.6mm can make a huge difference when pushed that far and makes the EJ25 weaker in structure when compared to the EJ20/EJ22, which means that it can't be pushed as hard in stock form. The EJ25 barters in a lot for low-end TQ, which is pretty much what it was only designed for, starting in the 90's.

Now, one could easily get around the physical limitations of the EJ20/EJ22/EJ25 and place the EJ25 crankshaft in an EJ20/EJ22. This will cause those engines to take in more air per stroke, which will lead to more power. Unfortunately, since the weight of the EJ25 crank is involved, this will also lead to more fuel consumption and a less available top rpm limit, as the weight of the crank will cause disharmonic vibration. Likewise, one could put an EJ20/EJ22 crank in an EJ25 and though low-end TQ will be lost somewhat, higher rpms will be possible to achieve and less energy will be needed to make that hybrid turn them. There is far more to hybrid building than just bottom end part swapping, however...

[kanner95bk]

Great post, thanks for the insight. Sticky?