AE86 Resource for DIY Tips, Tricks, OEM Part Numbers, Technical Info and MORE!!!!

Unknown

Cool Read From "Initial D World" on Facebook explaining the origin of the Fujiwara Tofu Shop.
https://www.facebook.com/photo.php?fbid=735086676507000&set=a.281008241914848.89842.280996181916054&type=1

Initial D World

We've done this topic several times in the past. Since we've gained some new fans recently, we thought it's a good time to revisit this topic. We've researched a bit more in-depth this time, so please have a read even if you followed this page for a long time!

The story of the tofu shop started in the 1920s. It was originally called「藤野屋豆腐店」(Fujino Store Tofu Stop,) named after the 藤ノ木 (Fujinoki) family. Like the name suggests, the tofu shop is a family business that was pass on through generations. 藤ノ木五十吉 (Fujinoki Isokichi) has inherited the shop from his father and operated the business for past several decades.

Through the years, the Fujinoki's ran a successful business of hand-made fried tofu and lived a quiet lifestyle. According to Fujinoki, he would wake up at 3:00am every day and worked throughout the day 'til 7:00pm when he closes the store. It was hard work. The introduction of Initial D in 1995 depicts a Fujiwara Tofu Shop that we are all familiar with. The Fujiwara Tofu Shop shown in Initial D looks very similar to Fujinoki's store. Fans of the series nearby started to take notice of Fujinoki's tofu shop. It started to became popular among a small group of people.

In 2005, the Initial D Live Action film crew found Fujinoki's tofu shop and negotiate with him to have the sign changed into「藤原豆腐店」(Fujiwara Tofu Shop.) The crew only stayed there for five days to film the footage because they only had to film the outside of the shop. After the movie crew left, Mr. Fujinoki was free to change it back to the original signage. He decided against that and boy was that a smart move.

With the debut of Initial D Live Action, the popularity of Fujinoki-san's tofu shop shot up like a rocket. Fans of the series from all over Japan would visit his shop and did many photo sessions in front of the shop. It literally became the "holy place" for Initial D fans to go to, just like a pilgrimage.

Unfortunately, Mr. Fujinoki's health condition deteriorates rapidly after 2006. He fell ill and passed away in 2008. Fujinoki-san did not have any sons, so the family business was passed onto his wife 美津恵 (Mitsue) temporarily. It just wasn't the same with her husband not around. The shop would be closed most of the time. Mrs. Fujinoki finally decided to close the store for good by late 2009 after being informed that the city was planning to redevelop the area and the tofu shop was one of the targets for demolition.

The tofu shop was demolished by early 2010. Many fans were very disappointed when they found out the shop no longer exists. It was a difficult moment for many to accept. Even knowing the shop no longer exists, many fans still visited the place. It is just an empty land with patch of weeds and gravel.

Fujinoki's eldest daughter 吉野圭子 (Keiko Yoshino) always wanted to see her father's tofu shop restored somewhere else. On September 17th, 2012, with the help of the director of Toy, Doll & Car Museum and the owner of カーランド "Carland", they were able to restore the storefront of the Fujiwara Tofu Shop along with a fully-functional AE86 donated by 得知雅人 (Masahito Tokuchi,) the owner of Carland.

The museum opens to the public on a daily basis. Be sure to check out the link below for direction. As a die-hard Initial D fans, I will definitely visit the museum when I visit Japan in the future. However, I will also visit that empty land that once stood the legendary Fujiwara Tofu Shop (or should I say Fujino Store Tofu Shop.) It's a holy land that gave birth to many young dreams. It must be a humble feeling to find the root of something that has influenced so many young people worldwide in the past two decades.

| Museum Address |
» 〒370-3606 群馬県北群馬郡吉岡町上野田2145
» TEL: 0279-55-5020
» Google Maps: http://goo.gl/maps/wG43w

| Original Tofu Shop Address |
» 群馬県渋川市渋川寄居町2167
» Coordinate: N 36°29'49.02" E 139°00'9.60"
» Google Maps | http://goo.gl/maps/ese1y
» Street View | http://goo.gl/maps/bZ4UZ

| Work Cited |
» 伊香保の博物館に「藤原とうふ店」を再現 | http://auto.hobidas.com/auto/carnews/article/133846.html
» 永远消失的「藤原豆腐店」| http://www.17utt.com/2012/0912/14173.html
»「頭文字Ｄ」のロケ地 | http://cass.jam.tc/taiwan/jayid1.html
» TOFU NO MORE: The real Initial D “Fujiwara Tofu Ten” location |http://noriyaro.com/?p=5461
» 館長のひとりごと : イニシャルD | http://blog.livedoor.jp/splendore_ikaho/archives/51674290.html
» 頭文字Ｄの旅（秋名編）| http://minkara.carview.co.jp/userid/651574/car/608610/2114066/photo.aspx
» 栃木エリアＤ峠ドライブツアー | http://plaza.rakuten.co.jp/777shootingstar/17000

Unknown

Extremely helpful webpage with "How To" and Part Number info.

http://www.toyodiy.com/tech/diy_toyota-corolla_engine.html

Unknown

This is a list of door hinges that share the same part number as the AE86. These may be easier to find at your local junkyard then AE86s tend to be.

Lower Hinge on the AE86 has the same part number as the following vehicles:

Front door lower hinge, 1983-86 Tercel (AL2#)
Front door lower hinge, 1984-87 Corolla (CE80, AE82)
Front door lower hinge, 1985-88 Cressida (MX7#)
Front door lower hinge, 1983-86 Camry (SV11, CV10)

Upper Hinge on the AE86 has the same part number as the following vehicles:

Front door upper hinge, 1983-86 Tercel (AL2#)
Front door upper hinge, 1983-86 Camry (SV11, CV10)

Unknown

http://www.billzilla.org/4agstock2.htm
4AGE manifolds
INLET MANIFOLD - 16 Valve
The big port heads, apart from the supercharged 4AGZE's, all use the TVIS (Toyota Variable Induction System) to improve the low to mid range torque. What it does is shut down half of each inlet port with a set of small butterflys to make the airflow go into the inlet port itself a lot faster. Certainly, with a stock engine the low end performance is noticably decreased when it's disconnected.
Here's a diagram of the system

You can just see the small butterflys in every second port in the Air Control Valve plate The TVIS is operated by a small vacuum powered device that sits under the inlet manfold, and the vacuum source for this is provided by a computer controlled air solenoid, that get's the vacuum source from the inlet manifold. When the engine isn't running, the TVIS isn't working, and so the butterflys are in the open position. When the engine starts, the computer sends a signal to the electrical solenoid, with then passes on the inlet vacuum to the TVIS vacuum solenoid, which then shuts the butterflys. So, if you want to try the engine to see what it's like without the TVIS, all you have to do is to pop the vacuum hose off (and block it) and the TVIS will stay open.
The computer signals for the TVIS to operate at 4,400rpm - above that rpm the butterflys are open, and vice-versa. At that rpm, the amount of power that the engine makes is the same with the TVIS open or closed, so you don't feel any increase in power when the system operates, though there is an increase in induction noise.
(Note that even with the TVIS completely removed, as with my current 4AGE, the 4AGE still changes note quite a lot at around those rpm's)
The small port inlet manifold has no TVIS, and so is a conventional plenum/runner type manifold, though it only comes in FWD configuration.
The RWD inlet manifolds all have the throttle body system at the front end of the engine, with the FWD's at the other end. There is basically no other differences with them.
For what it's worth, a reasonably common mod is to fit a small port engine to an AE-86, and to do this the FWD manifold is modified so that the throttle body is at the 'other' (front) end. This takes a fair bit of cutting & welding, but seems to be worth the cost and effort

Here's a friends 4AGE small port engine that has had the FWD inlet manifold converted to be a RWD manifold. You can see the extensive welding that's been done to make all that happen. There's a cap that's been welded onto the other end to block the hole up.

The inlet throttle butterfly is 55mm in diameter, and will flow more air than any amount of power that you can get out of the 4AGE with the factory inlet manifold, so there is no need whatsoever to fit a larger one, as some people do. I have seen a report on a dyno run that shows an engine with a 60mm throttle body fitted - ~20% more throttle area - making about 1 - 2hp more, which is more likely to be dyno error than anything else.
At the bottom of the throttle body is a wax pellet type of 'cold idle up', and it has engine water running through it so that when the water is cold the device lets an additional amount of air pass into the inlet manifold to keep the idle speed normal. As the water and wax warms up, the device passes less and less air, until the engine is fully warm. They tend to be a bit unreliable when they get old, and often need replacement.
The other occasional problem with the 16v throttle bodies is that people do not allow a little bit of slack in the throttle cable with the accelerator full-down, and this puts a strain on the cable and throttle body - I've seen a few break because of it so please mack sure that you're not loading up the throttle body like that.
INLET MANIFOLD - 20 Valve
Very good indeed - They have a single throttle butterfly for each cylinder, and so are about as good as a very good racing inlet system.
Hot property, they are!
One slight problem though, if you want to fit one to your 16v - They won't bolt on and so require an adaptor, and more importantly they have ZERO inlet manifold vacuum, so the computer won't work ... An aftermarket add-on using TPS (Throttle Position Sensing Vs rpm) only for the 16v's.
(That being said, I've read a few reports from various people that say that they've gotten the stock 16v computer & 20v inlet manifold to work together okay)
EXHAUST
The factory exhaust manifold is very good with all types, both FWD & RWD, and up to about 200hp they are better than just about every aftermarket exhaust manifold available. They are a 4-2-1 design, and all types fit all the engines, with the exception of the 20v manifold, which has the two bolt holes on the extreme ends in a slightly different place to the 16v ones. But - by slotting the holes on the 16v manifolds, they can be made to fit quite easily on a 20v; usually this is done to convert a 20v to a RWD car. You'd be far better off getting things such as lightweight flywheels, etc, to improve performance, as the engine will definitely benefit from these, rather than one of dubious increase at best ...

4AGE Blocks
There are basically two types of 4AGE blocks; The ones that are just single cam blocks used for twin cam work and have three ribs on the side, and the small port, 4AGZE, and 20v blocks which have seven ribs. The three rib blocks can only been overbored a small amount, roughly 1mm or 0.040", (82mm total) and the seven rib blocks can sometimes (but not always) go a bit further to 2mm or 0.080". (83mm total) An important note though is that the bigger the bore and/or the more power the engine is making, the more blow-by you'll be getting. I doubt if it's worth boring the block out to try to get more capacity for that reason.
The 20v blocks have a slight bend in one side, along the section where the sump bolts on., so that a 16v sump won't bolt straight on. But with some small mods they can be made to fit, I've heard.
The seven rib blocks on the small port 4AGE's also have an oil return pipe on the right-rear from the back of the head. The 4AGZE's & 20v's have the 'bump' in the block for that hole, but it's solid cast metal there instead.
Another good feature of the seven rib blocks is that they have an oil-squirter system that pumps oil onto the bottom of the pistons, thus helping cool them.
There's no other significant differences between all the blocks.

4AGE block, crank, con-rods, and pistons 4AGE Cranks, con-rods, and pistons
There's two types of crankshafts available; They both have the same size main bearings, but the 'lightweight' or 'small' one has 40mm con-rod bearing sizes, with the other 'big' one having 42mm bearings. The 'small' crank only comes with the TVIS engines, and vice-versa - The 4AGZE and the 20v engines all have the 42mm crank.
Both cranks are extremely strong, and only break with quite a bit of mis-treatment. The 40mm crank weighs about 11kg and the 42mm crank about 11.7kg.
As there is two types of crankshaft, there are also two types of con-rods; One 'big', one 'small'. (42mm and 40mm) Note that the 'big' con-rods are quite a bit heavier than the 'small' con-rods, and also have 20mm gudgeon pins Vs the 'small' con-rods 18mm gudgeon pins. Again, both types are very strong and give no trouble at all.

In this picture, you can see a 'small' con-rod, which has a small hole drilled in the side to lubricate and cool the piston, and on the left an AE-101/111 rod, which has a slot milled in the side, Cosworth style. If you look carefully, you can see the different sizes of the big-end and gudgeon pin bearings.

There are bascially three types of pistons - One for the 16v naturally aspirated, 20v, and supercharged 4AGZE. The 16v ones come with 18mm and 20mm gudgeon pins, (18mm = TVIS only) the 20v are 20mm and have three flycuts for the three inlet valves, (all 4AGE pistons have flycuts for each valve though) and the 4AGZE shares the 20mm gudgeon pin diameter. The 4AGZE pistons have a lower deck height to give a lower compression, and are also ceramic coated on the tops to improve heat rejection.
All these pistons give no trouble in regular service, though they are of the slotted type with the oil return ring groove, thus are weaker than the 'drilled' type. They are also cast rather than forged, (though the 4AGZE's are forged) and so if you are planning on increasing the power of your 4AGE by more than, say, 30hp then you would do well to get a set of aftermarket, eg, Wisco, pistons to make sure that you don't have any trouble.
FWIW, I have run my dead stock 4AGE up to 8500rpm without any troubles from the internals.

Unknown

Borrowed From
http://www.billzilla.org/4agstock.htm

The Stock 4AGE Description Page In this page I talk in some detail about the different types of 4AGE, and a little about which cars they come in.
The Toyota 4AGE engine started life in 1983 as a logical progression from the 2A and 3A single cam engines. There was also the single cam 4A-C engine, which initially shared an identical block & very similar internals as the twin cam version. The 4AGE soon progressed to having stronger internals, and so they diverged from there.
The twin cam 4AGE is basically a road going, mass produced version of the Ford Cosworth BDA twin cam racing engine. They share the same bore and stroke (81mm x 77mm), the same size valves (29.5mm & 25.5mm), and in some versions of the 4AGE very similar port shapes & sizes. When fully prepared for racing, they both produce similar hp figures at similar revs, so it would seem that Toyota has done an excellent job with them.

This is a 2 litre BDA ( B elt Driven, series A engine), which is basically identical to the 1.6 litre BDA. The parallels continue - The 4AGE is the first twin cam that Toyota made with a rubber drive belt for the camshafts, as was the BDA. The 4AGE was a development of the single cam 2A, 3A. & 4A engines, but I guess Toyota must have planned to make the 'A' series engine into a twin cam, perhaps again following the 'A' series Cosworth engines.

Quick link on this page to -
- The first 4AGE, RWD & FWD
- Brief summary of the different types
- 4AGE heads
Next page -
- 4AGE manifolds, 4AGE blocks, 4AGE cranks, con-rods, and pistons
On the last page -
- 4AGE oil system, 4AGE water system, 4AGE EFI, 4AGE other stuff
The total variants of the 4AGE are, to the best of my knowledge -
- Very early big port TVIS 16 valve, with black lettering & 6-bolts holding the flywheel on.
- Big port TVIS FWD/RWD 16 valve, usually with blue lettering on the cam cover and 'TVIS' on the inlet plenum.
- Big port TVIS FWD 16 valve, with red lettering. They have a seven-rib block with oil-squirters.
- Small port non-TVIS FWD valve.
- Silvertop 20 valve. Early & late type, minor variations in inlet system & VVT operation.
- Blacktop 20 valve.
- Early supercharged 4AGZE, low compression big port head, distributor.
- Mid-aged supercharged 4AGZE, higher compression big port head, crank angle sensor type ignition.
- Late supercharged 4AGZE, higher compression small port head, crank angle sensor type ignition.
More information on these engines below.

The first 4AGE, RWD & FWD
Anyway, the 4AGE started life as a twin cam head fitted to the single cam bottom end, though the crank was a bit stronger, the pistons also stronger, and a windage tray fitted between the sump and the block. The clutch and clutch plate are identical as the single cam 4A model.
The versions with MAP (Manifold Absolute Pressure) sensors make 127hp in standard trim, and red-line at 7700rpm. Some countries have the AFM (Air Flow Meter) sensor versions, which make 115hp. So how to tell the two apart? Well, the MAP sensor versions have a small black box that is attached to the inlet manifold by a rubber pipe. (This pipe lets the sensor sample the inlet manifold air pressure) The MAP sensor usually sits on the firewall, and looks like this -

And here's the AFM type, where the AFM sits between the throttle body and the air cleaner. The AFM is simply a sprung flap that swings back more and more as the engine sucks more air, thus making more power.

This is the Air F low Meter on an MR2

Brief summary of the different types
4AGE's come in both front and rear wheel drive form, and although they are very similar, there are a number of small differences that make swapping them over not quite as easy as it would first seem. I won't be getting into that area, as a good friend of mine, Phil Bradshaw, has already written an excellent pageon doing just that. Please note that the engine types described here in the next few page are of Japanese production, other countries may vary on these specs slightly.
With the RWD types, they came out in big port versions only - no small ports - in basically two types as mentioned in the previous paragraph. These can be found in the AE-86 Corolla and AA-63 Celica, with the AFM one having 115hp and the ones with MAP sensors having 127hp. The FWD ones are much the same, coming in the AE-82 Corolla, but with the AE-92 Corolla the small port 4AGE (non-TVIS) made its debut, with 100kw or 134hp.
Two odd types -
- I have also heard that there was a very early (1983) and now rare 4AGE TVIS FWD that had black lettering on the cam cover, but the main difference is that the crank only has six flywheel bolts verses all the other 4AGE's that have eight and so it looks like it has a 4A-C single-cam type crankshaft.
- Another odd 4AGE is one that has red lettering on the top, is fitted with TVIS & a big port head, but has a seven-rib block & a 42mm bearing crank. There are much easier to find around the world. They also appear to have no oil squirters on the inside of the block, unlike the regular small port types which do.

With the arrival of the AE-101, things changed a great deal; The naturally aspirated 16v 4AGE was no more - replaced by the new 20v 4AGE - and another newcomer was the supercharged 4AGZE. The 20v started with a claimed 165ps and the blown 16v 145hp, though the 'Z' had a great deal more torque, but was a lot less 'revvy'.
The AE-101 came with the slightly improved claimed 170ps 20v 4AGE, and there was also the options of two 4AGZE's, both with 165ps. (The later one having an integrated ignition coil pack system)
Many people seem to define the different types of 4AGE by the colour of the letters on the cam cover, but I think that this is not a reliable method, as from what I've seen different countries have different colours, cam covers have been repainted, and sometimes swapped. I only recognise the different types by them being a big or small port, RWD or FWD, AFM or MAP, and the number of valves.

4AGE Head Types
There are two types of 16 valve heads, and the one 20 valve - The majority of 16v 4AGE's have what's called the 'big port' head, and the remainder (only found on the AE-92 FWD Corolla) have the 'small port' head. The small port head is the prefered type for performance in a road car, as they are easier to get up to about 200hp out of. (More than about 200hp the big port is best)
Here's a pic of the big port head

And another of the small port

And to compare the two properly, here's both together. Note that these pictures where taken from slightly different angles, and so the port divider isn't the same position in the top & bottom of the picture, but the actual port faces relative to each other are pretty much correct

This is what the combustion chambers look like ...

... and they are quite efficient, able to make a good 100hp/litre with very few mods

Here is a cross-sectioned 16v head The rest of the head is much advanced over the 'old' BDA, in that it is a single piece design and it also doesn't require to have the camshafts removed to get to the shim adjusters when working on the valve clearances. (The BDA's head comes in two large pieces, and it splits horizontally just below the cam bearings to make it possible to get to the shim adjusters. This makes the head castings a LOT more expensive, less accurate, and potentially unreliable)
The 4AGE's use a 'shim over bucket' system for valve clearances, and by doing this it allows you to alter the valve clearances without removing the cams, unlike just about every other twin cam engine. Note that Toyota want you to use a 'special tool' to get the shims in & out with, but it's easy enough to do it with a couple of small screwdrivers to push the bucket down with.

16v 4AGE head, completely dissasembled 16v 4AGE heads specifications -
- Valve included angle (angle between the inlet and exhaust valves) - 45°
- Minimum valve spring seat pressure to allow for 7,700rpm - 35lbs, or 16kgs
- Inlet valve diameter - 29.5mm
- Exhaust valve diameter - 25.5mm
- Both valves have 6mm diameter stems.
- Cam bucket diameter 28mm, shim diameter 25mm

Cam Timings - (Japanese spec)	Inlet Cam	IVO BTDC	IVC ABDC	Duration	Lift (mm)
'Big port'		9°	51°	240°	7.56
'Small port'		8°	44°	232°	7.1
4AGZE		8°	44°	232°	7.1
	Exhaust Cam	EVO BBDC	EVC ATDC
'Big port'		51°	9 °	240°	7.56
'Small port'		44°	8°	232°	7.1
4AGZE		44°	8°	232°	7.1

The 20v head is a very different beast indeed!
The obvious difference is that they have three small inlet valves instead of the more common two. This is intended to give the engine better breathing, and as the 20v is about 145hp it seems to work. For lots more pictures of the 20v head, please check out the second page of my 4AGE Mods page.

The other differences are that the inlet port has a much better angle onto the inlet valves, and that the valve included angle is a good 10° less than the 45° of a 16v head, which is a good thing for making power. The exhaust side of things are very similar.

20v 4AGE head specifications -
- Valve included angle (angle between the inlet and exhaust valves) - 35° (I think ...)
- Inlet valve diameter - 26.5mm
- Exhaust valve diameter - 26mm
- Both valves have 5mm diameter stems
- Cam bucket diameter 23mm, with very small shims between the valve stem top & bucket

Cam Timings - (AE101)	Inlet Cam	IVO BTDC	IVC ABDC	Duration	Lift (mm)
VVT <4400rpm & >~7000rpm		0°	70°	250°	7.97
VVT >4400rpm		30°	40°
	Exhaust Cam	EVO BBDC	EVC ATDC	250°
		54°	16°		7.6

Cam Timings - (AE111)	Inlet Cam	IVO BTDC	IVC ABDC	Duration	Lift (mm)
VVT <4400rpm & > ~7000rpm		5°	65°	250°	8.2
VVT >4400rpm		35°	35°
	Exhaust Cam	EVO BBDC	EVC ATDC
		54°	16°	250°	7.6

Unknown

Borrowed from
http://www.sr20-forum.com/information-library/34413-crank-case-ventilation-fully-explained-naturally-aspirated-edition.html

Crank Case Ventilation fully explained. (Naturally aspirated edition.)

If you're reading this you've likely asked a question about crank case ventilation, catch can placement, correct PCV hose routing, or similar.
Grab yourself a beverage of your choice, sit back and relax. Keep reading to have all of your questions answered.

To understand what you're doing when you modify or repair the factory crank case ventilation system you should know how the factory systems works first before diving into modifying it or fixing it. It might also be nice to understand the history and evolution of the crank case ventilation system, so I'm going to start with the early SR20DE system and work up from there.

I know people like images so I won't hold off any longer.
Here's the factory system:

This image has been resized. Click this bar to view the full image. The original image is sized 852x693.

Now let me explain what's happening here. The piston rings don't seal perfectly, so there is some air that gets by them and we call that blow-by. This blow-by air is pressurized and will cause oil seals to fail and eventually will cause other major problems so it needs to be dealt with. Having a vacuum in the crank case is very good as it promotes ring seal and keeps windage losses (drag on the rotating crank caused by a cloud of oil in the crank case) to a minimum. Since having a vacuum in the crank case is good and having pressure there is bad, we must get rid of the pressure somehow.

The air comes in contact with a lot of oil in the crank case and basically turns into a mix of air and oil (along with a little bit of gasoline and water). This air/oil mix is represented by the red arrows in the crank case and as oil gets removed throughout the system I've made the color shift towards blue. I even showed little oil droplets condensing out of the air as it goes up through the "catch can" oil separator. I didn't show them everywhere in all the baffles, but you can imagine the same thing happening everywhere you see baffles.

The amount of air and oil can be quite significant, so Nissan put in two important pathways for the pressure to escape from the crank case because at times there can be a lot of air to evacuate.
On the left the air and oil can escape the crank case up along the timing chain portion of the block and into the valve cover. This is the usual pathway for the air to take.
On the right the oily air can escape the crank case (in times where there is excessive pressure to evacuate) through the provision in the side of the block, up through the oil separator (catch can) leaving the crank case.

So the goal is to have a vacuum in the crank case, and this is accomplished on some vehicles with a dry sump oil system, but on regular vehicles the intake manifold is used for the source of vacuum. Basically the engine is setup to consume it's own blow-by gasses. Not a super great idea because it coats the intake in oil residue and lowers the effective octane of your fuel, but it certainly is efficient, practical, and good for the environment.

How does blow-by lower your octane? Blow-by gasses with any amount of oil in them will lower the effective octane rating of your fuel because the vaporized oil will ignite at lower energy levels than 87 octane (R+M/2) gasoline. The more of it you allow to enter the cylinder, the more you will have to worry about detonation. This is usually not a big worry for naturally aspirated engines, but obviously forced induction is a different story.

All right if you've been paying attention we now have the blow-by gasses up and out of the crank case and in the valve cover now. The gasses are going to continue on through the small PCV (positive crank-case ventilation) port at the top-left corner of the valve cover which includes a one-way check valve so things can only flow out (and not in). The gasses flow out of the PCV port and into the intake manifold where they are sucked back into the engine to get consumed and pushed out of the exhaust. Simple enough.

Now the gasses have a bit of oil mixed in with it, so on it's way out of the valve cover it passes through a labyrinth of baffles designed to help condense the oil and collect the oil from the air. The more surface area the oil has to cling on to the more oil will separate from the air. The oil that is collected drains back down onto the valve train and eventually returns to the oil pan.

Here is another diagram showing the normal operation of the crank case ventilation system with half of the system greyed out:

This image has been resized. Click this bar to view the full image. The original image is sized 847x691.

That pathway is used around 90% of the time you drive the car. A little blow-by is pushed into the crank case but the intake manifold sucks it up and the oil separator in the valve cover keeps most of the oil from escaping the engine. The manifold keeps a good vacuum on the crank case during idle and partial throttle conditions which amount to most of your driving.

"Okay Ben, what happens when you're at WOT then?"

I'm glad you asked.

That's where the other half of the system comes into play. Now there are a couple things happening at WOT.
Firstly, there is no real vacuum to speak of in the intake manifold or plenum. With the throttle fully open, the entire intake track experiences atmospheric pressure and no longer produces any vacuum. This means there won't be any vacuum applied to the crank case and blow-by evacuation will be problematic.
Secondly, WOT produces the most blow-by because of the pressure in the cylinder and the lack of vacuum in the crank case (remember the vacuum promotes ring seal and without good ring seal there is more blow-by).

This means there is a lot more blow-by to deal with at WOT and there's no vacuum to suck the blow-by up. In the past, OEMs just vented the crank case to atmosphere and called it a day. In these times of pollution consciousnesses, spouting air with oil and gasoline vapors into the atmosphere untreated is a big no-no. So in an effort to control those emissions Nissan routed the gasses back into the intake to take advantage of the slight vacuum present in the intake (very slight) and also route the pollutants back into the engine to be consumed and eventually treated by the catalytic converter.

Because there is not really any vacuum present, the blow-by gasses build up pressure and relatively slowly move up to the valve cover via both the left and right pathways. These pathways are also larger than the regular PCV hose because flow is important now that the vacuum is gone.

Let's follow the path of the blow-bay gasses at WOT.
They start out at the bottom just as before and this time they go up the timing chain section and the catch can section on the right. The pressure in the crank case is now going to be about equal to that in the intake manifold, so not much of anything will flow through the PCV hose. The blow-by gasses will have to continue on through the valve cover where there is even more built-in oil separation labyrinth. Eventually the gasses leave the valve cover and meet up with the gasses that took the other route through the catch can. By now both routes have gone through an oil separator so the air is going to be relatively oil free.

Here is another diagram showing this part of the system with the regular section greyed out:

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Those are the basics of the 1991-1999 SR20DE crank case ventilation system.
Continue reading for a thorough explanation of the roller rocker (years 2000+) SR20DE and SR20VE (including N1 and 20V) crank case ventilation system.

Okay now that we have the basics down the rest should be a lot easier to get through.
Nissan basically upgraded the crank case ventilation system when they moved on to the roller rocker head and have kept it generally the same from then on all the way to the SR20VE engines including the N1 and the 20V varieties.

They basically did two things when they upgraded the system. They got rid of the stand-alone oil separator (catch can) and built it into the valve cover. They also moved the "PCV" port from the top-left of the valve cover way over to the right side. This simplified and cleaned up the engine bay by including the oil separator for the right pathway into the valve cover. It also increased the ability for the system to remove oil from the blow-by because of a minor but significant rerouting of the right pathway. I've tried to describe this visually by changing the colors of the arrows as they flow through the system. You should be able to notice that the arrows are more blue in these diagrams than in the ones from the old system.

Here's a diagram of the system:

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You should notice immediately that the stand-alone catch can is gone now, and that tube connects directly to the forward portion of the valve cover. The new valve cover has an additional oil separation pathway that it didn't have before which serves the purpose of the old stand-alone catch can. You'll also notice right away that the PCV hose has moved way over to the right and blow-by gasses have much farther to travel (through more oil separation labyrinth) before leaving the valve cover.

Here is what things look like at idle or partial throttle with the inactive sections greyed out:

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Hopefully these diagrams are making sense and looking familiar to you by now. As you can see, the blow-bay gasses are still forced to go through all of the oil separators even though we're at idle or partial throttle. This is not the case in the old system.

Now for a look at what happens during WOT:

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As before, the PCV hose is taken out of the equation because nothing is going to flow to the manifold now that the pressure in the intake manifold and the valve cover is about the same. Even if some blow-by gasses do go through the PCV hose, there is lots of it left and the other pathway to the intake track is vital to providing a wide enough pipe for the gasses to escape through.

That's about all there is to the newer system. It's a step above the old system in many ways that hopefully now you understand quite well.

So now that you know the basics, I'm sure you're wondering what (if anything) can be done to improve the system.
Well you certainly won't be alone. Plenty of people want to reduce blow-by, clean up the engine bay, simplify the crank case ventilation system, and prevent every last bit of oil from being sucked into the intake and gumming things up. However the system is a little more complicated than most people think and it's actually well designed from the beginning so it's hard to improve on.

As history has shown, this is a hot topic. About two years ago Vadim got bit by the bug and started messing around with his system and eventually after talking some sense into him he decided to mostly abandon his attempts as he was not getting great results. If you want to read about it, here's the thread: Finding a way to Reduce Oily Blow By Gases
Love you Vadim!

Just recently s132nr started another thread about upgrading the system and it was made clear to me that I had to make a comprehensive thread where people could learn the right way to go about working with the crank case ventilation system on our engines. Want to read how that thread went? Check it out here: oil catch can pcv 20v valve cover question

One more link before I get into the nitty gritty details of upgrading the system. Fred Cooke is my Australian brother-from-another-mother and he has his own crank case ventilation (not SR20 specific) explanation thread on his own forum. It is very easy to read and extremely thorough. It's where I finally got a handle on the situation and really helped me a lot in figuring out how it all works. It might be a bit late to link to it now, but here it is anyway: http://www.diyefi.org/forum/viewtopic.php?f=24&t=357
Fred really emphasizes the importance of making sure the system has enough flow. Tube diameter is important and 99% of catch cans on the market actually introduce a huge restriction to the system so you'll want to make sure you keep an eye on that. Really I should make that thread a mandatory read, but oh well.

More crank case ventilation question threads (will update as I find them):
removing black canister on front of valve cover
Oil separator box
Can I move/remove this?

Okay on to the different methods of improving, or completely messing up the factory crank case ventilation system. These methods will cover a huge mix of things I've seen done on people's cars, or that I thought up in my head. Some will be great ideas, some will be good ideas, some will be bad ideas, and some will be awful ideas. I'm going to keep things simple by rating each method on the important points so you can just give it a quick look and see immediately if it's a good idea or not.

WOT "catch can" elimination on 1991-1999 engines via cap method:

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