Engines 101 Question

"Audi-os, amigos" (audi-osamigos) 03/18/2014 at 17:04 • Filed to: None

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I have a confession, Oppo. I am a total engine n00b.

I can tell you every single power and displacement statistic of just about every single car made in the last 20 years, I have a very good knowledge about the mechanical engineering theory underpinning how cars work. I've loved cars since I was trainspotting them on the road at 4 years old.

But I've never worked on an actual engine. I know, I know. The mob forms to the left.

So please, with a spirit of patience and tutelage, humor me here while I ask you some questions about my car's engine, the Audi 1.8L Turbo, below:

Fig 1: What I believe to be the intake manifold, as explained in Fig 2.

Fig 2: This is obviously the dipstick. To keep the plastic from melting, it seems to me it would have to be wedged between the intake manifold, not the exhaust.

Fig 3: However, this looks like the turbo to me. Hence my confusion, as the turbo is obviously part of the exhaust process, not intake.

Fig 4: This is the actual block, yes? This normally has that bullshit plastic cover on it.

Thanks for helping me learn and get more into engines, Oppo, seriously.

Have a picture of my dream car for your trouble - a B6 S4 Cabriolet.

EL_ULY > Audi-os, amigos 03/18/2014 at 17:07

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3. Throttle Body

4. valve cover, it is the top cover of the head which is attached to the block

EL_ULY > Audi-os, amigos 03/18/2014 at 17:08

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turbo is down here, looks like a snail :]

Goggles Pizzano > Audi-os, amigos 03/18/2014 at 17:08

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EL_ULY is correct. (3) is throttle body.

RacecaR > Audi-os, amigos 03/18/2014 at 17:08

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#3 is the throttle body.

#4 is actually the valve cover, which is over the valves, which is in the head, which is on top of the block. Make sense? ;-)

SynchroMess (K.S.O.F.M) > Audi-os, amigos 03/18/2014 at 17:09

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1 and 2 your right, 3 is the throttle body and 4 is the valve cover.

MazdaMonkey > Audi-os, amigos 03/18/2014 at 17:09

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Fig 3 is your throttle body

Fig 4 I think you meant to say "engine," instead of block. The block is the lower part of the engine, which you can't really see in the picture. your number 4 is directly over the valve cover.

PowderHound > Audi-os, amigos 03/18/2014 at 17:09

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I believe 4 is the Valve cover? The actual block would be underneath that.

A turbo is part of both the exhaust and intake system. It uses exhaust gases to spool the turbo to pull in more air to the intake. I'm almost positive that is not your turbo.

Paul, Man of Mustangs > Audi-os, amigos 03/18/2014 at 17:10

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1&4 yes. 3 is the throttle body. The turbo is normally on the exhaust manifold, which usually ends up being sorta rusty steel tubes on the opposite side of the engine as the intake.

Audi-os, amigos > EL_ULY 03/18/2014 at 17:11

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THANK YOU FOR ANSWERING!

3. What does that do? Obviously related to the throttle, but which makes the fuel-air mixture richer/leaner? I understand that fuel injectors and computers replaced analog carburetors, but how does my gas pedal actually interface with my cylinders?

4. Okay. I understand how valves work in a 4-stroke engine, but what is the relationship between that cover and the valves themselves?

Thank you so much for answering. I have a voracious appetite for this stuff but no one to ask.

daender > Audi-os, amigos 03/18/2014 at 17:13

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1 and 2 are correct, 3 and 4 are not. 3 appears to be your throttlebody, the controller of how much air your engine breathes in. 4 is actually the valve cover, which is bolted to the cylinder heads (which are bolted to the block).

RazoE > Audi-os, amigos 03/18/2014 at 17:14

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throttle body lets air in. It is a plate that opens/closes as you press the pedal, although not necessarily directly connected. If it's electronically controlled, then it's "drive-by-wire". Older engines were directly connected to the gas pedal with a wire.

The valve cover is just that, a cover for the valves. That way debris doesn't get in and f-stuff up.

Paul, Man of Mustangs > Audi-os, amigos 03/18/2014 at 17:15

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It's a valve, essentially, that limits the air flowing into the engine, and therefore, the power. The computer determines the air-fuel mixture, and injectors in the rail at the base of the intake tubes squirt fuel into the engine according to the computer.

bob and john > Audi-os, amigos 03/18/2014 at 17:16

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3:throttle body control how much air goes into the motor. you know those drag cars with engine sticking out of the hood with "flap" in them? your throttle body looks very similar.


4 a valve cover is just that, a cover. doesnt do anything related to the valves other then helping to keep oil on the rockers and keeping other things from falling into them.

RazoE > Audi-os, amigos 03/18/2014 at 17:16

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Also, your turbo is definitely connected to the exhaust manifold, which on your engine should be on the left side. Follow that tube going to the intake manifold, it should come off the IC, which leads to the turbo.

Also think of an engine as a 2 piece lego. The part on top with the valves/camshafts (on a overhead cam engine, aka OHC [SOHC, DOHC]), the block is the lower half, with the pistons/crank, etc.

Audi-os, amigos > RacecaR 03/18/2014 at 17:17

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Okay! So! #4! Block = cylinders + the metal they are cut out of. That whole apparatus. Got that.

I understand the relationship between the valves and the cylinders in a 4-stroke motor, but how do the valves actually physically relate to the head? Are they....in it? Under it? Surrounded by it?

Audi-os, amigos > RazoE 03/18/2014 at 17:18

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WOW! That's so cool.

HappyHealToe > Audi-os, amigos 03/18/2014 at 17:19

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Inside the throttle body is a valve that opens when you press the gas. Air rushes into that manifold right behind it and disperses to each cylinder. On the other side of the engine, the exhaust exits the head (which sits on top of the block) and the expanding gasses spin the turbo. The turbo is out of direct view and kept insulated from the other engine components. Compressed air comes out of that turbo, goes down to the front of the car through a series of tubes, and ends up back at the throttle body, thus completing one loop of the system. At idle, only a little bit of air gets through the throttle body through a sort of pilot hole drilled into the circular valve face. This regulates engine speed.

crowmolly > Audi-os, amigos 03/18/2014 at 17:20

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3 is the throttle body. 4 is the valve or cam cover.

HappyHealToe > Audi-os, amigos 03/18/2014 at 17:21

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Here is a good gif of some suck/squish/bang/blow

Saracen > Audi-os, amigos 03/18/2014 at 17:21

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Ah, that's an engine bay I've looked at many times (used to have a B6 1.8T Avant).

(Not a stock turbo in this picture, but it gives you an idea where the turbo normally sits)

The turbo is on the passenger side of the block, buried under the intake snorkel. The US-spec 1.8T has a side mounted intercooler, mounted behind the fog light on the driver's side. The piping runs all the way across the engine from the turbo, into the intercooler, then back to the throttle body.

Audi-os, amigos > RazoE 03/18/2014 at 17:22

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AHHH OKAY. So the head contains the valves and camshaft, block is the cylinders, the metal they're "punched out" of, the pistons, connecting rods, and cranks?

McLarry > Audi-os, amigos 03/18/2014 at 17:22

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Your turbo is part of the exhaust system and the intake system. This is kind of hard to visualize, and it took me a while to appreciate how it can be part of both systems but keep them isolated from each other, so here's a picture:

The important thing is that it uses energy from the exhaust flow to pressurize the intake flow, but the two never come into physical contact with each other (you certainly wouldn't want your exhaust going through your engine again). Exhaust air spins a fan, which in turn spins another fan that acts on the intake. Hope this helps.

Audi-os, amigos > McLarry 03/18/2014 at 17:23

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Thanks! I've got a pretty good understanding of how turbochargers and superchargers work, but I've never actually looked at them! I'm like a doctor who's only ever read medical textbooks but never had patients.

Ron Stoehr > Audi-os, amigos 03/18/2014 at 17:23

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The throttle body is basically a valve that controls how much airflow is going to the engine. When you press the accelerator pedal it opens to let more air in. Then an airflow sensor senses and sends info to the ecm (engine control module).
The valve cover and in this case the can cover seals to top of the engine and keeps oil in and dirt out. Much like the oil pan on the bottom of the engine.

Zipppy, Mazdurp builder, Probeski owner and former ricerboy > MazdaMonkey 03/18/2014 at 17:24

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I was about to call you out on the "MAF", but you edited the post in time.

RazoE > Audi-os, amigos 03/18/2014 at 17:24

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Yup. Push rod engines have a single camshaft in between the two "banks" of cylinders (aka V8) that....push..rods...that control the valves, instead of the camshafts directly touching the valves themselves. Picture pressing a button versus pressing a stick that presses the button itself.

RazoE > Audi-os, amigos 03/18/2014 at 17:26

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Push-rod

Over head cam (SOHC, DOHC)

Audi-os, amigos > Saracen 03/18/2014 at 17:26

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Thanks for the beefy turbo pic! That actually really helps. So let me ask: What is the blue filter-looking thing next to the turbo?

EL_ULY > Audi-os, amigos 03/18/2014 at 17:27

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3. try to think of your pedal as an air pedal over a gas pedal. As your foot goes down, the throttle opens and lets more air inside. The car's computer reads the air and applied the proper amount of fuel determined by many factors.

4. The valves are lubricated with engine oil. The cover is simply there to cover the valves and keep the oil in. More of a head cap lol :]

I've been working on cars since I was 15 from little gas station service centers to Master Tech at various dealerships. ASE Master with L1 :] Any questions let me know. I also own an Audi

Audi-os, amigos > Ron Stoehr 03/18/2014 at 17:27

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Does the ECM then talk to the fuel injectors and tell them how much fuel to squirt, aka how rich to make the mixture, based on how much airflow the airflow sensor is sensing?

Chris Clarke > Audi-os, amigos 03/18/2014 at 17:28

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Headlight fluid reservoir.

Saracen > Audi-os, amigos 03/18/2014 at 17:28

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That blue air filter is the engine's intake filter. This guy is running a very large turbo, so all that plastic intake plumbing that a stock 1.8T would use will massively restrict airflow into the turbo, so he's running a large open element filter. It will be much louder, but clearly he doesn't mind.

Audi-os, amigos > RazoE 03/18/2014 at 17:28

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Engines are so fucking cool.

Audi-os, amigos > EL_ULY 03/18/2014 at 17:30

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Thank you, so much. Sincerely. I LOVE learning about this stuff.

MazdaMonkey > Zipppy, Mazdurp builder, Probeski owner and former ricerboy 03/18/2014 at 17:32

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Yeah, I didn't look at the picture close enough until I clicked submit. Typical impulsive primate in me.

EL_ULY > Audi-os, amigos 03/18/2014 at 17:32

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no problem, anytime

Audi-os, amigos > Saracen 03/18/2014 at 17:32

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Okay so how does the air get from the blue filter on the left to the throttle body/rest of the intake on the right?

ttyymmnn > Audi-os, amigos 03/18/2014 at 17:34

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Welcome to Oppositelock, where noob questions are answered honestly, politely and without condescension. That's what makes this such an amazing place.

jariten1781 > Audi-os, amigos 03/18/2014 at 17:35

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It's basically a butterfly valve. When you press the accelerator the valve turns more parallel to the airflow allowing it to increase. Wide open throttle is called that because it will be completely parallel hence being wide open. When you let off it becomes a block not allowing air to pass. Some systems are electronically controlled so where the handwheel is in the picture you have an electronic motor that's controlled by the pedal (and probably the ECU) that controls how it opens and closes. Older systems will use a cable connected to the valve shaft with a spring return.

CAR_IS_MI > Audi-os, amigos 03/18/2014 at 17:36

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F2. the dip stick tube is made of steel and *could go through holes in the exhaust manifold (the only plastic / rubber is the yellow bit). *your car probably has a cast log manifold, add in the space the turbo takes and you don't have much space to feed a dip stick tube.

F3. That would be your throttle body

F4. No thats a valve cover.

also, use this link below for more good info.

http://auto.howstuffworks.com/engine2.htm

Saracen > Audi-os, amigos 03/18/2014 at 17:36

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All of the air the engine breathes goes through the turbo. Even if the turbo isn't spooling much, air still passes through it.

Ron Stoehr > Audi-os, amigos 03/18/2014 at 17:42

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Basically, but on a modern electronically controlled there are a veritable plethora of sensors that the ecm monitors to determine the air/fuel mixture, spark timing, and other performance settings to optimize the performance for current driving conditions.

TheNeonDriver - Now with More BMW! > Audi-os, amigos 03/18/2014 at 17:46

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And a brief explanation, VIA Oppo and Automatch Tom

How a cars engine works - A gif based Gift

!!! UNKNOWN CONTENT TYPE !!!

The Ghost of Oppo > ttyymmnn 03/18/2014 at 17:48

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Thankfully he came here and not VW Vortex

mycarneverruns87 > Audi-os, amigos 03/18/2014 at 17:52

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Exactly correct. It is very cool how all the systems work together.

mycarneverruns87 > HappyHealToe 03/18/2014 at 17:53

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Thats what I was searching for to post up.

McMike > The Ghost of Oppo 03/18/2014 at 17:53

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Never ask questions in The Car Lounge. Stay here as long as you can!

mycarneverruns87 > ttyymmnn 03/18/2014 at 17:54

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I was thinking the same thing! Tons of info on a simple post.

jkm7680 > The Ghost of Oppo 03/18/2014 at 17:55

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Thank God! I remember asking a question about mounting my Europlate. Everybody blew the fuck up on me. Haha.

Everybody fucking hated me because my 97 Jetta Gt was stock. A good 70% of the people who I encountered were fucking pricks. There always is that other 30% of kind people, but I seemed to only find King Dick, and Captain Cunt.

CAR_IS_MI > ttyymmnn 03/18/2014 at 17:56

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What a pompous comment pontificated by the most prognosticating ass clown in the entirety if the internet. Presumptuously pessimistic.

(sorry, I had too many P's floating on my tongue.)

A3R0 > ttyymmnn 03/18/2014 at 18:00

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You has needz all dee star clickz!

ttyymmnn > CAR_IS_MI 03/18/2014 at 18:02

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No worries. Guilty as charged.

Devilishprune > Audi-os, amigos 03/18/2014 at 18:09

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I just wanted to thank you for posting this. I know about as much about engines as I know about neurosurgery, so it's nice to learn from someone else who is just starting out.

ghosty - electric space wizard > Audi-os, amigos 03/18/2014 at 18:13

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Never hesitate to ask questions here that may seem n00bish. There are other n00bs here (me) who just learned from your questions!

trynthink > Audi-os, amigos 03/18/2014 at 18:37

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Just to clarify on the GIF, it shows a dual overhead cam setup (abbreviated DOHC). In a DOHC configuration, there's one camshaft (a shaft with cams on it) that actuates the exhaust valves, and a separate camshaft that actuates the intake valves. These shafts are rotated by the engine from the gears (shown in the GIF) on one end of each shaft. The timing belt or chain wraps around these gears and a gear on the crankshaft (also shown in the GIF) and ensures that the camshafts rotate and push on the correct valves at just the right time in the cycle.

A single overhead cam (SOHC) works the exact same way, but both exhaust and intake valves are actuated from a single shaft of cams. As you can see in the GIF, the intake and exhaust valves are angled away from each other in a sort of V shape, so the single cam actuates the valves indirectly with a rocker arm. This is what a SOHC head looks like:

The rocker arms are the gold colored things that look like short arms and are bolted onto the tops of the valve stems. There are 12 valve stems visible in this picture. This engine has 2 intake and 1 exhaust valve per cylinder, so the side of the head closer to the camera is the exhaust side, and the four openings in the side of the head are where exhaust gases would go through the head, from the cylinder, past the valve opening, and out the exhaust manifold. If I had to guess, the threaded studs (what look like the ends of bolts) on the head are (in part) how the exhaust manifold attached to the head.

ttyymmnn > CAR_IS_MI 03/18/2014 at 18:37

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CAR_IS_MI > ttyymmnn 03/18/2014 at 18:39

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Kinja done ate whatever you done posted.

thebigbossyboss > RazoE 03/18/2014 at 18:39

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I think the car doesn't have to be that old to be connected by wire. Just cheap. The cavalier has a throttle cable.

thebigbossyboss > HappyHealToe 03/18/2014 at 18:40

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Don't worry about asking these guys questions. I have asked way dumber questions and have not been lynched yet. For me it was a big deal when I changed by spark plugs.

ttyymmnn > CAR_IS_MI 03/18/2014 at 18:41

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I have no idea what I wrote, but I'm sure it was pithy.

CAR_IS_MI > ttyymmnn 03/18/2014 at 18:43

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nice

HappyHealToe > thebigbossyboss 03/18/2014 at 18:48

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I actually love explaining car stuff to people. I wish I had more opportunities.

ZHP Sparky, the 5th > Audi-os, amigos 03/18/2014 at 18:49

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Aim higher! Here's a Rs4 Cabriolet instead (for sale locally in my area) :)

http://sfbay.craigslist.org/sfc/cto/437341…

HFV has no HFV. But somehow has 2 motorcycles > Audi-os, amigos 03/18/2014 at 18:51

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this is what you'll find under number 4.

Your camshafts, on the left/front the timing chain that connects the crankshaft to the camshaft/s(this is normally a belt but Germans are weird. and those four holes are where you spark plugs go down into the cylinders. This area is full of engine oil which is why it's covered, and why a bad valve cover gasket makes an oily mess of your engine.

http://www.bobistheoilguy.com/forums/ubbthre…

ttyymmnn > CAR_IS_MI 03/18/2014 at 19:52

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RazoE > thebigbossyboss 03/18/2014 at 20:30

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depends, my 05 xb has a cable, the 06 (same Body/engine) switched to Throttle by wire

XJDano > Audi-os, amigos 03/18/2014 at 21:17

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green cap is for blinker fluid, unless you don't use your blinker this may need to be refilled.

Ok with that out of the way, it seems that your questions have been answered. Do yourself a favor, search craigslist and see if you can find a motor that needs rebuilt for $50-100. then tear that thing apart and look at all the cool shit you don't get to see on the inside. then you have an engine block stripped down and ready yo make a table out of.

I asked what the difference between a turbo and supercharger once on a scca forum, luckily it was explained. I felt dumb, but I learned whats what. Also even if you don't work on your car having a FSM or Factory service Manual is handy as it explains all this crap and how to fix all the things.

Knowledge is power

Audi-os, amigos > Devilishprune 03/19/2014 at 09:33

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I can't be upset that I never learned if I was always afraid to ask.

Audi-os, amigos > ghosty - electric space wizard 03/19/2014 at 09:34

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Super glad to hear it!

Audi-os, amigos > HappyHealToe 03/19/2014 at 09:35

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THANK YOU. I had a cursory understanding of how the throttle body worked from other replies here, but I was wondering how idle was regulated.

philipilihp > XJDano 03/19/2014 at 11:03

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Found one for $1, supposedly! http://washingtondc.craigslist.org/nva/pts/437323…

They are clearly to be had for little money. I want to do this so bad, but space is tight.

OPPOsaurus WRX > McLarry 03/19/2014 at 11:07

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Well i learned something here. I thought the exhaust was reused to burn off anything that didn't combust the first time.

McLarry > OPPOsaurus WRX 03/19/2014 at 12:05

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Glad to help :)

You can tell a Finn but you can't tell him much > Audi-os, amigos 03/20/2014 at 13:28

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Here is a cool video showing assembly of the Mercedes AMG engines. I've only watched the first couple minutes, but it starts with a bare short block and I'm assuming goes until the engine is completed. If you've got any specific questions let me know, I used to work in the auto industry making pistons and have had a chance to tour a few engine plants.

Audi-os, amigos > You can tell a Finn but you can't tell him much 03/20/2014 at 14:03

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Thanks! Wicked cool!