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Questions tagged [engine-theory]

Use this tag when asking questions about the theory of engines. Do NOT use for practical problems, only theoretical questions

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What does the crankcase breather do?

I have seen multiple Honda motorcycles list "crankcase breather" cleaning as a regular maintenance item. It involves just emptying out the oil collected in a small reservoir tied to a hose. ...
Baran Zadeoglu's user avatar
1 vote
1 answer
26 views

working engine temperature oil vs coolant

When we say that the car must be at working temperature, i.e. (90 C, 194F) is this temperature that of the coolant or the oil? Thanks.
secuaz's user avatar
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2 answers
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Can LPG be used as fuel for cars?

I have a petrol engine car but I want to know that can I use LPG as a fuel for my petrol engine. I know I have to do customization for it but can I use LPG in a normal Petrol engine or does it affect ...
Helix Nebula's user avatar
0 votes
1 answer
73 views

Is it possible to run a car without a carburetor?

Is it possible to run my car without a carburetor, or will doing so cause damage and prevent it from running? Does it damage or wear anything? what actually happen to the car.
Helix Nebula's user avatar
1 vote
1 answer
36 views

Resleeving a small engine?

Can you guys please help me settle a debate with a mechanic friend of mine? He claims that it is possible to keep a small Honda or similar engine running literally for tens of thousands of hours by ...
Justify 's user avatar
1 vote
3 answers
147 views

What is the difference between a 2 stroke and 4-stroke engine?

I just wanted to know that what are the major differences in 4 stroke engine or in 2 stroke engine. The only difference I know is that a 4-stroke engine goes through four stages, or two complete ...
Helix Nebula's user avatar
3 votes
2 answers
308 views

Calculating engine air intake per minute

Hi guys i tried to calculate the amount of air liters per minute that an engine consume , so the engine is a V8 diesel 15L max rpm 3000. The 15L displacement is the total size so 15/8 = 1.875 L/minute ...
Tintin's user avatar
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1 answer
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Do (modern) ICE cylinder walls build a patina that unusually consumes engine oil during the break-in period?

I appreciate the possibility that newer internal combustion engines (ICEs) burn more oil throughout their life. This appears to be partly due to using lower viscosity oils (which are being specified ...
Sam7919's user avatar
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-1 votes
1 answer
89 views

What control the RPM of an engine?

can you tell me what controls the rpm of an engine? Is it more fuel, more rpm (if so plz explain this to me) or is it controlled by a computer?
Tintin's user avatar
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1 answer
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Crankshaft design

I am wondering why all crankshafts I see are machined so that the piston rod counterweights are all tapered at the rod bearing end of the counterweight? As you can see in the picture the ends of the ...
nuk's user avatar
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2 votes
5 answers
812 views

When does the spark plug ignite the air fuel mixture?

Some people say it's at the end of the compression stroke, some people say beginning of the power stroke.. What do you guys think ?
venomx's user avatar
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1 answer
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Engine comparison: How can a smaller/more efficient engine excel over its "bigger sibling"?

Recently, after a discussion with friends, I stumbled over the engines available for a Fiat Panda Mk4 (yes, this is a "long story short" situation and now I'm stuck in a rabbit-hole). And I ...
NicApicella's user avatar
2 votes
2 answers
620 views

Horsepower and turbo

I am a little confused about performance and engine numbers. I have two cars. The oldest is a Škoda Fabia Combi 1,2 TSI and the other is a Nissan Micra 1,2 5D. MAN. According to the specs, the Fabia ...
JoSSte's user avatar
  • 259
1 vote
2 answers
107 views

What would be the long-term result of driving without a thermostat?

Would there any damage done to an engine if you run it without a thermostat permanently? Let's assume the vehicle is driven in a climate that is warm and temperatures never drop below freezing.
TheLegendaryCopyCoder's user avatar
4 votes
1 answer
1k views

Why are sheet metal engines not popular?

What are the reasons engines use casting and not stamping when manufacturing blocks and heads? There were couple of stamped engines before but none of them took off. https://www.macsmotorcitygarage....
Timothy Scherer's user avatar
3 votes
1 answer
161 views

Do valves still open and close during engine braking

While trying to investigate some rattling noise in my single cylinder motorcycle engine, the question of whether valves are closed during engine braking jumped into my head. I was assuming that the ...
Amine Hajyoussef's user avatar
0 votes
1 answer
85 views

What happens when the air-fuel mixture ignites but the piston/crankshaft briefly can't move?

With engines such as in lawnmowers or motorboats (or even manual gearbox cars when the clutch is fully released), what does typically happen when there's a sudden increase in resistance during or ...
Boris B.'s user avatar
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2 answers
91 views

Does engine braking still save fuel at right above idle?

I'm trying to drive economically and my understanding is that as long as there is enough momentum in the car to keep the engine spinning while in gear at above idle the engine won't inject more fuel, ...
Aden's user avatar
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2 votes
2 answers
520 views

Why are two stroke direct injection engines uncommon?

Traditionally, there have been two kinds of engines: two stroke and four stroke, and diesels exclusively were four stroke (apart from maybe very large marine diesels). The two stroke engine has some ...
juhist's user avatar
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1 vote
1 answer
287 views

What does a throttle valve actuator do in carburetors?

i tried looking online but could not find much information about throttle valve actuators in carburetors. I think they look like this part in the picture below circled in red. What is the purpose of ...
Timothy Scherer's user avatar
1 vote
2 answers
1k views

Place the accelator pedal all the way to the floor, and hold it there. Do not pump it

What does "Do not pump it" refer to in "Place the accelator pedal all the way to the floor, and hold it there. Do not pump it"? To pump the accelerator? If so, what's the purpose? ...
Maurice's user avatar
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1 vote
1 answer
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Rotating “dippers” that throw oil into the pistons and cylinders

What are rotating dippers in "rotating 'dippers' that throw oil into the pistons and cylinders"? Are they containers for taking up water, or maybe in this case, oil? Thank you!
Maurice's user avatar
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1 vote
0 answers
86 views

Given compression ratio for a naturally aspirated engine, how do I calculate the expected compression pressure?

I've started learning more about cars, and I have a question. How do I know what compression pressure I should expect during a compression test? With a naturally aspirated engine, I think I can use ...
Wren T.'s user avatar
  • 123
2 votes
4 answers
1k views

Why VVT is never used in diesels?

There is only a mitsubushi diesel engine that uses VVT but other than that there is no diesel engine that uses VVT or VVL. Why gasoline engines do utilize them but diesels dont?
Timothy Scherer's user avatar
2 votes
1 answer
118 views

When switching off the engine, do the cam and crank shafts always come to rest in an initial state?

Is it the case, when the engine comes to a halt, that the cylinder/piston/valve phases always finish up in the same starting or initial position relative to each other?
Jim's user avatar
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8 votes
2 answers
5k views

Why do bad motor mounts cause the car to shake and vibrate at idle, but not when you give it gas and increase the rpms?

I have a 2000 FIAT Siena 1.4el with the FIAT Lampredi Monoalbero engine, and the car is 22 years old now still with its original engine mounts. The whole car, and also the steering wheel, both shake ...
Timothy Scherer's user avatar
2 votes
1 answer
1k views

What is the purpose of expander/spacer in the oil control ring?

I was reading about oil control rings in the piston ring topic. Most modern engines use a 3 piece design for oil control rings where you have top rail, bottom rail and spacer-expander (sandwiched ...
Abhishek P G's user avatar
2 votes
2 answers
295 views

Is calculating the compression ratio as easy as they say using the formula?

Often in elementary texts the compression ratio is defined as (Vs+Vc)/Vc. Vs = Swept volume Vc = Clearance volume But the calculation becomes difficult when calculating the clearance volume of ...
Abhishek P G's user avatar
0 votes
1 answer
611 views

Reverse flow head vs Cross flow head

Wikipedia says that Cross Flow cylinder heads induct the charge better because the gases doesn't have to change direction from intake to exhaust. Thus the higher inertia of flow of gas in one ...
Abhishek P G's user avatar
2 votes
3 answers
631 views

Atkinson Cycle: Does the efficiency of a high-compression engine come from compression ratio, expansion ratio, or both?

I understand that, in an internal combustion engine, efficiency can often (up to a point) be improved by increasing the compression ratio, this being a major reason why diesel engines (which do not ...
DodoDude700's user avatar
-1 votes
1 answer
47 views

3 wheeled light commercial vehicle sound

I'm new to this platform. So I'm not sure if my inquiry is appropriate to publish here. If not, kindly direct me to the appropriate forum. I've noticed that three-wheeled commercial vehicles produce ...
Robin's user avatar
  • 1
0 votes
4 answers
221 views

Does a carburetor have constant fuel mass flow, constant liquid volume flow, or constant molecule count flow?

I have a generator with carburetor. It seems to consume a bit more fuel than I expected, 0.44 liters per hour for 386 watt production, or 1.14 liters per kWh. I'm also bit more annoyed by the exhaust ...
juhist's user avatar
  • 14.6k
0 votes
0 answers
85 views

Overhead valve Vs Overhead cam

Sure overhead cam is better at high revs because valve accuracy is superior.At normal average revs like say 3000rpm the advantage is not really there but the extra cams will chew more mechanical power ...
Autistic's user avatar
  • 2,083
2 votes
1 answer
102 views

Choosing the best timing marks

This question is somehow related to my previous question here: Compression of valve springs and camshaft rotation In that question, I asked about the pattern of camshaft rotation and how valve springs ...
LFY MP7.3's user avatar
  • 968
3 votes
2 answers
1k views

Compression of valve springs and camshaft rotation

As you know, in most cars it is not easy to turn the intake or exhaust camshaft by hand. You probably need to use both hands, grab the cam sprocket and apply a lot of force to rotate them even with ...
LFY MP7.3's user avatar
  • 968
1 vote
1 answer
3k views

Is timing set wrong if TDC doesn't have all valves closed?

I had to redo my timing and I think I may have done it wrong because, on my left (passenger) engine lobe (V6), when each of the three cylinders are in TDC (top of orange tape on the rod in the picture)...
amphibient's user avatar
  • 6,663
1 vote
1 answer
184 views

How does Honda ensure the all the pins and holes are lined up when VTEC is activated? Shouldn't they interfere?

If the outside rocker arms are actuated by a different cam profile than the middle rocker arm, how could these pins ever line up? Isn't it likely that the initial outside pin forces itself against the ...
noobquestionsonly's user avatar
2 votes
1 answer
83 views

Gasoline glow engine mechanics

I own a wide array of model engines. Typically those engines are either glow engines using nitro fuel, spark engines using gasoline or "diesel" engines using "kerosene". However I ...
Yanick Salzmann's user avatar
0 votes
1 answer
291 views

Camshaft valve clearance and fuel consumption

Does the clearance between the camshaft and the top of valve tappets (AKA lifters AKA shims) affect fuel consumption? I am asking because it seems to me like the lesser the spacing, the more the cam ...
amphibient's user avatar
  • 6,663
0 votes
2 answers
16k views

Can an engine run without oil for a few seconds, if the oil change was just done

I accidentally started up my engine after draining the oil and inserting the oil filter. I know that running an engine without oil causes the parts not to be lubricated and thus, causing damage. In my ...
Luke's user avatar
  • 1
2 votes
1 answer
426 views

Why don't timing pins lock the crank and cams precisely?

During my timing belt replacement, I noticed something which I think is worth mentioning here. As you know, locking pins (two for camshafts and one for crankshaft) are used to lock the engine in exact ...
LFY MP7.3's user avatar
  • 968
0 votes
2 answers
215 views

A/C compressor and crank pulley bolt

I have heard something from some mechanics but don't know if it is true or false. They say when you are driving on the highway and your A/C is on, the compressor keeps kicking in and out which puts a ...
LFY MP7.3's user avatar
  • 968
0 votes
3 answers
114 views

Effect of same engine but with slightly less capacity (cc) and hp

There's a vehicle whose engine is 1332cc which produces 94 hp in its home country. It was recently launched in my country with the same engine, but they downsized it to 1299cc (91 hp) for tax benefits....
ifadey's user avatar
  • 187
1 vote
1 answer
797 views

There's no replacement for displacement

I grew up with the saying "There's no replacement for displacement" when referring to engine size, performance, etc. Does that saying still hold true today? It's getting harder and harder to ...
mikem's user avatar
  • 225
0 votes
2 answers
958 views

Why does rpm drop when you disengage clutch and let go off accelerator pedal after revving it?

The obvious answer to this question would be that you are no longer supplying fuel to cause combustion and the frictional losses slows down the rotating and reciprocating parts of engine causing ...
Abhishek P G's user avatar
0 votes
1 answer
391 views

Can inline plunger mechanical injection pumps pull through the fuel?

I know that they have lift pumps that bring the fuel towards the plungers so that the plungers can push and pressurize the fuel towards the injectors but i was wondering if lets say we removed the ...
Timothy Scherer's user avatar
0 votes
0 answers
121 views

Why do Tri-Y Headers give more low end torque and struggle at top and why 4-1 Headers give better top end torque?

Everywhere i read says Tri-Y is better for bottom end and that the 4-1 is better for top end. Why exactly is that? I thought Tri-Y would have more top end "breathing" and make more torque at ...
Timothy Scherer's user avatar
6 votes
3 answers
962 views

Control Systems of Modern Engines

This may be a bit of an odd request. I teach high school computer science, in part through game design. I have a student who wants to be an auto mechanic who was placed in my game design class because ...
dlu's user avatar
  • 14.5k
0 votes
1 answer
140 views

What are the pros and cons of valves being placed in a line vs valves being placed side by side in 2V engines?

As you can see in the picture below the valves in this ferrari dino dohc 2 valves per cylinder v6 engine are placed side by side and not in a row. And as you can see here in the other picture below ...
Timothy Scherer's user avatar
0 votes
1 answer
146 views

Is it true that crankshaft counterweights help with extending the life of the main bearings?

I have heard that use of counterweights in crankshafts also help with bearing life because "counterweights reduce peak main bearing inertia loads". Is this true? If its true how does that ...
Timothy Scherer's user avatar

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