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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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1answer
60 views

Engine braking in an automatic: Does it save fuel?

This is a question more to satiate my curiosity than something I want to apply in practice. It's also my first question here, so apologies in advance if I'm doing anything wrong. I've recently ...
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6answers
49k views

2.5L four-cylinder able to tow 2,700lbs?

My wife and I are looking at purchasing a new Subaru Outback. In the manufacturer's specifications, it states that for the 2.5L (four-cyl), that the towing package allows us to tow up to 2,700lbs. In ...
7
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2answers
211 views

How much oversize should you target when choosing a throttlebody?

This is in addition to my previous question about throttle bodies. I know it may sound a bit subjective, but I think it has a clear technical aspect, and I have done a considerable amount of homework. ...
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3answers
1k views

Why do electric motors produce peak torque instantly vs gasoline engines

On a separate forum, someone had asked why electric cars do not have transmissions. The simple answer was that electric cars produce peak torque at any RPM but the gasoline engine needs to rev up to ...
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2answers
3k views

Higher idle RPM on first start at morning

Unlike starting the car in the afternoon, after you've already started it at another time of the day. I understand that the higher RPM can be because of the temperature, however on hot days it's still ...
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1answer
778 views

Why can a motorcycle rev higher than a car, in spite of both reaching the same speed?

Basically, a car (street legal 2.5L) has about 7k RPM on its tachometer and a Motorcycle has about 14k RPM. Why is there a difference? Is there any relation between the displacement of the engine ...
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7answers
4k views

Is it possible for a diesel engine computer to detect (and prevent) a runaway condition?

Although diesel runaway is not so common... ... the consequences are spectacularly catastrophic. On old-school engines, I can understand that there isn't much you can do about it except try to cut ...
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3answers
87k views

What does a flywheel do and what is it connected to?

I understand roughly how an engine works and that there is a crankshaft which is able to turn the flywheel using internal combustion. I have just realised that I have got absolutely no idea how the ...
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1answer
61 views

Why is there only one compression ring per groove in a piston?

Why is there only one compression ring per groove in a piston? Two half sized rings in the same groove would take up the same amount of space as one piston ring but if you offset the rings gaps, in ...
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5answers
5k views

Oil vs Coolant Temperature

Could an engine be run dry, as is the case with solid blocks, meaning no coolant, if a sufficient oil cooler were to be installed? Essentially, if we could keep the oil temperature between 210 and ...
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2answers
30 views

Helmholtz Resonance

I was watching an episode of Engine Masters on the Motortrend channel. David Freiburger was talking about Helmholtz Resonance. What is Helmholtz Resonance and how does it apply to engine building?
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0answers
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H100 Hyndai - engine proble

have a problem with my H100 hyndai 2009 model, strange noise from the engine, no power and a little clear smoke from the exhaus - and the engine is shaking. please help.
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0answers
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Cleaning ground rotor magnets dust and particles after rotor assembly damage

I happen to have an FZ8 motorcycle which is famous in warmer climates like Greece for a very serious failure (along with FZ1 and R1) in the rotor assembly. In many cases the glue holding the magnets ...
34
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3answers
8k views

Why are the blades of car radiator fans unevenly spaced?

Fans that look like this: Is it to somehow help the balance of the engine?
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5answers
2k views

Two-stroke vs four-stroke design

Besides the apparent differences in fuel-injection, ignition, and valve timing, are there any other differences in the design/build of two-stroke and four-stroke engines?
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2answers
294 views

Differences between drive by wire and drive by cable

What are the main differences, advantages, and disadvantages of using a drive-by-wire versus drive-by-cable system?
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2answers
269 views

2014 Jeep SRT 6.4L oil filter was too small - what kind of damage?

What possible damage could my engine incur from having an oil filter installed that is smaller than the suggested size? I have damage but I’m interested to hear what this forum has to say about it ...
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3answers
5k views

What engine oil should you not mix together?

Can you mix 0w-40 and 30w oil together and get something like 15w oil? How would that math work? When is it a problem to mix to different types of oil together other than oil weight?
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1answer
73 views

Car struggles to pull off up hill

Could anyone help with another issue/potential issue I have? When I am parked on a hill, facing upwards, I put my car into first gear and when I pull off it feels as if I am towing something heavy, ...
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2answers
497 views

How would a speedometer work on a different engine conversion setup?

Currently we are looking at doing a v8 setup in a Mercedes W115. My one concern is that I want the originals in the cabin to work which includes the Speedometer which is cable driven. No how would you ...
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1answer
60 views

Trying to understand the diesel cycle

I understand that in a diesel engine, the fuel is injected after the air has been compressed, while in a gasoline engine, it is injected while the air is being draw in. But, then there are a few ...
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1answer
5k views

Where do spark plugs get their electricity?

Where is the electric charge coming from and does it have a large amount of electric charge to it?
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1answer
60 views

Compression ignition in petrol engines

First and foremost, this is not a question about reparing or maintenance. I'm familiar with how both petrol and diesel engines work, and I have a question about (possibly) making petrol engines more ...
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3answers
11k views

What is valve float and how does it impact engines?

The Wikipedia entry is hard to grok: Valve float is an adverse condition which can occur at high engine speeds when the poppet valves in an internal combustion engine valvetrain do not properly ...
5
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3answers
755 views

Does engine braking use petrol?

I'm driving an automatic, and often go down a big long hill. Lowering the gear means I don't need to hold my foot on the brake the whole time, but does it burn up a lot of petrol?
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0answers
25 views

Does an oxygen sensor's lambda value represent the same when running on LPG?

I have converted my car to LPG, and i've been tuning it today with a wideband lambda controller. It runs pretty okay, but i'm not yet satisfied. The weird thing is, it accelerated best when the ...
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4answers
42k views

What's the cause of Diesels' typical clatter noise?

I guess it's related to their basically running off knocking, but if I were to explain it to someone like this, it wouldn't convince me neither. [Edit] From http://www.ford-trucks.com/forums/369700-...
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6answers
6k views

What is regenerative braking and why don't we use it?

I know that many electric cars use regenerative braking to enable the car to become more efficient by converting what would otherwise be lost heat energy in to a more useful, reusable form of energy. ...
19
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1answer
7k views

What is happening when a two-stroke engine is said to be “four-stroking”?

Many years ago, I was involved in a hobby of building and flying model aircraft. The aircraft used alcohol-fueled 2-stroke engines with glow plug ignitions. When these engines ran rich (and always at ...
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3answers
24k views

Can a car operate without a catalytic converter?

So I was reading this Quora question which answers in the affirmative, but here's my misgiving: I was under the impression that the oxygen sensor which the ECU uses to adjust the fuel-to-air ratio, is ...
9
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5answers
59k views

Can revving the engine in neutral cause damage?

I pulled up at a light the other day next to a kid driving (what I assume to be) his dads 5.0 Mustang. As he proceeded to bounce off the redline and roast away half the clutch when the light turned, I ...
20
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5answers
22k views

Why do Harley Davidson engines suffer from such poor performance?

The modern Harley Davidson engine has very poor power output. Even when highly modified a 130HP engine can cost tens of thousands of US Dollars. Here are specs on one of the modern engines. Harley-...
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3answers
2k views

Can I attach a DC blower to intake manifold of my 150CC Yamaha FZS FI engine?

I am planning to add a 12V DC blower (https://www.amazon.in/gp/product/B00LPUXVWS) to intake manifold of my Yamaha FZS FI 149CC engine. I thought it could work more like a supercharger, except it will ...
20
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2answers
54k views

How is engine load determined?

I'm struggling to find information on how engine load is defined. Is it really just a fancy word for torque demand? There are three parts to this question: Is there a theoretical equation that is ...
2
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1answer
85 views

Why 3 x 2 barrel carbs on a v8 does not 4 x 2 make more sense with one two barrel per two cylinders

You hear of a "Six Pack" and "Tri-Duce" (carb setup with three two barrel carburetors) ... Wouldn't 4x2 barrels or 2 four barrels be better?
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3answers
85 views

How do paired injectors work?

I'm currently in the process of searching for a cheap standalone ecu, but the main limitation of them is the fact that they have only 4 injector outputs. I have heard and read in the ecus ...
10
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4answers
198k views

What actually happens when there is not enough coolant in a car engine?

I know that a lack of engine oil can destroy an engine, so I was curious as to whether it is just as bad to drive a car with a very low engine coolant. What is engine coolant? What exactly are all ...
29
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8answers
7k views

Why is engine displacement frequently a few CCs below an exact number?

I've noticed that engines are rarely exactly 1.5 liters or exactly 4.0 liters, and I'm okay with that. It makes sense that engines would have some arbitrarily ideal size for specific applications, so ...
16
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2answers
26k views

What is crankshaft grinding and why is it done?

I saw a lot of YouTube videos referring to crankshaft grinding, while watching videos about working on crankshafts. I don't understand what crankshaft grinding does. If we grind a crankshaft, then ...
1
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1answer
117 views

What actually happens when there is no Thermostat ( bypass thermostat)in coolant system?

What actually happens when there is no thermostat (bypass thermostat) in coolant system?
2
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0answers
29 views

How to analyse engine oil analysis results?

I got an engine oil analysis done on my 1991 CAT 3116 with 124,000k miles on it. I received a sheet of what I presume to be the result of some kind of spectrometry. As I'm not an analytical chemist, I ...
5
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2answers
105 views

How can my car run on 85 octane but be recommended to run on 91?

My manual recommends I use 91 octane, especially when at altitude or towing, but says I can get by on 85. To my understanding, the octane rating is a measurement of fuels tendency towards preignition, ...
2
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1answer
5k views

How much force is needed to push a piston down? [closed]

Combustion from fuel and air is used to push a piston down. When they combustion it creates a lot of force, my question is how much force is needed to push the piston all the way down when the vehicle ...
10
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7answers
11k views

How did they start diesel engines before the glow plug was invented?

According to this Bosch page, their glow plug was developed in the early 1920's. Yet the diesel engine was around for at least 20 years prior to that; the French used it in a submarine in 1904, for ...
11
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1answer
33k views

How does intake manifold runner length effect the power curve of a car?

Recently I learned that a number of things such as the cam profile, compression ratio and the intake manifold runner length and volume can all effect the power curve of the engine. Here is an ...
1
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1answer
112 views

Dangers of subjecting engine to over temp

It was explained to me long ago that if an engine gets too hot, it's at risk of seizing. The reason, as I understood it, was as follows 1) There's a certain gap between the piston and bore. As both ...
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2answers
49 views

What would cause this

first I replaced a motor mount on my 2001 Honda Odyssey and then a few weeks later that plug was like that but I did not blow it all the way out of the cylinder it was still partially threaded in ...
1
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1answer
54 views

What is the mechanism that causes an engine's RPM's to increase?

When the driver applies pressure to the gas pedal, the rate of the RPM's increases. Why? I can infer that this has something to do with more fuel/air in the cylinder and/or an earlier spark but ...
8
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2answers
46k views

What happens to a car engine when giving max throttle while not in gear

I was driving (well standing still actually) during rush hour, and I was suddenly wondering what would happen to a car engine when I would push the accelerator pedal all the way down while the engine ...
7
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2answers
1k views

Exhaust Backpressure and Its Impact on LTFT Values

This is a follow-up from my initial question which can be found here : LTFT and STFT values are off and don't make sense. Car : BMW 2015 F10 M5 Modifications : Eisenmann Race Catback Exhaust, ...