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
42 views

How are ignition timing and fuel injection timing controlled?

I understand how the valve timing is controlled by a camshaft with a connection to the crankshaft using either a belt or chain, but the valves aren't the only things that need to be in sync with the ...
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18 views

How to design an exhaust pipe to increase scavenging at specific RPMs

Good day all. I'm looking for advice on an exhaust design problem. It is easy to find videos explaining exhaust scavenging, but how do you control it? Surely there must be some physics that can be ...
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67 views

Which engine type gives more HP- two or four cycle?

Same max. RPM and CC of course. And if possible, an explanation would be nice. Thanks!
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1answer
40 views

Engine performance

On a straight four diesel engine Can you replace some pistons bearings and leave other unchanged , Will that have any negative effects on the performance of the engine
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39 views

Exhaust back-pressure Q on simple 2-stroke yard-equipment engines:

I am having trouble getting a precise answer- is back-pressure necessary on a little single-cylinder 40cc 2-stroke like a chainsaw or a blower? I ask because people frequently modify mufflers to ...
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1answer
51 views

How does enough oil remain after combustion to lubricate during exhaust stroke

To my understanding, cylinder walls are lubricated by retaining a tiny amount of oil in the honed or otherwise manufacturing prepared cavities in the cylinder walls, so that when the piston rings ...
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1answer
44 views

Load in higher gear vs fuel consumption

I saw a video explaining that put the car in higher gear where possible to avoid high revs thus maximising mileage, this lead a thought in my mind about what happens if the revs are low and gear is ...
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2answers
113 views

Why oil changes and not oil replenishment

Provided that the oil filter of an engine would be swapped every x time intervals as needed to be kept clean, I was wondering if, instead of removing all engine oil and replacing it with new (clean ...
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2answers
107 views

Engine oil metal shavings origin

Yesterday when changing oil on a Ducati 848 EVO 2012 motorcycle after about 4000km (which is soon enough considering it went through a track day) I noticed a small concentration of microscopic metal ...
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1answer
112 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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1answer
109 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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2answers
45 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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8 views

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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1answer
72 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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69 views

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 ...
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1answer
71 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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0answers
87 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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1answer
328 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
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 ...
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3answers
120 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 ...
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1answer
228 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?
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2answers
134 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, ...
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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 ...
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2answers
51 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 ...
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1answer
175 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 ...
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2answers
588 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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0answers
26 views

Optimizing temperature and spark for horsepower

I recently completed a heads+cam project on my car to increase horsepower. I ended up falling about 50hp short of my goal, and am looking for every little knob I can turn to eek out that last little ...
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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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1answer
60 views

What happens inside a 4-stroke gas engine when it's first (cold) started at below 0f?

I'm asking in order to understand the risks (if any) specifically to an engine if I (cold) start it on days that are below 0f, and I don't use an oil pan heater or similar device. If we need to be ...
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2answers
85 views

Why is compression necessary?

I know that proper compression is necessary for all engines to run well, but I have never understood why. I researched it and I learned that compression makes the explosion more powerful but it still ...
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1answer
94 views

Is there anyway a shade-tree mechanic can check MAF calibration?

When it comes to testing MAF sensor on my vehicle, the factory service manual just suggests two PASS/FAIL tests: an out-of-circuit resistance reading at a particular ambient temperature validating ...
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3answers
767 views

Wasted spark ignition systems on a multi- cylinder engine

In a wasted spark system if the firing plug on the compression stroke requires 10,000 volts and the wasted spark coil is designed to put out 20,000 volts, is the voltage split in half. How exactly ...
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2answers
35 views

How does atmospheric condition affect operation and consumption

In most modern engines the intake air parameters such as temperature, pressure, humidity etc can be monitored via sensors and so the exact fuel mixture can be trimmed to best efficiency. Still aren'...
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2answers
779 views

Why don't cars have multiple disk clutches as motorcycles do?

We know from our experience so far that wet multiple disk clutches like these used on motorcycles have a way longer life that single disk clutches used in car engines. Why don't cars use the same ...
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4answers
658 views

Engine pre-startup automatic lubrication to prevent wear

As explained here (Is it true that most of the engine wear during its life time occurs during a cold start up?) most of the wear of an engine is during startup and especially during cold startup. Why ...
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3answers
4k views

Why don`t we use extremely thin oils in engines

I understand that lower viscosity oils are way easier to pump and move around engine parts, also they form a thinner "film" on friction surfaces which could improve parts measurements precision etc. ...
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1answer
43 views

Driving down hill in gear with throttle engine sounds bit high

basically, i am not know much about bikes engine. i got a question when i riding bikes in downhill with lower gear the engine sounds very noisy I think engine runs more than the ideal speed, my ...
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1answer
96 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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4answers
23k views

Is revving the engine to redline on idle at morning bad? [duplicate]

I own a Ford Ecosport Diesel Turbo 1.5 TDCI. Every morning when I start the car, I put it on neutral and rev it up to 6K RPM for 3 seconds then bring it back to normal idling without revving and start ...
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2answers
156 views

Could a wind turbine work for a car?

Could I attach a little fan to power a motorcycle alternator to be more efficient then running off the engine? Attach any where facing the wind on the vehicle to increase mileage from eliminating ...
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2answers
816 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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3answers
140 views

Does clutch and gearbox order matter?

Does it matter if engine power goes through the gearbox before the clutch, or through the clutch before the gearbox? I'm not sure if there has to be a specific order of clutch & gearbox, or if it'...
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3answers
11k 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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2answers
2k views

Relationship between torque, power, specific fuel consumption, and AFR

How does Torque, power, and specific fuel consumption change with AFR? And why is it so? I found graphs relating these in books as well as websites but I couldn't find any good explanations.I have ...
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1answer
1k views

How to calculate the compression height of a piston?

To better help understand about pistons, I have the following questions: What is the compression height of a piston? How is it calculated? Why is it important to know when building an engine?
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3answers
275 views

Can a stock ECM be modified to function with some modules disconnected [closed]

Engine in question: VOLKSWAGEN PASSAT 2015 - 2.0L, (VIN V, 5TH DIGIT, DIESEL), (ENGINE ID CVCA) I hope to buy a rear-end collision Passat with this engine, and use as many parts as I can in a custom ...
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1answer
586 views

How are compression rings lubricated?

My question relates to the lubrication of cylinder walls and piston rings. It is my understanding that pistons in cars consists of 3 rings; two compression rings and the oil/scraper ring. As far as I'...
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7answers
15k views

Why are engines labeled as 2L or 3L?

Why is an engine said to be a 3L or 2L for that matter? I understand that V6 represents 6 cylinders, so I'm a little bit confused. I'm still busy with my motor studies.
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358 views

Starter Motor Power

I have two 6 cyl. diesel engines one with turbo and starter motor 4KW and the other without turbo and starter motor 2.5 KW What happen if I replaced 12V 4KW with 12V 2.5KW starter motor?
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170 views

heater not not working

Isuzu heater is not working despite having bought thermostats at several occasions, I checked for pipe leaks, checked for blower fan , but still cannot see the cause of the problem

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