Engine displacement

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Engine displacement Empty Engine displacement

Post by SouthernFist7 on Sat Mar 24, 2012 10:54 am

What's the benefit of choosing the engine upgrade that increases the displacement of the engine (for example 4.0L to 4.3L?)?

Thanks!


Last edited by SouthernFist7 on Sat Mar 24, 2012 4:41 pm; edited 1 time in total
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Engine displacement Empty Re: Engine displacement

Post by BiggLou55 on Sat Mar 24, 2012 4:23 pm

That's not the total output, that is the the total combustion volume or displacement (of air) of the engine. Put simply, it's the total volume of all the combustion chambers together (Bore and Stroke; bore is the diameter of the cylinder and stroke is how far the piston travels). More volume = more fuel and air for combustion = more power....

Remember an engine is basically a big air pump... You get more power moving more volume through the cycles as well as with less restriction (intake and exhaust) and more pressure (turbo/supercharger). Basically the more oxygen molecules and fuel you can stuff into the chamber (volume & pressure), the more power you will produce. the faster you can move the air through the engine (Restriction/Flow), the more power you will produce.

Your standard gasoline engine is 4 cycles (or can be termed as strokes), hence the term 4-stroke or 4-cycle. The first stroke is the intake (down with the intake valve open pulling in the fuel/air mix from the intake); the second stroke is compression (up with all valves seated) and at the top of the stroke (max compression) is where the fuel air mixture is detonated by the spark; the third stroke is called the power stroke where the detonation of the fuel and air mixture forces the piston down; the fourth stroke is the exhaust stroke (up with the exhaust valve opened).

check this out for more info

You can actually change displacement two ways. The first is increasing the bore of the engine (hence the term bored over). the second is to change the length of the connecting rods (when someone says they threw a rod, that is what connects the piston to the crank), which increases the stroke of the piston.

It's the same principle as weight reduction. The less weight the car has, the quicker it becomes (quick = acceleration and handling; Fast = Top Speed). With weight reduction, you do not increase top speed since that is limited by drag and transmission gearing. Reducing weight increases handling and acceleration. Reducing weight may also reduce launch due to less weight over the drive wheels. Increasing HP increases the counter-force the car has to "push" the air aside. Increasing Torque increases the maximum turning force of the engine. More displacement increases the torque more than the HP. Think of it as more surface area on the piston head for the pressure of the detonation to push on. Think of Horsepower as the pressure of the detonation. HP is a linear force where torque is a turning force. The linear force of the piston is translated to turning force by the crank shaft.

Best way to remember is this:
Horsepower = Max Speed
Torque = Acceleration/Launch
Weight = Acceleration/Handling

There are plenty of other things like timing (crank and cam), fuel air mixture (thottlebody/intake/injectors), etc., but that will have to be another thread... Wink

If you have the SpikeTV channel, I highly recommend watching the Powerblock on Saturday/Sunday mornings. I've been watching for years and learned a TON!!

Hope this helped...


Last edited by BiggLou55 on Mon Mar 26, 2012 10:18 am; edited 4 times in total (Reason for editing : Added info and made some grammatical changes)
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Post by BiggLou55 on Sat Mar 24, 2012 4:36 pm

Added some more info to my post above....
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Post by SouthernFist7 on Sat Mar 24, 2012 4:44 pm

Extremely helpful. So an increase in the displacement is going to mostly increase torque, with a minor increase to hp?

by the way Lou, your advice about adjusting the values to the far right side of slave monkeys spreadsheet really helped me -
SF
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Post by BiggLou55 on Sat Mar 24, 2012 4:53 pm

You're welcome....

Increasing displacement will increase both HP and Torque, but you will see a larger % increase in torque over HP. At least you will in real-world applications. The larger displacement engines have more torque than smaller displacement engines. This is also why turbo and supercharging are so popular in smaller displacement engines. Increasing the combustion pressure increases torque, especially turbo chargers. Also heat plays a big part in combustion as well. The cooler the air is entering the combustion chamber, the more power that will be produced. This is due to the air expands as it is heated. That is the reason for inter-coolers on turbos and super chargers. As the forced induction system compresses the air, heat is generated. that heat is then dissipated by the inter-cooler prior to heading to the intake for combustion.
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Post by SouthernFist7 on Sat Mar 24, 2012 5:07 pm

Good god this stuff is complicated. I may need to go back to rad racer. If I could only find those 3d glasses.....
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Post by Markve91 on Sat Mar 24, 2012 5:46 pm

Yeah the displacement upgrade the engines has more of an effect on torque than hp compared to the other upgrades.

Lou, really good read, I always enjoy learning new things. I guess thats why I enjoyed physics class so much. Smile

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Post by marmuttlebow on Sat Mar 24, 2012 6:36 pm

2 phrases. ome to mind here.

There's no repalcement for displacement. (as inferred, off the line, bigger engine, typically gets off the line quicker).

And of course the high school fave, "suck, squeeze, bang, blow."

I'd provide more info, but typing it all out on the phone is a pain. Just remember the formula
Pv=nRT
What you need to remember is temperature is directly proportional to pressure and volume. I can't remember if this is Boyle's law, the gas law, or the perfect gas law. Been too long since I've been in school let alone a physics class.
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Post by MFKR RAMBO on Sat Mar 24, 2012 7:19 pm

If I wasn't on my phone right now I would contribute on this as engine building is something I have learned a great deal about. The game doesn't go into great detail on the engine side of things. Tuning for back pressure, piston speed and piston acceleration, offset grinding, volumeric efficiency, flow rates,ect. When you mentioned the bigger v8s having more torque, you were right by saying yes they have more displacment but an oversquare, square or undersquare motor also plays the major portion of deciding HP and tq.

Haha now this is what I love. Time to start arguing. There is a replacement for displacment. Called technology. When I get home ill post some thermal heat and stress images that compare a Larger NASCAR engine to a more modern day F1 engine. Arrow Weight to power is also huge as well as HP per liter. V8 cars claim to rule everything? No. I'm a Honda nut and this has been used in many of arguments. Honda s2000 has more horsepower per liter than a Corvette zr1 from the factory. I'll add more on the computer later.

Final thing. Building a engine. Fixed bore fixed stroke. What do you go with? Long rod or short rod and why?

To be continued when I get home
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Post by marmuttlebow on Sat Mar 24, 2012 7:28 pm

LOL, I stand corrected then. My bad.

I will blame teachers or lack thereof as I never learned the"technology" add on. That wasn't part of the lesson.

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Post by BiggLou55 on Sat Mar 24, 2012 7:51 pm

MFKR RAMBO wrote:If I wasn't on my phone right now I would contribute on this as engine building is something I have learned a great deal about. The game doesn't go into great detail on the engine side of things. Tuning for back pressure, piston speed and piston acceleration, offset grinding, volumeric efficiency, flow rates,ect. When you mentioned the bigger v8s having more torque, you were right by saying yes they have more displacment but an oversquare, square or undersquare motor also plays the major portion of deciding HP and tq.

Haha now this is what I love. Time to start arguing. There is a replacement for displacment. Called technology. When I get home ill post some thermal heat and stress images that compare a Larger NASCAR engine to a more modern day F1 engine. Arrow Weight to power is also huge as well as HP per liter. V8 cars claim to rule everything? No. I'm a Honda nut and this has been used in many of arguments. Honda s2000 has more horsepower per liter than a Corvette zr1 from the factory. I'll add more on the computer later.

Final thing. Building a engine. Fixed bore fixed stroke. What do you go with? Long rod or short rod and why?

To be continued when I get home

Please remember, My post is simplified. Put into layman terms, if you will. You have to be able to visualize the concept before you can understand the advanced stuff.

I look forward to your advanced stuff Rambo. Very Happy
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