Torque and related - Knowledge Base Q

[a_k]

Revamped

Engine (NA) produces torque at certain high RPM and then its drops, this is because of the Volumetric Efficiency declines i.e. the engine can’t breathe any faster. Mechanical efficiency also declines at higher RPM, due to increased frictional resistance which further reduces torque at the output. As RPM declines from high levels these limiting factors diminish, allowing torque to increase.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com<img src=" /><o:p></o:p>
Q: This suggests that torque will continue to increase as RPM drops !?
<o:p></o:p>
Q: Big bang requires more fuel mixture, so what is the significance of combustion chamber size?
<o:p></o:p>
Q: Compression ratio is calculated at 100% cylinder filling, does it means that cylinder is not filled 100% all the time at different RPM with air/fuel, air or fuel only?
<o:p></o:p>
Q: Heat in engine is transferred from combustion chamber to walls into coolant, but through study of thermodynamics it is clear that fuel mixture when hot ignites better, so a 4 cylinder engine of let say 2500cc and a V6 2500cc will have different characteristics just because 4cycl have small combustion chamber, which allows the heat transfer at slower rate??<o:p></o:p>
Further in the statement at top the mechanical efficiency also drops, is that mean a big V8 engine will lose more as compared to small I4 engine?<o:p></o:p>

Q: Finally how to get a flat torque curve?<o:p></o:p>

[a_k]

Q's rephrased

[saadzae92]

Good questions!

I better do some more reading.

thank you.

[Xulfiqar]

engine torque is highly related to the build (style) of the lower block and also the cam timing in an engine. Other factors of volumetric efficiency also come into play as different head designs promote or prevent air flow at different engine speeds.

lets take engines that actually shove out gorilla torque - turbo diesels. Their operation principle is regardless of air volume and controlled by fuel volume. Their stroke is longer than their bore, the rod is quite long which causes the piston to "live" at TDC longer, this action causes maximum shove and hence a brute force pushing the piston downwards (which we record as higher torque).

I'll post along as required. Its quite interesting.

[TeamAMS1]

<font size="3">Engine (NA) produces torque at certain high RPM and then its drops, this is because of the Volumetric Efficiency declines i.e. the engine can’t breathe any faster. Mechanical efficiency also declines at higher RPM, due to increased frictional resistance which further reduces torque at the output. As RPM declines from high levels these limiting factors diminish, allowing torque to increase.<o:p></o:p></font></font><br> <font 0[/IMG]Q: This suggests that torque will continue to increase as RPM drops !?
<o:p></o:p> its basically the head unit and the manifold(runners/plenum) which is all that causes low VE but upgrading CAMS/using larger bore and higher compression will keep the power up top(cams well they are of 2 types basically low duration(low/mid range cams) high duration(rough idle/top end cams) torque does drop after a certain rpm but it doesnt just vanish
Q: Big bang requires more fuel mixture, so what is the significance of combustion chamber size?
chamber size is something to play around there is no such thing as best compression or chamber size it depends on how good the clearance is(piston to valve contact) and how good the cam works with the given compression
<o:p></o:p>
Q: Compression ratio is calculated at 100% cylinder filling, does it means that cylinder is not filled 100% all the time at different RPM with air/fuel, air or fuel only?
<o:p></o:p> sorry not following u
Q: Heat in engine is transferred from combustion chamber to walls into coolant, but through study of thermodynamics it is clear that fuel mixture when hot ignites better, so a 4 cylinder engine of let say 2500cc and a V6 2500cc will have different characteristics just because 4cycl have small combustion chamber, which allows the heat transfer at slower rate??<o:p></o:p>
Further in the statement at top the mechanical efficiency also drops, is that mean a big V8 engine will lose more as compared to small I4 engine?<o:p></o:p>
debatable (need someone to pick one) lol
Q: Finally how to get a flat torque curve?<o:p></o:p>[/QUOTE]
depends on engine design but power is all in the timing(cam+ignition) fuel is just a saver! if only engines were bullet proof so we wouldn't care of running lean lol

btw nice topic :x

[Xulfiqar]

no engine is 100% volumetric efficient because it takes rotation for the piston to move down and the valve(s) to open at the same time.

a general assumption is that 4 valve pentroof chamber engine is 90% efficient, 3 valve about 85 and 2 valve about 70 to 75%. but torque is more related to lower block design, e.g. the subaru EJ engines are boxer engines and have SOLID torque because of its firing pattern, rotating mass and good centripetal balance.

[PKTUN]

?? bas ?
very zabardast parh kar maza aya aur samhaj bhi aya jazak ALLAH