Volumetric Efficiency?!

[Simon13]

I'm just mincing on the net and trying to learn a bit more

So VE is how much air the engine can take into each cylinder as a % of the cylinder size

Correct my maths or conclusion on this but.......my engine for this is an M20

From what i've read 100% VE in a road engine is pretty good. Race engines can manage up to 130%

"A rough guide though is that if you multiply the torque per litre by 1.4 you get a close approximation of the VE as a percentage" from the web site

So i've done this for an M20 2.5 and Alpina spec 2.7

2.5's make 166lbs correct? so divided by 2.5=66.4
66.4 x 1.4= 92.96%VE

Which would make it very good for a road engine?!

2.7 pina 213lbs 213 divided by 2.7 = 78.88
78.88 x 1.4 = 110.4%VE - which is very good!

As a 3.2 M3 lump 321bhp is 112%VE

So the M20 has a pretty good incduction system in the first place?

I'm rambling and i know it's not the whole picture but.....

[Yaninnya]

It is extremally rough guide as it is not taking into account the bore/stroke ratio. Long stroke engines are more torque and big bore ones got more power (and it is extremally rough as well).
Basicly in standard engines VE is far lower than 90%.
Jan

[Turbo-Brown]

I believe the S50B32 engine achieves an astounding 102% VE at somewhere over 6200rpm (can't remember the exact figure but it's bloody good for a roadgoing engine!)

I'd guess that looking at your AFR against crank speed would give a better indication of VE, but I've not really thought that through, just typed it out

[Gunni]

You can only measure VE through air flow measurements not HP output, there are so many things within the engine that have affect of output.

But I have it established from one of the best minds on engines that VE has to do with the pressure differential between
exhaust manifold and intake. Change the exhaust manifold and VE changes at some points in the rev range.
Which is normally not mentioned.

Also that 1.4 thing is not that good of a guide, what it is doing is basically using the convertion from lbs to NM
to establish 100nm/liter as 100%VE which is not true,.

More on VE. 100% is maximum, that is just so, as it´s Volume that doesn´t take into account any density.
What is measured as 130% is 100% VE x 1.3 density charge through ram air effect and scavenging done by the exhaust manifold pulses.
Basically the mean pressure into the engine is 30% higher then ATMO over the course of the intake valve opening.
What also happens makes the 30% is the fact that it´s the exhaust pulses that are creating a depression in the exhaust manifold and cylinder which in turn changes the overall pressure differential over the engine

So if it´s 105kpa in the intake at that point and 70kpa in the exhaust.
That is the same as 100kpa in the exhaust and 135kpa in the intake(i.e same as 0.35bar boost)
It´s the high pressure difference when both valves are open that get the air charge moving ALOT sooner and at a higher speed and the high speed is maintained better after the exhaust valve closes, then it´s a case of the intake wave pulses that stash the air into the engine until the valve closes.

engines are fun

[maxfield]

A little over ones head

[Simon13]

Good read Gunni! I understand all of that so the last bit means certain cams are helping get the air in and out quicker at certain rpms?

Should you avoid reading US stuff on the net? I just typed in "increasing torque" on google and just read what it came up with alot of stuff i found a good read!

"If you are going to run a big cam, one of the bonuses is that you can increase the compression ratio slightly without incurring a detonation penalty. The increased compression will boost the low-end torque and extend the top-end power range. Experienced engine builders have found that 9:1 compression engines require at least a 270-degree (advertised duration) cam. On the other hand, 10:1 engines are happy with a 280-degree cam, and a 290-degree cam will allow you to run nearly 11:1 compression. Depending on other engine variables, such as combustion-chamber shape, bore diameter and ignition timing, some engines will detonate under these conditions"

What do we think of this as i thought it was interesting? Just another piece i've found tonight!

[Jon_Bmw]

Have you been doing english and maths lessons at your polish workstation simon!

[billgatese30]

Good read Gunni! I understand all of that so the last bit means certain cams are helping get the air in and out quicker at certain rpms?

thats basically how tuning the correct amount of cam overlap in twin cam engines can give good sometimes give suprising gains

[Gunni]

Good read Gunni! I understand all of that so the last bit means certain cams are helping get the air in and out quicker at certain rpms?

Should you avoid reading US stuff on the net? I just typed in "increasing torque" on google and just read what it came up with alot of stuff i found a good read!

"If you are going to run a big cam, one of the bonuses is that you can increase the compression ratio slightly without incurring a detonation penalty. The increased compression will boost the low-end torque and extend the top-end power range. Experienced engine builders have found that 9:1 compression engines require at least a 270-degree (advertised duration) cam. On the other hand, 10:1 engines are happy with a 280-degree cam, and a 290-degree cam will allow you to run nearly 11:1 compression. Depending on other engine variables, such as combustion-chamber shape, bore diameter and ignition timing, some engines will detonate under these conditions"

What do we think of this as i thought it was interesting? Just another piece i've found tonight!

This is true as it´s relating to dynamic compression.

I did get a A on my engine design paper ;)

[reggid]

Good read Gunni! I understand all of that so the last bit means certain cams are helping get the air in and out quicker at certain rpms?

Should you avoid reading US stuff on the net? I just typed in "increasing torque" on google and just read what it came up with alot of stuff i found a good read!

"If you are going to run a big cam, one of the bonuses is that you can increase the compression ratio slightly without incurring a detonation penalty. The increased compression will boost the low-end torque and extend the top-end power range. Experienced engine builders have found that 9:1 compression engines require at least a 270-degree (advertised duration) cam. On the other hand, 10:1 engines are happy with a 280-degree cam, and a 290-degree cam will allow you to run nearly 11:1 compression. Depending on other engine variables, such as combustion-chamber shape, bore diameter and ignition timing, some engines will detonate under these conditions"

What do we think of this as i thought it was interesting? Just another piece i've found tonight!

Sure raising the CR will boost lowend (compared to not raising it) but probably not enough to offset the loss in dynamic compression at low rpms from the late intake valve clsoing point so you still generally lose lowend with a bigger cam.

What i find interesting is that the power gained from upping the CR is theortically very small and only due to change in thermal efficiency (Otto cycle analysis) however this analysis doesn't account for the VE changes.

the relationship between VE and torque is very close with the other factors being combustion efficiency (you get the air in but you need to release the energy in the fuel to generate any force/torque/power) and parasitic losses (how much of the torque goes into driving ancillaries).

I generally use VE principle tell whether tq numbers are likely BS by looking at Nm/L given that is somewhat linked to VE. The the S54B34 in the E46 M3 CSL claims to have the highest of any production car IIRC at 114Nm/L (370Nm/3.246L) for example say someone claims a NA SOHC 2.7L making more than 230lbft (116Nm/L) then i find it suspicous in all honesty.

[Yaninnya]

Experienced engine builders have found that 9:1 compression engines require at least a 270-degree (advertised duration) cam. On the other hand, 10:1 engines are happy with a 280-degree cam, and a 290-degree cam will allow you to run nearly 11:1 compression. Depending on other engine variables, such as combustion-chamber shape, bore diameter and ignition timing, some engines will detonate under these conditions"

You shoud stop reading this. Enormous BS. I wonder, to what "experienced engine builders" he was talking to?
Performance engine building is not a basic math. Yes, you can (and you shoud!) support yourself by a theoretical calculations but first of all you need to have quite long experience to allow yourself to estimate like this. And it will be not as simple as this!
Jan

[Gunni]

But the point that is beeing made is correct, at lower rpms it´s got low ve and thus not as much air beeing compressed at a slow rate that allows the charge to raise it´s temps quite nicely and may allow for detonation.

It´s how they put it out which leaves much information needed.

[Simon13]

What do we think of this then? It's just a snippet of the whole page

"So in first and second gear this is a pretty important effect - I built an engine recently and managed to remove nearly 3 Kg from the outside of the standard flywheel - so that would be equivalent to lightening the car by over 100 Kg in 1st gear - not to be sneezed at in terms of acceleration from rest. With special steel or aluminium flywheels even more "moment of inertia" can be saved. The recent trend in racing engines to using very small and light paddle clutches and flywheels is therefore more effective in terms of the overall performance of the vehicle than it might first appear. Copyright David Baker and Puma Race Engines"

here's the link

http://www.pumaracing.co.uk/FLYWHEEL.htm

[stuartgallafant]

If this is what happens to you when you move in with a bird, then Amen to be single!!!

[Simon13]

it happens to us all lol I'm having a very homo week

More reading! Makes sense to my small brain.....

"Cylinder heads are where the power is, but there are limitations. You are generally limited to what's available, and, for most people, porting is a luxury. Increased airflow always means more top end power. For the most part, it is better to run a larger valve, if possible, and a shorter camshaft. This allows the larger valve opening to do the work of filling the cylinder while the cam remains relatively mild. Torque will be increased. Bigger valve heads may give you more overall torque than a simple cam swap. If your heads have stock-sized valves and you put in a larger cam, you will have to spin the engine faster to make the same torque and power.

That's the simplified version, but there are other considerations. The length, area and volume of the intake system all affect the engine's output. Most hot street engines will benefit from bowl porting and a good valve job, but you should avoid significantly enlarging the ports. The minute you start enlarging the port, you are bleeding off potential torque. Unless your engine will spend a lot of time at elevated engine speeds, don't start hogging out those ports.

If you have the ability to modify heads, you can extract more torque and horsepower by porting for efficiency, but the process is tedious at best. Street enthusiasts aren't generally in a position to flow heads and check port dimensions. If you are, the intake port area should be about 80 percent of the valve area, and the port should enlarge at a 2- to 4-degree taper out to the plenum. This is pretty standard on most available heads.

Exhaust ports should not be enlarged significantly unless you're running nitrous oxide, which produces a greater exhaust requirement. Most good aftermarket headers have been sized and built to create a negative pressure at the exhaust valve during overlap. This ensures good cylinder scavenging and reduces the potential for exhaust reversion: Exhaust gas speed remains high, and the pulse waves are tuned to aid the exiting exhaust charge."

[Yaninnya]

But the point that is beeing made is correct, at lower rpms it´s got low ve and thus not as much air beeing compressed at a slow rate that allows the charge to raise it´s temps quite nicely and may allow for detonation.
It´s how they put it out which leaves much information needed.

It is but only for someone who know it because than you already know massive amount of other informations which are nesesary to do it right. For me it is just unfair info for all other which don't know how to do it because it is so uncomplite.
Also I can say that CR 9:1 needs a 255 cam, 10:1 a 285 and 11:1 at least 305 and it will be correct. But only for just feew engines.

For the most part, it is better to run a larger valve, if possible, and a shorter camshaft. This allows the larger valve opening to do the work of filling the cylinder while the cam remains relatively mild. Torque will be increased. Bigger valve heads may give you more overall torque than a simple cam swap.

Sorry but that is just bollocks. It is better to run a as large valve seat as possible - yes, but valves as small as possible. Also you can gain loads more by reshaping valve seat than just fiting bigger valve. Bigger valves are necessary evil. If you just can't get any futher gains form your port/valve seat and you need to enlarge them/replace, than you just must fit bigger valves (reshaped ones!).
Jan