Question on air consumption

[CanAutM3]

Originally Posted by BMRLVR

The M156 has nearly identical Lb/Ft per litre to the S65 so it may be roughlythe same VE at redline. A quick look at a dyno chart to see what the curve does as it approaches redline.

I would guess that the M156 and S65 would have similar VE at torque peak since they have similar torque per liter figures. However, the M156 in standard C63 guise (451hp) has much more torque drop off compared to the S65. It only produces 79% of its peak torque at peak power compared to 88% for the M3 (83% for the 480hp M156).

This would lead me to believe that the M156 has less VE than the S65 at redline...

Any flaws in my logic?

[M3takesNYC]

Originally Posted by bruce.augenstein@comcast.

Power and torque per liter is definitely harder to come by in a big engine than in a smaller one.

Not to put down the S65. It deserves all its awards.

Bruce

Why Bruce? I would say a more true statement in my mind is a larger displacement engine is "less necessary" to get as much hp/torque per litre given you have more to work with to reach your intended goal power/torque. But why is it harder to tune a 6 litre vs a 4 litre for example to make max power?

I guess you start to become limited when you start to have longer strokes and thus can't really build a high rpm motor due to lack of air flow and thus each litre of engine is not pushed to its limit of power production without revving it out I would assume.

Although in the SLS the AMG 6.2 V8 revs to 8k.

Interested to here more from you Bruce I didn't think of this before

[BMRLVR]

Originally Posted by CanAutM3

I would guess that the M156 and S65 would have similar VE at torque peak since they have similar torque per liter figures. However, the M156 in standard C63 guise (451hp) has much more torque drop off compared to the S65. It only produces 79% of its peak torque at peak power compared to 88% for the M3 (83% for the 480hp M156).

This would lead me to believe that the M156 has less VE than the S65 at redline...

Any flaws in my logic?

No flaws at all....... Exactly what I was getting at, I just did not have time to compare dynos when I replied. That would mean that the M156 is "roughly" 9% less volumetrically efficient at redline. The torque curve is essentially the VE measure for an engine....... with a small error since it can not compensate for increased frictional losses as RPM's increase.

Originally Posted by bruce.augenstein@comcast.

Add the E60 M5 engine at 76.8 lb/ft per liter

Definitely........ The torque curve of the S85 is much peakier than the S65, serves to show that in order to flatten the the torque curve of the S65 they compromised on specific torque output.

[bruce.augenstein@comcast.]

Originally Posted by M3takesNYC

Why Bruce? I would say a more true statement in my mind is a larger displacement engine is "less necessary" to get as much hp/torque per litre given you have more to work with to reach your intended goal power/torque. But why is it harder to tune a 6 litre vs a 4 litre for example to make max power?

I guess you start to become limited when you start to have longer strokes and thus can't really build a high rpm motor due to lack of air flow and thus each litre of engine is not pushed to its limit of power production without revving it out I would assume.

Although in the SLS the AMG 6.2 V8 revs to 8k.

Interested to here more from you Bruce I didn't think of this before

A "big" engine gets somewhat limited because a longer stroke, longer rods, etc. are subject to higher loads from centrifical force, but perhaps the even bigger elephant in the room is that the speed of sound is a constant that can't be exceeded by either intake or exhaust flow. Thus, it's harder to completely fill larger cylinders at high rpm than smaller cylinders. Just the depth of a large cylinder with a long stroke means that it takes longer for the fuel/air mixture to get there. Yeah, we're talking milliseconds here, but at high rpm, milliseconds are all we've got to complete a given task.

With torque per street-legal liter maxed out at around 90 foot pounds, high rpm is the only way to make big power per liter in a normally aspirated engine, so power per liter goes down (at any given state of tune) as cylinder sizes go up - again because big cylinders are harder to fill and empty at high rpm than small cylinders.

Bruce

[bruce.augenstein@comcast.]

Originally Posted by BMRLVR

...The torque curve of the S85 is much peakier than the S65, serves to show that in order to flatten the the torque curve of the S65 they compromised on specific torque output.

I'll comment on this in the other string...

Bruce

[bradleyland]

Originally Posted by bruce.augenstein@comcast.

A "big" engine gets somewhat limited because a longer stroke, longer rods, etc. are subject to higher loads from centrifical force, but perhaps the even bigger elephant in the room is that the speed of sound is a constant that can't be exceeded by either intake or exhaust flow. Thus, it's harder to completely fill larger cylinders at high rpm than smaller cylinders. Just the depth of a large cylinder with a long stroke means that it takes longer for the fuel/air mixture to get there. Yeah, we're talking milliseconds here, but at high rpm, milliseconds are all we've got to complete a given task.

With torque per street-legal liter maxed out at around 90 foot pounds, high rpm is the only way to make big power per liter in a normally aspirated engine, so power per liter goes down (at any given state of tune) as cylinder sizes go up - again because big cylinders are harder to fill and empty at high rpm than small cylinders.

Bruce

This point taken to the extreme:

R/C car engine

Displacement: 0.28 in^3
Power: 3.1 HP @ 33,000 RPM
Force: 0.49 ft-lb @ 33,000 RPM

That's 106.5 ft-lb per liter. Although, it is a two-stroke, so that's not a fair comparison to a four-stroke engine.

[e1000]

Originally Posted by bruce.augenstein@comcast.

Coupla things -

As far as ram air goes, I remember an article from a number of years back wherein the designers/runners of a Bonneville streamliner were queried in regard to the NASA ducts they used for intake. At the time, the NASA design was considered to be the most efficient intake (probably still is), and these guys said they basically got back to ambient air pressure after subtracting surface friction on the way to the engine inlet.

I think you mean NACA ducts.

http://en.wikipedia.org/wiki/NACA_duct

Although I freely admit Wikipedia isn't always the best resource, but it does state:

"This type of flush inlet generally cannot achieve the larger ram pressures and flow volumes of an external design"

[the_road_less_traveled]

Originally Posted by CanAutM3

If we stay with the 80% volumetric efficiency assumption and figure that the engine runs about 15% rich at WOT, that would equate to about 1.7 liters of fuel per minute at 8400RPM WOT.

Note: these are only approximations to provide a ballpark figure .

What elevation, temp, and density are assuming?

[CanAutM3]

Originally Posted by xfirer1guy

What elevation, temp, and density are assuming?

Standard atmosphere: 15degC, 101.3kPa, 1.225kg/m^3 and 0.76 kg/l for the fuel.

The biggest assumption here is the 80% volumetric efficiency at 8400RPM WOT.

[FogCityM3]

Confirmed it is 17 cubic meters of air per minute (17k cubic liters). Source = BMW International Media Launch presentation, pg 26.

Originally Posted by bruce.augenstein@comcast.

Could be, but as just mentioned I am slightly skeptical because I feel the torque peak is unnaturally low, rpm-wise, and a teensy bit anemic.

Bruce

[FogCityM3]

http://www.autospies.com/images/user...%20details.pdf

pg 26 of the presentation.

Originally Posted by CanAutM3

That number sounds optimistic as it implies a volumetric efficiency close or higher than 100%.

Can you link the source?

[///M Power-Belgium]

Originally Posted by mhabs

Confirmed it is 17 cubic meters of air per minute (17k cubic liters). Source = BMW International Media Launch presentation, pg 26.

That's what i told.... already on page 1 of this tread !

[CanAutM3]

Originally Posted by mhabs

http://www.autospies.com/images/user...%20details.pdf

pg 26 of the presentation.

Thanks a lot for sharing the link, that is a fun read. I am not sure however how scientifically the 17m^3/min was established. It is a marketing presentation. If you go a few pages down, they also quote the same number on the page about optimized aero and cooling...

[bruce.augenstein@comcast.]

Originally Posted by e1000

I think you mean NACA ducts.

http://en.wikipedia.org/wiki/NACA_duct

Although I freely admit Wikipedia isn't always the best resource, but it does state:

"This type of flush inlet generally cannot achieve the larger ram pressures and flow volumes of an external design"

Yeah. Now that you pointed it out, I think I meant NACA ducts too.

In any event, these NACA ducts were on a forward edge of the body, so they were in fact in a high pressure area.

Bruce