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Holden Engine Efficiency

Kiddo

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So i was reading an article on Autospeed about engine designs, and came across something called the BMEP calculation. Below is a snippet from the article explaining what it is and how its worked out;

BMEP refers to the average pressure that acts on the piston during the engine’s four strokes. The higher it is, the more the design has been optimised. And the key thing about BMEP is that it takes into account engine rpm, engine volume and engine power output. It’s the only equation to use when comparing engines from the perspective of saying which is more highly developed. It doesn’t matter whether the engine uses pushrods; 2 valves per cylinder, 4 valves per cylinder or 5 valves per cylinder. It doesn’t matter whether the engine revs to 8000 rpm or 1500 rpm. You can use the equation to directly compare any 4-stroke engine, whether it’s 660cc or 5.7 litres

And you can even use it to compare naturally aspirated and forced induction engines. The BMEP figure for a forced induction engine will have a major advantage, but it’s still a valid method of comparison.

OK, so how do you use this wondrous formula? Keeping it all metric, it looks like this:

BMEP = kW x 1200/litres x rpm

So i thought I'd calculate the BMEP for popular holden engines, as an unbiased comparison on their design.


RB30E VL Commodore - 114 kW at 5,200 rpm - 8.8
RB30ET VL Commodore - 150 kW at 5,600 rpm - 10.7
3.8 Buick - 125 kW at 4,800 rpm - 8.2
Ecotec - 147 kW at 5,200 rpm - 8.9
5.0 V8 (VS HSV Clubsport) - 185 kW at 4,800 rpm - 9.25
L67 Supercharged - 171 kW at 5,600 rpm - 10.4
LS1 (VT) - 220 kW at 5,000 rpm - 9.2
LS1 (SV300) - 300 kW at 6,000 rpm - 10.5
LS2 6.0 (HSV) - 297 kW at 6,000 rpm - 9.9
LSA Supercharged 6.2 - 430 kW at 6,000 rpm - 13.8
 

Pollushon

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Seems clever enough although comparatively it has its flaws.

No one drives at max rpm constantly, in fact it only makes up a small proportion even on performance vehicles . Engines often have an optimal rev range for fuel used vs. revs vs. power output that isn't this.

To combat this and get objective readings you'd need a flywheel output dyno graph.
 

Jesterarts

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Given that the point of the figure is to compared the efficiency of the engines relative to capacity, there is no flaw.

You take the engine to its most efficient power point, so the highest power read out and then take into account rpm and capacity. The most efficient engine being the one that can get the most power per litre for each rpm.

Have I missed something?
 

Pollushon

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Maybe. My point being for example a vehicle might produce 200kw @ 4500 and 230 @ 7000. Let’s say it’s a 3.0L V6 for argument sake. I’m purposefully augmenting the specs to make the difference more profound.

200kw @ 4500 = 17.5
230kw @ 7000= 13.1

Now factor in all the other kw to rpm points in a torque curve and a final maximum RPM efficiency reading might prove to be a bad way to ‘judge’ the engine efficiency. I think it would be useful setting a standard across points of torque and averaging that for comparisons.
 
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VR38

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From what I can see it really boils down to the relative compression ratio each engine uses, of course the engine with the highest compression ratio (along with it's correct octane fuel) will be the most efficient.
This we can see with the charged engines at max RPM would be at max boost.
 

delcowizzid

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haha i worked out the v6 turbo at 19.6
 

delcowizzid

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aris bigblock :D
 
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