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How well can you balance power with efficiency?

We've had plenty of car challenges and competitions - how about a plain and simple engine challenge? The goal - design an engine which is powerful, efficient, and reliable. The formula we will be using is

[Performance Index]*[Efficiency^1.5]*[Reliability^0.5]/[Liters]

The efficiency is in %, seen in the final engine tab. Yes, this formula puts a lot of emphasis on efficiency - this is to offset the power density advantage of smaller engines.

Here is the ruleset:
Year 2016 or earlier
Max 95RON
No race intakes
No race exhausts
Must have catalytic converter
Loudness under 60
ALL QUALITY SLIDERS 0 (I will consider opening a separate category for no quality restrictions)

Current leaders:
Turbocharged
USDMFTW - 2083 i6 - 149.1
phale - 1.6L I6-SS Efficient Plus - 144.1
koolkei - 2.5L I4 Turbo - 128.2

Naturally Aspirated
MrChips - CMW X70 B60X0 - 91.5
UMM - I416ECR - 90.1

Simply post a screenshot of the final engine tab in this thread to enter. Don't forget to name your engine something cool if you want

Here is the best I can come up with, a 1.6L I4 Turbo with 0 quality sliders:



It produces 255HP with 25.72% efficiency, so the calculation is (255/1.600)*(0.2572) = 41.0

Please use as many decimal places as possible in your calculations!

Good idea, but too few metrics used to determin the score.

Not having reliability weigh in means if you use more then 50 reliability you are handicapping yourself.

Score of 42.8

HP/Liter*Eff*Reliability? That would be pretty interesting. Also, I could use Performance Index instead of HP to prevent setting the rev limiter at the max RPM.

However, I have discovered that this favors small engines too much - I was able to achieve 48.4 with the tiniest possible I4. If reliability is factored in, then small engines will have an even bigger advantage. Any suggestions?

Any balancing to take the advantage away from small engines would mean putting greater emphasis on higher power output. You may wish to consider multiplying the total power output by a small exponent.

Alright, after some experimenting and comparing between various engines, I have come up with a new formula:

[Performance Index]*[Efficiency^1.5]*[Reliability^0.5]/[Liters]

So yes, the new formula weights efficiency above all else, which is interesting because larger engines are generally more efficient, but less power-dense. I was able to get similar numbers from a 0.4L I4, a 2.4L I6, and a 4.0L I6.

By the way, I originally came up with the HP/L*Eff idea because I use it very often as a quick way to determine the quality of an engine. It's easy to calculate at a glance and I can use it to quickly compare different engines. Generally a HP/L*Eff above 30 is good. While it's clearly not a good formula for a competition, I encourage you to design engines with HP/L*Eff in mind - I do that for all of my engines.

So this is my best engine under the new formula:



It achieves a score of 135.7

Here is an album comparing a 0.4L engine, 2.4L engine, and 4.0L engine: http://imgur.com/a/p7d4D
The 2.4L scores 135.7
The 4.0L scores 134.9
The 0.4L scores 133.5

Have at it guys! I want to see what you can come up with!

im trying this.

and here's a simple calc in excel.
https://drive.google.com/open?id=1azMNr ... qzjsQjo36g

need somebody to try to open it to verify

and so far, i found that the formula prefers much sportier engines since it only takes into account only the peak power and not overall powerband.

nope, stuck on 128 score.

File works for me. I've got a similar excel file which I will use to tally the scores.

Some tips from my experience:
Obviously, VVL is going to be absolutely critical here. If you're unsure about how to tune VVL, TurboJ will hopefully have a video on the topic soon (see this thread). I find that 35 works well for the first cam timing, the second one will vary widely.
Optimize ignition timing for efficiency. Higher is not always better.
The sizing of the bore and stroke is going to be very important. Generally, you want to figure out what RPM will allow for maximum performance index, and set the stroke length so that it can make the max PI with high reliability. (This is something I'm still trying to improve on myself.)

Just got a score of 144.1 with a 1.6L I6 Turbo. There's definitely a lot of different approaches to this one There's probably still room for improvement since the rev limiter is right at max HP.



Also comes with a beautiful torque curve as a bonus.

Here's my take on a small I4 NA engine

Feel free to comment.


Score: 80.3

I wonder what score i can get from my tractor v8, 6.04 L mohv

You're on the leaderboard

Since the equation weights efficiency so heavily though, I think you can do better with a more efficient engine.

Well... MOHV isn't competitive since you don't get access to VVL, but here's a 6.04L V8 DOHC-4 which scores 113.2:

For challenge's sake since I'm an advocate for large engines being simple and reliable which explains the LS family popularity in part