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
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)
HP/LiterEffReliability? 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.
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/LEff 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/LEff 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.
Here is an album comparing a 0.4L engine, 2.4L engine, and 4.0L engine: 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!
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.
but i found out that sometimes looking for something a little bit more effective in making power ends up making slightly higher score. i mean i got 28-29% easily, but the performance is just shit. and isn’t higher boost means slightly higher efficiency? im on roughly 0.7-0.8 bar.
i’m not the greatest at making the most efficient engines, but i’m pretty good at making an efficient overall car
Boost efficiency depends on the compressor size. When reducing boost starts reducing efficiency, lowering compressor size will increase efficiency (up to a point). Then you should be able to lower boost again. Less boost gives more octane to use for compression ratio. I basically start with the economy preset and then make it more efficient, lol. Also for more power raise A/R.
Since the equation weights efficiency so heavily though, I think you can do better with a more efficient engine.[/quote]
I can probably squeeze a little more efficiency out of that engine, but not with that bhp i think. Also i have the redline at 8500RPMS and top bhp at 8300RPMS which hurt the reliability a bit. But i think thats more realistic then have the redline at the same RPM as the top bhp.
Let’s see what other people came up with, a go from there
There’s probably still room for improvement since the rev limiter is right at max HP.
