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Hey guys here is an attempt of mine to create a small, eco friendly yet usable engine. I think its a pretty solid engine with a decently flat torque curve, low build cost and pretty good fuel economy. The downsides I see are the responsiveness, man hours and service costs, all seem like they could be better.

Any thoughts for improvements?

Just outdid myself on the questions I posed earlier. Way less man hours, roughly the same material and service costs, all while picking up a considerable power boost. I was suprised I was able to get the turbo to spool to full tilt that fast with such a small engine. It came back with almost 52 mpg in a run of the mill sedan, not too bad!

I would raise your fuel type to Premium if it isn't already. A lot more room there since you're only using 90.9 RON on a forced induction motor! You also might consider raising your RPM. Turbos have spool time, which yours is at 2600 in the first and 2900 in the second. That leaves a very short power band with the turbo spooled. Also, I like the torque curve flatter like in the first engine, but I suppose that depends more on application. Pretty good economy for a turbo though!

Here is my attempt.

And this my attempt: (is an NA engine with 2.0 liter: is better than the 1.2 for this points: 1) Better maintenance cost; 2) lower price to build (Correct me if is incorrect); 3. Better emissions and fuel consumption).

Yea I used 91 octane as a challenge to myself. Most real world engines these days are moving away from the premium fuel requirements so I figured I would do the same. Also in regards to the RPM limit, I would like it higher but the low friction cast pistons would not

The torque curve on the first motor is flatter because I used VVL and in the second version I took it out to save on man hours.

Ill go tinker with another variation and see what I come up with.

Decrease your stroke for higher rpms.

Just revised the engine for 95 octane and was getting roughly 150hp and 138tq, needs some tweaks though. Unfortunately I did have to ditch the low friction pistons though because the power band moved to far above their rev limit.

Quickie Turbo 1.2L I4 on Regular Unleaded:



I couldn't see everything you used on your engine, but judging from your post I attempted to copy your components. I used your low-friction cast pistons and VVL/VVT. My efficiency took a small hit at only 29% but is only 11.0 psi of boost at the same cost and comparable man-hours. I did manage ~4k more miles on MTBF. I could probably shave off some cost and recoup my efficiency by optimizing the turbo more, but to be honest I'm absolutely horrid with turbo engines. Mine does outweigh yours by about 20 lbs, which tells me you have a long-stroke tiny bore engine. I used 77.5 X 63.5 bore X stroke for 1198cc. Also, notice I have 130hp at 7500, which is also my redline. I could probably go a tad higher, but I didn't do much optimization on size.

You did a good job with your motor, but basically, there's more in that motor of yours. I'm sure you will find it soon though.

In the engine above turbo spools way to late in the rpm range to be economical.

Worst part about being stuck at work? I cant tweak my engine lol. I agree that turbo motors are a bit tricky to understand with all of the variables involved. I do tend to go with a long stroke and small bore to decrease engine size, however in this application being only 1.2L it doesn't really matter, so I will adjust later.

Quick question, any reason why you went with a Journal Bearing instead of Ball Bearing on the turbo?

Also for the camshafts when going VVL I found that 21 on the low end is the sweet spot for MPG and power, while right around 65 on the top end is where you get best results for power. I think you can ditch that forged crank as well, the cast one should be able to take the RPMs and power, don't quote me though.

I like the feedback guys, I find these small turbo engines are the most fun to build.

Version 3.0

I changed the bore x stroke ratio to allow for a higher rev range. Also adjusted the turbo and cam profiles. The torque curve is a bit strange but its pretty good for such a small engine. Without any fancy turbo tech the soonest you can get one to spool on such a small engine is around 2800, so having this carry around 100tq from 3,000rpm to 7,300rpm is pretty good. I have yet to test the latest version inside my "test car" to see the differences in 0-60 and mpg, but all stats are similar aside from the power gains.

143hp at 7300 rpm is not economical even if the combustion efficiency is high. Whats more, engine that has high torque and low hp produces relatively more hp at low rpm, which is what makes for better fuel consumption in the real world. This engine also has no power band, you get a massive drop in power once you change gear. Your second engine is very good in my opinion and generaly im glad you opened this tread cause i think those engines are the most interesting. It will be even more interesting when the turbo section will be completed and hopefully you will be able to reach full boost at 1500rpm like a real TSI engine.
Here is an engine i made some time ago, originally for 95 octane fuel, produces 120hp at 5000rpm and 140lb-ft and has 31.5% of combustion efficiency. I tuned it for 91 octane.

(Disregard automation figures, it produces 115hp from 5100rpm right until 6200rpm )

I'm guessing you did not use VVL on that engine you have there? I do agree that the HP is very peaky, however my torque band is pretty flat from 3k all the way to redline. When driving a car the torque is what you "feel" hence why it is so important to have a wide flat band, rather than one that spikes. Without VVL in your engine I know this can be very difficult or not possible but having torque drop from 130 at 4k and go to less than 100 at redline, I feel like the engine would not pull very well up top. Granted this is a simulator and does not replicate real world applications. I would like to get some other opinions on the matter as I think both of us made two very different engines under the same idea.

Can you post the engine LUA file here so I can DL it and put it in my test car? I'm curious to see the differences in my family sedan.

There is no need for VVL in this engine. I mean, it will increase performance and fuel efficiency but only slightly and it wont be cost effective, since i wont use high profile as the idea is to make it a low reving engine.
About the ease of driving, i think flat power band is even better and it wont feel weak at the high rpm's because you get the whole 115hp all the way
The thing about the flat torque curve is that it has the most linear power change so it is considered to be the most predictable, but if you have no change in available power at all then its better, its like an electric motor.

Report the results!