Since diesel engines are not in the game yet, I’ve been trying to create some high torque, low rpm turbo engines good for towing etc…and I can’t make one with significantly more torque than bhp (i.e. 350bhp, 450lb-ft), with a relatively flat torque curve, unless the turbine is in the red.
I’m by far and away no expert, so does anyone have any tuning tips to help with creating really high torque engines (without loads of power and preferably lots of displacement) similar to diesels e.g. a cummins.
Thanks 
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For a high torque/power ratio, I’ll make a list of things to do.
-Use an engine with as many cylinders as possible. The more the merrier under most conditions
-Crank the stroke&bore as high as you can without going too big. Watch the size chart though, you want them all to equal out for the optimal displacement and cylinders.
-Set your cam very low or to 0. High end power may be lacking but you’ll exceed in the low end.
-With the turbo, play with all the values but try to keep the turbo small or the A/R ratio low. Having both too low will absolutely kill higher end power and maybe the lower end too. Play with it until your comfortable.
-With the intake, all I can really say is to play around with it and find what you like.
-Lastly, exhaust. As a general rule, keep the exhaust smaller but not too small for optimal torque & power and use the mufflers and cat as a tool, not just as a screw it and just select none. Many times, I used to just set all of them to none and lost out on some potential power and torque.
Hope this helps out with your engine building.
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I will chime in and may echo some of the same:
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Yes, more cylinders help
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To achieve more displacement in a smaller package, make an under-square engine (the stroke is bigger than the bore). This will also help shift the power curve to the lower rpms.
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Low cam, not 0 though. (Automation extremes should almost never be used, they are a bit funky)
Depending on engine and year it can be anywhere from low teens to low 30s. Usually finding the most fuel efficient point is a good start
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Since Automation Turbos are stuck in the 80s, you either tune for fuel economy (low AR & less than 10psi boost) or use the turbo tuning guide found on these forums. Key is to make sure the turbos are NOT green in the air flow data screen. Instead, make sure either the Turbine or Compressor is yellow to red.
AR around 0.600 to 0.775 is probably what you want to shoot for if you tune for fuel economy.
Otherwise see the Turbo Tuning Thread
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Depending on year and head type, some negative quality on the top end can help keep the curve in the lower rpms (if you’re making a pseudo-diesel) and pushrod heads are a good choice for a high torque, low rpm engine.
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A slightly restrictive exhaust can boost efficency and torque, and make the area under the curve bigger. The best tune for this is whatever boosts your torque best before causing knocking for a naturally aspirated engine. For a Turbo, the same applies but to a much lesser degree.
That’s all I have for you right now, if you have any questions just keep posting them
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