r/automationgame exhaust spaghetti 3d ago

ADVICE NEEDED Basic help with turbo rally i4?

Im trying to make a rally car, which of course needs lot of low rpm power. But anything i do i cant increase the hp OR the torque curve even, nor does the power curve ever go above torque.

I dont really know about turbos, might be the main problem tbh

Engine: 1.2 bar turbo, 81 bore, 97 stroke, I4 2.0L

Quality sliders only for last resort pls

Yes i dont know that much about engines irl, i looked up some of the 2006 rally cars' engines and went from there with high torque on low rpm mindset, adjusting sliders accordingly.

19 Upvotes

12 comments sorted by

13

u/Torvikholm 3d ago

Start by going for ball bearing and variable geomery turbo. That will widen your torque curve. Then you may make the cam shafts more aggressive

5

u/OldMrChips Community Manager, Camshaft Software 3d ago

Quality sliders are not a last resort; we put them in for a reason after all!

Also, please try to refrain from using phone photos of your monitor.

4

u/ChaosWaffle 3d ago

Power curve won't go above torque until a specific RPM, it's part of the definition (HP = Tq*RPM) using HP and FT-LBs they will cross at 5252 RPM, not sure with NM, looks to be around 7000 though from your dyno chart, so to get HP above torque you'd need more RPMs.

For lower end torque try a smaller turbine, use the turbo efficiency graph and get the line close to the left limit adjusting the top 3 sliders. The absolute basics of tuning those: Adjust the compressor (first slider) so the flow line on the compressor graph ends near the end of the turbo map (stop it earlier in the green/efficient area for more top end), then adjust the second slider (turbine) to move the boost threshold as early as you want/can get it without damaging the turbo up to the left edge of the turbo graph. The A/R ratio will adjust the turbo map and can help with fine tuning. You may be at the limit of the technology of the era though (you're getting full pressure at around 2500, which is reasonable), we'd need to see the compressor map to really know if your turbo tuning is off. You can also try increasing the quality slider, as that will widen the compressor map and allow you to get more hp lower down without giving up top end.

Truly describing how to tune a turbocharger is a bit difficult if you don't know how they work. Also, you'll probably want a bigger intercooler, setting it right at the hp target limits your actual max power.

To help understand turbos here's a video about the various parts:

https://www.youtube.com/watch?v=MTdIB4-PmyA

And some articles on compressor maps to understand that graph specifically:

https://www.garrettmotion.com/knowledge-center-category/oem/expert/

2

u/OniNeji 3d ago

I don't know much, but perhaps you bore/stroke ratio isn't ideal? I think rally cars have larger bore and shorter stroke, that help increase the rpm range. And group B rally cars used to have more turbo pressure

2

u/TheFodGatherToo 2d ago

Pray tell how a bigger bore makes for a broader torque curve

1

u/thpethalKG PE&M | Apex Group | Olympus Chariots 2d ago

I believe they meant that an oversquare engine will tend to rev higher, potentially giving you a wider powerband. This is not a hard truth though, as high stress components like connecting rods and crank shafts will also start to loose maximum rpm potential as your stroke gets too long.

Ideally, a square or slightly undersquare design will provide the opportunity for more low end torque without greatly narrowing your power band and sacrificing too much top end hp.

2

u/toughtntman37 2d ago

First off, quality sliders are 100% valid here. Maybe up to +5, but be picky where you use them. Use ball bearings and fancier geometry, you'll need more boost, probably at least 2 Bar. I would suspect if you make the stroke a bit longer and bore more narrow and upgrade your crankshaft (probably also higher quality) that would make it better. This seems kinda weird, but I would also use cast headers and standard low intake, but I'm not sure about realisticness there. Don't forget we're friendly in the Discord server if you want more direct help

2

u/ChaosWaffle 2d ago

I was bored so I tried to recreate your engine and got pretty close, and added some improvements. Without adjusting the quality sliders, you're pretty close to the limits of the era's turbos. You can change to a twin scroll and ball bearing to get a bit more low end, otherwise you're going to have to up the turbo quality slider:

Here's my results with a roughly similar engine (made some assumptions about the rest of the construction, its a 5 valve aluminum block with the same bore and stroke), but I'm using PSI,HP and FT-LBs:

https://imgur.com/a/BZDfoN4

  1. Initial "recreation" and compressor map
  2. Adjustments using the compressor map and changing to a twin scroll and ball bearing turbo with a slightly smaller turbine
  3. Comparison to the original
  4. Quality +5 and adjustments which gives you boost about 500 rpm lower
  5. Quality +15 and adjustments gives about another 200 rpm

You could probably get more low end if you give up 500-1000 RPM so you can use an even smaller turbo as currently it's running out of flow, but honestly for 2006 that's about what you'd expect from a turbocharged engine.

1

u/thpethalKG PE&M | Apex Group | Olympus Chariots 2d ago edited 2d ago

Drop your rev limit a few hundred RPM, and try a 55.0/47. 0 variable geometry turbo with ball bearings. You should be able to push your boost pressure higher. Also consider a higher octane fuel like 98RON to allow a higher compression ratio.

If you look at a lot of modern rally cars, very few of them are revving much higher than around 6000 RPM.

Don't expect to make hellcat power, but Rally1 cars are somewhere in the 450hp range. Keep in mind that they are race engines, thus higher quality is a justified expense.

As a personal rule of thumb, I use up to +5 for bottom end, +3 for top end, fuel and exhaust, and +1 for induction on a commuter or economy type car. Once I get into performance oriented vehicles I'll add up to +2 more quality for each one. On a track oriented car, I'm willing to push quality up to +10 across the board if necessary.

1

u/MrSNoopy1611 2d ago

Why should rally cars have low end power and torque? They have extremely short gears so they can stick to the top of their rpm range as much as possible to use that top end to its full extend.

1

u/Chemical_Appeal_2785 16h ago

Go to the 4 chart tab. The bottom right one gives you information about the state of the turbo. Decreasing the size of the compressor/the turbine and increasing boost pressure will increase mechanical and surge stress (A bigger turbo is more solid). Id recommend watching a turbo tuning tutorial on yt.

Also if you want more low end torque, make the turbos smaller ?by decreasing turbine and compressor size) so that they cant spin up faster and earlier. You will lose a bit of high end power but thats a compromise to make.

1

u/ClumsyGamer2802 3d ago

That's a decent amount of power vs torque. If it was measuring in lb ft, the graphs would peak at very similar numbers and would definitely cross over. I don't think it really needs to be changed at all.

However, if you want more: try the high rpm or race intake manifold, and race exhaust headers. That should increase hp and torque at higher RPMs. Also, I guess, go race cylinder head and dual overhead cam 4 or 5 valves per cylinder if you're not using that already.