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M1tch

Odd question - limiting torque through tuning

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Hi all,

Bit of an odd one, just wanted to ask how best to limit the torque output via the engine mapping, the basis of this question is owing to the torque limit on my transmission - basically looking to limit peak torque in certain scenarios. I will be getting my forged engine fully mapped on a rolling road but just wanted to ask the question now.

Basically my forged engine will have the capacity to have a higher torque output than my upgraded gearbox is rated to, I know that my gearbox can cope with slightly more than its rated torque but am looking at how to limit peak torque when needed - a bit like an engine rev limiter.

I am guessing I should be able to limit the torque by pulling timing out in certain cells at certain boost levels using a 3D table?

Eg:

7 psi - no adjustment

14 psi - no adjustment

21 psi - some adjustment

28 psi - more adjustment

For my build, here are my limits (to give everyone an idea):

  • 1.8 Litre engine
  • Forged rods and pistons (9.5:1 compression)
  • Supertech valvetrain rated to 8,500rpm
  • CSS strengthened block able to cope with around 600bhp
  • Stock gearbox with upgraded 3rd and 4th gears - rated to 295ft/lbs although have chatted to someone who ran 365 ft/lbs through them

Now, a stock engine with a low boost turbo (7psi) makes around 220 bhp and 185 ft/lb torque, and probably around 250bhp and 200ft/lbs at 12 psi, have seen figures for a forged engine making around 420bhp and the 365 ft/lbs at 35 psi on a GT3071 turbo, I am looking at an EFR 6758 for my build which should flow well at lower boost but not run out of legs at the top end.

Is anyone able to guesstimate the sort of torque I should be expecting? I think I should be ok with a bar of boost in terms of torque but anything more I think I might need to run a limit of some sort to keep it around the 300ft/lb mark - basically looking to make the most power I can (as the rest of the engine can make it). I have also seen these engine make around 500bhp at 7,500 rpm and 28psi on a 6262 but the peak torque is probably at around 460 ft/lbs - tad much!

Plan for my build is an 11 second 1/4 mile car but daily driven - plan to run full power at the drag strip then drop boost pressure to a lot lower for the road - basically looking to make sure that the gearbox holds ok for the couple of drag runs to prove it can run the time but then turn it down at all other times.

Sorry - was a bit of a long post but was just wondering what everyone suggests.

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14 hours ago, Ducie54 said:

On my ride I reduce timming at peak torque and boost in the lower gears. 

I am planning to run boost by gear and think I might look to run some reduced timing, just wasn't sure if there was a 3d table that is usually used to adjust.

7 hours ago, Stevieturbo said:

If you're trying to reduce torque...why would you be running 28psi in the first place ?

 

Use common sense. Use less boost.

I will be looking to run the car at various boost levels, will look to gradually increase the boost levels to see where the torque is, just looking at ways to limit the peak torque in the mid range as the higher RPM parts of the map won't need adjusting as the torque would be lower but the top end power will be there. Eg the torque might be within limits for the entire map apart from a small section at say 4k-5k at peak torque so knocking the peak torque back slightly would mean that the box should be fine but I would still be able to attain top end power.

To be fair I probably don't really need to be pushing the boost too high anyway, the goal of the project is to run an 11 second 1/4 mile meaning I probably only need to be running mid 300bhp to get there so might not need to run big boost, I guess part of my issue is that I don't know how much power and torque my setup might make.

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