Jump to content
GregM

Limiting Torque

Recommended Posts

Hi guys, I'm having a crack at tuning my car myself, its an Evo 5.  The block is still stock with 170,000km on the clock.  My last tune was on the factory ecu running SD, so have been looking at the logs I did with that and set up of the rom for some guidance.

I know what will kill my engine is torque and need to be careful.  From the original tune, the timing and boost were limited in the 4000 - 5000rpm range, timing drops and wastegate duty cycle drops, to reduce torque. 

I've seen comments around where in the rev range the torque kills the engine, and I've seen people say in the mid range, and then others up top.  My old tune was limiting in the mid range.  

I've done  a log with wastegate duty cycle and timing not limited in that mid range, and torque was obviously higher.  I'm starting to drop timing and boost in that mid range, to match to what my old tuner had, to reduce that torque.  As a comparison, my old tune had peak torque at 391Nm at 5900 rpm, and I just had it at 413Nm at 4795rpm.

What are peoples view on torque and weak rods.  Should torque be limited in that mid range, or is it up top that kills it?  I've always been told mid range, like my tuner has tuned it like in the past.  It would be good to get some opinions.  

Share this post


Link to post
Share on other sites

Two main conrod failure mechanisms in my understanding.  Tensile failure typically due to excessive RPM/piston mass.  Compression failure (bending) typically due to high cylinder pressure.  I suspect in your situation the compression failure would be the main concern. 

Torque is directly related to cylinder pressure, typically that will be highest where you have peak VE (say 4500RPM) then as RPM increases the cylinder head/cam/shaft/turbine all start to lose efficiency so cylinder pressure (VE) fades away.  Since power = torque x RPM, you can make the same power by with high cyl pressure at low RPM or less cyl pressure at higher RPM.  So your strategy would be to limit cylinder pressure (torque) to whatever you think is an acceptable limit but then as the VE starts to naturally fade away at high RPM you can increase boost/timing/whatever to keep the torque curve artificially flat.

 

Share this post


Link to post
Share on other sites

Thanks Adam, what I'm doing seems to be working right. Abit annoying having to drop the torque down, but so far the engine has held together for a long time by doing that.

Share this post


Link to post
Share on other sites

Thanks, using modeled fuel, so yip.  Pretty annoying purposely having to reduce the torque.  Tempted to take my chances and not reduce the torque, as I'm only going to max 18psi boost.  At peak torque, I'm only at 13psi, so tempting........

Share this post


Link to post
Share on other sites

Just re-reading your info Adam.  I guess I need to work out if Evo rods rail due to tensile failure or compression failure.  I'm getting told they fail due to tensile failure now.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

×
×
  • Create New...