Rich + More Ignition, Or Lean + Less Ignition, What Is A Safer Way To Tune?

[StealthX]

What does MBT stand for?

mean best torque

the point at which, as you advance ign timing, the engine makes the best torque.

say at 3,000 rpm and 10deg timing, the engine makes 200nm, 12deg might make 205nm, 14deg makes 207nm, then 16 deg makes 205nm, then your ign timing for MBT is between 14 and 16deg.

happy to be proven wrong, thats just how I understand it...

[Rolls]

Thanks for that

[StealthX]

P.s. for the mathematically minded fellas out there, I've always struggled with understanding the relationship between power and torque...

I know the power is the amount of work done with respect to time, and that torque is a rotation force, but dont understand how they interact!?

If is accurate to say that torque is the derivative of power with respect to engine RPM???

Edited July 7, 2011 by StealthX

[Don Dada]

mean best torque

the point at which, as you advance ign timing, the engine makes the best torque.

say at 3,000 rpm and 10deg timing, the engine makes 200nm, 12deg might make 205nm, 14deg makes 207nm, then 16 deg makes 205nm, then your ign timing for MBT is between 14 and 16deg.

happy to be proven wrong, thats just how I understand it...

Is it always the case that torque will drop off after MBT if you keep adding timing?

I was of the impression that it would just stop making any more torque.....I'm guessing it might be dependant on the set up itself?

[Rolls]

P.s. for the mathematically minded fellas out there, I've always struggled with understanding the relationship between power and torque...

If is accurate to say that torque is the derivative of power with respect to engine RPM???

Power is directly proportional to torque x rpm.

Think of torque as the instantaneous force, rpm is how many times a second that force is being put out, hence why your power can still increase even though torque is decreasing.

Another analogy is torque is the force of each cylinder explosion, rpm is how many explosions per second. So if you have lots of explosions but they are weak (low torque, high rpm) or not many explosions but they are very powerful you can have the same power (high torque low rpm).

[JonnoHR31]

P.s. for the mathematically minded fellas out there, I've always struggled with understanding the relationship between power and torque...

I know the power is the amount of work done with respect to time, and that torque is a rotation force, but dont understand how they interact!?

If is accurate to say that torque is the derivative of power with respect to engine RPM???

relative power = torque x rpm

basically if you have a perfectly flat torque curve from 0 rpm to redline (never happens, i know, just an example) the power will double when you double the rpm. so if your making 100kw at 2000rpm, you'll be making 200kw at 4000rpm, 300kw at 6000rpm and 400kw at 8000rpm etc.

torque is the force that is exerted by each combustion cycle, power is the overall force produced by the engine (as revs increase each combustion might be less powerful on its own but its happening faster, therefore more combustion cycles in a set period of time).

[StealthX]

Is it always the case that torque will drop off after MBT if you keep adding timing?

I was of the impression that it would just stop making any more torque.....I'm guessing it might be dependant on the set up itself?

Yeah not sure on that one... I was under the impression that more ignition timing past MBT will make more heat, thus less dense intake charge and less power. sorta like a turbo out of it's efficiency range. boost = timing and power = torque.

Power is directly proportional to torque x rpm.

Think of torque as the instantaneous force, rpm is how many times a second that force is being put out, hence why your power can still increase even though torque is decreasing.

Another analogy is torque is the force of each cylinder explosion, rpm is how many explosions per second. So if you have lots of explosions but they are weak (low torque, high rpm) or not many explosions but they are very powerful you can have the same power (high torque low rpm).

right! got it....

thanks!

[Dose Pipe Sutututu]

MBT is actually maximum brake torque, or peak torque, i.e. the peak of the torque curve. After the point where the maximum amount of torque can be achieved cylinder pressure drops, ideal for more timing to be added to continue to make power.

If you look at many stock ignition maps (not stock PowerFC maps) you will see after the peak torque, igntion timing will increase. Do a trace map on a stock ECU for any newish car and you'll see after MBT, more timing is added. A good example would be a 4G63T map.

[DVS JEZ]

I guess that's just my opinion though. Jez I will need to send you another email BTW! You may be disapointed, may not haha.

look out guys we have a trader among us. First of all he was putting a toyota motor in his skyline. But now he is buying a silvia with sr20.

All good im an ex silvia owner.

[Axeman83]

a couple of points. the formula for Power is torque in ft lbs x rpm over 5252, this gives power in hp. secondly adding timing after peak torque does not increase EGTs in my experience. if anything it lowers them. even when detonation occurs they will keep dropping, altho damage will obviously occur.

[Rolls]

It makes sense for timing to always reduce EGTs as you are keeping the explosion in the cylinder for longer so more heat gets absorbed.

Edited July 10, 2011 by Rolls

[DVS JEZ]

Its not an explosion Rolls. Its a burn

[Dose Pipe Sutututu]

best way is to bang on a EGT gauge, you will see jap guys prefer to use that as their main gauge as well as the A/F gauge.

[scotty nm35]

I use both too, its the only accurate way to see whats going on isnt it? Im sure most tuners would prefer to have them in the dash if possible. I used to run the egt sensor in the dump and noticed a 100 degree increase in temps now its in the manifold.

When tuning last month I noticed as we increased boost past a certain point the power didn't increase but torque continued shooting up, how can this relate to your equations?

[Lithium]

Thats because torque is on a finer scale the whole way through, its why I prefer to tune to MBT using the torque curve - its easier to spot differences. Its also way torque curves often tend to have huge dips etc if the dyno software allows you to scale to just minimum torque to max torque, instead of 0-max torque.

[Rolls]

Its not an explosion Rolls. Its a burn

its actually a deflagration ; )

(I knew)

I use both too, its the only accurate way to see whats going on isnt it? Im sure most tuners would prefer to have them in the dash if possible. I used to run the egt sensor in the dump and noticed a 100 degree increase in temps now its in the manifold.

When tuning last month I noticed as we increased boost past a certain point the power didn't increase but torque continued shooting up, how can this relate to your equations?

That is because peak hp isn't at peak torque. So you might have had more tweaking around peak torque to do, but not at peak hp.

Edited July 11, 2011 by Rolls

[ido09s]

The engine will give you the answer. We have tried tuning lean with minimal timing but running it at low 11's with more timing doesnt make much difference to our car. A richer tune will leave more room for safety unless its on the ragged edge with timing.

Most RB's i have seen that are running 20+psi have always liked to be tuned in the mid to low 11's

[Rolls]

Wondering if people have any new thoughts on this?

[Dose Pipe Sutututu]

Just dial in timing till the motor stops making power or knocks for a certain rpm, then proceed to next rpm band.

Joys of e85, keep pumping in timing till the power drops as it doesn't knock.

[scotty nm35]

Joys of e85, keep pumping in timing till the power drops as it doesn't knock.

I have almost the opposite opinion, more boost, 11:1afr and keep the timing on the lower side of MBT for best longevity, especially at the point the torque hits hard.

E85 knocks just like petrol but at a much higher boost. Definitely need knock ears on the block for WOT tuning...