[monster111]

i was curious what are you guys timing after peak torque towards redline for a high boost turbo motor.

let say you have a flat peak torque of 5.5k-7krpm and timing is at 12 degree at 28psi. towards redline do you slowly increase it or decrease it?

some reading says that cylinder filling is decreasing after peak torque so you should increase timing to compensate for slower burn.

lets discuss.

 

[transzex]

decrease total timing

 

[ddd4114]

On an atmo engine, peak VE tends to occur between peak torque and peak power. That's when you'll need the least timing (all else being equal). You're correct that once VE starts to drop, you'll need to add timing.

For a turbo engine, variable boost pressure complicates the relationship between VE and torque, so it's hard to say. If you're not decreasing boost pressure after peak power and your output begins to drop, then you might need to start adding timing.

If it's a high-boost turbo engine, you're probably going to be knock-limited anyway.

 

[rdc]

I spent 10 years studying Ignition curves on two stroke and four stroke engines.
As a rule of thumb. Most engines want to start low. Then ramp up to 3000-4000 RPM.
Then hold stable And then start drooping off.
Then when you think its all done you want to bump up the timing again. This is because the VE of the engine has started to fall and charge impurity needs more timing.
(This last bit is mostly for two strokes. i.e. when its ve starts to drop at around 13,000 RPM you want to bump up the timing by a few deg.) To get a few RPM on the over rev. Its not going to help you make more power which is why most four stroke boys dont bother about this.
Typically at 13,000 RPM we are anyway firing almost at TDC. And instead of 4 Deg BTDC we take the timing up to +4 Deg. And it gives us another 300 RPM on the over rev.

One thing Id like inputs on is how does cam duration and lift effect ignition timing.
i.e. when switching from a low duration cam to a high duration cam do you drop timing or increase it.
My Logic says you increase it. If its anything like a two stroke motor.

Off course if your mentally stuck in the 1920s. Then you just keep increasing the ignition timing as the RPMs climb. LOL.

 

[monster111]

good info, rdc.

another question is most dyno tuning will be done in 4th gear so we tune to eliminate any knock on 4th gear load.

will this timing be too low for 1st, 2nd and 3rd gear load?

what if the motor is a NA motor which is not knock limited? will adding more timing in the first 3 gear show any gain on the road?

 

[rdc]

It is because our engines are not knock limited that we insist on tuning the maps on a dyno.

JD would be the right guy to answer this question.
Since he has had so many cars on the Dyno.

but in my exp. Weather we tune in 3rd or 4th the power output is more or less the same. Because your MBT isnt going to change much based on which gear your in.

 

[Ron Farver]

I spent 10 years studying Ignition curves on two stroke and four stroke engines.
As a rule of thumb. Most engines want to start low. Then ramp up to 3000-4000 RPM.
Then hold stable And then start drooping off.
Then when you think its all done you want to bump up the timing again. This is because the VE of the engine has started to fall and charge impurity needs more timing.
(This last bit is mostly for two strokes. i.e. when its ve starts to drop at around 13,000 RPM you want to bump up the timing by a few deg.) To get a few RPM on the over rev. Its not going to help you make more power which is why most four stroke boys dont bother about this.
Typically at 13,000 RPM we are anyway firing almost at TDC. And instead of 4 Deg BTDC we take the timing up to +4 Deg. And it gives us another 300 RPM on the over rev.

One thing Id like inputs on is how does cam duration and lift effect ignition timing.
i.e. when switching from a low duration cam to a high duration cam do you drop timing or increase it.
My Logic says you increase it. If its anything like a two stroke motor.

Off course if your mentally stuck in the 1920s. Then you just keep increasing the ignition timing as the RPMs climb. LOL.

I know this is an old post but some things don't change over time. I am trying to find an ignition advance curve for my D15A3 engine. Recently I installed an Electromotive XDi2 Ignition Controller on my engine and I now need to create the ignition advance curve in the software but I have no idea where to start. It is a basically stock engine with Integra P29 pistons for increased compression and dual Weber 45mm DCOE carbs for intake. I am hoping you can help me.