I posted this in here do to the wealth of knowledge in this section. I felt I would get a more thorough, educated answer.

With the different cams I've installed, to get them to idle smoother, I've simply been adding timing at idle and smoothing out from there, not touching the fuel.

Even though it has worked well for me in the past, is this the correct method to achieve the end result?

Any insight would be greatly appreciated.

 

Yes, adding timing is a popular way of getting aggressive cams to idle smoother. You can also increase the idle rpm slightly.

 

Open loop, idle it rich around a 13.0 AFR

 

John, do you prefer adding fuel rather than increasing idle timing to "tame" aggressive cams? If so, for what reason(s)?

Thanks in advance.

 

I do both. Its not uncommon for me to have 14-15* at idle on aggressive cams.

 

can you define "aggressive cams". I have s2's with 5* timing with around 1050 idle rpm. Pretty tame without too much lope.

 

Kelford 280/276, S3s, Cosworth M3s on Evo VIIIs or some of the larger cams on IXs.

Your car with the MIVEC set to -1.2 and the BISS adjusted should idle at -10. IX's and S2s get along famously.

Aaron

 

same here. Mivec S2's, 6* of timing and idle RPM set to 1031 (+/- 30 rpm)

you can here a slight lope and occasionally feel the it.

forgot to mention the mivec map has 0* at idle

 

Rap, John, thank you.
I did forget to mention that I was increasing the idle anywhere between 97X-100X rpm. It's good to know I've been on the right track. It always felt like it needed that extra touch of something. I just wasn't confident.

And as far as what's happening inside the cylinder is... More fuel is being ignited sooner to create more pressure to turn the crank at a slightly higher target idle to create the smoothness?
So what we are doing is increasing the cylinder pressure (again) that the increased overlap has reduced at idle?

I just like to have an image of what is actually going on in the cylinder as changes are being made.

 

Dont know whats happening inside the cylinder but I can tell you that leaner always makes it "lope".

 

Also, leaner AFR will cause the engine to want to rev higher and richer AFR will cause the engine to want to rev lower. This can make it a little tricky to adjust the BISS if the fuel mixture isn't close to your desired AFR before you begin to make adjustments.

Also, advancing the ignition timing naturally increases engine speed, just as retarding it decreases it. From the factory, the ECU will adjust ignition timing at idle +/-8* to control idle RPM in conjunction with the Idle Control Valve. Sometimes, +/-8* allows too much of a swing for the car to maintain a consistent idle RPM. This can be adjusted to compensate.


-Jamie

 

Negative mivec advance, and negative ign timing at idle? I understand the negative mivec, but the negative ign timing I am not sure if I understand it correctly. JW if that was supposed to be a ~ instead of a -..?

 

That was a figure of speech. The IXs are so resilient with the MIVEC you could do that if you wanted to. Running 5* doesnt surprise me with MIVEC at -1.2* and the BISS adjusted on S2s on a IX. I normally run timing between 10-12* still just to make sure its stable.

Aaron

 

I think the "-10" JB was referring to wasn't ign timing, but vacuum at idle...or I could be wrong.

 

-10* means advance of 10*, where "-" sign means that the spark is fired BTDC. In fact numbers in the ignition tables are scaled so that the ignition BTDC is positive number for convenience only, as you rarely use ATDC ignition and so while editing your ignition tables you do not need to put there that "-" all the time.