Cold and hot idle setting strategy ?

[Jaso74]

Scratch that last bit , I just realised that the dashboard value I changed to iac steps had returned back to an O2 reading and I though it was looking funny . I will try again tomorrow with the idle steps and adjust idle stop if needed .

[Jaso74]

Tonight I backed off the idle screw and achieved the 15 to 20 iac steps. Have it running at 825 rpm in park and 800 in drive . Did not drive tonight but will try tomorrow some time . So now have 50 or so kpa idle , 20 ish idle iac and running at around 27 degrees spark timing . I don't really know if this cam has a rougher idle than I expected or if there is still gains to be had in idle quality . Don't get me wrong it sounds good but I thought in the 355 capacity it might be a little smoother.
Transition between park and drive is smooth .
I could prob try some different idle ve adjustment and see if there is gains to be had there too I guess .

[vlad01]

Sounds like excellent progress

A cam of that size, even ones smaller than that sound rough at idle, but as soon as you bring even a little speed into it, they smooth out.

Completely normal behaviour. When the duration goes up and overlap increases, low air speed conditions like idle, the poor cylinder filling and poor mixing makes it run rough.

But as mentioned before, a leaner AFR helps get the best from the worse so to speak in regards to idle.

I generally like an idle AFR of around 14 to as lean as 14.7 for larger cams, it really helps the poor mixing, even though it's "lean" in reality, the localised pockets of air and fuel mixture inside the cylinder are not well mixed, so the fuel rich areas are rich indeed, so by leaning it out overall, the unmixed areas burn closer to the ideal mixture and improve the idle.

A trap with WB readings is, if the fuel is not burning, it will read lean as it's the lack of o2 the sensor is reading when rich. So if it's so rich that is doesn't burn properly or at al, it will read lean. A misfire actually will peg the WB full lean if you had a sensor for that cylinder only.


Back to the cam, this is why big cams like less fuel. And why small cams like it richer as they mix much better.

Once the engine is running above idle where the air speed is dense and fast enough, mixing and complete combustion is a non issue, even on some wild engines.

[Jaso74]

Thanks again for the detailed info Vlad.
I'm very happy with my idle setup progress now and will continue to try to get the tune as best I can. I am finding that as I go I'm going back to the reference material and there is pretty much always something there that helps.
The fact that guys like yourself are avaialble to help is a fantastic asset to newbies like myself new to tuning.

[Jaso74]

Question , when using the "VE - closed throttle VE vs RPM " , Is it normal to match these VE figures to main table at same rpm cells like the 400,800,1000,1200 rpm ?
Or does it being an independent table mean it does not need to match ?
It is set standard at 50% on all cells.

[vlad01]

I'm not entirely sure, it sounds like that option is turned off by default, hence the cells all having 50%.

I assume you'd need to match them or better yet, tune them to those cells when that table is active. I have not used this option before and so far never needed it.

[Dylan]

Fair chance you'll be able to get away without using that. Try first not using it.

[Dylan]

And tick the flag to force open loop. Forget about the narrow band sensor.

[Jaso74]

I have been using the idle ve table in closed loop but I only initially adjusted the few cells and slight adjustments to the matching afr , mostly I was trying to lean it off a bit for warm up cycle . I actually can't remember now why I ticked enable for it to be honest, I probably did it when I was having some idling issues and was trying to fix it.
So if I was to select force open loop does that mean it simply uses the main ve map/afr map and enriches for cold start only via those other cold start/ idle specific settings ?

I think from memory I read a few using the closed loop idle ve/afr tables when having trouble to achieve good idle quality with big cams and low vac situations .

[Dylan]

Are you only making VE changes from data off a hot engine? Like 85+ degrees coolant temp?