Just thought I would through this out here where the guys modded motors frequent.

I am presently at 10*btdc for idle, with 0 split. What are you running?

 

My ports are as early opening intake as possible with nearly stock closing and slightly earlier opening exhaust with stock closing.

My motor seems happiest idling with timing zeroed out on the Haltech and no split.

 

Anyone else cares to share their idle timing values? Also what AFRs do you idle at and what idle egts?

 

10 BTDC leading and 5 ATDC trailing ( a 15 split )

idle is lamda 1 ( LPG fuel.. 15.4 :1 )

mild extend port ( late close )

i find on petrol with this porting it will have liked a little less leading timing, at around 5 BTDC

5 - 10 BTDC leading seems to suit the flame rate of modern fuels better than what was recommended in 1986
and also brings a steady more consistent idle to mild porting

 

Which ECU?

For the PFC, unless the ISC control is turned off by setting the three idle speeds to ooo, the PFC will not run the actual timing setup you put in.

Larger port engines tend to need more idle timing to run best.
Even stock ports need more timing. And all like negative split for idle.
Both idle, low load cruise, and initial acceleration under 0 boost run better with some negative split.

Since my fuel, air, and timing are all manually controlled, the best idle timing varies between summer and winter. No ISC, no O2 FB, no timing CNTL. PFC!

I run around 12/29 winter and 19/25 summer. The engine idles smoother with a load like the AC on than with no load. No load AFRs around middle 12s and AC load around 13s.
I do not tune idle by AFR. I tune it for best smoothness with lease amount of fuel by adjusting air, timing, and fuel.

I am not the only one using negative split for best idle.

 

i cant get mine to idle any leaner then 12.5 AFR without it getting low or loopy. no iac. timing 15* split and -5*.800-1000 rpms

i would LOVE it to ldle leaner.

 

Absolute leanest mine wil idle is 13.0afr, anything over 13 it begins to stall. This is with 10BTDC -no split on a large street port.

 

Don't look at AFR when tuning idle, just make it run well. AFRat idle/low load is trivia, not a target to tune for.

(Really, all points of the map are trivia as far as AFR number is concerned, but idle/low load is where you can easily play around with "give the engine what it wants" without risking having a pile of engine parts)

Less timing allows you to lean the mixture out. This is because less timing = less engine power = throttle needs to be open more for a given idle speed = less manifold vacuum = less exhaust gets pulled up during the intake stroke = more burnable mixture = less fuel is needed to guarantee that it will be near free oxygen.

My bridge port will idle happily at 700rpm. Timing is not what the Internet says you need for a bridge port to run. It also is idling at very near atmospheric at that point, because "idle" becomes "struggling to stay running" at that point.