This started out as a "figure out the high RPM miss under load on my blown 396 w/9psi and a 236/236 cam and 9.0:1 cr", but it's gotten very odd. I could throw parts at it until it goes away, but I'd like to run this by you all for input first.

Since installing this engine I've noticed it likes a lot of advance to idle well (up to about 38-40 degrees at 900rpm) and sounds like its retarded under load. That's purely subjective, but it sounds like I've dialed in a bunch of retard with my Crane's boost-retard dial, but I haven't.

I pulled the blower inlet pipe and started to chase the miss in just normally aspirated mode. I started with 35 degrees of total timing and it there's no miss. So I started adding timing and rerunning, waiting for knock retard or audible ping.

Well I kept right on going past 40... past 50... and up to 60 degrees total advance with no ping and no knock retard in the logs. With 60 degrees the miss was back and much more pronounced under load. So I set it back to 35 and and the miss is gone.

Now as far as I'm concerned there's no way an engine could take 60 degrees of total advance and not ping. So what else could be wrong here?

I know the FAST is at least commanding advance becase it has a big effect down at idle.

I have checked the FAST software and it's set up for a 6 degree crank reference angle (normal for optispark) and 96 uSec inductive delay (standard).

I'm going to pull the Crane out of the mix entirely and see what happens, but I'm very curious to hear other theories!

Thanks,
Dave

 

I removed the Crane, change to a factory coil and ICM, and still no ping and no knock at 50 degrees of total advance.

So that leaves me with:
a) The FAST ecm, or
b) The Optispark, or
c) A motor that is incapable of pining

Given the time and expense of (a) and (b) I'd hate to do either without at least a theory or something to troubleshoot!

Thanks!
- Dave

 

lmao @ "retarted"

 

You might want to email Intmd8 or Znines to get some answers. What is your VE at idle? I would not be listening for ping I would be tuning the combo with a conventional approach.

We are running stock timing with my FAST and my LS1 setup at idle. My VE is around 40. I have 83 lb injectors.

 

The timing sounds awfully high... Are you using any kind of interface harness or piggy-back setup to retain the stock PCM? There are different values for the ref andle depending on what kind of interface you use (white racing interface versus stand alone harness used VERY difference crank ref angles).

If you think the reference angle might be wrong, a good way to check the ref angle is with a timing pointer (like on gen 1 SBC motors). First, find TDC... to do this, I rotated the motor to ~TDC, pulled a valve spring off the #1 cylinder's intake valve, and put a dial indicator on the valve stem to find TDC more precisely. Once you have it dead on TDC for cyl 1, install a timing pointer and make a mark the balancer for TDC. Zero out the timing in FAST, fire it up, and check to make sure the pointer/mark on the balancer are lined up using a timing light. It might run a little rough with 0* for timing while you're checking it, especially if the your ref angle is wrong.