SDFever

Personally, two takes on this.

1. Bob Loyd has done more on this than just about anyone else and I always support his incredibly well-written story from the 496 Myth Busting Thread.

2. 12.5 - and you have to take into account that not all O2 sensors and equipment will read the same. Leave yourself a small bit of headroom. It won't cost a thing. We learned a lot by making sure the exhaust was 'completely' dry vs. what is the case in most boat engines. All headers leak and you have to manage the collector area. It's simple maint; nothing more. Most of the people using a stock 496 with the cast pistons will enjoy a longer life if they sipmly raised the FP 2 LBS. It's more of a matter of fuel cooling the pistons and not so much for AFR or tuning. That engine came from GM Powertrain with AC Delco 41983 spark plugs. DUMB in a boat. Bump fuel slightly and put something like #8's in it. Works great.

Remember, fuel makes HP. Period. To run a marine engine on the lean edge is not giong to work. Just be slightly on the fat side of lean, watch the plugs and enjoy your boat. Raylar spent a lot of time designing a combustion chamber to promote a fast burn and there for requires less total timing for best power. Even with the latest stuff going on with the Dart Gen 7 we wound up with mostly a 28 degree setting. The learn table is + or - but that's the number.

Rage

Sorry no. PCM555 pulls timing from the particular cylinder that is identified as detonating. This info came from Dustin Whipple.

donzi matt

How does it go by identifying the knocking cylinder with only two knock sensors? Does it just go off of crank position at the time of the spike to determine which cylinder it is?

SB

Good question DM - we know individual misfires are found that way, but knock ? That would be cool.

Rage

Item 1. Correct no question Bob's the man.

Item 2. Lot of good info and perspective, thanks. I need to bore down on your earlier comment "if you are using a bosch type sensor with the Innovate hand-held then i'd recommend setting it almost one point richer compared to say an NTK in a nice, dry environment." Are you saying that all Bosch sensors consistently read almost one point leaner that an NTK sensor? If yes how did that fact come to your attention? Did you try both with your Holley EFI and saw this relationship or some other info source?

So the 600HO dyno test was run with 27* max timing with AFR in the mid 13's with I assume 89 octane and your Holley EFI chose 28* for your motor with the same heads and ~12.5 AFR and ? octane. Since the Raylar heads are faster burn than the GM 8.1L heads one can believe that the GM heads should need more timing to be optimum for similar conditions. Of course the unanswered question is how much more. I remember seeing a Tyler Crocket comment on the Dart 8.1L heads with 107 cc chambers that 31* is about it with 91 octane but of course those are Dart not the GM heads. My chambers used to be 111 cc's with 87 octane 12.8 AFR and 32* based on the dyno EGR tuned GM HP3 Gen 1 engine heads. Interesting. Would you consider 12.8 on the fat side of lean?

Rage

My guess is that would have to be it.

Keith Atlanta

*I think it may loos some of that capability as performance increases.

Rage and SD Fever need to chime in on this but... I am pretty sure that Whipple ECU reprogram reduces the knock sensor sensitivity as the performance characteristics increase due to cam lope and other variables. Its been awhile so I only remeber this tidbit.

To add to that, he specifically did on mine due to the stellings box universal joint vibration causing interference.

Ryan00TJ

This was a concern of mine before buying the Stage 2 cal for my 496 HO. I wanted to keep all the factory Merc 555 guardian features. I asked this question to Whipple and bobl of FTM, both stated the Stage 2 cal keeps in intact.

Found this..... FWIW

Rage

I remember you bringing up your described history on this a long while back. I can not recall inquiring further with Dustin but probably did. Every knock detection system I have found has a calibration requirement where the units sensitivity has to be adjusted with engine running w/o knock. Holley, J&S Safeguard, Turbo Knocklite, etc. so no reason why Merc ECU would be immune. Piston slap is always mentioned as a biggy.

Rage

Questions for those with the Holley EFI. When the Holley EFI detects a knock event what is its response capability?
Spark
1. Retards spark all cylinders in response to knock event?
2. Retards spark on cylinder bank where knock event detected?
3. Retards spark on cylinder where knock event detected?
Fuel
1. Provides more fuel all cylinders in response to knock event?
2. Provides more fuel on cylinder bank where knock event detected?
3. Provides more fuel on cylinder where knock event detected?

What if any adjustments are available to tailor how the spark retardation is performed?
1. What is trigger to start retardation? knock amplitude? knock vibration frequency? quantity of knocks/sec?
2. What is trigger to stop retardation? knock amplitude? knock vibration frequency? quantity of knocks/sec?
3. Is there a programmable relationship between knock severity and retardation severity?

If there is something online that explains all this that would be great.