Offshoreonly.com - Detonation Issues - "Why is the Gen 7 496 such a bad platform to build"

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Should have thought it thru before posting. Got a Holley tech to inquire. Holley response to knock is to retard the entire engine and no plus fuel option. I did not bother to inquire about the last questions. The tech ID'd the software download location. I will pursue answers offline. Thanks.

I'm not sure anyone can give you a definitive answer to this question. Looking at your data logs I see what you are getting at. Looks like you were in the mid 14:1 A/F during these logs. A couple of the latter ones went leaner than that, but I believe these were after you hurt the engine and the throttle was open further to obtain the same rpm, which would put you into a different map cell. My opinion is that 14:1 will not hurt the engine under such a light load. I will suggest that a marine engine should never see anything leaner than about 13.5:1 Years ago I did an experiment with the first aftermarket ECM I had. I was trying to find the most economical cruise tune. I had someone drive the boat while I ran the laptop. We trimmed the boat for an ideal cruise at about 2800 rpm and left the throttle there. I then started tweaking A/F to see how it responded. What I discovered is that it was very unhappy any leaner than 13:1. RPM would start falling off quickly. Best was right at 12.8. This was before E10 fuel came out so it should be a little richer with E10. I guess what you can take away from this, is that there is no "lean cruise" scenario in a boat.

Quote:

Originally Posted by Rage (Post 4378038)

I would like to get back to the initial question that started this thread.

Question. What is the leanest naturally aspirated engine AFR [ with GM Gen VII 8.1L, Merc 496HO heads] that is safe from detonation damage from idle to 2200 rpm? Plane out is ~2200 RPM. Significant MAP/engine load increase begins at ~4000 rpm. Knowledgeable responses only please.

Now that is about as informative an answer on the posted question one could hope for! Thank you Bob.

Just got the boat on the trailer and heading home today. Pull the engine in garage tomorrow to fix it.

Quote:

Originally Posted by bobl (Post 4378533)

Years ago I did an experiment with the first aftermarket ECM I had. I was trying to find the most economical cruise tune. I had someone drive the boat while I ran the laptop. We trimmed the boat for an ideal cruise at about 2800 rpm and left the throttle there. I then started tweaking A/F to see how it responded. What I discovered is that it was very unhappy any leaner than 13:1. RPM would start falling off quickly. Best was right at 12.8. This was before E10 fuel came out so it should be a little richer with E10. I guess what you can take away from this, is that there is no "lean cruise" scenario in a boat.

WOW Thats really good to know! Thanks Bob

I am going to throw in another problem with efi that probably does not affect v bottoms but will in a cat. when I was with Alcone Motorsports we ran Sterling Open Class engines that used EFI technologies electronics. we found that in flat water on a long straight run we had to keep pulling back on the throttle to keep the engine off the rev limiter (7850 rpm). by the end of the run we were seeing 40-50% throttle position at 7800 rpm. there was no mapping for that so the engine was going lean. there was also no good way to run like that on a dyno so we had to create a map manually for it to run there. we were at a race when we figured this out so we had to work on the fly to fix the problem. point being, there are conditions that are outside of your thinking or outside the dyno environment that happen in a boat that are hard to find or understand with out a data logger. we were lucky that the system we had was as advanced as it was and gave us mountains of data to work with.

Quote:

Originally Posted by Rage (Post 4378392)

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.

As I'm sure everyone is aware, there should never be any knock retard under normal operating conditions. It is simply there to save your engine from bad gas, plugged filter, excessive IAT, etc. If you see KR anywhere in your datalogs, then the tune needs more work. On the Holley system, you have a table that allows you to choose how much timing it is allowed to pull, at what rpm and load, and how fast. Also, how fast to try and ramp it back in. On the sensors, you can adjust the frequency, and sensitivity. It reads engine noise on a scale of 1 to 100, with anything over 80 recognized as knock. I like to set them up so they're very sensitive, and on noisy engines you may see false knock at idle and low rpm, but it doesn't matter because you can tell the ecu not to pull any timing down there. Once the rpm comes up it will smooth out and quiet down. Both knock level, and knock retard are recorded in the datalogs, so you can check it out after a run. Also, you can program an output to let you know if the ecu is puling timing. This can trigger an alarm if you want, or a secondary rev limiter to put you into a guardian mode. The system works very well, and can save your engine.

This is for everyone but I replied to Keith since he's always been a gentleman -

SPECIFICALLY referring to the 496 knock system (not 502's or...). I said it before; if you rely on an 8.1 496 knock system (talking stock) to help you in any way you are crazy. I've pulled live and historical data on a ton of 555 computers and never once have i seen that system give a good knock code. It will in fact allow you to burn your engine to the ground.

More frustrating, you can and will get knock codes sometimes on failed crank attempts. No offense but i hate that box. Just sayin'.

This includes some modified 555's as well.

Quote:

Originally Posted by Keith Atlanta (Post 4378285)

*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.

Quote:

Originally Posted by Rage (Post 4378257)

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?

All I'm saying here is that the NTK Sensors seem to be much higher quality and price reflects that. Experienced tuners use them for a reason. They generally live longer as well. My reasoning for the Innovate hand-held with bosch config stems from seeing that config having a lot more inconsistencies and/or larger fluctuations while underway. I have not used the hand-held with a 200-300 dollar NTK though..

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?

Sorry, that's not my 600 on larry's report. And with all due respect, anyone using any fuel below 91 in a modified boat engine is just asking for it. Why even have the debate? Yes, i'm on record for using 89 several years ago and i did not have any big problems. But i was closer to the ragged edge than i ever realized. And my usage contributed to the survival duration at that time. Regarding the fat side of lean,,,, we could spit this hair all day and get different opinions. My advice going into the tunning process is to have a lot of experience or pay someone who has it. Maybe you are restricted to 87 and i could have forgotten this but i say again - find a way to get the best fuel you can obtain.

The flu shot just gives you small doses of flu... but why go there if you don't have a reason to fear it to begin with? Bob says 13.5. If he has a way or method to mostly guarantee that it's ok on something that he clearly has worked on and setup then I have no opinion. But you can NOT use his or anyone else's number purely on it's own. There are a ton of variables. Far too many.. But yes, my experience with this engine and including the gen 7 is to stay in mid 12's. Bob will probably agree with me that there is no real horsepower gain by trying to be at the top. Fuel makes power. Gotta remember that. AND it cools the top of the piston. If you are racing then it's a whole different story. If you are a rec boater and hate to be towed in, just turn it down.

The Holley system is all together nicer and better; just my opinion. But even the guys at Westech say not to use knock sensors in a boat with solid engine mounts. Mine has a ton of vibration and at slow and fast idle speeds when pushing through waves it actually can trip it.. I think you are much better off to have an 02 (but not in learn mode) only as a monitor and have the digital fuel pressure sender functional. Put that number on your dash and have fun. You can use scaling to have the fp open the pulse width and/or detune if it goes away for some reason.

Frequency and sensitivity

Quote:

Originally Posted by Rage (Post 4378392)