MILD THUNDER

You gonna dyno one of them Matt?

donzi matt

I don't think so, at least not in this form. Bobl from Full Throttle Marine did some pretty extensive testing and with a very similar setup to mine and a whipple tune in the ECM it made 553 horsepower through the full wet exhaust. I think I will wait and see what the boat runs and if it delivers what I think it should I won't worry about it. If it is a slug I will dyno them after pulling them back out next fall. I would like to dyno them after the stroker kits and larger cam to see what it makes on the ported intake. There is no real data out there on that and I would like to know what kind of power it makes.

I forgot to mention I also got O2 bungs in all 4 risers, now I need to start looking into a 2 channel data logging wideband setup for each motor. I am huge fan of the NGK AFX setup, primarily because it uses the nearly bulletproof NTK sensor instead of the chitty Bosch sensor, but it doesn't datalog or do 2 channels, so time to do some research on a good setup. I don't really want to add anymore gauges to my dash so I might mount the controllers in the bilge and be done with it.

abones

Innovate make a nice dual channel unit, but you my not like it due to the fact they use the Bosch LSU 4.9 sensors

Rage

This post seemed to have all the knowledge 496 HO people involved. I hope my inquiry is relevant. If not I will repost separately.

I had been running a 2004 Mercruiser 496HO Gen 7 engine with Innovation Marine HP3 Gen II engine setup plus Raylar 517ci stroker crank and Mahle 4032 alloy forged pistons (030 over bore) with Rayar Cool Cap intake manifold, HP3 heads with 2,25 intake/1.82 exhaust valves and Jim Valako porting which dyno'd at ~625cshp on 87 octane since 2008. Refresh required in 2014. During refresh also increased TB from RV Morris bored / Jim Valako ported 77m to 92mm TB and increased cam lift from HP3 Gen II .596/.596 to .666 intake/.629 exhaust maintaining HP3 Gen II cam duration and LSA. to obtain 74.8% total exhaust/intake flow ratio versus 83.1% from previous setup. The engine recently detonated with the new engine configuration destroying two of the forged 4032 alloy Mahle pistons during AFR data logging sessions with 91 octane. Cause is believed to be fuel pressure regulator going lean off set point.

Question. What is the leanest naturally aspirated engine AFR 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.

donzi matt

What RPM were you at when the motor burned down? What was the AFR at that point? Do you have timing numbers for the point where you lost the motor and was there any adjustment to your timing table since the changes were made to the motor? In my experience increasing stroke on an engine generally requires less ignition timing, but you changed a lot of items at once so you can't necessarily go on a generality like that. It sucks you burned down a fresh motor like that but it opens the door for quite a bit of learning about tuning a setup like yours. One last question, are you still on the 555 ECM or have you converted to a MEFI setup?

Rage

The motor would still run but knew something was wrong. Leak down test confirmed it and pulled heads to find the broken pistons. Still running the 555 ECM. Maybe you misunderstood. The motor was bored,stroked, Raylar intake, HP3 Gen II cam, heads, back in 2008 and ran great for 350 hours. All I did this time was refresh, bigger throttle body and valve lift. Dustin retarded the timing a lot in the midrange rpm's this time versus previous build. When motor quit I lost all Diacom and Innovate data logger recordings of the run. But did watch the AFR during that run and the AFR was in the high 12's low 13's for cylinder #8 where the previous engine ran best. The fuel pressure was confirmed set at 48 psi at start but was 47.4 psi after run. However I suspect the initial damage likely occurred during the non instrumented run from the launch ramp to the boat slip the day before. After that run the fuel pressure was found to be at 42 psi instead of the 48 psi set point. Attached is AFR, MAP and timing data for current and preceding engine config.

donzi matt

I did misunderstand, I apologize. I thought you added the stroker crank this year. That's what I get for posting before my coffee.

To make sure I am understanding you correctly, were you just running from idle to 2200 from the ramp to your slip when the fuel pressure was low? If so I have a hard time believing at that low of a load that you would have melted a piston.

Rage

No, sorry for the poor writing skills. The fuel pressure was low (42 psi) during the run between the ramp and the slip but I did do a brief burst of higher rpm's during that run. Most of that runs rpm before and after the burst was ~2500 - 3500 rpm I guess. Also the pistons did not melt. A chunk broke off of two pistons at the same location, the intake valve relief. Pictures attached. The Idle to 2200 rpm inquiry has to do with the fact that is the only rpm range where the new engine shows leaner AFR than the previous engine when fuel pressure is at the set point that as arrived at from the fuel pressure vs AFR tests on the new engine. This is planning for the future when engine is repaired and I am wondering/asking if that could cause a detonation problem that could damage the engine then when it comes time to make more AFR runs to provide data for Dustin to recal the fuel tables.

donzi matt

Looking at that damage, it certainly looks like detonation broke the top ring land. Do the Mahle pistons keep the relatively short ring land like the stock pistons or do they move the top ring down for strength? I would say with ~15% less fuel pressure than expected that would certainly damage the pistons.

As for your leaner condition at idle to 2200, personally I don't think you have much to worry about as far as damaging the motor, but I could see it having a lean sag around 1600 where it looks like AFR bumps up to mid 14's. Probably wouldn't hurt anything to have Dustin clean that up in the calibration a bit.

Is this normally what you see for an AFR line on this motor? Looks like it is all over the place, but I am not sure if you are measuring each cylinder individually or what. I am used to a much flatter AFR curve but I am also not used to measuring individual cylinders, just complete banks.

SB

Rage, can you put just 8/28 and 9/2 runs together ?

On the 9/2 run, it looks like 1600rpm and especially 2400rpm (high AFR spikes) could be detonation causing those 'high spike' AFR readings. The 8/28 run appears possibily same thing, but I can't quite make them out. Too fuzzy on my computer screen.

Thanks.