underpsi68

Detonation

jeff32

yep... real question is
why it would happen with a stock merc engine built to run on 87... there is a cause thts needs to be found so it does not happen again in a couple hours...
of course this one is a little warmed up
but still need to find why it happened!

underpsi68

stock BOOSTED engine.

I have been playing with boosted engines for over 30 years. Stress level is definitely higher for me on these setups. The safe window gets smaller and smaller.

I would think fuel injector issue if it's only 1 cylinder.

I started out using fmu's. And quickly switched over to real tuning. FMU's work, but are a band aid imo. Taxing on the fuel system.

SecondWind

Ditched the silent choice, good move. Now the build get’s a lot more interesting.

Brad Christy

Jeff,

The short answer is: “Stock cast pistons”. It does appear that the failed piston suffered a lean condition, but I’m not convinced that was it. The TechMate showed 16secs of guardian mode, but no codes. Personally, I think it was just cumulative detonation damage over time, due to injectors not meant for boost, and, when the piston failed, the damage escalated. Builder also suspects water in the cylinders contributed to it, but not enough to get the chocolate milk effect.

We are addressing every conceivable shortcoming of the 496 platform, including rebuilding the entire fuel delivery system from the tank to the intake, including bumping up to 60lb injectors. At the end of the build, it’s gonna be a brand new engine, built WAY more stout than OEM.

It is also possible that my practice of 50/50 mixing 93 and 89, to maintain an average of the "recommended" 91 may have been an issue. The mixing is fine, but 91 may not have been enough. We'll be running 93 from here on out.

Thanks. Brad.

Brad Christy

UnderPSI,

As Smitty relayed above, the injectors appear to be fine. He tested the snot out of them, and they performed perfectly. I’d agree with the suggestion, but testing shows otherwise. Another possibility is that the ECM took a dump, but the TechMate isn’t showing anything out of sorts. Who knows?

As mentioned, we are ditching the FMU, replacing it with a proportional boost reference regulator, and swapping the PCM555 for a Holley HP ECM that we can tune, and bumping to 60lb injectors. We should be able to tune it pretty well perfectly from that point.

Thanks. Brad.

Brad Christy

ICDEDPPL

Those heads and pistons look real clean. Never seen that on any blower motor. No soot at all.
IMOP you tune is lean and mixing fuel octanes? common Brad,really? First you`ll never know what the final octane will be and secondly why? Trying to save a few buck? it`s a blown engine with a lean tune, you need as much octane as possible. I ad a bottle of boostane to every tank. and use 93.

Brad Christy

Dan,

Hey.... I asked on here and got the OK.... And it's not a REAL supercharger, anyway. They just call it one in the ads.

Seriously, though.... I was always very careful to pump equal amounts, always erring on the side of more 93 than 89. With my mild boost set up, I figured I was OK. Live and learn. Straight 93 from here on out. As much as it's gonna suck at the pump.

As far as the soot.... Trust me.... All that went to the transom. As far as I understood it, it was set up "pig-ass rich", as per at least one option I got. I think the only time it was actually lean was when we were running hard, and the boost was overpowering the OEM injectors. Gonna fix that.

Thanks. Brad.

underpsi68

If that's the case, octane was a BIG factor.

Most of us at times have done something similar. In the end, it never saves money. It costs more money and time.

I would go with 80lb injectors if it was me.