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Best A/F ratio for HP & reliability with 87 Octane

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Old 12-15-2005, 10:34 AM
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Default Re: Best A/F ratio for HP & reliability with 87 Octane

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Originally Posted by stevesxm
i am not saying i have ANY specific knowledge of the merc efi programming. when i refer to " learning mode" i am refering to specific knowledge of OTHER manufacturers ecu's for efi specifically automotive . but most manufactures use the same approach. i have no direct experience w/ marine efi. having said that , however, the theory , concept and execution are precisely the same. all that changes are the fuel and ignition curves which may or may not be marine specific but are far more likely to like aircraft where the engines run at steady state rpm more than they do varying throttle position... but regardless.... what is critical is getting your hardware defined once and for all and the fuel and ignition curves defined for what you plan to do with it... the factory stuff i am certain has a very wide power band is is made for the average joe who is spending most of his time at 60 -80 % throttle and wants good acceleration and good cruise... it is my experience that the factory curves are a great place for most people to be. smart people working there.... the aftermarket guys dump the rev limiter, pump the timing and richen it up a bit to cool the combustion chambers and claim they are wizards.... more often than not the area under the curve ( hp vs rpm ) is LESS than what the factory gave you... a few more hp at the extreme top end ? sure ... but who cares.... you don't spend much time there and the first time you get average fuel and burn a hole in a piston or rattle the top ring out you are really gonna hate yourself.
stevesxm,

Seems best to better explain my goals here. I am evaluating several approaches that increase the hp of the 496HO from 425hp to ~500-525hp to gain ~ 4-5mph. I do not want to exceed 525hp because of the fraility of the cast aluminum piston and the Bravo 1X drive. This is not a consequences be damed search for every last HP/mph at WOT. I want to retain most if not all the drivability and longevity of the stock package. Hp increase is second. That is why all the questions and research. I want to fully understand the mods and their consequences. I am also on a budget so I am looking for the best bang for the buck. I spent most of my mad money when I purchased the 2005 Nordic Rage.

The Raylar approach uses the stock 496HO Merc ECU (since it is my understanding that they can not be reprogramed this includes the stock fuel maps and max timing of acording to the Merc Hot Line of 27 degrees). The HP at 5000 rpms appears to be gained from a combination of hotter cam, increased compression ratio to 10:1, higher flow AL heads and intake manifold, increase of fuel pressure from 43 psi to 50 psi and a few exhaust mods to the Merc manifolds.

I particulary like this approach because I do not have to become an ECU programer (with all the risks that brings) and all the Merc failsafes remain. This all reportedly works with 87 octane.

Mimmicking the HP3 is another. The spec sheet on this engine configuration states +525hp at ~ 5200 rpms with 87 octane. The big differences between this approach and the Raylar is the GM ECU which will require custom programing, the heads are cast iron, 9.1:1 compression ratio, 5200 rpms and the fuel pressure is 58 psi. I do not know what exhaust system is used for the rating since this is a crate engine.

The third is an off the shelf package from a well know custom marine engine house. Again the GM ECU will require custom programing.

I am interested in the knock protection/failsafe features of the Merc PCM555 ECU and the Gen4 GM ECU. Particulary interested in the PCM555 "learning" curve algorithm after a knock event that some have mentioned. Apparently the Merc unit does not provide a knock sensor sigal output for data logger pick up but the GM unit does. I am getting the Innovation LM-1 unit to record the running parameters to dial in the final set up as best I can. Dyno testing is not an option.

1.) Any means or contacts to learn more about the PCM555 detonation "learning" curve algorithm is soliciited.

2.) Any suggestions on how to monitour knock events with an LM-1 for the PCM555 is solicited.

3.) Finally, any documented instances of burning a hole in or other wise destroying a piston with the latest Merc PCM555 ECU? In theory it sounds like it can not happen because of the built in fail safes.
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