Offshoreonly.com - Target Air Fuel ration N/A engines.?

Offshoreonly.com (https://www.offshoreonly.com/forums/)

- General Q & A (https://www.offshoreonly.com/forums/general-q-20/)

- - Target Air Fuel ration N/A engines.? (https://www.offshoreonly.com/forums/general-q/339679-target-air-fuel-ration-n-engines.html)

Quote:

Originally Posted by SB (Post 4498190)

Cruise and 4,000 rpm in the same sentence. Boy do we boaters change the meaning of that term huh.

I find myself "cruising" at 4000 most of the time. Thats low 60's mph wise for me. The hull seems happier there than it does at 50. I def dont consider it a "light load" situation though.

I know that there is no such thing as "cruise" with a boat because if a boat cruised then a boat would need brakes and boats don't need brakes. But at 4K that seems to be when the hull is the most free from the water and the engine is working under the least load, relatively. I'm just trying to figure out how to richen up that 4K area.

Quote:

Originally Posted by articfriends (Post 4473888)

I know i have taken 10 to 15% fuel out of tables on merc mefi tunes at wot and 20+% at part throttle even after bigger cams etc, numbers started in high 10's, low 11's. I tuned a 500efi w azsm throttle body, pocket ported heads, bob m cam that i built a few years ago, 27 fountain that went from 75 ish mph to 80mph on a good day, took ton of fuel out of stock tune in midrange to get to 13. to 13.2 range cruising , guy called me up and said boat used 38 gallons of gas to make same trip he previously used 45 gallons on , was concerned it was on edge of burn fown, hes approaching 75 plus hours since build, estatic that it goes faster AND gets better mileage, mercs tunes are pig rich on older stuff, lots of room to clean up efi tunes IF you dont have a low flowing injector on motor. IF a motor has 12.2 on tail pipe o2 but 3 cylinders at 11
0 and one with bad injector at 15.0 you would see 12.2
or so and melt a piston during sustained wot, food for thought!

Peak power tunes will be pinging and shortening engine life. Tunes that much more aggressive than Mercs will be risky IMO.

Merc tunes the way they do to keep the engine from killing itself under a variety of load conditions.

Quote:

Originally Posted by MILD THUNDER (Post 4470231)

Ive heard a bunch of firing order swap cams. Never heard a cam with identical specs , in an identical engine, with identical tune, back to back with just a different firing order.

Carb idle tuning, and timing can also have a dramatic effect on the idlle sound

A bit of an older post, but when we were dynoing mine with the C swap cams, changing the carbs/ intakes made a noticeable difference in sound. Once you knew which was which you probably could've picked which carb was on it by sound alone.

What do you think about the color of these plugs after a long hard run at 6000+ RPM....sorry about the triple attachment��

Quote:

Originally Posted by BenPerfected (Post 4498409)

What do you think about the color of these plugs after a long hard run at 6000+ RPM....sorry about the triple attachment��

Was the motor shut down at 6,000 and had the plugs pulled?

X2. Kinda looks like you got a little idle time before shut down. Besides that from my iPad looks good. Did you rub the color off the base ring? Don't see any aluminum on porcelain.... My plugs would look like this whenever I pulled them and everybody would look at the white porcelain and never fail to say how lean I was running. BS.

Need to run it and shut off at 6000, then cut threaded part off plug to get a "true" reading, them pics it's hard to see...

I am same way, 42-4400 "cruise" mid 50's MPH, any less then 55, it starts hoppin...

Quote:

Originally Posted by MILD THUNDER (Post 4498196)

I find myself "cruising" at 4000 most of the time. Thats low 60's mph wise for me. The hull seems happier there than it does at 50. I def dont consider it a "light load" situation though.

We shut the port engine down and idled the last short distance to the dock. Per the engine builders request, we pulled the #3 & #6 plug and sent him a picture of each plug. His comment was they were perfect. Also we have zero soot on the transom. Much of the credit goes to the 1150 CFM Holley Marine Dominators. We quit bothering with the AFR meter as these carbs are spot on out of the box. We now also just touch the key to fire the engines and we can now idle at less that 500 RPM in gear. Docking is easy without stalling and not touching the throttles. Not bad for 500 ci 9.5 to motors making 780 HP. Only took us 20 yrs to find the right high HP combination that works in a pleasure boat.