280 offset setting? Any Values?

[David Johns]

Anybody running fuel offset up around 103-105%.(For any good reason?)
I am just curious. I rebuilt my motor in early spring "After 2 back to back meltdowns" and fatten it up alot to protect my wallet. I have 31hrs on the motor now and I love to run the He** out of it. Now I would like to take the training wheels off it and post some real top end numbers. At a clean cut off all cylinders apprear to be rich. Are any of you guys reading your plugs and running around 100% or less? What do your plugs look like. Any PICS? I believe I am giving up some top end power being so rich. I just had the dealer take me down to 103%. Has anybody experienced any noticable difference in RPM increase, MPH etc. at lower values? If not, I will probably save the motor and continue to throw fuel at it. :cool:

Thanks!
2005 Hydrostream Voyager
2000 2.5-280
85mph. 7300rpm with 26 ET so far. Plenty more to go. Learning to drive.

[G Rowe]

Hi David.

We currently maintain around 8 280's on the offshore circuit here in New Zealand.
We leave the offset at 0 and am yet to have one dust itself, they burn spot on if anything we could go leaner. We had alot of trouble with the bosh pumps slowly loosing efficiancy, do you know your fuel pressure at W.O.T? Im guessing your motor is stock.
What octane fuel do you use, we run at least 96 or higher (good fuel here).
If interested more than happy to send some pics of pistons from a motor refresh.
Im guessing running a rich offset is covering up another possible problem....

[Jay Smith]

David ,
We build 280's and "breath" on em a bit two and I haven't had any problem with them in the middle ( 0 ) . I do widen the air gap a bit to .045" - .050" some love and some I have to put back to stock of .030 " ish according to the way the motor accepts the change........

[froggy]

David,

I run at 98% or -2% in the summer as it is hot in Oklahoma. However, as of today, 93 octane is not available here and the highest octane is 91 so I'll have to re-evaluate the fuel curve.

You would be surprised how inconsistent the stock bosch injectors are. I had mine checked, cleaned and matched just a couple weeks ago. My injectors were 12% apart with #1 flooding and #5 lean. I'm lucky I didn't burn #5. Now my injectors are 1.08% apart but I can't get 93. Life is tough!

froggy

[Jay Smith]

GOOD POINT FROGGY,
I have heard through good sources ( The Brucatos ) and by just sending my own rebuilds to have them cleaned that the quality of the injector from bosch installed on the stock 280 were a bit lower quality side than the normal injector.( guess Mercury bought a ton of "seconds" cheap) ! If there were a few that are not flowing quite enough it might explane the need to turn up the duration time the injector is open. ( richen ) to make your motor happy.........

My thoughts only !

[Markus]

What octane fuel do you use, we run at least 96 or higher (good fuel here).
If interested more than happy to send some pics of pistons from a motor refresh.
Im guessing running a rich offset is covering up another possible problem....


That's 96 RON, though, isn't it?

I.e. equivalent to US pump octane 91 (RON+MON)/2

[G Rowe]

That's 96 RON, though, isn't it?

I.e. equivalent to US pump octane 91 (RON+MON)/2

Now you mention it im trying to get that info. I started looking at some threads on fuel, av gas etc.
What a can of worms when you start trying to figure that out (what to run and what not to run etc)

[PropWash]

Markus is correct - 96RON in New Zealand is approx 91 in US (AKI = (RON +MON) /2). The MON of New Zealands 96RON is about 86 or 87.

[Markus]

For pump fuels, you can typically subtract 5 from the RON to get (RON+MON)/2, i.e. MON is 10 or 10.5 points lower than MON.