Who knows how to set the "RUN BPW multiplier based on BARO and MAP (altitude and load)" in a MEFI 3 program. I went to Powell form Phoenix and I run way to fat.

Not sure where to lower the multiplier in the table. Every other program I look at has value of 1.0 or higher in some boxes.. mine are all 1.00

Im guessing I want a value less than 1.0 to reduce fuel at altitude?

Smitty maybe ???

This is a multiplier. A value of 1.0 = 0 change to the base map. A number over 1.0 will add that to the base map, a number under 1.0 will subtract that to the base map. If you are at idle, normally at sea level, then your at 70KPa and then you go to high elevation and its baro is 85KPa, then your now at 55KPA at idle, and your bpw is 1.25, then your baro multiplier at 85KPa is 1.10, then your actual bpw is 1.375. The baro multiplier is not RPM based, its a global multiplier at that given manifold psi and baro psi.

Baro is taken at every key on. At Powell, you may see a KPa of 80-85, which is lower than the standard 98-102KPa one would normally see at or near sea level.

Most cals require that you have a positive compensation to work properly. But this is if the base map is correct. The key is to have a good base map at sea level, then you can use the Altitude compensation to add/subtract what you need.

Aswesone response, I was hoping an expert would chime in!

I'm not gonna lie, I'm still confused...i get that the Baro is set at key on and I get that this is a multiplier for my base map.
What is confusing me is that I am to understand I want less fuel at altitued because air is thinner but if I multiply by say 1.10 I am adding 10% to the BPW which is adding fuel.

Are you saying that I will be running in the lower Kpa or (MAP) range of the "RUN BPW" table at the same rpm therefore running the lower BPW number assigned to that box and the multiplier will bring be back up to the proper BPW?

Also, what increments would you suggest and would do the same number across one range or variable like in the table attached from a supposed stock 4545 mefi3?

OK forgot how to attach an image, i guess you can only do it through URL.

Basically yes.

Yes, the percentage is roughly 10% at 1.1. Its not exact, but good for reference.

Your entire map is going to change the exact amount the baro is off. If your baro is down 20KPa from normal boating, then your going to see 20KPa everywhere. In a naturally aspirated config, that means instead of reaching 95-100kpa at WOT, your now going to be 75-80KPa. Because of this, your normally lean here because at sea level, you don't need as much fuel at this point. So you use the multiplier to add fuel.

But, if your map is not accurate in these areas, especially at idle, then you may be subtracting fuel, etc. If you are POSITIVE you will never go in the map area at sea level, then you can change the base map, otherwise you should tweak the baro table.

To give an example, at Tahoe, 6000+ feet, at 75KPa baro, 70KPa manifold psi, we run 1.22. The table changes as it gets closer to 100KPa but thats with a SC.

Baro compensation is just that, a compensation. You don't see any extra math or changes on the diagnostic data side. It just either adds BPW or subtracts BPW depending on what the engine needs to run properly. Again, the key is to have a great base map, then when you go to elevation, all you have to do is tweak the baro table a touch and its done. If you don't have a good base cal, then your gonna be fighting it.

Does the MEFI 1 controller use the baro compensation? I see it available in the stock calibration but the multiplier is 1.00 across the board.

Ironically I was just at Powell doing nearly the same thing. I was fiddling with the base cal and completely forgot about the baro compensation Good thing I have every calibration I've made on file so switching back is easy.

Is this Dustin posting for Whipple??

I totally appreciate you replies man and don't hate, but I forgot to mention I am running an M1SC at 7psi.

My current AFR's (last time I checked) in Arizona are in the 13.6ish range cruising and come down as I get into boost to the 12ish range. Runs around 130deg. I have been running like that for almost 5 years now and feel pretty good with it. (plugs always look a tad fat tho)

To put it simply, I remeber running fat last time I was on Powell and did not spend much time under boost. I want to take fuel out and think I need the multiplier to be less than 1.00 but every other map I read has multipliers of 1.00 or above. Am I backwards in my thinking?

I believe it is Dustin responding in the posts.

The key as Dustin mentioned is to get a good sea level BPW/MAP table, then tweak the baro table for altitude running as it's a global change.

The difficulty lies in getting a good sea level table as many of the MAP areas are virtually never accessed by the controller or are extremely transient in nature and the motor doesn't spend a lot of time in that region. (i.e. 5200 rpm at 40 kpa or 600 rpm at 100 kpa). It makes tuning those spots somewhat difficult.

Now if you feel your sea level table is fairly good but you still feel the need to pull fuel at altitude on the baro table then using a .9x multiplier would be appropriate.

I'm running a N/A application and a MEFI 1 (old but works great). I target 12.8-13.2 for all the steady state stuff. I target 13.6-14.0 idle/neutral on a warm motor. Cold start idle/neutral is a 12.2-12.5 AFR range for me. WOT I'm in the 12.5-12.8 range. I keep at eye on knock and knock retard and tweak the Merc EST table if needed. Playing with this stuff is a blast.

Keep in mind the run time BPW vs coolant temp can swing the AFR around quite a bit too. Make sure the motor temps are stable before making any big changes.

Yes, thats me.

Boats have very narrow operating ranges, therefore, if you need more fuel, then chances are you have not extrapolated or interpolated that cal at the lower KPa's. This is very common, most just tune the areas there running in, not the area where there not running so thats why I say it needs to be a proper cal for sea level. You should see a trend, if your idiling at 80kpa, sea level, neutral, cold start and 75kpa at normal temps, then 85 in gear, you should see a common trend between 70/80/90 Kpa, that should reasonably continue at 100kpa and also 60/50/40... So, when you go to Powell, it will run in these areas.

I normally test these by modifying timing to change engine torque and then I can get higher vacuum or lower vacuuming to get an accurate number. Then, my baro tables work perfect at high elevation. Under load, I run different props to get different load, such as high rpm, low manifold psi or big props and high manifold psi, low rpm.

But, in general, you have to make the numbers whatever they have to be to run right so if you have to go lower, then thats what it is. Its not normally that way, but if thats what it takes, then by all means, go for it.