omega0684
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| posted on 7/8/08 at 03:51 PM |
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Alpha N fuel tables
i have changed my ms to aplha N (currently working ofline and im not connected to the MS)
How do you know what values to start from when creating an Alpha N fuel table, can you just use the same values as in your speed density table and
change the values on the y axis of the table to the resistant values from the TPS calibration?
would something like this be ok?
[Edited on 7/8/08 by omega0684]
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matt_claydon
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| posted on 7/8/08 at 04:43 PM |
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It'll be rough but will probably run. What you really want to do is get some data logs and see how TPS and MAP were related at a given RPM and
then copy the appropriate VE values from the old table to the new table. Pick a few points and you'll work out how the tables will correlate.
I'd advise you use hybrid Alpha-N which still factors in MAP unless you have a reason not to use the MAP sensor.
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omega0684
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| posted on 7/8/08 at 08:33 PM |
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i thought that hybrid alpha n is only used for Boosted engines?
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matt_claydon
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| posted on 7/8/08 at 09:03 PM |
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Nope, it's compulsory for boosted engines as TP doesn't relate to air flow at all, but works very well for non boosted.
Basically you are trying to calculate the amount of air going into the engine. A Mass Air Flow meter is probably the most accurate way, but since they
are complicated to set up we tend to use RPM and MAP or TPS to estimate the amount of air going in. By using Hybrid Alpha-N you are using both MAP and
TPS so should get more accurate fuelling.
The problem of only using TPS is that it takes no account of the density of the air, so if you map it at a typical 100 kPa atmospheric pressure then
when you drive up a mountain or are driving in an atmospheric low (or high, not that we get those very often any more!) with atmospheric pressure down
to 950 kPa then for the same TP you'll be getting 5% less air in and so all your fuelling will be 5% out. You can use the MAP sensor to
effectively compensate for this so if you've got one you may as well use it.
[Edited on 7/8/08 by matt_claydon]
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omega0684
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| posted on 7/8/08 at 09:29 PM |
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my MAP sensor is built into the MS unit, and is reluctant to drop below 95 kpa at idle, i've checked all the connections and can't find a
leak anywhere, everyone is saying that it should be more like 40-50 kpa at idle?
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matt_claydon
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| posted on 8/8/08 at 06:12 AM |
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You won't get it that low with bike TBs, I was gessting 65-70 at the absolute best. 95 is not good though so in that case it might be best to go
pure Alpha-N, if only to eliminate any potential problems.
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paulf
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| posted on 8/8/08 at 06:36 PM |
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It is possible , my 1800 zetec with 38mm throttle bodys ticks over at 45 kpa and is running on Speed density .I tried Alpha N once but found SD easier
set up as I didnt have a wideband at the time and it is easier to understand the relationship between load and speed etc .
I am just fitting a new engine and wideband so may try the hybrid Alpha N set up although in my experience it is possible to get good results with
Speed density set up.
Paul.
quote:
Originally posted by matt_claydon
You won't get it that low with bike TBs, I was gessting 65-70 at the absolute best. 95 is not good though so in that case it might be best to go
pure Alpha-N, if only to eliminate any potential problems.
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chasmon
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| posted on 28/8/08 at 08:28 PM |
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JUst to bring this one up again as I want to try Hybrid Alpha-N mapping.
The equation then has the TPS term and the MAP term...
Will this mean my fuel table will change as the MAP value is in KPa and will increase the fueling by up to 100x  Or is it done more like
MAP/atmospheric?
Cheers!
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