NA BMW ITB's: alpha N? or map
Turbo Mini Forums

Hi.

I'm doodling along, planning my 16v BMW conversion. i stripped the head this weekend (gorgeous head ..the rest of the block is a work of art too, shame i can use it).

my plan :
K1100lt 16v head
1330 bottom end
MS II

the MAP signal from ITB's is supposed to be a bit of a hassle as it goes to atmosferic rather quickly and affects resolution and pulses quite a bit.. ad to that: that i would see if i can use a Long intake/CAI plenum along with the ITB's to see if i can get the powerband to shift downward (if i can get the maths to work)

which would cause the map to go even more odd.

my options:

-just use the TPS hookup provided on the BMW throtle bodies.

-Use a damping plenum to clean op the MAP signal (would still have a pretty low pressure differential to work with).

barometric correction seems a good option (i like mountains)

- use Alpha-N ..which is supposed to be good for ITB's

- use Aplha- N blend wich i don't get at all..

anyone has deep thoughts about this?

cheers

JR

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

Yes Alpha N

Or

Alpha N with Speed density blending

The latter gives you the option to run Alpha N at low rpms where the map signal is dirty, then changes to Speed density when the MAP is smoother at the highr rpm.

I believe you can 'T' all the ITB's together to get a cleaner MAP signal

Edited by Sprocket on 23rd Apr, 2007.

Alpha N with SD blend is the way to go if you can, some ECUs don't give you that option, just one or the other.

If your going to T the ITB's together to help with the MAP signal then make sure you use decent fittings or else you might find yourself chasing an idle balance problem.

Every day is a school day ...........

How fast and how expensive ...... the same question...

None of this makes any sense to me what so ever...Lol..I really should start researching it.

Anyone know of any good reads that explains about injection setups and sensors etc?

Sorry don't mean to thead jack...

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1/4mile in 13.2sec @ 111 terminal on 15psi

Dave Walkers book from Haynes is quite good. Obviously focuses on the Emerald ECU but it will get you going.

Every day is a school day ...........

How fast and how expensive ...... the same question...

This is a good place to start

http://www.megamanual.com/mtabcon.htm

And falling way behind is this

http://www.vems.hu/manual/html/

Hi,
+1 Haynes Engine Management book, good read. Covers carb and engine tuning stuff too.
Cheers,
Gavin :)

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My Mini build diary

matty..

i read the post an kinda realised it is mumbojumbo to the max if you dont know the lingo

basicly..

if you have a plenum (box) with one ThrottleBody (TB's) you can measure the vacuum ( manifold absolute pressure.. or MAP) which is behind the butterfly in the box which will tell you how much air the engine is ingesting. at full throttle the pressure across the butterfly should be near zero (otherwise the TB used is too small) at idle vacuum is high.. a petrol engine is on a leash ( bar a FSi which is pretty much a diesel engine on petrol)..It wants to rev itself to pieces but it is throttled.. unlike a diesel which is regulated bij the amount of fuel you put in..(on a side note.. that is why a diesel needs a seperate vacuum pump for powersteering, brake boosters..it has no throttle valve so no manifold vacuum)

ITB (individual TB's one per port) don't have a box just a tiny bit of volume .. as a result opening the butterfly onluy a tiny bit makes such a bit leak compared to the tiny space that vacuum goes to atmosferic pressure quite rapidly.

one can connect all the vacuums from all TB's to each other and add a litle extra chamber (say plastic big fuel filter.. cheap and has extra damping in the form of filtering material)

so you can use TPS (OR APHA-N) (throttle positioning sensor) which is a potentio meter which tells you if the butterfly is open or closed or somewhere inbetween..

if i have x throttle opening and me engine is turning y revolutions i must be getting about this much air....so I inject z amount of fuel.then llok ( by means of the lambda sensor ) how the mixture is..


the blend option does a bit of both ...


there is a thread here where Bill Survington explains this quite well.. wich i remember reading while i re-read it just now.. but now i get it :)

I tyhink for me the best option would be either straight alpha-n (if used with the rampipes as supplied by the various kits) or alpha N blend which would probably work better with my long intake idea.

personally i would think that the rampipes as supplied are too short ( the originals are 5 times as long.. and the BMW engineers look like they have not been bodging in the rest of the block)

Edited by Sir Yun on 24th Apr, 2007.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

Cheers guys, Had a breif scan over MS manual....gulp....there seems to be link after link after link!!!

It bugs me when I don't know how or why something works so looks like Ive got a lot of reading to do! LOl

Sir Yun, thats cleared up a fair bit , thanks. :)

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1/4mile in 13.2sec @ 111 terminal on 15psi