lance1a
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| posted on 19/8/11 at 05:39 AM |
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Mornin' itb questions
Hiya, first post so hello to all. I don't have a Locost but need specific help from guys such as yourselves rather than the cut n' pasted
stuff one normally gets. So I have a set of inlet manifolds to fit a BMW M20B20 six pot and would like to try to see if I can make use of them.
Initially I was thinking of running bike carbs again (as I did on my M10 engined e30 318) but after issues with pin-holes on the diapragms I thought
bike ITB's would be a safer bet. I have since bought a set of 40mm ITB's (and ahve a similar set on watch) though I may have bought to
hastily and gone for something with a smaller diameter?
I HATE electrics (and only have the full use of one hand so fiddling about with small connections is a problem) but understand that I can use a few
different setups to replace the functions of the cars ECU. So am I right in thinking I need a crank signal, coil pack (or COP) something like
Megasquirt, and what about MAF/AFM for the ITB's? Also what happens about the TPS on the ITB's....is it required still with a stand alone
system?
Please be patient......I work on classic cars not any of this electronic stuff so I'm almost completely in the dark here.
I'm also thinking along the lines of camshaft change (and possibly replacing the M20B20 valves with M20B25 ones from the 2.5L).
So....break it to me gently......am I barking up the wrong tree and should I opt for a blower instead and keep it simple?
Your views will be much appreciated.
BTW....I will get some measurements regarding the intake up....for all I know it might clash with the brake servo and be a project killer from the
start.
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r1_pete
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| posted on 19/8/11 at 07:21 AM |
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Hi and welcome, its a massive subject, the best thing to do is resign yourself to an evenings googling and reading, things to search on: Omex,
MSextra, extraefi...
Here's a couple of links to get you going, the megamanual is pretty good at describing tuning theory, and the function of all the sensors and
inputs you mention in your OP...
Megamanual
MSextra
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MikeRJ
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| posted on 19/8/11 at 11:20 AM |
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With ITB's it's difficult to get a reliable and useful MAP signal, since the volume between the inlet valve and the throttle butterfly is
very small so the vacuum quickly builds up during the intake stroke and then quickly disappears once the inlet has shut. Some have had reasonable
success by joining all the vacuum signals from the ITBs into a small plenum with various nozzles to restrict and damp the pulses, but it's a
compromise between speed of response and stability of the signal.
For a normally aspirated application, the throttle position sensor coupled with engine RPM provides a more reliable load indicator - this is often
refered to as "Alpha-N" where "Alpha" refers to the angle of the throttle, and "N" is the rotational speed of the
engine. This can not be used for any forced induction application, since it has no way of compensating for manifold pressure.
The megasquirt (and probably other ECUs) also allow a blended mode, where you can combine Alpha N and MAP signals to get the advantages of both.
Obviously this requires the extra sensors to be wired in and needs more calibration.
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