 Posted: Fri Aug 10, 2007 4:40 am Post subject: |
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| Hi, I'm somewhat puzzled. The ditributors on my engines are mechanical advance and therefor are tunable with springs and stops. The vacuum is only an addition for road economy applying extra advance to fire lean mixtures on overun and light throttle.
On modified engines the vacuum can be disconnected to prevent them from actuating at full throttle which can be a possibility. Modified engines will normally require less total advance because of better combustion characteristics ( faster flame front from better cylinder filling and more homoginised mixture from better squish) Total advance (static plus distributor) is the crucial setting. Examples from the past: The old Lotus Twincam in racing form would produce max HP at 38 degrees total and last about 4-6 laps. At 36 degrees it would lose about 3HP and last all day. The ford BDA rally engines would run between 28 to 32 degrees total. Less than the Twincam because of better squish. Some supercharged and Turbocharged motors run dizzies with top end retard althogh these days it's all usually handled be an ECU. Why anyone would recommend points over electronic triggering is beyond me. Electronic maximises the dwell angle which is the period that the primary windings in the coil are being saturated. An important factor in the amount of spark delivered. Points can only be a compromise in this area because of the mechanical limitations of lobe shape to avoid points bounce (just like valve bounce) and the reason that performance cars pre electronic ran special heavy duty points with a tougher spring. The original Mini Cooper S is an example. Most dizzies with mech advance(like the 333s) have a stop to limit the advance and this can be modified with ingenuity. The rate of advance or curve is modified by the control springs used. Hpoe this helps regards Eddie |
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| Posted: Wed Aug 08, 2007 9:52 am Post subject: |
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| guys, sorry to hijack your thread, but it sounds like you can help me......I am currently about to swap my carbed 1.5 sud engine in the back of my UVA fugitive for a carbed 1.7 8v (hydraulic heads) with the bosch electronic distributor and coil that you mention.......how the bloody hell do I wire this thing up?.......is it a straight swap for the other coil and wiring?.....or a bit more complicated?
some form of simple wiring diagram would really help me.......where can I get a standard alfa wiring diagram, as I cant find a service manual for the later boxer engines interesting about the vacuum advance, I will look for this on my distributor and ensure its working correctly. |
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| Posted: Sat Aug 04, 2007 7:12 pm Post subject: |
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| Thanks Lee, but at a glance it looks like more effort than I wanted. I'll look into it though. I think I might have to compromise. | |
| Posted: Fri Aug 03, 2007 6:43 pm Post subject: mapable ignition |
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| Hi , i had the same problem as yourself, and had to compromise with the alfa distributor for my application ,see alfa sprint 16v. i fitted mappable ignition which is called megajolt ,its worth the time and effort to do because there is no compromise. I fitted this to my own car for a total of 160 pounds inc rolling road tune. all software is supplied you just need a lap top. http://www.autosportlabs.org/viewforum.php?f=7
hope this helps. Lee  |
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| Posted: Fri Aug 03, 2007 1:29 pm Post subject: Distributor modification |
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| At a recent rolling road tune up (following the addidition of fast road cams and flowed heads), it was suggested that my Bosch distributor would benefit from being changed to mechanical advance and points, rather than the vacuum advance (1987 1700 8valve).
Apparantly the advance curve was out at high revs so the mod would give better power and be more appropriate for the current engine set up. *Has anyone done this? *Where would I get the parts and would it be a simple modification? *Does anyone know if a Mallory distributor is available for this engine? (the advance curve on a Mallory is adjustable) Any suggestions would be helpful Thanks Rich |
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