DIY_EFI Digest Tuesday, September 14 1999 Volume 04 : Number 524 In this issue: Re: DIY_EFI Digest V4 #523 Re: Bailey AFM-1 Vapor Pressure Re: Low impedance waste spark coils? See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. ---------------------------------------------------------------------- Date: Tue, 14 Sep 1999 07:43:47 -0600 From: bearbvd@xxx.net (Greg Hermann) Subject: Re: DIY_EFI Digest V4 #523 > >Date: Mon, 13 Sep 1999 13:55:22 -0700 >From: "John Dammeyer" >Subject: Re: Low impedance waste spark coils? > >>From: "Clay Buccellato (Anthony)" >>Subject: Low impedance waste spark coils? > >>As far as I can tell, the only coil packs currently available are the >>factory units from Ford and Chevy. I've been told that they suffer from >>insulation breakdown on the secondary side, if you try and drive them >>very hard. I'm looking for the waste-spark equivalent of the Crane >>PS-92, or MSD pro-power. I want lightning bolts :) > >We're currently using the Ford units for aircraft applications and haven't yet >had problem that we are aware of. Where did you hear that the insulation >breaks >down on the secondary side? I'm currently dumping a 1.5uFd Cap sitting at 225V >into it through a triac. Works great. > >Regards, > >John > Jacobs makes a maverick spark unit for Hardley Ablesons that might do just what you need. I think it is rated at about a joule per spark. Greg ------------------------------ Date: Tue, 14 Sep 1999 11:12:27 -0700 From: "Jacky" Subject: Re: Bailey AFM-1 What is the address for APE's web site? Jacky ------------------------------ Date: Tue, 14 Sep 1999 09:00:56 -0700 From: "John Dammeyer" Subject: Vapor Pressure Hi guys, Thanks for those equations. Neither of those are probably appropriate for real time calculations from cranking up to 7000RPM and 7"Hg to 30"Hg inside the intake manifold with my little 8 bit processor. I'd have to create some lookup tables. But that does bring up an interesting point. Al Grippo, in his paper where he shows how do derive pulse width, aludes to 3.1Kpa correction for vapor pressure in the intake manifold, assuming 75% humidity and 85F temperature. Now, will this be the vapor pressure of the gasoline as it changes state from liquid into gas or water as it expands in the manifold? My understanding of fuel injection is that the MAP sensor will detect the pressure inside the intake manifold before fuel is injected. Then the appropriate calculations (or table lookups) are done and the fuel is injected. Obviously, squirt an incompressable liquid into a closed volume and the pressure would go up a bit but I doubt this impacts the manifold pressure significantly. However, once that gasoline turns into a vapour it must exert some extra pressure. Is that what is calculated in the formula? Or, given that RH is really a derived term and the proper variable for moisture is dew point are we more concerned about the change in pressure caused by the air mixture (containing some water) warms up inside the intake manifold. Wouldn't the MAP sensor detect this? In the Grippo (and Bowling) formulas the larger the vp the smaller the pulse width. This probably implies that some of the pressure measured by the MAP sensor is due to water content vapor pressure and therefore there is less oxygen in the air charge for combustion and so less fuel is needed. Question is, how much of an impact would that really make if the fuel injection system is tuned sitting at the edge of the Pacific Ocean with perhaps 80%RH and then run inland where the RH for the same ambient temperature is only 30%. For that matter, what happens when the engine is run when the temperature equals the dew point (fog in the air)? I guess I have to pull out the books again and figure this out a molecular level. Cheers, John >Date: Mon, 13 Sep 1999 17:45:46 EDT >From: A70Duster@xxx.com >Subject: Re: Vapor Pressure of Water > [snip] >Date: Tue, 14 Sep 1999 11:55:50 +1000 >From: Stuart Baly >Subject: Re: Vapour Pressure > [snip] >Cheers, >Stuart Baly. >Bureau of Meteorology, Australia. > > ------------------------------ Date: Tue, 14 Sep 1999 11:22:29 -0700 From: "Clay Buccellato (Anthony)" Subject: Re: Low impedance waste spark coils? > We're currently using the Ford units for aircraft applications and haven't yet > had problem that we are aware of. Where did you hear that the insulation breaks > down on the secondary side? I'm currently dumping a 1.5uFd Cap sitting at 225V > into it through a triac. Works great. > John I heard of the secondary insulation deficiencies from Lance at Speed-Pro, in regards to the GM coils he was using. He built his own CD unit, and the coils sparked really well... for about five minutes. Do you happen to know the primary winding impedance of the Ford coils you have? I believe some of the aftermarket systems drive as high as 470V into a 0.1 - 0.2 ohm primary. I don't know the size of the capacitor. What I'm looking for are "race" ignition coils with low primary impedance, that are capable of being driven very hard by a high voltage CD system. Also, I would like the well proven multi-spark feature (from the coil driver unit, of course). Experience has shown me that hot ignitions are well worth the effort. I want to make sure I purchase the best components. Electromotive has a nice waste-spark system with spark sorter, from which they claim 120 millijoules spark energy, and a long spark duration. Emotive coils are moderate-impedance (.3 - .4 ohms primary side), and are switched 14V inductively. As a point of reference, the Crane PS-92 coil has .2 ohms primary. Have you looked into any coils other than the Ford units? What made you select them? I take it you haven't tried driving them really hard with an aftermarket CD box? (not that 225V isn't good for driving a coil, but higher energy units have been built. I'm going racing, so I've gotta get the really hot unit). - -- -Clay ------------------------------ End of DIY_EFI Digest V4 #524 ***************************** To subscribe to DIY_EFI-Digest, send the command: subscribe diy_efi-digest in the body of a message to "Majordomo@xxx. A non-digest (direct mail) version of this list is also available; to subscribe to that instead, replace "diy_efi-digest" in the command above with "diy_efi".