DIY_EFI Digest Monday, December 6 1999 Volume 04 : Number 678 In this issue: Getting facts straight!! (2/2) Re: Signal of AMC 16 Re: DIY_EFI Digest V4 #672 re: Add-on systems which affect output pulse width? See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. ---------------------------------------------------------------------- Date: Sun, 5 Dec 1999 16:17:59 -0700 From: bearbvd@xxx.net (Greg Hermann) Subject: Getting facts straight!! (2/2) (continued from 1/2) I have no hard numbers to back up this contention, YET, but I suspect that if a port injected engine had MUCH BETTER fuel atomization than is attainable with current art injectors, and a much quicker fuel squirt--one timed with the high velocity flow of air in the port--that it would not only make more power AND have a lower BSFC at WOT conditions, but would ALSO want a mixture somewhat RICHER of stoich for maximum power than is the case with current art port injected engines! WHY?? evaporatin fuel on the back side of a hot intake valve allows fuel vapor to displace air--reducing output, whereas--getting finely atomized fuel into the cylinder, and not vaporizing much of it 'til after the I valve has closed not only avoids displacement of inlet air by fuel vapor, but takes full advantage of the heat absorbtion effect (as detailed above) during the compression stroke. - ------------------------------------------ As to the best ECONOMY mixture--going lean of stoich tends to insure burning every last bit of the fuel, and thus improves economy. The limit is usually when one approaches a lean misfire condition. (Misfires waste fuel.) Better fuel atomization and distribution BOTH work to push this limit further out. Also--the basic Otto cycle efficiency, even at WOT, improves with a leaner mixture. Good chamber geometry and good mixture turbulence during combustion push the lean limit further out, as well as allowing better efficiency through higher compression ratio (by avoiding pre-ignition and/or detonation). Furthermore-- leaner mixtures at part throttle (with a spark ignition engine) reduce pumping losses, improving economy even further at part throttle. SO--how far lean of stoich is best for economy--the answer is--"As far as you can get away with!"--not some set rule! It all depends on a large number of engine design factors. So--what are we left with that is magical about stoich? The facts that a stoich mixture is the point where a three way catalyst works best for cleaning up tailpipe emissions and that it is also the point where a standard EGO or HEGO exhaust oxygen sensor (as opposed to a UEGO WBO2 sensor) switches its output. Period. In closing--I would like to say that this list will return to far better health once it finally get put onto a different server, and can FINALLY get off of the #$%^^&^*& digest mode--too many of the really knowlegeable people here have been driven into the lurk mode by the digest format! AND--the trick to getting good information off of the internet is the same as it is anywhere else in life--one has to learn to sort useful information out from BS!! There are always plenty of people in any field who are willing to spread BS indiscriminately, usually without knowing any better, but sometimes with premeditation and for profit! Good, old fashioned fundamental education taken together with the ability and experience with applying it is one of the most effective tools for accomplishing this sorting process! Unfortunately, high performance engines seem to attract more than their proportionate share of the BS and the profiteers (particularly the ones who feed on ignorance)! Although I am NOT going to be so bold as to say where, I WILL promise that there is a bunch of good information in this last series of posts--it's up to all of you to figure out where! Back to lurk mode, at least 'til we are off digest mode! Regards, Greg ------------------------------ Date: Mon, 6 Dec 1999 10:01:24 +0800 From: dzorde@xxx.com Subject: Re: Signal of AMC 16 Mike, I had a similar problem trying to interface my Chev HEI to the aftermarket ECU, made the car undrivable as it saw multiple crossovers of the same trigger. Try something along the lines of. 0.1uF 1k coil ------||------/\/\/\/\/---------|--------------ECU < > 1k > | ---- 15V zener diode 5W /\ | gnd regards Dan dzorde@xxx.com Date: Sun, 5 Dec 1999 00:56:23 -0500 (EST) From: Mike Comai Subject: Ref. Signal off of AMC I6 I am currently trying to get my first major retrofit up and running. I have everything installed and when I try to start it the injector's don't fire. I was told that I need a filter on the negative side of the coil and to feed the filtered signal into the Reference line on the ECM (which I am using a '747). I was given a design for a filter which looks like this: ------------------------------ Date: Mon, 6 Dec 1999 10:14:04 +0800 From: dzorde@xxx.com Subject: Re: DIY_EFI Digest V4 #672 I'm doing this on my current s/c set-up (although car is not yet driveable), anyway a blow off valve just venting of the air during idle and light cruise. Put your foot down, the valve shuts and there is instant 17psi boost. Unlike a turbo, you don't get a pop when it opens, but more of a constant whistle as it lets a lot of air out unless wot. Due to the extremely hot air (currently don't have an intercooler yet) I'm reluctant to recirculate it through the intake filter (but due to the very loud whistle created by all this air veing vented in the engine bay I need to do something). Can anyone see a problem with feeding the air from the blow off valve into the exhaust system before the muffler and quieten it down this way. The line could be fed in at 45deg angle with the exhaust flow. Dan dzorde@xxx.com Date: Thu, 2 Dec 1999 19:02:36 -0500 From: "Jonathan Davis" Subject: Re: KLUTCH!!! Another way to do this, perhaps would be a large bypass valve that recirculates any boost until WOT. Something like that would be intoxicating to drive - nice fat kick in the pants at WOT... ------------------------------ Date: Mon, 06 Dec 1999 02:19:16 -0500 From: Chris Conlon Subject: re: Add-on systems which affect output pulse width? "Andrew Brownsword" wrote: > It seems to me that this could be problematic if the ECU was designed to >expect a particular voltage range and the stock airflow meter generated that >full range ... in other words there is no buffer for going beyond the >expected range of values. This seems fairly reasonable for an N/A engine >since it is extremely unlikely that the car will have to deal with >1 >atmosphere. I'm not going to get into this, really. You may very well run into problems, especially with ignition timing, when you try to trick an NA ECU into running much boost. (If you aren't reprogramming it, that is.) > The alternative is to modify the ECU's output, which is a time dependant >pulse width. It simply isn't possible to have full remapping control over >the output because by the time you know what the pulse width is, the time at >which you have to send it to the injectors has passed. It occurred to me You can get very close, though, and very easily, in at least a couple different ways. This presumes you're running injectors a good bit larger than stock and will not need to lengthen the pulse. Take your basic HC11. Wire a switch (power mosfet most likely) in series with each injector drive circuit, watch for voltage drops, ground ref, etc. Control each switch via output compare line. Also wire up input compare lines so they can detect when the ECU is *trying* to fire the injector, independent of your switch's position. (If you have more than 4 independent injector drive circuits, see 68332 instead.) Now you can easily read RPM and load, more or less, via input compares. You have a map, and for each rpm/pulse width point, look up a new pulse width. (Or just multiply by old injector size / new injector size, correct for short PW, etc etc.) Leave each output compare line (switches) on, until the ecu fires that circuit. You'll get an interrupt and time count via input compare. Calculate how long you want the pulse to be, program output compare to turn off at that time. When IC turns off again, take another interrupt, turn OC back on. You can update RPM and desired-PW info at each injector firing if desired. It is "behind reality" but not by much. Issues exist with p&h drivers, need a dummy load, etc, or just supply your own drivers. (Assorted details omitted, none too tricky.) I already have to do this (and more besides) for my semi insane supercharged MR2 project, ugh. Lucky for me the ECU already understands boost, timing retard, knock sensing, etc, it just needs a few white lies about airflow & injector sizes. Now I had some questions for you, since you seem to know Ford/Mazda stuff well. I did some searching for answers but got confused and set it aside. I'd like to get an MX-3 v6, and do some engine swapping. I've heard that a 2.5l v6 from the MX-6 (or 626?) will basically drop in. Wasn't there a 2.5l *turbo* Ford Probe GT engine at one point? If so would it drop in w/o much work? Basically I think the MX-3 is cute and would get one if I knew I could grab a decent turbo engine (well, a whole front cut) from something and drop it in pretty easily. (Ignoring ECU hassles of course, got to have some fun!) I know there are aftermarket turbo kits, etc, but I was hoping for a factory turbo motor. Am I just real wrong or was there such a beast? I'm pretty sure there was a not-common MX-6 turbo... comments? Thoughts? TIA, Chris C. ------------------------------ End of DIY_EFI Digest V4 #678 ***************************** 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".