DIY_EFI Digest Friday, August 13 1999 Volume 04 : Number 465 In this issue: Re: DIY_EFI Digest V4 #464 New Project - 514 9V power supply Signetics N82S2708N Re: DIY_EFI Digest V4 #462 See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. ---------------------------------------------------------------------- Date: Thu, 12 Aug 1999 16:43:20 -0400 (EDT) From: William T Wilson Subject: Re: DIY_EFI Digest V4 #464 I hate digest mode. Somebody please fix it. :} > The most common pitfalls are not coming to terms with writing "real > time" applications and how very "real time" the engine management > game is. Something that is extremely lacking - not just in engine management but in many technology applications - is people actually quantifying what they want the stuff to do. Let's say your engine turns 10,000 RPM (because it's a nice round number and is pretty much an upper bound for anything amateurs are likely to do). Let's say it's a 4 cylinder engine or a rotary; a V8 has twice as much to do but turns about half as fast, so it all works out. Let's also assume you're using TBI injection. Now, if my brain is working (which it often is not): 10,000 RPM is equal to 166 RPS. Since you have one pulse for every other revolution for each cylinder (assume 4) you'll have 4 * 166 / 2 = 332 pulses per second. Now, that doesn't seem all that bad, but consider all the stuff that has to be done for that pulse and how precise it has to be. It's easy enough for a computer to do 332 things per second but for it to do one thing precisely every 3 msec is a little different. First you must sense the current RPM. You can't do this in the same thread that does anything else because by the time you get the RPM sensed you'll have missed a pulse. If you have 6 teeth with one missing on your sensor widget (that's a technical term) you'll be getting 50,000 pulses a second, which means you need resolution of 100,000 pulses a second (so you can find the missed one) which means you need additional hardware to help with this, *already* your laptop is by itself inadequate. Assuming you have a unit which sends you a 16-bit value (adequate for any RPM) 10,000 times a second. You need to read your serial port at a bit rate of 19,200 bps just to make 9600 RPM max. 38,400 if you want to be safe. The good news is that if you miss one of these it's not the end of the world. Then you need to send the injection pulse. First you need 3msec timer accuracy. The hardware clock can do that, but if your system is too heavily loaded, you'll lose out. This is where Windows really falls over; it's simply not that precise. Most of the time Windows can't even play mp3's and run Netscape at the same time without cutting out even though the total cpu load is less than 25%. The trouble is, you can't block (i.e. run in a tight loop to ensure precise timing) while you do this because about half the time, some other cylinder will need a spark while you're timing the injection pulse. So you have to pass it off to the OS and go tend to the other guy's spark. If you have a V8 instead of a 4-cylinder you'll have twice as many sparks and longer injection pulses so you'll have even more trouble with that. Somewhere in there you have to find time to check the TPS, correlate it with the RPM and boost level (if applicable) and find out how much fuel you're going to squirt for the next pulse. If you are running closed loop you'll have to check the value of the O2 sensor... oh, bad news. A/D converters are slow - so you can't do that read instantaneously. But you need to know this ahead of time because otherwise you don't want to go lean accidentally. Any of this stuff is easy enough to do, but getting all the scheduling right is the hard part. > On the Engine Management side things are a lot more difficult. You can get a good handle on things just by connecting an A/F meter to see how much fuel is being pushed in at various RPM's. You can then simply capture this data for a good starting point. > Let us know what you find out ? Can a 300mHz 32 bit wintel run an > engine ? No chance. Windows cannot do this. Linux probably can if you are comfortable with programming for real time applications, but you would probably be safest with a genuine real-time OS, which of course is a very specialized skill and probably expensive for the software. You kind of reach a point of diminishing returns with PC hardware. The CPUs today are designed for computationally intensive applications which engine management is certainly not. Your real bottleneck is the I/O, most PC systems are very poor at this and it's the most important part of engine management. ------------------------------ Date: Thu, 12 Aug 1999 21:45:44 -0500 From: Tom Sharpe Subject: New Project - 514 I'm starting another Cobra project and need an engine. Does anyone have any EFI experience with the Ford 514 crate motor??? 600hp@6250rpm (w/ dominator). With the 460 crate motor??? How about the 351W strokers??? I would like to buy a clone efi system if someone has already done it. Anyone have a 427 side oiler laying around cheap?? 429 BOSS?? Cammer??? didn't think so!! TIA Tom ------------------------------ Date: Thu, 12 Aug 1999 21:50:04 -0500 From: Tom Sharpe Subject: 9V power supply I need 2 mv @xxx. My radioshak book says I can do it with a resistor and diode. Can any EEs out there give me values or part numbers??? TIA Tom ------------------------------ Date: Thu, 12 Aug 1999 21:59:03 -0500 From: DC Smith Subject: Signetics N82S2708N Does anyone have the pinout/specs (anything?) handy for the Signetics N82S2708N. One of our CAE TWA 727 flight simulators at work smoked one of these ROM's and I can't find any info on it anywhere. I can use the chip from it's sister ship next to it, to burn a new one. This is in the motion cabinet electronics. These machines are pretty complicated for sure. It has been down for 5 days. Check out: http://www.flightsafetyboeing.com/ (I don't know what all is on it..) This is electronics, but no EFI content, so please reply privately, if deemed necessary. Thank you all. *********************************************************************** Dan Smith 84 Regal 12.03@xxx.45 GSCA# 1459 St.Charles, Missouri mailto:morepoweral@xxx.net http://www.tetranet.net/users/morepoweral *********************************************************************** ------------------------------ Date: Thu, 12 Aug 1999 20:43:05 -0700 From: "Steve" Subject: Re: DIY_EFI Digest V4 #462 > Date: Tue, 10 Aug 1999 16:56:01 -0600 > From: "Kevin Yachimec" > Subject: Re: Turbo header design > Big snip > minimized. I have a promotional paper from Allied Signal outlining manifold > design for their turbos. It covers both their new pulse type turbos (like > the ones you see on all those 10 second Honda's with equal length headers) > and their standard turbos, if I can find it I'll post it 'incoming'. > Yes, please post it to the list or an FTP site if it's too big for email. Thanks, Steve ------------------------------ End of DIY_EFI Digest V4 #465 ***************************** 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".