DIY_EFI Digest Tuesday, August 10 1999 Volume 04 : Number 461 In this issue: PC based engine management system Re: DIY_EFI Digest V4 #460 RE: DIY_EFI Digest V4 #460 Re: Turbo header design Re: 2 pessure sensors ? See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. ---------------------------------------------------------------------- Date: Tue, 10 Aug 1999 11:31:10 +0100 From: JMACKENZ@xxx.com Subject: PC based engine management system Hi, I'm new to the digest and have joined because I've set myself a long term project to design and build a road legal drag car (ie nothing too stupid or expensive) for which the engine is fully managed from a laptop computer. I'm doing this mainly as a challenge for fun and will share all my results / code etc when I have anything worthwhile. I've never attempted anything like this before and any cars which I have built previously have always used carbs rather than EFI but I will put the effort in to make sure I succeed. My knowledge of the workings of common engine management systems is very limited and this is the first area which I need to learn about. Does anyone have a good document or website which describes basics / details of the engine management system including the fuel maps? I'm also looking for a description of the what is sensed from the engine (ie airflow / MAP / oil / water temperature / crank position etc) and what effect this has on the fuel delivery volume / timing and the ignition timing? Also I need to figure out or buy an input / output device for the laptop (PCMCIA / Parallel / RS232 ?) which will allow me to sample all the inputs and output to fuel injectors etc. Any advice on this would be most appreciated! What I'm looking to achieve initially is to have an engine (very probably a Rover V8 from a 1984 Rovertec Vitesse) for which the fuel delivery is managed via a hardware interface to a laptop which runs custom written software. I would then like to add in the ignition timing then a supercharger or Janspeed twin turbo setup (or both). Eventually my goal would be to include servo throttle control and other stuff to basically allow the car to drag a 1/4 mile based on an optimised program without any driver intervention except for steering! I know this is a huge never-ending project but it'll keep me entertained for a long while and it'll be worth it in the long term. I know I'll destroy numerous engine parts. I'm lucky that I have a lot of technical support and enthusiasm from friends. I'm aware that the first year will be spent in the garage but this is no different to most of my projects! In addition to standard tools, the equipment I have (or have access to) includes the following; Emmisions meter Numerous volt / current etc meters Digital oscilloscope EEPROM programmer My background - I'm a degree qualified Electronic / Mechanical engineer with a great interest in cars. I work in IBM as a senior WW test engineer for Thinkpad (Laptops) manufacturing which means that I can program in C / Turbo Pascal and Rexx and have a pretty good understanding of computers. Working in IBM also gives me access to the skills required for ciircuit design etc which I'm a bit rusty on myself. I will be working closely with a friend who has a lot of experience with building strange cars and engines but he also has little knowledge of EFI systems. If anyone can offer me any initial (and hopefully ongoing) help and support then I would be most appreciative. I am a complete novice in this field just now but I'm a fast learner if I get the help I need. Best Regards James MacKenzie ------------------------------ Date: Tue, 10 Aug 1999 07:06:35 -0600 From: bearbvd@xxx.net (Greg Hermann) Subject: Re: DIY_EFI Digest V4 #460 >Does anyone know what the Fuel Vapour pressure for Gasoline is or where >to look it up on the WEB? I'm assuming (perhaps wrongly) that it's the >pressure generated by the fuel as it evaporates. The number used in >Grippo's document suggests 3.1Kpa but that's at 85F. What would it be >at -40F. The vapor pressure of gasoline is VERY much a matter of the blend. And most refiners vary it from summer to winter, etc. To give you an order of magnitude idea, the vapor pressure of iso-octoane is 1.72 psia at 100 degrees F. I do not have a listing of its critical point temp--pressure. There is a relationship from physical chemistry that will let you calculate the vapor pressure at any temp for about any single compound given a couple of bits of info about it. Regards, Greg ------------------------------ Date: Tue, 10 Aug 1999 09:34:23 -0400 From: "Jensen, Mike" Subject: RE: DIY_EFI Digest V4 #460 Has anyone ever built a home dynamometer? If so does anyone have any plans or could someone explain how they did it? Perhaps there is a site on the web that I have yet to find. If anyone could point me in the right direction it would be most appreciated! Michael H. Jensen Mechanical Designer Environmental Tectonics Corp. 125 Jamesway Southampton Pa. 18966 Phone (215) 355-9100 Ext. 276 Email mjensen@xxx.com> -----Original Message----- From: DIY_EFI-Digest-Owner@xxx.edu [SMTP:DIY_EFI-Digest-Owner@xxx.edu] Sent: Tuesday, August 10, 1999 5:00 AM To: DIY_EFI-Digest@xxx.edu Subject: DIY_EFI Digest V4 #460 DIY_EFI Digest Tuesday, August 10 1999 Volume 04 : Number 460 In this issue: Re: DIY_EFI Digest V4 #457 Re: DIY_EFI Digest V4 #457 Re: DIY_EFI Digest V4 #459 See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. - ---------------------------------------------------------------------- Date: Mon, 9 Aug 1999 19:07:29 +0000 From: xxalexx@xxx.com Subject: Re: DIY_EFI Digest V4 #457 I have 16 pin connectors, and looking for new sources. Alex http://www.obd-2.com and a welcome back to CSH-HQ > Subject: ALDL Connectors > > Been posted in the DIY archives. Both 12+16. Try OBD for the 16 in search > Bruce > > > Date: Sat, 7 Aug 1999 19:58:45 EDT > >From: Mikepoore@xxx.com > >Subject: Looking for ALDL connectors > > > >Does anyone know where I can find 12 pin and 16 pin GM ALDL connectors? I am > >looking for the male ends. I've got my interface working, but I would like to > >connect and disconnect it a little easier than pin by pin. > > > >Mike Poore > > ------------------------------ Date: Mon, 9 Aug 1999 19:08:17 +0000 From: xxalexx@xxx.com Subject: Re: DIY_EFI Digest V4 #457 I have 16 pin connectors, and looking for new sources. Alex http://www.obd-2.com and a welcome back to CSH-HQ > Subject: ALDL Connectors > > Been posted in the DIY archives. Both 12+16. Try OBD for the 16 in search > Bruce > > > Date: Sat, 7 Aug 1999 19:58:45 EDT > >From: Mikepoore@xxx.com > >Subject: Looking for ALDL connectors > > > >Does anyone know where I can find 12 pin and 16 pin GM ALDL connectors? I am > >looking for the male ends. I've got my interface working, but I would like to > >connect and disconnect it a little easier than pin by pin. > > > >Mike Poore > > ------------------------------ Date: Mon, 9 Aug 1999 22:03:31 -0700 From: "John Dammeyer" Subject: Re: DIY_EFI Digest V4 #459 Phil wrote > >Hi All, > John wrote >> Why would Honda put the MAP sensor just behind the throttle >plate? > >Good question. I guess from the tone of what you wrote that you >suspected that this could be an issue. > Well, I thought it a bit odd. After all, the Fuel Pressure regulator is attached to the middle of the plenum. >I agree with you it probably is. They could of course have a >table of correction factors for air temp vs non linearity vs >volume. True, and perhaps at the high end it really doesn't matter. >Next issue is why are they using an ambient sensor ? Doesn't the >engine >know what air pressure it is subject to ? Guess you've never owned a SAAB 99 with mechanical fuel injection. ;-) Whenever we took it on holidays from home at 2200' ASL down to Sea Level we always found the engine ran poorly. Got it back up to home altitude and that wasn't a problem. The 900 series etc. use MAF so they don't care; they already know how much air is being sucked into the engine. Other vehicles with MAP use some sort of ambient air pressure sensor. I even disected an after market fuel injecton box and sure enough, they had two Motorola Pressure transducers inside: one for ambient and one for MAP. The 'Grippo' formula uses MAP/(MAP at WOT) to scale the PW. Additionally there is a second part of the formula that uses MAP at Wide Open Throttle (I had assumed Ambient Air Pressure due to the location of the HONDA MAP sensor) minus Fuel Vapour pressure divided y the temperature. This number gets smaller as either ambient pressure goes down or temperature go up thereby reducing the PulseWidth; less air, less fuel required. Kind of like reaching 8000' ASL and adjusting the Lycoming's mixture on on your Cessna till EGO readings are correct again. Does anyone know what the Fuel Vapour pressure for Gasoline is or where to look it up on the WEB? I'm assuming (perhaps wrongly) that it's the pressure generated by the fuel as it evaporates. The number used in Grippo's document suggests 3.1Kpa but that's at 85F. What would it be at -40F. Interesting too, if the MAP is taken somewhere further inside the plenum then the WOT value will probably be lower than Ambient Air Pressure. If you used one sensor, then you could save Ambient Air pressure the moment the ECU powered up just before cranking. Of course if the vehicle runs for an hour straight up a mountain then the fuel ration will just get richer and richer. So the trick is to reduce the PW as the air density decreases. Al Grippo's equation reads: Air Density = (0.0391568(Barometric Pressure - 31)) - ------------------------------------------------- (Manifold Temp/10) + 459.7 Barometric Pressure, Manifold Temp and the 31 (3.1 Kpa) are all scaled by 10. Bruce Bowling does the same thing but in "Hg. In either case, this provides the number required to shorten the PW as altitude or plenum temperature increase. Next we get to drag our test frame with GCF (remember... Giant Computer Fan) up a small hill from Sea Level to 2500'. Hopefully I should see the O2 sensor keep the same values but I'd like to test at 10,000 without leaving the ground. > >> For a race car calculating a new injector value PW every stroke >may be a >> requirement but is that really needed for marine or aircraft >> applications? > >Yes. and on second thoughts Yes. > >If the calculations are done per cycle then the sudden throttle >and/or >load change will encounter maximum of 2 bad combustions. > >Now that probably sounds excessively picky but if your engine >goes from >250 hp to 125 hp in 1 revolution and then back again the stress >cycles on the crank are enormous. Even bailing wire has a cyclic >strain limit. Good point. We'll call that the BWCSL. ;-) I understand what your saying though. I'll check through my code and see how many lean combustions I might have. Obviously MAP will lag TPS so a change in TPS is probably a better indication that it's time to enrich the mixture. > >Question ? Who blows up all those F1 engines. I'd like to try!!!! > >Try creating a 4 byte map. > >MAX. Vacuum 1000 rpm Max Load 1000 rpm >Max vacuum 6000 rpm Max Load 6000 rpm > >if you interpolate b/w these 4 points and each on it's own is >correct >then you will be on average spot on. (This doesn't include >camshaft timing alterations) this would require the 6 point map. > >By 65,000 points I didn't mean memory locations I meant possible >calculated values from rpm 8 bit X vacuum load 8 bit. > >thus 255 x 255 = possible outcomes. OK. I see what you mean. > >You will at some stage have to get those 4 measurements as they >are the basis for all further corrections. > >Full load 6000 rpm is easy just pull the stick all the way and >the prop will do the rest. > >Full load 1000 rpm has more air per cycle than 6000 rpm so give >it 10% more We can bog the engine down with the dyno to get that. > >Light load 1000 needs the rubber band to be removed. Hmmmmm.. I think you forgot the page number of the Bosch Blue Book for RB (rubber band) analysis. ;-) >There ! that's 4 bytes of eeprom all used up. You make it appear really simple. I guess in many ways it is, after all a simple SU carburator can do it. > >You have only to get rpm from the timer ticks vs a single A/D >Vacuum Load and you are ready to go. Your last air, water and >accel corrections are waiting from the last stored calc. apply >these and squirt. > >Given a 1 mHz internal clock and 6000 rpm you have 10 ms or >10,000 clock cycles to get this done. say 2000 instructions >executed >at worst. Yes, but I want to be able to play space invaders too. 8-). > > > P.S. if this to and fro is boring the pants of others please >chime in and tell me firmly. Shussh everyone. This beats the pants off the standard questions of "I have a xxx ECU for my sports car and I want to modify the tables ... what do I do?" regards, John ------------------------------ End of DIY_EFI Digest V4 #460 ***************************** 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". ------------------------------ Date: Tue, 10 Aug 1999 14:29:13 -0400 (EDT) From: Pat Ford Subject: Re: Turbo header design Hi Greg: Is there any simular design rules for intakes ?? Previously, you (Greg Hermann) wrote: > > > FOR THIS PARTICULAR V-8> (IT HAS A 90 degree crank) > > Firing order > > 1 8 4 3 6 5 7 2 > > With this firing order, take every other cylinder in the firing order if > you want 180 degree (crank rotation) spaced pulses into a pair of 4 into 1 > collectors: > > 1, 4, 6, & 7 go into one collector (two end cylinders from one bank, and > the two center cylinders from the other bank. > > 8, 3, 5, & 2 go into the other collector. (the two end cylinders on the > other side, and the two middles from the first side. > > If you want PROPERLY done tri-wyes, go 1/2 way around the firing order, so > that the pulses in the pairs of tubes which combine at the first wye are > spaced evenly, 360 (crank) degrees apart: > > 1 & 6; 8 &5; 4 & 7; 3 & 2. As you can see, each pair takes one tube from > each bank of the motor. > > Then, at the second wye, pair 1-6 with 4-7 and pair 8-5 with 3-2 so as to > get evenly spaced pulses at the second wye in each header. > > If you wanna go with REALLY long tri-wye branches, (surprising how > fantastically good this is for street, high torque, & 4x4 type apps.) start > out with a regular set of 4 into one headers (of the smallest tube size you > can find), cut them off a bit before the collectors, and do the snaking > back and forth under the bell housing/tranny to get the correct first wye > pairings. The second branches want to be the same length as the first ones, > but there are no crossovers if you plan ahead. After the four second > branches combine into two (tertiary) pipes, you want a length of pipe of > length equal to all the first and second branches. At the end of that pipe, > you need a gap (no diameter change of offset in the pipe) in the pipe about > 3/4 inch long. Put an empty plenum chamber around that gap. The volume of > the plenum needs to be maybe double the internal volume of the last > (single) length of pipe feeding it. Just run a full size tail pipe and low > restriction muffler behind the plenum (Not much vehicle length left after > this, anyway!) > The headers will effectively see the plenum as an open ended (to > atmosphere) pipe. DO NOT omit the plenum, it is worth quite a bit of HP and > response! > For street stuff, usually, primary tubes 1 trade size SMALLER than the size > which can be swedged square to fit into a flange and match the port > properly work out to be the correct size. (If a 1-7/8" tube can be squared > at one end and fitted into a flange so that the inside of that tube matches > the port shape, then run the primary tubes with 1-3/4 " tubing.) You want > the internal AREA of your primary tubes to be about equal to the > cros-sectional AREA of the exhaust port. The above is what usually works > out right. (Especially if the engine designer did his homework!) The extra > work involved in getting down to the smaller tube size is why most off the > shelf headers use too big a tube size! Figure the length of the primary > tubes so that each of their internal volumes is about 140% of the > displacement of an individual cylinder. (For instance, for a 350 cid V-8, > using 1-3/4" tubes (which are about 1-5/8" inside diameter in 16 gauge > tube, this would mean you want (at least) 24 inch long primary tubes.) (And > if you are using lighter than 16 gauge tubing, don't bother!) > If the primaries are 1-3/4", then 2" is usually about right for the > secondaries, and 2-1/4" for the next ones. (A quarter inch increase in tube > size at each successive wye is usually about right. > > 1-3/4" diameter primary tube size was only an example. It is prolly BIG for > a street 350, 1-5/8" or 1-1/2" is more likely to be right (but with more > tube length so as to get to the same internal tube volume!) > > If you build a set of tri-wyes this way, they will sound and run like > nothing else! The throttle response will be astounding! But it is a ROYAL > pain in the #@$% to do it! > > All my experience says that the biggest gain from headers is from giving as > much of the exhaust gas as possible somewhere to go freely during the > "blowdown" part of the exhaust stroke--before the piston starts back up > significantly. Yes, it's nice to have a low pressure pulse in the exhaust > port at overlap, and that pulse helps to scavenge clearance gasses if you > have it there at the right time, but the longer you can keep the blowdown > stage flow sonic, the less work the engine will have to waste pumping > exhaust gas out of its cylinders, and the more sonic energy there will be > available for creation of a scavenging pulse! > > Regards, Greg > > - -- Pat Ford email: pford@xxx.com QNX Software Systems, Ltd. WWW: http://www.qnx.com (613) 591-0931 (voice) mail: 175 Terrence Matthews (613) 591-3579 (fax) Kanata, Ontario, Canada K2M 1W8 ------------------------------ Date: Wed, 11 Aug 1999 04:41:52 +1000 From: Phil Lamovie Subject: Re: 2 pessure sensors ? Hi All, John wrote; > Other vehicles with MAP use some sort of ambient air pressure sensor. I > even dissected an after market fuel injection box and sure enough, they > had two Motorola Pressure transducers inside: one for ambient and one > for MAP. Please don't even mention that device. There has to be a good reason why an absolute sensor with integral nitrogen reference is made. Only one I can think of is so you can map engine vs absolute pressure Then if you fly or dive the fuel is corrected as the manifold pressure is always correct. if the full throttle vacuum is 30 kpa you could use the measurement to check your altimeter or if it read boost you would be holidaying by the dead sea. If you reference all calculations to absolute values (kelvin kPa etc.) you can correct with confidence. How does the second pressure sensor (if they are both differential ) know any better than the first. Lack of first principals gives rise to many "interesting products" but you wouldn't want to drive one. You will find that the only pressure the ECU needs to concern itself with is the plenum pressure. This is proportionally linked to air mass that is being CURRENTLY ingested. If you correct for absolute air temp, absolute rpm and absolute pressure the job's done. You could get creative and correct for fuel temp as was done 50 years ago by Kugelfischer et al. This first principle was "lost" with the advent of bad quality electronic fuel injection (read bosch D Jetronic) and no body does it anymore except for a small australian firm of no repute whatsoever and even then only for Liquid LPG Injection where it matters. more than the 5 % that is does for petrol. Remember all current pollution test are conducted after 24 hour heat soak at 24 deg C . means they can save money by not fitting a fuel temp sensor (the environment is not a customer of GM or Ford and thus doesn't count) Page 188 of you guessed it gives; Properties of Liquids/Gasoline(IC-Engine)) density = 0.72 - 0.75 g/cm3 melting point = -50 to -30 deg C boiling point = 25 - 210 deg C (most be some heavy fractions in there) thermal conductivity = 0.13 W/(m-K) specific heat = 2.02 kJ/kg-K volume expansion coefficient = 1.0 x 10-3/K the last is a thought provoker isn't it ? As the volume of fuel is a function of pressure diff across the injector which should be a constant as the regulator is referenced to the plenum then the only variable is ms of injection time. If you know the amount of air in mass and add an appropriate ms value of fuel from a dyno load generated map then the vapor pressure is piffle (is it ok to use strong words on this list ?) > The number used in Grippo's document suggests 3.1 Kpa but that's at >85F. What would it be at -40F. And when would it make a difference ? What does the engine think of 50 kpa of vacuum at sea level and 50 kpa of vacuum at 2000 ft/ASL and are the fueling requirements not met by the original map. The engine has no mechanism for differentiating between a partial throttle sub atmospheric plenum at sea level and a WOT at 10,000 feet which also results in a sub atmospheric plenum. The only thing that matters is the values in the table. They must be derived as absolutely as everything else. And dyno work is very absolute your in obfuscation Regards Phil Lamovie injec@xxx.au cogito ergo zoom ------------------------------ End of DIY_EFI Digest V4 #461 ***************************** 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".