DIY_EFI Digest Wednesday, 4 September 1996 Volume 01 : Number 259 In this issue: Re: Cams and FI Re: d disease Re: Knock sensors Re: Ancient History Re: D disease Re: DIY_EFI Digest V1 #258 re: Ancient History Re: Ancient History water injection & detonation supression Re: hi compressions: wasDIY_EFI Digest V1 #258 Re: J&S Knock Sensor Costs Re: Knock sensors Re: Data/Spec. Sheets Data/Spec. Sheets Re: water injection & detonation supression re: Knock sensors re: hi compressions Re: Data/Spec. Sheets re: water injection & detonation supression re: Ancient History re: Ancient History Air flow calculation See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. ---------------------------------------------------------------------- From: rickydik@xxx.com (RD Rick) Date: Tue, 3 Sep 1996 15:07:32 -0700 Subject: Re: Cams and FI I wrote: >>My '73 914 just happens to have a high lift cam with a lot of overlap. >>It won't idle decent below about 2000 rpm. To pass a smog check, I set >>the lifters out to .030", and then it idles fine. Clatters like hell. >>I've never had backfires with it. >> >>An additional problem is the low vacuum, about 12", below 2000 with >>that engine. The Djet responds to low vacuum by squirting more fuel, >>which makes it richer until it dies. I have found a fix for the ECU to >>alter the fuel curve, but haven't tried it in the car yet. Talltom replied: >Don't know if it's relevent, but we've run more radical cams than that regularly>and get good idle at 1200-1300 rpm with a pissing in the wind system.(k) The >accepted mythology is this can't be done, but being as we do it I have a tough >time believing it. Our theory sez that as long as the pulsation isn't large >enough to pressurize clear out to the barn door(cone) it don't matter what >kind of cam you have... > Don't know if 914 ever used pissing in wind with barn door systems. Yes, the 1.8 is Ljet, but my 2.0 with big cam is a 2.0 Djet. I am thinking of converting it to Ljet just to fix the idle. Last week I even put a barn door airbox in place of the aircleaner on my stock 2.0, and it created only one inch of vacc at WOT/5800, which is about 3% power loss per my charts. Is your 1200 idle with a 4 holer, or a V8? RD ------------------------------ From: rickydik@xxx.com (RD Rick) Date: Tue, 3 Sep 1996 15:13:32 -0700 Subject: Re: d disease I wrote: >>The Djet and Ljet EFI in the aircooled opposed VW and Porsche 914 >>engines sprays directly at the intake valve from three inches away. >>With the Djet, the fuel is squirted in at the beginning of the intake >>stroke two of the cyls, and at the beginning of the power stroke on the >>other two cyls, so its operation is compromised... >If it's any help Mercedes applications I believe inject just before or slightly >after intake valve opening. > Here I'm really going to screw myself, but here goes. It would seem to me that >one could use a mercedes brain on a four cylinder and set the points up so that>the sequence you want is accomplished. > All I ask for the idea is enough of the mercedes brains to keep me supplied>before you guys grab them all up.:-) Hey. super idea! Will the Merc dist. fit in the VW hole? I promise you the second V8 ECU I find. >Just for those who aren't thoroughly neaseated yet, maybe I should mention>the fact that we haven't checked into DIGIFANT yet! :-> What's Digifant? RD ------------------------------ From: "Robert J. Harris" Date: Tue, 3 Sep 1996 15:31:52 -0700 Subject: Re: Knock sensors Remember the Reichstag - ---------- > From: Todd Knighton > To: diy_efi@xxx.edu > Subject: Re: Knock sensors > Date: Monday, September 02, 1996 4:01 AM > > Tom, > My first question is, how tall are you really?!? ha, ha. > > I've found that if I run the ignition timing too close to the limit on > the dyno that the knock sensors hit, the runs will be very > inconsistent. But if the engine is set up properly, and the knock > sensors never need to do any thing then the engine performs well and > consistently. > Knock sensors are for worst case scenario's. Bad gas, carbon buildup, > impropper octane, exceedingly high temperatures. I've never found a > system that works well enough to let it run on the sensors. > We use the knock sensors with the monitor from J&S to tune the engine > till there is no more knock showing, not to leave it run on it. A > properly calibrated engine should never see knock anyway! > > Todd Knighton > Protomotive Engineering > > > > > I did a Corvette with a turbo on it and used a old buick spark retard > > system, and while it worked, I wasn't really very happy with it. It would > > retard 3 degrees for every clatter it didn't like, and hold it for 20-60 > > seconds. The problem was that it was inconsistent, back to back runs would Dumb Idea forming - maybe. By knock sensor, I assume we mean the knock caused by the fuel air mixture igniting prior to the timed spark - generally at medium load and rpm. Since this occurs before the timed spark, nothing you can do to the timed spark directly affects the knock. Retarding the spark lowers power thereby lowering the temp/pressure part of the equation - eliminates knock. Why not use the sensor to directly change a parameter that controls knock - temperature? Instead of retarding timing and losing power - why not richen mixture? More fuel - more evaporative cooling - lower temp - rat noww Richening mixture small amount has no negative effect on power. Early turbos (pre EFI and intercoolers) often ran as high as 40% rich to cool the charge to keep from detonating. Simple algorithm - already have feedback loop for O2 sensor. Step bang the correction a fixed ammout richer. O2 sensor corrects back over time. No more knock, no power loss, far less critical to tune, no need to f with ignition timing and if it false alarms - worst effect is lowered fuel mileage. Just a thought for what its worth ------------------------------ From: Arnaldo Echevarria Date: Tue, 3 Sep 1996 19:43:15 -0400 Subject: Re: Ancient History At 02:44 PM 9/3/96 -0500, you wrote: >I think 12 mpg from a 455 is fantastic. Can't see how you get this >good -- FI or carbed. What's your rear end ratio? > >tom OK, I new I'd get some mail when I said that, so for the curious, my car is a: '78 Trans Am 1970 455 2bolt main from a Bonneville stored heads from that motor (10.25:1 cr too high) HEADS: using 6X heads (2.11", 1.66" I think) approx CR between 9.0:1 to 9.6:1 (too much conflicting info) CAM: .444/.465 lift, hydraulic, stock rockers. Manifold: stock 4bbl headers (1 7/8"), flowmaster transverse muffler (2 little mufflers inside one big case, 2 1/2" tubing) Best time with old rotten 245/60/15 Grand Prix tires: 13.3 @ 107mph (75degree weather) (This is in Orlando, Fl) Best time with new 295x50x15 BF radial t/a's: call me next week. Tranny: TH400, just rebuilt Torque converter: $20 new unit. can't be that good. REAR END: 3.08 posi (to answer your question...) Actual mileage: 11-12 city if the secondaries don't open. <9 if the foot gets heavy :) 12.5 - 13 highway, cruising at 2600rpm, which is about 65mph. 11 mpg cruising at 3200rpm, or about 80mph (and yes, speedometer error is accounted for, I'm not one of those 30mpg 5.0L owner ---- but then again, two years ago in car craft some guy with a 455 got 20MPG(??!) in one of the real street eliminators. Yeah right! ..or did you see the buick turbo v-6 that got 48mpg and ran low 13's in the 1/4 mile?) timing: 10 degrees with 87 octane gas, 12-14 with 93 gas (with vacuum advance) CARB: quadrajunk 4bbl 750cfm (got it for free at junkyard, I've rebuilt it; actually it works pretty good but gas mileage still sad) .....when I had the holley 600cfm vacuum secondary carb, I couldn't break into the teens for gas mileage. Holleys suck for gas mileage.(besides the fact that the carb was too small) Weight of car: 3720 w/out driver I'm actually considering lowering the rear end ratio some more. I've had good luck with ultra-low geared cars and long stroke engines. For example, I used to have a '83 trans am with: 305 (believe it or not, relatively speaking, big stroke vs bore) .465/.488 cam 9.8:1 cr (93 octane gas only on this one) t-5 2.73 gears (!!!!!) - --> final drive ratio: 2.06:1. This car would go 72mph at 1900RPM in 5th. Everyone would tell me that ohh it'll kill the engine it'll lug it it can't handle it bull! With time slips to prove: 14.3 @ 102mph 21 mpg (with a HOLLEY! My friend had a similar setup with a Q-jet and got 23mpg) ...now that car was a BLAST to drive..... (sorry to get off topic) ------------------------------ From: talltom Date: Tue, 3 Sep 1996 18:41:57 -0700 (PDT) Subject: Re: D disease > >From: rickydik@xxx.com (RD Rick) >Date: Tue, 3 Sep 1996 14:54:56 -0700 >Subject: Re: Bosch d disease > >talltom wrote: >>>From: rickydik@xxx.com (RD Rick) >>>Date: Mon, 2 Sep 1996 12:06:45 -0700 >>>Subject: Re: DIY_EFI Digest V1 #256 >> >>>I may be able to help you, Tom. I have a Djet tester, 17 years of >>>driving Djet 914's, lots of spares, psuedo-schematics, oscilloscope, >>>etc., and a distributor machine to do dynamic things. >>>What is the nature of your problem? > >> What I've got is a Cadillac style V8-6-4. The way this happened is >that the >brain on my mercedes 4.5 started dropping a circuit or two of >injectors, and>now >is to the point that it's so disgusting that I tore >the rest of it apart for >long put off tweaking. >> I came to this grandiose conclusion because I've checked everything >else>repeatedly and it checks good. >> My questions are a little ignorant as I don't mess with porsche's >and air>cooled>vw's(they're to close to the ground):-> is are the >d-jetronic systems they use>equipped with four injector circuits? If >so, do you think any of your schematics>would be useful in surgery? >Dist. machine, ocilloscope... I'm jealous! > >Yeah, the Djet tester I have was made by EFI Associates LA. It can >test the 8 cyl Merc, but I don't know if my harness will fit. Is your >ECU about 8" x 12" and have the 25 pin connector on the end? If so, my >tester should work. What part number is the ECU? I don't have much in >the way of schematics, but that vintage electronics is my cup of tea. Yep! All of the above. Weighs about 15 pounds too! I'll get the number for you soon. >I could check your dist, too, and dynamically test its inj. contacts. I've had it apart twice and I don't think that's the problem, but it's nice info in case I'm wrong.(NEVER!) >The Djet in 4 cyl engines has just two injector circuits. I'm 6' and >fit the 914, but my 6' 4" son hates it. You would need a bubble >canopy. :) I suspect the reason your son hates it has to do more with his age than his size. Am I right? Is this a teenager? >RD > >------------------------------ > >End of DIY_EFI Digest V1 #258 >***************************** > >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". > > ------------------------------ From: talltom Date: Tue, 3 Sep 1996 18:41:53 -0700 (PDT) Subject: Re: DIY_EFI Digest V1 #258 > How important that is depnds on how well >calibrated the seat of your pants is or how important that last 0.01 in >the 1/4 mile is. Having been refered to as a hemroid, I'm glad to see that somebody else thinks hemroid sensitivity is usefull!:-) >Therefore another approach is to outrun the fuse, >which fast burn combustion chambers can do. Anyone notice how high the >compression ratios of modern 4V engines (and even some 2V) are getting? Yes I have and I'm pissed! Would you say that is due to combustion chamber design, or to more precise tuning capability? While I've got your attention, have you seen the throttle valve the later vw's are using? It looks like anything else, but when you look close the blade fits into a recess machined into the bore, kind of like a ball valve. To me it looks like this setup would eleviate the harsh throttle opening at the bottom end and allow full sail in an individual cylinder basis. Whaddya think? >Ed Hernandez, still catching up... >Ford Motor Company >ehernan3@xxx.com Bye the way, bullistic bottom end throttle response can be fun. Loaned my car to girl who had dropped her clutch and couldn't drive without clutch.(georgous redhead!-) I followed her home in her car being as I could drive it without clutch. When I asked her why she was in such a hurry that she smoked the tires and gas was flying out the back(somebody had stolen the gas cap) she said she wasn't used to the throttle and didn't have that problem with her Datsun. ------------------------------ From: RABBITT_Andrew@xxx.au Date: Wed, 4 Sep 1996 09:31:44 est Subject: re: Ancient History >> Liquid fuel does not burn - period. It must be vaporized before it >>burns. All forms of carboration - including fuel injection - atomize >>the fuel hoping enough vapor will be formed to start combustion so >>that the heat and violence of combustion will finish the job. Power >>and fuel efficiency are directly related to how well that is done. >Um, sorry. Gasoline vapor explodes, it does not burn. Liqiud gasoline >burns.... You definitely DO want to minimise the vapourisation of fuel until the inlet valves are closed. When fuel vapourises its density drops by a couple of orders of magnitude, displacing air and reducing your effective Volumetric efficiency. All the applications that Robert J. Harris quoted in his original post were high-speed, high power applications, and sequential fuelling is not going to give you anything here. What sequential injection does give is better low speed, part load combustion stability leading to better real-world driveability. ------------------------------ From: "George M. Dailey" Date: Tue, 3 Sep 1996 21:30:49 -0500 (CDT) Subject: Re: Ancient History At 02:44 PM 9/3/96 -0500, you wrote: > >>and gets 12mpg (city) using a Quadrajet 750cfm; I want to improve that to >>15-17mpg. > >>Arnaldo E. >>aec@xxx.net >> > >I think 12 mpg from a 455 is fantastic. Can't see how you get this >good -- FI or carbed. What's your rear end ratio? > >tom > Damn skippy, I got 8mpg city (carbed), 13mpg city (GM TBI) with a 350 small block chevy 2.73 gears on a full size chevy truck. If you want really big mpg increases try the 700R tranny. GMD ------------------------------ From: "George M. Dailey" Date: Tue, 3 Sep 1996 21:30:17 -0500 (CDT) Subject: water injection & detonation supression Gentlemen, OEMs use exhaust gas to supress detonation, right? Exhaust gas recirculation systems to be exact, EGR. This seams superior to water injection. Is it? gmd ------------------------------ From: rickydik@xxx.com (RD Rick) Date: Tue, 3 Sep 1996 20:24:29 -0700 Subject: Re: hi compressions: wasDIY_EFI Digest V1 #258 Somebody smart wrote: >>Therefore another approach is to outrun the fuse, >>which fast burn combustion chambers can do. Anyone notice how high the>>compression ratios of modern 4V engines (and even some 2V) are getting? Talltom replied: >Yes I have and I'm pissed! Would you say that is due to combustion chamber>design,>or to more precise tuning capability? I have read that the big reason for four valves is to get the spark right in the center. Flame front has much shorter distance to travel, meaning higher compression without detonation. You could probably get the same effect with four spark plugs per cyl. BTW, I believe detonation is what happens after spark but the mix explodes before the flame can travel far enough to get the whole mix burning. Pre-ignition is another phenomenon in which hot parts or diesel effect ignite the mix before spark. That's as I understand it. Comments? >While I've got your attention, have you seen the throttle valve the >later>vw's are using? It looks like anything else, but when you look >close the>blade fits into a recess machined into the bore, kind of >like a ball valve. >To me it looks like this setup would alleviate the harsh throttle >opening at>the bottom end and allow full sail in an individual >cylinder basis. Whaddya think? I think I'll take a look for myself. What year VW? RD ------------------------------ From: Todd Knighton Date: Tue, 03 Sep 1996 21:44:18 +0000 Subject: Re: J&S Knock Sensor Costs talltom wrote: > Yeah, from what I've heard about that J&S stuff it sounds pretty neat. Kind > of afraid to ask price, but I did make note of the address, and someday when > in pain will inquire. > About $325.00 with monitor, I think. \Costs less than a set of pistons and rings! Todd ------------------------------ From: Todd Knighton Date: Tue, 03 Sep 1996 21:51:34 +0000 Subject: Re: Knock sensors Robert J. Harris wrote: > > Dumb Idea forming - maybe. By knock sensor, I assume we mean > the knock caused by the fuel air mixture igniting prior to the timed > spark - generally at medium load and rpm. Since this occurs before > the timed spark, nothing you can do to the timed spark directly > affects the knock. Retarding the spark lowers power thereby > lowering the temp/pressure part of the equation - eliminates > knock. Nope, we were talking about knock caused by ignition timing being set too early, not Pre-ignition caused by hot spots, carbon buildup, or improper heat range of spark plugs. > > Why not use the sensor to directly change a parameter that > controls knock - temperature? Instead of retarding timing and > losing power - why not richen mixture? More fuel - more evaporative > cooling - lower temp - rat noww > > Richening mixture small amount has no negative effect on power. > Early turbos (pre EFI and intercoolers) often ran as high as 40% rich > to cool the charge to keep from detonating. > > Simple algorithm - already have feedback loop for O2 sensor. Step > bang the correction a fixed ammout richer. O2 sensor corrects back > over time. No more knock, no power loss, far less critical to tune, > no need to f with ignition timing and if it false alarms - worst effect is > lowered fuel mileage. > > Just a thought for what its worth this all might work for pre-ignition, but not the knock sensing we're talking about. Though, richening the mixture does tend to slow the burn rate of the mixture, thus even if the timing is set too early, it typically won't knock. Talk to Autothority about this, they're the kings of too much advance and too much fuel. Maybe that's how they get those magical 25% increases over stock! ;) Todd Knighton Protomotive Engineering ------------------------------ From: Todd Knighton Date: Tue, 03 Sep 1996 22:01:12 +0000 Subject: Re: Data/Spec. Sheets Tom, Motorola has a lot of data sheets on their MPX4250A, etc. line of pressure transducers we've been using. National Semiconductor will send you free LM1949N's for injector drivers. Cherry Semiconductor is more proud of theirs, but will send you all the data sheets you want. I understand that GM and Ford both used these drivers on their throttle body injection stuff. The MAF's are a tough one. There used to be a book, called the "Bosch Bible" by most, been looking for it too. It used to give specs on all their stuff. Now the only way you can get parts is to know the car it came off of. If any one knows where to get this Bosch spec book let me know. Throttle position sensors are pretty self explanatory. Temp sensors typically all follow the same curves, pull a curve out of an oem to linearize it, then convert directly to deg C or F or whatever your fancy. Todd Knighton Protomotive Engineering tom cloud wrote: > > Can anyone shed light on where to get data on the various transducers > used in EFI systems? (esp. EGA, MAP, MAF, etc.) > > I would like to find data on specific auto makers' components. They > obviously have the data and I cannot see any reason why they would care > if individuals have it -- can't be trade secret. Their engineers have > to have access to it. It's gotta be published somewhere. > > Can anyone help ? (Todd ?) > > Thanks, > Tom Cloud ------------------------------ From: RABBITT_Andrew@xxx.au Date: Wed, 4 Sep 1996 13:00:30 est Subject: Data/Spec. Sheets >Can anyone shed light on where to get data on the various transducers >used in EFI systems? (esp. EGA, MAP, MAF, etc.) Talk direct to the guys at Bosch, Siemens, Nippondenso, Hitachi, CTS, Colvern etc about any of their gear. Just fax them with a professional looking note asking them for data sheets on X, Y or Z and they'll probably reply. They are out to do business after all. Just don't tell them how small your business is in the first instance! :) ------------------------------ From: dzorde@xxx.au Date: Wed, 04 Sep 96 13:22:44 Subject: Re: water injection & detonation supression If that's the case it would be great if the EGR could be controlled. ie knock sensor runs a normal bypass solenoid, and opens it when knocking is detected to let enough exhaust gas in to eliminate pinging.. Dan dzorde@xxx.au ______________________________ Reply Separator _________________________________ Subject: water injection & detonation supression Author: diy_efi@xxx.edu at INTERNET Date: 9/4/96 12:46 PM Gentlemen, OEMs use exhaust gas to supress detonation, right? Exhaust gas recirculation systems to be exact, EGR. This seams superior to water injection. Is it? gmd ------------------------------ From: RABBITT_Andrew@xxx.au Date: Wed, 4 Sep 1996 13:38:46 est Subject: re: Knock sensors >Dumb Idea forming - maybe. By knock sensor, I assume we mean >the knock caused by the fuel air mixture igniting prior to the timed >spark - generally at medium load and rpm. Since this occurs before >the timed spark, nothing you can do to the timed spark directly >affects the knock. Retarding the spark lowers power thereby >lowering the temp/pressure part of the equation - eliminates >knock. this is pre-ignition (which is not the same as knock) and is caused by hot-spots on the combustion chamber surface. Knock is caused by (or so the accepted theory goes - see Heywood for the full explaination) high pressure, heat from the charge, and heat from the radiation of the flame causing areas in the combustion chamber to spontaneously ignite, before the flame front passes thru. By retarding spark, peak cylinder pressure is reduced, thereby removing one of the factors causing the spontaneous ignition. ------------------------------ From: RABBITT_Andrew@xxx.au Date: Wed, 4 Sep 1996 13:28:58 est Subject: re: hi compressions >Somebody smart wrote: >>>Therefore another approach is to outrun the fuse, >>>which fast burn combustion chambers can do. Anyone notice how high >the>>compression ratios of modern 4V engines (and even some 2V) are >getting? >Talltom replied: >>Yes I have and I'm pissed! Would you say that is due to combustion >>chamber design, or to more precise tuning capability? >I have read that the big reason for four valves is to get the spark >right in the center. Flame front has much shorter distance to >travel, meaning higher compression without detonation. You could >probably get the same effect with four spark plugs per cyl. BTW, I >believe detonation is what happens after spark but the mix explodes >before the flame can travel far enough to get the whole mix burning. Mixture preparation has a lot to do with it. If you atomise smaller, the burn-rate is faster, and thus you get the same torque with retarded ignition. This allows you to run a high compression ratio, giving efficiency gains in areas where you're not spark limited for MBT. Charge motion is also a big player in mixture preparation. With four valves (nothwithstanding the advantages of increased valve area), you can arrange what is known as 'tumble' which is akin to (but arguably better than) 'swirl' in a 2-V design. ------------------------------ From: Land Shark Date: Tue, 03 Sep 1996 23:48:38 -0600 Subject: Re: Data/Spec. Sheets At 22:01 9/3/96 +0000, you wrote: > The MAF's are a tough one. I currently have the curves for three Bosch MAF's .. Derived by actual flowtesting of the MAF .. These are 12v supplied Hot Film Mass Air sensors with four wires, 12+, gnd, signal, and sig. common They do NOT use a 5v ref .. The three I have max out at 5v at the following airflows 820kg/hr, 80mm diam. 860kg/hr, 89mm diam. 1300kg/hr, 89mm diam. If anyone really needs them, I've got 'em! .. Jim ------------------------------ From: RABBITT_Andrew@xxx.au Date: Wed, 4 Sep 1996 13:10:46 est Subject: re: water injection & detonation supression >Gentlemen, OEMs use exhaust gas to supress detonation, right? Exhaust >gas recirculation systems to be exact, EGR. This seams superior to >water injection. Is it? EGR is primarily used for NOx control, although it is a variable that is sometimes manipulated for knock suppression. It works by increasing the specific heat of the charge, hence reducing the overall combustion temperature. Water injection works in the same way. EGR enters the cylinder in the gas phase (as opposed to liquid), displacing air hence reducing the effective volumetric efficiency. This is OK (beneficial actually) at part-load, but not WOT. ------------------------------ From: RABBITT_Andrew@xxx.au Date: Wed, 4 Sep 1996 13:46:32 est Subject: re: Ancient History >> What I want to know, is what happens when you have radical >> cam timing? This nice puddle of fuel on the inlet valve >> gets blown back up the inlet duct when the valve opens? >> Makes nice flames, if you don't run an air cleaner :-) >> But this surely can't make for repeatable fuel volume supplied >> to the cylinder? > >As Ralph pointed out, the vacuum goes down at lower rpm due to valve >overlap. A vacuum responsive FI would make the mixture too rich for >the engine to run. I think carburators are more tolerant of this low >vacuum at low rpm because they are passive devices and because they >are less precise in fuel metering. carbs don't use manifold vacuum to meter fuel. All they use is the depression created by airflow through a metering venturi. ------------------------------ From: Jeremy Date: Wed, 4 Sep 1996 17:55:25 +1000 Subject: re: Ancient History At 01:46 PM 9/4/96 est, you wrote: > >>> What I want to know, is what happens when you have radical >>> cam timing? This nice puddle of fuel on the inlet valve >>> gets blown back up the inlet duct when the valve opens? >>> Makes nice flames, if you don't run an air cleaner :-) >>> But this surely can't make for repeatable fuel volume supplied >>> to the cylinder? >> >>As Ralph pointed out, the vacuum goes down at lower rpm due to valve >>overlap. A vacuum responsive FI would make the mixture too rich for >>the engine to run. I think carburators are more tolerant of this low >>vacuum at low rpm because they are passive devices and because they >>are less precise in fuel metering. > >carbs don't use manifold vacuum to meter fuel. All they use is the >depression created by airflow through a metering venturi. How about SU carbys? Dont the pistons get sucked up according to manifold vacuum? Jeremy ------------------------------ From: Johan Rodling Date: Wed, 4 Sep 1996 10:32:58 +0100 Subject: Air flow calculation Hi out there! I'm doing some calculation on a EFI based on Motorola 68HC11. At this stage it seems as it would work up to about 10k-12k rpm's and up to V12 engins. Now, my problem is that I dont know how to calculate the air flow. So, if anybody knows the formula for this, please let me know. Yes I know of Bowlings web page, but I'd rather have the math's. Unix is simple, but it takes a genius to understand its simplicity. -DMR '74 Jaguar XJ5.3 L (V12) - ------------------------------------------------------ Johan Rodling Email: Johan.Rodling@xxx.SE JoRoTech HB Phone: +46 (0)18 36 90 91 Borje, Stromsborg Fax: +46 (0)18 36 91 02 S-755 92 Uppsala, Sweden Mobile: +46 (0)708 385 380 ------------------------------ End of DIY_EFI Digest V1 #259 ***************************** 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".