DIY_EFI Digest Friday, 7 June 1996 Volume 01 : Number 159 In this issue: Re: MAF vs MAP Re: How about no MAF or MAP? Re: no MAF or MAP? Forced induction on a 2.5 Liter 4 cylinder Re: MAF vs MAP Re: no MAF or MAP? MAF vs MAP See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. ---------------------------------------------------------------------- From: atsakiri@xxx.com Date: Thu, 06 Jun 96 08:42:35 -0400 Subject: Re: MAF vs MAP > >As for acceleration enrichment, we've entered a new arena. Now > >we're discussing A/F ratio control, not measurement of inducted > >air. If the approach is to add additional fuel, without trying > >to measure air then calculate the amount of fuel (based on > >measured air and desired A/F ratio), then why add a MAP sensor? > >The throttle position sensor is already there. Am I missing a > >benefit of MAP-based enrichment over throttle-based enrichment? > > >Anthony Tsakiris > > Ah, but you forget - throttle position does not have a direct relationship > to engine load. You can have different manifold pressures with the same > throttle > position under varying engine loads. Thus, the MAP would be giving valuable > information that the TPS could not. This may or may not have a drastic > effect on mixture demands, but I'm betting that it would sure affect > driveability and fuel consumption. This may explain why some MAF based > systems have MAP sensors. Agreed, but the MAP sensor has the same problem, doesn't it? You can have the same MAP under varying engine loads due to varying EGR flow rates. Also, varying altitude may complicate a strictly MAP-based approach. The MAP sensor can surely sense differences due to ambient pressure, but does a MAP measure of 0.6 bar indicate part-throttle at sea-level (and therefore imply stoichiometric A/F ratio) or wide-open throttle at high altitude (and therefore imply non-stoich A/F)? Vehicle manufacturers tend not to think of these things from a control systems perspective (i.e. command signal, controller, plant, sensors). They think of them, just not in the process of designing controllers to achieve desired behavior. I digress. It's a very interesting problem, made all the more difficult by those pesky cost constraints. Anthony Tsakiris MAP = manifold absolute pressure TPS = throttle position sensor EGR = exhaust gas recirculation A/F = air/fuel - --------------------------------------------------------------------------- The opinions expressed are my own and not necessarily those of my employer. ------------------------------ From: Pete Sterrantino Date: Thu, 6 Jun 1996 09:23:40 -0400 (EDT) Subject: Re: How about no MAF or MAP? On 5 June, Mike Klopfer wrote: >constants. The following is my understanding of models given in the paper >SAE 93085? "Transient A/F Ratio Errors in Conventional SI Engine Control". >In the paper SAE 93085? cited above the authors include a volumetric The paper you are referring to is SAE Document Number 930856, titled: Transient A/F ratio errors in conventional SI engine controllers. I've collected a small SAE paper number database regarding fuel injection and just thought I could save somebody the time... Pete Sterrantino ------------------------------ From: Land Shark Date: Thu, 06 Jun 1996 09:18:32 -0600 Subject: Re: no MAF or MAP? At 11:57 PM 6/5/96 -0700, you wrote: >>System you are referring too is know a N alpha >>Saw a SAE writeup a while ago. Will dig it up if you want. YES YES YES :) Anything you can dig up on Alpha-N is greatly appreciated TIA, Jim Conforti PS: Converting a bunch of MAF Motronic systems to A-n ------------------------------ From: Jim Steck <72614.557@xxx.COM> Date: 06 Jun 96 20:10:12 EDT Subject: Forced induction on a 2.5 Liter 4 cylinder >> The Whipple unit as sold by Keanne-Bell and Bell Engineering is the best supercharger. Gets boost lower and uses less HP. Tests done @ Ford show that Eaton, Paxton etc for 8psi on 4.6L motor used 70 hp to make boost while the Whipple used 35hp. Bell's kits are very well thought out. << If you test an Eaton supercharger at flow rates well beyond its design limits, it MAY require 70 hp, but I have performance charts for the Eaton Model 90 (Ford T'bird) and the Sprintex S102 (Whipple). At 400 CFM and 10 psi boost (more than 250 hp), the Eaton requires 28.5 hp and the Sprintex requires 22.6 hp . . . better, but not exactly half. A typical adiabatic efficiency for centrifugal compressor (Paxton) at a pressure ratio of 2.0 is 85 percent. The Sprintex is less than 70 percent. Sorry, sounds like advertising hype to me! Jim Steck AutoComponenti ------------------------------ From: Darrell Norquay Date: Thu, 6 Jun 96 21:44 PDT Subject: Re: MAF vs MAP At 08:42 AM 6/6/96 -0400, Anthony Tsakiris wrote: >Agreed, but the MAP sensor has the same problem, doesn't it? >You can have the same MAP under varying engine loads due to >varying EGR flow rates. I don't really agree, here. If you ignore atmospheric pressure variations for a moment, I think MAP is much more "closely coupled" to engine load variations than you suggest. I don't think the EGR actually represents a large volume compared to the volume of air inducted into the manifold. Few percent maybe. I don't think this is enough to alter manifold pressure significantly. In any case, all the EGR would do (purely from an AFR standpoint) would be to "dilute" the incoming air slightly in terms of O2 content. This could easily be compensated by reducing the injector DC slightly. Closed loop operation would take care of this, but the computer also "knows" the EGR setting and could compensate. >Also, varying altitude may complicate a strictly MAP-based >approach. The MAP sensor can surely sense differences due >to ambient pressure, but does a MAP measure of 0.6 bar >indicate part-throttle at sea-level (and therefore imply >stoichiometric A/F ratio) or wide-open throttle at high >altitude (and therefore imply non-stoich A/F)? Most MAP sensors are really differential pressure sensors with one port open to atmosphere. This automatically compensates for any differences due to altitude or Barometric Pressure, and essentially measures the difference between atmospheric and manifold pressure. Some systems (Cadillac springs to mind) have a separate BP sensor as well as the MAP, and compensate that way. Some systems use an absolute pressure sensor (referenced to a hard vacuum) and simply take a reading before the engine starts to determine current BP, and remove the BP as an offset. This obviously doesn't work too good if you drive up a mountain without stopping the engine once in a while to "catch up". What do you say, Ed? (By the way, your editor works perfectly... I now have a "real" mail system anyway, (Eudora), and it doesn't care. regards dn MAP = Manifold Absolute Pressure sensor TPS = Throttle Position Sensor EGR = Exhaust Gas Recirculation AFR = Air/Fuel Ratio BP = Barometric Pressure DC = Duty Cycle ------------------------------ From: pfenske@xxx.ca (peter paul fenske) Date: Thu, 06 Jun 1996 22:41:08 -0700 Subject: Re: no MAF or MAP? >At 11:57 PM 6/5/96 -0700, you wrote: > >>>System you are referring too is know a N alpha >>>Saw a SAE writeup a while ago. Will dig it up if you want. > > YES YES YES :) > > Anything you can dig up on Alpha-N is greatly appreciated > > TIA, > > Jim Conforti > > PS: Converting a bunch of MAF Motronic systems to A-n > > Hi Jim > Just looked through about 30 file folders of EFI stuff. > Sounds like I'll have to climb under the stair well > Wasn't terribly interested in N Alpha at the time. > so really packed the stuff away. > Will keep trying > Peter > > ------------------------------ From: RABBITT_Andrew@xxx.au Date: Fri, 7 Jun 1996 15:05:54 est Subject: MAF vs MAP >>I don't think the EGR actually represents a large volume compared to the volume of air inducted into the manifold. Few percent maybe. I don't think this is enough to alter manifold pressure significantly.<< EGR rates are more that just a few percent, maybe as high as 30% at some speed-load points. In any case, it's enough to give you a 3-4% fuel consumption advantage over an LA4 cycle. >>Most MAP sensors are really differential pressure sensors with one port open to atmosphere.<< This I can't quite believe, (since the A in MAP is 'Absolute'). If you know the absolute manifold pressure, why do you need altitude compensation? Any ideas? Andrew Rabbitt Orbital Engine Company ------------------------------ End of DIY_EFI Digest V1 #159 ***************************** 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".