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  • Fuel / fuel saving methods and options

    Hello guys!!
    Been driving the s2 around and boy does it get attention hehe. Love the car!

    Just the fuel guage seems to go down very fast!!

    I am understanding that modern performance cars are able to return around 35mpg with running around 300bhp.
    I know from the past the mpg is 18mpg on an s2 chipped - roughly speaking.

    Is there anything we can do to the s2 to make it more fuel efficient? a variable vein turbo? like the new modern engines, or buy some sort of tech to attach to make it fuel more intelligently?

    What do the new cars have that our s2's dont have?

    Thx in advance guys,

    Chris

  • #2
    There is a big difference between manufacturers claimed mpg and reality. I ran a new S3 a couple of years ago and was getting 24 mpg on shorter runs and around 33-34 on longer runs. My Nothelle tuned S2 is running about the same power and gives roughly the same mpg.
    The best mpg mod you can make on any car is to lighten your right foot.
    Nothelle S2 Avant
    Wr Ur Quattro in restoration
    S2 Coupe getting a tidy up

    Comment


    • #3
      As Dave say above, a light right foot it really the only practical option, I don't think a more modern turbo which would require a custom map and other major work would really make a great deal of difference. Even if it made the car 5 MPG better everywhere it would be a long time before you recouped the investment, unless of course your doing a huge amount of miles every week.

      My old RS2+ spec 3B (380bhp) which weighed 1350kg's with a full tank (a good 100kgs less than stock) could be terrible on fuel if I drove it like a hooligan,10/15mpg was quite easy to achieve, I could get the trip computer to say 5mpg if I was really enthusiastic which I think was incorrect. On the flip side when I took the car up to Scotland I did a couple of tanks worth of sensible motorway/A road cruising on the way up and down and got a genuine 34mpgs a couple of times, the trip computer was surprisingly accurate in this case, corroborating what I'd calculated from the amount of fuel I'd actually used/miles covered.

      Driving in the same way over the same journey I could only get just over 31mpg out of my RS2 which is running a very similar amount of power which I put down to the car being considerably heavier.

      Some basic things you can do is make sure you don't having any dragging brakes, the rear callipers can be a bit sticky as you probably know and be sure the engine is running correctly and getting up to operating temperature nice and quickly.
      1992 C4 100 2.8 Avant quattro, daily driver.
      1995 RS2, MTM K26/7, 380 BHP conversion.
      1996 C4 2.8 30V quattro, future project car...

      Comment


      • #4
        Originally posted by Chris5044 View Post
        Hello guys!!

        What do the new cars have that our s2's dont have?

        Thx in advance guys,

        Chris
        To answer this question it comes down to a few things. Better aerodynamics play a large part at speeds above 50mph, less drive train losses, smaller (hence more fuel efficient engines) and of course more modern engine management.

        That said a petrol engine will always want to run at 14.7 AFR when cruising regardless of if was built in the 1970's or 2021, so 34/5mpg really is best you'll ever get out of an 2.2 S2 engine not matter what you do it, unless you were to some how trick it into running very lean (say 20 AFR) which it really wouldn't like and would result in engine damage from preignition (pinking) if run like that for very long. I had wideband AFR data on my S2 and that would run at spot on 14.7 AFR when cruising but would drop to 10.5 AFR on WOT which was probably a touch rich but that's how it was mapped and there was no way change that unless I messed with the fuel pressure.
        1992 C4 100 2.8 Avant quattro, daily driver.
        1995 RS2, MTM K26/7, 380 BHP conversion.
        1996 C4 2.8 30V quattro, future project car...

        Comment


        • #5
          Hi Chris,

          One thing new cars have that we don't, is very young perishable components. An good example would be the engine vacuum system. Our cars would have come with the familiar fabric-covered rubber vacuum (vac.) hose. Some of the other system components may be plastic and also now need replacement. Know also that vac. leaks are not limited to the formal components of the vac. system (sys.) So even though this sys. alone is responsible for delivering signal to the FPR, any eng. vac. loss anywhere can cause too much fuel pressure to be applied to the injectors at lower throttle openings; where perhaps most driving takes place.

          The other invisible loss with vac. leaks is that, although the air that is leaking in is simply then burned, because the car has not measured that air, it cannot meter the precise corresponding amount of fuel we'd like it to. The engine management can't sense fuel pressure (least mine can't), but in any case its maps depend on it being absolutely minimal at idle precisely so that it can and will change instantly from full min. to full max. pressure in that very short interval where the throttle goes from closed to open; and vac. drops to zero. Only the vac. sys. can deliver that necessary large change in fuel pressure, and it needs to be in perfect shape to do that. If the ECM doesn't see mixture numbers it likes, the default, for engine protection, is to run rich. At low throttle settings, where MAF airflow is already minimal and perhaps less accurate and small precise matching fuel quantities are needed, this may present as a drive-ability issue, as well as delivering poorer mileage.

          To ensure max. vac. is both gathered and delivered, one could inspect and test the entire sprawling network with the same vigour and methods you turbo guys pursue a boost leak. It would be helpful to learn where to measure, and know what vacuum your engine should and does deliver at warm idle, then it could be quickly re-checked in future. One can break the system down into sections (one learns that the tentacles of this sys. are spread widely) and do leak-down tests on each. Properly sized reinforced synthetic vac. hose (for my 7A mind you, I used about 3m) was had in bulk from my friendly neighbourhood BMW dealer. An inexpensive MityVac (perhaps best if it also hasn't also been used for brake-bleeding!) can be used to measure vac. As you may discover if you haven't already, it's a game of inches and inches lost (or not!) over time.
          Last edited by Lago Blue; 23 November 2021, 03:41.

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          • #6
            Very good points made above, the small bore pipe work is just as important as the main boost hose's, yet it often gets overlooked. I replaced all mine on my 3B with new very high grade diesel engine fuel injector leak off pipe as that's what I had to hand, the stuff I used was the same bore as original but with a slightly thicker wall and same type of fabric outer coating. There's three outlet's on the back of the inlet manifold for this pipe work and it's important that circuits are done as per the factory diagram, when chasing over fuelling on WOT I finally traced the issue to the FPR sharing a hose with the DV, which was how I found it but not how it was supposed to be. I can't actually remember what's supposed go where off the top of my head but do recall being pleased when I finally found the problem.
            1992 C4 100 2.8 Avant quattro, daily driver.
            1995 RS2, MTM K26/7, 380 BHP conversion.
            1996 C4 2.8 30V quattro, future project car...

            Comment


            • #7
              Originally posted by K Simmonds View Post

              That said a petrol engine will always want to run at 14.7 AFR when cruising regardless of if was built in the 1970's or 2021, so 34/5mpg really is best you'll ever get out of an 2.2 S2 engine not matter what you do it, unless you were to some how trick it into running very lean (say 20 AFR) which it really wouldn't like and would result in engine damage from preignition (pinking) if run like that for very long. I had wideband AFR data on my S2 and that would run at spot on 14.7 AFR when cruising but would drop to 10.5 AFR on WOT which was probably a touch rich but that's how it was mapped and there was no way change that unless I messed with the fuel pressure.
              Petrol engines are set to run at 14.7 AFR because of emission reasons. They would happily run a lot leaner when cruising and without preignition or pinking problems. Those are more of a problem for full load situations.
              Last edited by JariP; 22 November 2021, 21:38.

              Comment


              • #8
                Originally posted by JariP View Post

                Petrol engines are set to run at 14.7 AFR because of emission reasons. They would happily run a lot leaner when cruising and without preignition or pinking problems. Those are problems for full load situations.

                Totally different kind of animal, but F1 engines at the moment are said to run somewhere around 30 AFR at full load. And they stay alive because they are running lean enough. Some say that the problems Honda was having while developing their F1 engines was that they were trying to run them too close to stoich. They had to go leaner to make the engines survive and then they came competitive.
                That's very interesting, I didn't know that, modern road going petrol engines all still run at 14.7 under low load conditions as far as I know, is that just a happy compromise of some sort so they won't preignite when load is suddenly applied or to tolerate wild variations in octane rating? Surely the leaner you run the cleaner the emissions or am I missing something?

                30 AFR under full load is super lean, though they are incredibly high tech motors running on very high grade fuel and as you say a totally different kind of animal.

                Edit, been thinking about this... If the AFR is higher than 14.7 say 20 as I suggested will there be unburnt oxygen in the exhaust gases? Whereas at 14.7 all the petrol and oxygen is burnt?

                Edit again, to answer my own question yes, there will be an excess of oxygen as explained very nicely in this article I've just found...

                https://x-engineer.org/air-fuel-rati...stoichiometric.
                Last edited by K Simmonds; 22 November 2021, 22:46.
                1992 C4 100 2.8 Avant quattro, daily driver.
                1995 RS2, MTM K26/7, 380 BHP conversion.
                1996 C4 2.8 30V quattro, future project car...

                Comment


                • #9
                  Very high fuel pressure (aka fuel stratified injection) means modern engines can run very lean when cruising, then they'll drop a cylinder to improve consumption some more. Lean running means more heat hence electronic thermostats needed to improve coolant flow.

                  'tis the devils work, give me an old car anyday !!

                  Comment


                  • #10
                    Originally posted by John. View Post
                    Very high fuel pressure (aka fuel stratified injection) means modern engines can run very lean when cruising, then they'll drop a cylinder to improve consumption some more. Lean running means more heat hence electronic thermostats needed to improve coolant flow.

                    'tis the devils work, give me an old car anyday !!
                    Even more information to make my brain hurt.

                    I have no intention of buying a new car, unless I'm made to by armed hippies.
                    1992 C4 100 2.8 Avant quattro, daily driver.
                    1995 RS2, MTM K26/7, 380 BHP conversion.
                    1996 C4 2.8 30V quattro, future project car...

                    Comment


                    • #11
                      Modern stuff can run at 17-18:1 at cruise, due to port design, high compression, variable cam timing, all working together....

                      Comment


                      • #12
                        Originally posted by Tractor Dave View Post
                        There is a big difference between manufacturers claimed mpg and reality. I ran a new S3 a couple of years ago and was getting 24 mpg on shorter runs and around 33-34 on longer runs. My Nothelle tuned S2 is running about the same power and gives roughly the same mpg.
                        The best mpg mod you can make on any car is to lighten your right foot.
                        As above. We’ve got an 8P S3 and our ol’ girl (Nothelle chipped) S2 Avant and on the local pot.pot/ school run stuff and around Sussex SDP stuff the S2 averages about 3 mpg better than the S3.

                        Even the Ur matches the S3 for the same local ‘jaunt’ over the A272. The published data v reality are two different things.
                        85 WR Urquattro, 85 20vT International liveried RallyRep
                        93 MTMS2 Avant

                        Comment


                        • #13
                          My 2 litre 205hp BiTdi Transporter, aerodynamics of a portacabin, averages around 40mpg, pretty much twice the mileage of any of my cars, 2 x S2s, B5 RS4, UR (ok maybe 3 times the Ur’s K-Jet).

                          S2 Coupe 3B Project


                          Ur quattro restoration

                          S2 Avant

                          Boost is the new rock and roll!
                          sigpic

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                          • #14
                            If you drive everywhere at 50mph and don't thrash it I have heard 30mpg is possible in an S2. 26 is the best I have ever seen, once, on a trip to Wales. You could always unplug the N75 which limits boost. Otherwise buying a diesel might be the best option!

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