Lewis Maudlin Posted February 14, 2006 Share Posted February 14, 2006 OK, here is what I am trying to figure out. I have an SR20DET powered 280Z. I am running the stock (restrictive) MAF and 370cc injectors. I am considering switching to a standalone and the Z32 MAF and 550cc injectors. I am concerned about this killing my cruising fuel economy. I am not worried about my fuel economy when I have my foot in it. Intuitively, the larger MAF and larger injectors would pump more fuel and air and use more gas. However, at cruising speeds without boost, wouldn't the same amount of air and gas be being used to turn the same number of rpm's to go the same speed using the same amount of gas? What am I missing in my rationalization? Quote Link to comment Share on other sites More sharing options...
AK-Z Posted February 14, 2006 Share Posted February 14, 2006 You also have to consider load on the engine and fuel ratio when with boost and when with out. Quote Link to comment Share on other sites More sharing options...
Lewis Maudlin Posted February 14, 2006 Author Share Posted February 14, 2006 Yes, I am talking about cruising speed. Same speed, no boost. I think boost is a non issue. I think that the engine load should be the same since the car should be turning the same rpm's to go the same speed. Quote Link to comment Share on other sites More sharing options...
AK-Z Posted February 14, 2006 Share Posted February 14, 2006 I think that the engine load should be the same since the car should be turning the same rpm's to go the same speed. Not necessarly, the turbo increases airflow into the chambers thus adding more volume into each chamber, so more fuel has to go (air/fuel ratio). Also what matters is the compression. Turbo engines have lower compression than NA ones (but I'm sure you already know that) so its going to run a bit sluggish and your not going to get the fuel economy you want just by yanking off the turbo off a turbo engine, its going to run rich. You need to change the compression ie. change the c/r and/or pistons and also have it advance timing under load (vacuum advance, or computer controlled). Quote Link to comment Share on other sites More sharing options...
Lewis Maudlin Posted February 14, 2006 Author Share Posted February 14, 2006 Clearly, I am not making myself clear. At cruising speed, the turbo is not boosting. The Boost gauge reads 20psi of vaccuum or somewhere close. That is why the turbo is not a factor. My question remains. Quote Link to comment Share on other sites More sharing options...
Lason Posted February 14, 2006 Share Posted February 14, 2006 I see what your saying and I agree. At a constant cruise youll be using the same if not marginally a little more air/fuel. The only drop I see if your habbits pulling from red lights and getting on the highway, etc but that wasnt your question. Quote Link to comment Share on other sites More sharing options...
Bernardd Posted February 14, 2006 Share Posted February 14, 2006 OK' date=' here is what I am trying to figure out. I have an SR20DET powered 280Z. I am running the stock (restrictive) MAF and 370cc injectors. I am considering switching to a standalone and the Z32 MAF and 550cc injectors. I am concerned about this killing my cruising fuel economy. I am not worried about my fuel economy when I have my foot in it. Intuitively, the larger MAF and larger injectors would pump more fuel and air and use more gas. However, at cruising speeds without boost, wouldn't the same amount of air and gas be being used to turn the same number of rpm's to go the same speed using the same amount of gas? What am I missing in my rationalization?[/quote'] A larger maf will see the same flow airflow at cruise because it's..............the same airflow. The stock ecu needs the maf vq table changed to the z32 table and the k value and injector latency needs to be corrected for the larger injectors. There are two other tables you need to adjust to get back to stock fueling and timing. I can't say anything about the standalone without knowing which one you're considering and even then I wouldn't bother to change to a maf standalone. Most people go to a speed density when going standalone. Quote Link to comment Share on other sites More sharing options...
Lewis Maudlin Posted February 14, 2006 Author Share Posted February 14, 2006 The standalone I have been looking at is the APEXi FC with commander. I think I will go with it since I have little experience and it has idiot settings. Quote Link to comment Share on other sites More sharing options...
BrandonsZ Posted February 15, 2006 Share Posted February 15, 2006 It's 99% in your settings and tune. But it may change slightly because a larger MAF is inherently less accurate than a smaller one, however newer technology appears every day so the newer bigger one may actually be more accurate. This is only important because the MAF is definately helping to control your A/F at low freeway speeds and RPM. But it's mostly about your tune. You may even see an improvement if you tunr better. emember there is an "economy" way to tune and a "power" way to tune as much as there is an "emmissions" way to tune. Hope this helps, probably not. Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted February 15, 2006 Share Posted February 15, 2006 There is such a thing a volumetric efficiency. If you drastically alter your intake flow velocities at cruise, then it most certainly can and will affect your cruise economy. Think of replacing a dual plane manifold with a high rise single plane. You (might) get more power potential at high RPM due to the better flow capacity, but this can often come at the cost of low RPM performance. I personally have no experience with that type of engine and have even less idea what changing the MAF will do to the low RPM flow. But the idea that the engine is pulling the same load and turning the same RPM, therefore it must be flowing the same CFM of air is not a correct assumption. And if your EFI is working correctly, the gas is proportional to the air flow, so the answer lies in what happens to the air flow. Quote Link to comment Share on other sites More sharing options...
Lewis Maudlin Posted February 15, 2006 Author Share Posted February 15, 2006 Cool, thanks for the answers, I will let you all know what my mpg does. I am switching to GT2871R, 550's and Z32 MAF. I think 350rwhp with 2300lbs is better than 250 or so. Quote Link to comment Share on other sites More sharing options...
BrandonsZ Posted February 17, 2006 Share Posted February 17, 2006 There is such a thing a volumetric efficiency. If you drastically alter your intake flow velocities at cruise' date=' then it most certainly can and will affect your cruise economy. Think of replacing a dual plane manifold with a high rise single plane. You (might) get more power potential at high RPM due to the better flow capacity, but this can often come at the cost of low RPM performance. I personally have no experience with that type of engine and have even less idea what changing the MAF will do to the low RPM flow. But the idea that the engine is pulling the same load and turning the same RPM, therefore it must be flowing the same CFM of air is not a correct assumption. And if your EFI is working correctly, the gas is proportional to the air flow, so the answer lies in what happens to the air flow.[/quote'] Yes theoretically CFM remains constant, air speed decreases as area increases. If you kept original computer settings, the car would be fooled into thinking it needed less gas than it is supposed to. Small changes in this is mostly ok on production cars because they intentionally make the car run slightly rich. Of course once you add ram air intake and open up the factory MAF slightly you've used that up and get much closer to even which could increase performance slightly, similar to rejetting a carb one step leaner when you are one step richer than you need to be. however Airflow is not entirely dictated by the MAF, and do not expect 40% increase in power. Open the intake, port & polish, change the cam, then open the exhaust and you might get 40%. Let us know. Quote Link to comment Share on other sites More sharing options...
Lewis Maudlin Posted February 18, 2006 Author Share Posted February 18, 2006 increase from 250hp to 350hp will be almost assured. I have ordered. I have a Garrett GT2871R on its way. I also have 740cc fuel injectors, a Z32 MAF and an APEXi standalone fuel management system on its way. I expect 365rwhp since I ordered the .64 A/R instead of the .86 A/R. I think the quicker spooling engine is better than the extra hp. According to the guys at SR20forums.com they tested two SR20DET's with the same setup except 550 injectors running 100% duty cycle and got 363rwhp on the .64 A/R GT2871R and 386rwhp on the .86 A/R GT2871R but the .64 A/R spun up 500 rpms lower or quicker. That left the choice of 500 rpm's or 23hp. I chose the lower rpms. Slower top end, better bottom end. I will be dyno'ing in about a month and let you guys know. Quote Link to comment Share on other sites More sharing options...
Lewis Maudlin Posted February 18, 2006 Author Share Posted February 18, 2006 Yes theoretically CFM remains constant' date=' air speed decreases as area increases. If you kept original computer settings, the car would be fooled into thinking it needed less gas than it is supposed to. Small changes in this is mostly ok on production cars because they intentionally make the car run slightly rich. Of course once you add ram air intake and open up the factory MAF slightly you've used that up and get much closer to even which could increase performance slightly, similar to rejetting a carb one step leaner when you are one step richer than you need to be. however Airflow is not entirely dictated by the MAF, and do not expect 40% increase in power. Open the intake, port & polish, change the cam, then open the exhaust and you might get 40%. Let us know.[/quote'] BTW, intake is aftermarket and already ported and polished. No cam change. And the exhaust is a tube manifold with 3" mandrel bent exhaust to a 3" inlet - 4" outlet Megan racing muffler. I don't think I can open the intake or exhaust any more. Quote Link to comment Share on other sites More sharing options...
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