Does a PCV Valve affect fuel economy?

Discussion in 'Fuel Economy' started by 99HXCivic, Nov 28, 2007.

  1. 99HXCivic

    99HXCivic Well-Known Member

    Does a PCV Valve affect fuel economy? I don't know if it's working well on my HX, and I want to get better than 41.64 mpg (last tank). My HX has a Short Ram Intake and a Catback Exhaust, so I expect better than 45 mpg.
  2. Blake

    Blake Well-Known Member

    Neither of those two items (short ram and catback exhaust) will improve FE on the the speeds where you would be getting 45mpg. So I wouldn't expect your car to perform any different than before installing them. Infact, it could have a negative impact on your FE.

    PCV valves are super cheap, and I used to change them every other oil change back when I drove a fiero... Couldn't hurt to replace it, if it was bad, then yes you'd be having some mileage issues I'd say.
    Last edited: Nov 28, 2007
  3. Daox

    Daox Well-Known Member

    PCV valve will effect fuel economy if it is plugged up. As caryfd227 mentioned they are very cheap at about $2 from your local autoparts store. If that is still too much for you they are very easy to clean out with a bit of carb cleaner spray.

    I'll also second his note that the intake and exhaust do nothing for you as far as mileage goes, if you are driving for mileage. In fact, if you went with larger diameter intake and exhaust piping, your probably hurting your fuel economy more than helping it.
  4. shifty35

    shifty35 Well-Known Member

    The trick to high FE on your HX will be to stay out of VTEC. I want to say it engages somewhere between 2500 rpm and 3000 rpm on the D16Y5. You can wire up an LED to the solenoid to determine when it's on, and you want that light to rarely, if ever go on.

    May be unavoidable at interstate speeds - what's your cruising RPM at 50-55 mph?

    My last Civic had a fairly heavily modified D16Y8, and I had a 95 coupe with a turbo D16Z6, so this is well inside my realm of experience.

    Also, what type / brand of tires? A wider, more agressive sport tire will do a lot to lower your mileage.
  5. 99HXCivic

    99HXCivic Well-Known Member

    My car came with the short ram and exhaust, and I like it that way and I do think it increases HP and thus mpg.

    My PCV Vavle seems clogged - doesn't click when I pinch the inlet tube - so I'll replace it and hope for better mpg. This PCV Valve is weird - seems like it has a casting attached to it.
  6. 99HXCivic

    99HXCivic Well-Known Member

    I cruise at 60 to 65 mph so the RPM is at 2500 or below on my D16Y5. Everyone here is speeding at 65 to 75 mph.

    I have 3 different sets of tires on my car - it came that way! I'll be looking for a good set in 8000 miles maybe.
  7. Blake

    Blake Well-Known Member

    :eek: wow... Yeah, I say thats probably a place you could get some big increases in not only FE but traction!

    I know the one on the fiero was just a metal tube, but when I was in advanced auto yesterday I happend to walk by the PCV section... there are a bunch of funky looking ones :)

    Oh I'm sure it increases your horsepower, theres no doubt about that. But the idea that increasing your Horsepower increases your fuel mileage is a common misconception. Unless your just reducing frictional resistances (ie pulleys, polishing manifolds, etc) your not increasing your fuel mileage.

    What does making power take? Air and fuel... any time you increase the amount of air going into your engine you change the air/fuel ratio. Your cars ECU automatically adjusts for the change by ADDING fuel.

    I'm not tell you to take off your intakes and exhaust. Just know that those things do not help your FE and most likely hurt it.
  8. Daox

    Daox Well-Known Member

    Caryfd227 is completely right about the intake and exhaust. The stock intake & exhaust systems only reduce power when they become a restriction (meaning they can't flow enough air/exhaust). The only time they become a restriction is at high load and high rpm. High load is used quite often when driving for fuel economy, but high rpm is definitly not and is specifically avoided. Therefore, when driving for fuel economy your stock system will never become a restriction. If you do some simple testing with a vacuum gauge you can find this out easy enough.

    Just so you know I'm not biased in any way (I just like people to understand things), I too have a cold air intake, header, high flow CAT, high flow muffler, and mandrel bent piping on my Paseo. The head has been shaved and ported, and the throttle body has been bored. Pretty much all these things reduce mileage (the head shaving is the only thing that would help mileage). So, I'm in the same boat as you are.
  9. southerncannuck

    southerncannuck Well-Known Member

    Slowing down is the easiest thing to do. I've been playing with the Scanguage and got some numbers for you to consider. My Fit (auto) yields 47.5 mpg at 55 mph. This becomes 41 mpg at 60 mph. 40 mph gives me 57 mpg. I haven't tried 65 mph yet. I may never, who knows.

    It does seem that I meet nicer people in the right lane than when I was one of the crazies. I still can't figure out the hurry was all about.

    Best of luck with your HX. It has incredible potential.

    Louis B
  10. shifty35

    shifty35 Well-Known Member

    The important thing in intake -> manifold -> head -> exhaust is not volume (diameter) but velocity. Increasing the diameter also increases the volume of incoming air (potentially) but also can reduce the velocity of said air.

    The net effect is that you make more power with the throttle wide open and LESS with the throttle cracked in the high-MPG style. Thus, the stock intake and exhaust systems tend to increase MPG at the cost of the top-end HP available with larger diameters.
  11. southerncannuck

    southerncannuck Well-Known Member

    The trick to high FE on your HX will be to stay out of VTEC. I want to say it engages somewhere between 2500 rpm and 3000 rpm on the D16Y5. You can wire up an LED to the solenoid to determine when it's on, and you want that light to rarely, if ever go on.

    Can a scan gauge tell when the VTEC is activated?
  12. 99HXCivic

    99HXCivic Well-Known Member

    I just bought a Dash Dyno SPD - maybe it's better than the Scangauge because it does data logging of 16 parameters and I can later review my ride data with the Auterra software. The shipment comes UPS tonight!

    I want my HX fully modded for high fuel economy! So next on my list is synthetic oil change, low rolling resistance tires (maybe the Bridgestone B381), and window tint. Why, I was still using A/C 1st week of Nov here in Houston, Texas!

    I'll read my Service Manual for VTEC activation poit too. Maybe I hit it when I do 70 mph.

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