Recirculate BOV for better MPG.

[S14DB]

Friend and I were having a discussion that made sense. When you have a MAF and you vent to ATM the ecu thinks the air went through the engine and you run rich for a few sec. This is wasted gas and decreases MPG. When you recirc the air stays in the system and extra fuel is not added for air that is no longer there.

Has anyone noticed a major MPG diff when switching from Recirc to ATM or vice versa?

[steve shadows]

This is true.

You can also make sure the bov is tight.

and best of all get your car tuned with a brake eddy dyno haha

[Dutchmalmiss]

I would have a more frequent misfire when I was running atmospheric, AND gas mileage was probably decreased about 2-3mpg maybe?

Converting to a recirculated setup fixed all that and the stalling issue, too.

One question though, when running a recirculated setup, if it matters at all, what setting would I adjust the BOV to, being that it's adjustable?

It's a Blitz BOV fyi

[burnsauto]

I would have a more frequent misfire when I was running atmospheric, AND gas mileage was probably decreased about 2-3mpg maybe?

Converting to a recirculated setup fixed all that and the stalling issue, too.

One question though, when running a recirculated setup, if it matters at all, what setting would I adjust the BOV to, being that it's adjustable?

It's a Blitz BOV fyi

that all comes down to you really.. some guys keep a little harder to keep response in the low end of things...while other guys like to have as little compressor surge as possible.

it took me a few days before i got the tension JUST right on my bov...not too soft that its opening with just a few lbs of pressure...but not tight enough that it doesnt blow off unless im at full boost.

[g6civcx]

Well, if you're talking about fuel economy then your air/fuel should be somewhere around 14-15:1.

I thought about it and I don't know if venting to atmosphere during off-throttle transition really affects fuel economy that much because theoretically, the ECU normally reduces fuel when the throttle is closed and the engine is above idle.

I guess it would only affect economy during part-to-full throttle upshifts. Otherwise when the throttle is closed there is not much fuel entering the engine any way.

Thoughts?

One question though, when running a recirculated setup, if it matters at all, what setting would I adjust the BOV to, being that it's adjustable?

Adjust the BOV on the car. I like to set the spring as soft as possible without stalling.

[Darius]

If you are talking fuel economy, 14-15:1 is not where you want it to be operating. Stoichiometric is for the cleanest burn. Leaner gives better economy and richer gives better power and engine safety. This is wayyyy generalized, but you get the idea.

Even if you aren't recirculating the BOV, the engine is still seeing the same amount of air and still dumping the same amount of fuel in whether the air actually makes it into the combustion chamber or not. However, since most people are on a closed-loop system and using the O2 sensor to tell the ECU that the fueling is too much/too little, the ECU corrects to help lean it back out to 14.7. I don't understand why it would make a 2-3 mpg difference that some have seen.

[g6civcx]

If you are talking fuel economy, 14-15:1 is not where you want it to be operating. Stoichiometric is for the cleanest burn. Leaner gives better economy and richer gives better power and engine safety.

I don't understand.

You say 14-15:1 is not good.

Then you say stoichiometric is for the cleanest burn.
Then you say leaner gives better economy.

So by your logic, stoichiometric = cleanest burn = best economy.

What's the problem with 14-15?

[98s14inaz]

I ran recirculated on my ka-t and my gas mileage was fantastic, I bet it would have been even better with out that pig rich jwt tune. Several friends ran atmospheric on similar set ups, I always got better mpg than them. So yes, IMHO your theory is correct, recirc gets better mpg.

[Ninjabread]

How about no BOV at all?

Yep.

[xsparc]

what about if you had a blow through setup? like the maf is on the hot pipe after the BOV?

[g6civcx]

what about if you had a blow through setup? like the maf is on the hot pipe after the BOV?

There is a lot of debate about this topic. I personally think that this is the ideal setup for a MAF. The only improvement over this is to go with a MAP.

But some people swear that the ECU calibration goes out of whack. I think they just rerouted the MAF improperly.

If you look at how a MAF works, it's just a heater filament that maintains temperature based on how much air flows cools it. I'm not sure how the air flow would be different on a blow through.

[xsparc]

I think it all has to do with the setup. MAF needs to be like at least 6 inch back from the from the TB and the BOV should be like a foot from the MAF. mainly so when you do blow off, there is little to no turbulance in the MAF.

just guessing here

Another problem might be that since the MAF was not designed for a blow through setup, it might leak internaly from the pressure.

[HyperTek]

i had blow thru on my old s13 and loved it.. HKS intercooler, i just cut a section out of the pipes and placed it in there.
http://a633.ac-images.myspacecdn.com/images01/39/l_65921e5f551b797af4b43903bdad6208.jpg
*dont mind the clutch fan, there was a elec fan and the clutch fan was ditched*
Z32 maf, trim off the flange and it will accept 3inch couplings. Apexi SAFC to adapt it to the ecu. stock sr20 settings.
Just mount it in a spot where there is minimal piping bends.. smooth air flow.

I liked it no problems, might not be for everyone tho, i just liked tinkering with the idea to get the most out of what i had.
Also had solid motor mounts that car was a beast

[drift925]

Friend and I were having a discussion that made sense. When you have a MAF and you vent to ATM the ecu thinks the air went through the engine and you run rich for a few sec. This is wasted gas and decreases MPG. When you recirc the air stays in the system and extra fuel is not added for air that is no longer there.

Has anyone noticed a major MPG diff when switching from Recirc to ATM or vice versa?

Well technically no extra fuel is ever added. The italicized part is right (Instead of using that fuel effeciently to make power, its lost. Lost fuel equals lost mpg) but the bold part, no extra fuel is ever added, remember the air is already accounted for and thus the computer already has the values for how long the injectors should stay open for.

[Darius]

I know I was confusing as hell on that last post...I suck at trying to explain this sometimes.

Nothing is wrong with 14-15:1 AFR. I meant to say that the cleanest burn emissions wise (least pollutive to the environment) occurs at stoichiometric ratio of 14.7:1 AFR.

You will obviously get better fuel economy if you run higher AFRs (i.e.17:1 at idle), but you also run the risk of getting knock and high EGTs. That is why you need to tune for those things when dialing in your fuel and ignition maps. If you have a standalone, obviously.

I agree that blow-thru is the way to go but for some reason it reads a higher air flow rate (higher voltage) than if it is a draw-thru on the same setup. So you max the MAFS out at a lower hp than with a draw-thru installation on the same setup. Plus, plastic MAFS housings on 25 lbs of boost don't tend to hold up to the heat and pressure. They either crack or you tighten the couplers down on them so hard that they crack anyways.

I still don't understand why recirculating would improve mileage noticeably. Maybe because people like the ricer sound of it and are a little more throttle happy than those that are recirc'd. ;)

And drift925, it might lose power due to inefficient fuel use, but it is during an off-throttle event so it's not making power anyways

[g6civcx]

Nothing is wrong with 14-15:1 AFR. I meant to say that the cleanest burn emissions wise (least pollutive to the environment) occurs at stoichiometric ratio of 14.7:1 AFR.

I understand, but we're talking about fuel economy, not emissions.

You will obviously get better fuel economy if you run higher AFRs (i.e.17:1 at idle), but you also run the risk of getting knock and high EGTs. That is why you need to tune for those things when dialing in your fuel and ignition maps. If you have a standalone, obviously.

So what should the ideal AFR be?

I try to tune the cruise profile of my carb to be around 14-15 and the power profile around 12-13.



I agree that blow-thru is the way to go but for some reason it reads a higher air flow rate (higher voltage) than if it is a draw-thru on the same setup. So you max the MAFS out at a lower hp than with a draw-thru installation on the same setup. Plus, plastic MAFS housings on 25 lbs of boost don't tend to hold up to the heat and pressure. They either crack or you tighten the couplers down on them so hard that they crack anyways.

Question. Is it safe to run 25 lbs on the MAFS?

[S14DB]

I have an Sard R2D2 and a stock S14SR BOV setup. I don't care about sound, just efficiency(performance/mpg).

[HalveBlue]

I might as well throw in my 2 cents.

No, an atmospheric BOV will not decrease fuel economy.

And here is why:

The MAF is measuring how much air is coming in through the intake system and adjusts how much fuel is being sprayed accordingly.

Supposing that you didn't have an atmospheric BOV the air/fuel mixture would combust as expect.

With an atmospheric BOV you're simply discharging that air, thereby temporarily occurring a rich air/fuel mix.

Basically, the amount of fuel being injected is the same regardless of whether or not you run an atmospheric BOV. The only difference is that with an atmospheric BOV you will create a rich mixture because all that air is being discharged instead of being used in the combustion process.

[S14DB]

But the air being recirc would result in less air going past the maf. So, less fuel would go in after the blow off.

[g6civcx]

But the air being recirc would result in less air going past the maf. So, less fuel would go in after the blow off.

I'm not sure if recirc = less air being sucked in past the MAF.

[S14DB]

Turbo is still spining sucking in air. Recir dumps air between maf and turbo. So, that's less air that has to come in past the maf.

[harangatang]

I am pretty sure that a bov doesnt decrease/increase mpg by any noticeable amount.
I get 30-33mpg cruising hwy and city driving

hks ssqv on my cold pipe, non-recirculated
(stock redtop)

[louisdaboois]

recirc bov doesnt effect mpg because of what halveblue said. regardless of how much air actually enters the combustion chamber, the ecu already sends the signal to the injectors telling them how much to squirt so that set amount of fuel is going to be used regardless.

proper air fuel mix for awesome economy in my experience has been around 16-17 idle. 14.7-15 cruising (around 10-15 in/Hg). 13.5 at atmospheric. and 12.2ish under boost. i ran 28-32 mpg in the city and 36 on highway. that on a t25 ka-t w/ an enthalpy tune and safc.

you guys need to read corky bell's books. lol.

[96Turbo]

right on...after the air is measured by the MAF, the ECU's already decided how much fuel it's going to inject. so whether or not that air actually reaches the combustion chamber (blown off by atmospheric BOV, or recirculated)....the fuel is going there no matter what.

therefore.....there really shouldn't be a difference in MGP

[S14DB]

What about the air that comes in afterwards? You go rich after the bov dumps when the air that is lost is replaced though the MAF.

[renegade_ewok]

Turbo is still spining sucking in air. Recir dumps air between maf and turbo. So, that's less air that has to come in past the maf.
But that air has already been metered and fuel has already been injected to compensate for it.

[monkeyslide17]

So it seems that I am saving gas by using the recirculating fitting. Fulled up on monday and still have plenty of gas to go.

[mrmephistopheles]

You're all idiots. If you want to save gas, don't get into boost.



:keke:

[g6civcx]

You're all idiots. If you want to save gas, don't get into boost.



:keke:

Right on, or don't go pass 5PSI of vacuum on carbs.

[HalveBlue]

Or ride a friggin' bicycle!

[S14DB]

What about the air that comes in afterwards? You go rich after the bov dumps when the air that is lost is replaced though the MAF.

But that air has already been metered and fuel has already been injected to compensate for it.

Are people not getting the concept that the maf response is instantaneous and there is no Limbo time between when the air enters the maf and when the ecu adjusts?


You run rich AFTER you blow off. The system takes in more air for the air that was lost and you dump fuel. When you recirc you take in less air thru the maf and don't run rich.

[lflkajfj12123]

the system does not know air was lost

the only reason the mixture becomes slightly rich is because there is less air not more fuel being delivered

running rich is obviously wasting the fuel that was delivered so yeah you'd be using all of that fuel when you recirculate the BOV

the same amount of fuel will be delivered but it will be used better thus increasing mpg!

[lonelydrifter]

Anyone Recirc an Sard R2D2? without that $100 KIT!?!

[renegade_ewok]

Are people not getting the concept that the maf response is instantaneous and there is no Limbo time between when the air enters the maf and when the ecu adjusts?
I get it, trust me I know what happens when you vent a BOV to atmosphere (I come from the suby world haha)

From the factory, I am pretty sure that the SR20 ECU is setup to run under a recirced setup. The MAF read the air rushing past it to the turbo and meters accordingly. However, when you would recirc and let off the throttle the ECU will compensate for all the air that has been metered so far. No air is lost in the system as it recircs the air right back into the turbo inlet, post MAF and the ECU accomidated for it with providing the right amount of fuel to run safe.

When you vent, however, the ECU will still compensate for the air that it metered as said above because if it didn't all that extra air = knock/detonation/bad stuff, just one key difference: there is less air in the charge pipes and the system.

Everything would run the same under boost, but when you let off the gas and the BOV vents, the normal cycle that the ECU undergoes when it recircs still happens. The extra air that is in the charge pipes or the system that the MAF metered gets expelled out of the system while the ECU is dumping fuel without actually getting that air, thus the rich condition as opposed to the normal more lean condition that is normally experienced when you recirced.