Intake air flow modification

[zpiloto]

Wanted to see how intake air would affect FE with increased airflow and then with a restricted airflow. Removed the original 18” airduct that went from the air box to the forward corner of the engine compartment and replaced it with a 4” long piece of 2” diameter PVC that is directed towards the exhaust manifold. Reset the ECU and did runs with car configured with normal, 2” hose, and restrictor plate on a 41 mile test loop. The restrictor plate was made buy covering 2” hose with cardboard with a 1”x1”hole cut in the center. Each mod showed an improvement. With the restrictor there was a slight decrease in acceleration but good drivability. Max RPM was 3575 and Max speed was 60 MPH.
The restricted airflow shows promise but I forgot to reset the ECU for that run. During the run with the restricted airflow when I would shift into neutral to coast the idle RPM would only drop to around 1300 until the car would come to a stop then drop down to it’s normal 650 RPM. Towards the end of the run the idle was dropping to 1000 RPM so I think that it will eventually get back to its 700-800 RPM range which will save on fuel. Scan gauge results below.

Conditions: Beginning of runs calm winds 76
End of runs calm winds 70

Normal 36.4 MPG
40.0 MPH Avg

2’ Hose 37.0 MPG
38 MPH Avg

Restricted 37.3 MPG
39.0 MPH Avg

[Matt Timion]

Excellent test. I'm going to throw this into the Experiment's forum in hopes that other people repeat your test and post their results as well.

[SVOboy]

I had that idea to block off some flow a while ago, but never mentioned it cuz I forgot, , I'm glad someone clever with a scangauge got about to testing it.

[MetroMPG]

what's the fuel-saving theory behind restricting airflow?

[SVOboy]

I believe it is less airflow per throttle position, more throttle, less pumping losses, therefore equal power for less.

[zpiloto]

I’m just guessing but there is probably a sweet spot on the amount of air restricted to get the best fuel flow and still have performance acceleration without getting squashed getting on the highway. I basically reduced the airflow by 2/3. The original area of the 2” opening was 3.14 reduced to 1. I might try ¾” x ¾” opening in the restrictor and see if it chokes off to much air. The way it is set up now the acceleration starts to drop off once the RPM reach about 3200. My normal shift point on the automatic is 2500 RPM. I think that most of the fuel saving comes from the acceleration factor so if you were doing a lot of highway miles it might not show any improvement.

[krousdb]

Originally Posted by SVOboy

I believe it is less airflow per throttle position, more throttle, less pumping losses, therefore equal power for less.

Perhaps this is part of the reason behind the smaller diameter throttle body on the D15Z1, 40mm vs 56mm I think?

[SVOboy]

Perhaps this is part of the reason behind the smaller diameter throttle body on the D15Z1, 40mm vs 56mm I think?

I am in agreement, but the manifold is also vastly different to suit that so it's not just the smaller TB. I'd say a D15Z1 IM/TB would be quite a good FE upgrade, considering the way it is designed with the resonance and all that that Bunger explained.

[MetroMPG]

Originally Posted by SVOboy

I believe it is less airflow per throttle position, more throttle, less pumping losses, therefore equal power for less.

i don't get it. help me out here.

assume 2000 rpm constant load and no restrictor plate. let's say the throttle is open at 4 out of 10.

now add a restrictor plate. to maintain 2000 rpm, now the throttle must be open to, say, 6 out of 10.

since we're at the same engine speed (load/power output), we must be consuming the same amount of energy (gas), and also inhaling the same amount of air.

it seems to me like all we've done is shift the location of the intake restriction from the throttle plate towards the restrictor plate - with no net change in pumping losses.

[diamondlarry]

Another thing I would be concerned about is the TPS. On OBD2 at least, the TPS plays a part in fuel injection rate. If you had to open the throttle more it seems like the ECU would want to dump in more fuel.

[SVOboy]

There are two reason why this works. One is that the higher the gear, the lower the frictional losses. By getting to 5th quickly, the total number of engine revolutions is reduced, with a corresponding reduction in frictional losses. The second reason is pumping losses. This is the work done to force air past a partially closed throttle plate. The more closed the throttle is, the higher the losses. Accelerating quickly reduces throttle losses, because the throttle is open. In addition, engine speed is lower in fifth, so to generate the same amount of power, you have a larger throttle opening (and hence lower throttle losses) - this is another reason to get to higher gears as quickly as possible.

The best fuel economy is gained by a combination of the gas petal to the floor with shifts at as low an rpm as possible to sustain your desired acceleration. This ensures a fully open throttle during the entire acceleration event and gets you out of the lower gears as quickly as possible, for lower frictional losses.

Taken from insight central, a slight description of throttle position and frictional losses, I will try to find something better.

[Matt Timion]

Originally Posted by SVOboy

I am in agreement, but the manifold is also vastly different to suit that so it's not just the smaller TB. I'd say a D15Z1 IM/TB would be quite a good FE upgrade, considering the way it is designed with the resonance and all that that Bunger explained.

if you ever go to a CX/VX/HF intake manifold be sure to get a different intake hose as well as air box top. The smaller bore TB requires a different intake hose.

Lucky for me I found on in a CRX HF a few months back and have been saving it for my engine swap.

[krousdb]

Originally Posted by SVOboy

Taken from insight central, a slight description of throttle position and frictional losses, I will try to find something better.

Here is a quote from Wayne Gerdes, also about the Insight. It seems to contradict the quote above:

Originally Posted by Wayne Gerdes

Given the IMA based Insights best FE came about by riding leanburn (even during acceleration!), I was always the go-slow, no-assist, bring her up in a low RPM driving scenario kind of guy. I never ever touched VTEC and never had I seen > 4 bars of 20 of assist during my own brand of low G accelerations … Unless something needed to be ran away from or traffic was building behind for example. On warmer days (80 + degrees F), she would allow me to reach 100 mpg in less then 3 miles using this approach. No one using the WOT, 1-2-5 shifts, or heavy assist w/ maybe 1/2 throttle all the way to WOT had ever seen those kinds of numbers using those higher G acceleration rates that I know of. Because of the slow and steady accelerations, I know the mechanical friction losses are at a minimum and the strain on any given component was minimal at best let alone did I rarely if ever touch the pack. I am an absolute believer in longevity from whatever we drive and the go slow approach should yield superior results to a larger throttle plate opening/lower pumping losses at higher RPM’s.

See the entire thread here:
http://www.cleanmpg.com/forums/showthread.php?t=255

I am absolutely tentitive on the WOT approach, while simultaneously feeling a definate maybe on the go-slow approach. There you go. The choice is obvious.

[SVOboy]

I actually saw on insightcentral some controlled testing contrasting these two types of acceleration and WOT won. Lemme try and find it.

EDIT: http://www.insightcentral.net/forum/viewtopic.php?t=4139&highlight=full+throttle

[krousdb]

Originally Posted by SVOboy

I actually saw on insightcentral some controlled testing contrasting these two types of acceleration and WOT won. Lemme try and find it.

EDIT: http://www.insightcentral.net/forum/viewtopic.php?t=4139&highlight=full+throttle

Well it seems that the guy performing the test did get better results with WOT. 75.6 vs 74.4 MPG I think?. But WOT is easy to do. What is hard is mastering gentle accel usng leanburn. Wayne had a lifetime average of 92.8 MPG in his Insight before he sold it, over 90k miles IIRC. His best tank, on which he used the gentle acceleration technique was 109.0 MPG for 1523 miles.

At least in the case of the Insight, I would put my money on gentle acceleration with leanburn.

[Matt Timion]

I think that someone should invent a "gentle accel" cruise control. Tell it your target speed and then it will slowly accelerate over the period of like 3 or 4 minutes to that speed.

[Compaq888]

I think the WOT theory is good, think about this.

My best mpg comes from my 4th gear because the torque converter locks up.

My strategy has always been accelarate slowly and smoothly on the streets and I rarely get into 4th because by the time I get up to 4th gear there is a red light. But if I were to accelarate first and get into 4th gear and stay there I would get 35mpg+. I think at 40mph I get 40mpg+. Until 4th the torque converter doesn't lock up. So I think on the streets I would gain some mpg if I get into 4th sooner and stay there because accelarating slow almost never gets me in there.

[MetroMPG]

but we've kind of shifted from a discussion about the potential FE benefits of using an intake restrictor, vs the potential benefits of using WOT on an otherwise unrestricted (or stock) intake.

i understand the theory behind WOT.

but i still don't understand the theory behind adding an additional intake restrictor (i say additional, because the throttle is also a restrictor by definition).

i think svoboy was onto something when he said:

I am in agreement, but the manifold is also vastly different to suit that so it's not just the smaller TB.

in order for pumping losses to be reduced, you want to have as close to ambient pressure as possible in the manifold. i don't understand how adding a restrictor upstream of the throttle addresses that. sure the throttle is open further, but the upstream airflow is now restricted, so the pressure in the intake manifold can't be as close to ambient as if there were no additional restrictor.

[Compaq888]

I've restricted my intake and it did increase my mpg by 1 but it killed power. Everytime I had to go up a small hill it would downshift because the car barely moves as is in 4th. I also opened up the intake and lost 1mpg but there is more power in the low end and the engine breathes better. I think the best setup would be to have a special box that opens up based on rpm conditions. Like in front of the airbox. It's better to stay in highest gear and use more fuel than to downshift and use even more fuel.

[SVOboy]

You could make that intake switcheroo deal if you want, it'd be rather easy with just a hacked up vtec activator or you could make something special to read the rpm signal off the distributor and have it going that way.

[Compaq888]

Originally Posted by SVOboy

You could make that intake switcheroo deal if you want, it'd be rather easy with just a hacked up vtec activator or you could make something special to read the rpm signal off the distributor and have it going that way.

I have a MSD digital window switch. I can make anything attached to it turn on or off at any rpm I desire. But I don't want to spend anymore money on my car. I'll just use what I got and attach a long hose from the bottom of the car to the airbox. That way when the car goes up really steep hills it will stay in 4th or when I accelarate a little bit harder. After extensive research my car gets the best gas mileage with the stock intake system. The stock intake system is just not good for going up steep hills because it doesn't supply enough air.

[kickflipjr]

Originally Posted by MetroMPG

in order for pumping losses to be reduced, you want to have as close to ambient pressure as possible in the manifold. i don't understand how adding a restrictor upstream of the throttle addresses that. sure the throttle is open further, but the upstream airflow is now restricted, so the pressure in the intake manifold can't be as close to ambient as if there were no additional restrictor.

How does this work. Buy adding more restriction you can open up the throttle more. It doesn't seem like would work. Restriction=Bad. Velocity=Good.

Maybee a second throttle that you could adjust on the fly would work. It would be a better way of restricion (even though i don't think this is a good idea in the first place).

[Compaq888]

Think of it like this. You need restriction for constant speed. You need a good flow for accelaration.

[krousdb]

Originally Posted by MetroMPG

but i still don't understand the theory behind adding an additional intake restrictor (i say additional, because the throttle is also a restrictor by definition.

Admittedly, I too am having difficulty understanding the benefit of a second restrictor. The only thing I can think of is that on vehicles that use a TPS, you could achieve higher vacuum at a certain throttle position, thereby causing the ECU to trim the fuel differently. meh. Or maybe the MAP sensor would give a different reading causing a different fuel trim, but I don't have a MAP sensor so, again, I say meh!

[SVOboy]

Or maybe the MAP sensor would give a different reading causing a different fuel trim, but I don't have a MAP sensor so, again, I say meh!

Where'd your map sensor go?

Mehbe someone else with a fuel meter could go and test this out, meaning you.

[krousdb]

OK, then maybe I dont have a TPS. I don't have both do I? Anyway, I would like to know why two restrictors works better than one before testing.

[SVOboy]

I don't have both do I?

Yeah you do. Your TPS is on the side of the TB facing the firewall and has three wires coming out of it, and you MAP is on the top of the TB with three wires and says MAP sensor on it or mounted on the firewall right behind the TB and says MAP on it. B7s I have been seeing at the junkyard in civics with firewall mounted sensors, which makes me think that my IM/TB is not from a b7, or something, mehbe just the rail and tb, I dunno.

Anyway, I would like to know why two restrictors works better than one before testing.

Anyway, I would like to think that this is just the opposite effect of sticking a big *** 4" CAI, except with a small *** 1.5" HAI. So it'd follow basically the same principles, and as kickflipjr was saying, it would increase velocity as there is less cross-sectional area.

[Matt Timion]

Originally Posted by SVOboy

Yeah you do. Your TPS is on the side of the TB facing the firewall and has three wires coming out of it, and you MAP is on the top of the TB with three wires and says MAP sensor on it or mounted on the firewall right behind the TB and says MAP on it. B7s I have been seeing at the junkyard in civics with firewall mounted sensors, which makes me think that my IM/TB is not from a b7, or something, mehbe just the rail and tb, I dunno.

Wait, you've been seeing B7s with with firewall mounted MAP sensors? Firewall mounted MAP sensors were obd0. OBD1 Map sensors should be on the intake manifold/TB. I can take a picture of my z1 if you guys want to see where it's mounted.

[MetroMPG]

Originally Posted by SVOboy

Anyway, I would like to think that this is just the opposite effect of sticking a big *** 4" CAI, except with a small *** 1.5" HAI. So it'd follow basically the same principles, and as kickflipjr was saying, it would increase velocity as there is less cross-sectional area.

but the HAI feeds the engine less dense air, that's why the throttle has to open further. it needs a higher volume to do the same amount of work.

if you don't change the density of the air, then forcing the throttle to open further because airflow is being starved by an upstream restriction offers you no advantage.

analogy:

1. you're drinking a thick milkshake through a straw with the "mouth" end 75% closed (squished).

2. you squish the "cup" end of the straw 75% closed, which permits you to open up the "mouth" end fully.

have you experienced a change in the amount of effort to drink through that straw? any effeciency gains from the perspective of pumping/throttling losses? i don't see any.

[SVOboy]

Wait, you've been seeing B7s with with firewall mounted MAP sensors?

Yeah, three of them today, wanna fight about it?