Interesting autospeed article on ram air intake
 

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I think modifying the stock intake (like in that article) or installing a CAI, is a great way to improve HP & MPG's. Win-Win!

interesting, i know that in the performance world ram air really doesnt make much of a difference, in fact a trans am ws6 (only real performance difference being ram air) is equal to a regular trans am on the drag strip.

but for fuel economy im sure minimizing the pumping losses must help but whether or not it is measurable is going to be another story.

Yeah, I'm not so interested in his lkm numbers since he's not very scientific, but the vacuum gauge read is interesting.

I installed forward facing cold air intake on 3 cars equipped with warm air intakes from the factory. All 3 picked up fuel economy.

I routed my intake to draw from right behind one of the inlets on my lower front lip and @ highway speed I saw 1 to 0.5 in increase in plenum vacuum. I assume I lowered my overall intake pressure drop by mounting a forward facing intake.

Ram air is kinda like using gravity to coast right?

Wai
 

Tjts1, I'm not sure what you mean when you say "factory-installed warm air intake." Either way, I dont think a CAI could help. A CAI should bring in more dense air, which means the engine needs a smaller volume of it to produce the same torque, which means a less open throttle plate, which means pumping/efficiency losses. WOT is really the only time the engine takes advantage of the CAI, and indeed it should be more efficient at WOT, but I dont think WOT is applicable to a fuel economy discussion. The only two ways a CAI could improve fuel economy (not efficiency) is if the CAI actually brought in warmer air, or if you scaled down the motor to constant performance.

Vince, ram air is arranging the intake system to take advantage of the velocity of the incoming air to artificially "boost" the engine. Unfortunately it's been proven many many times that the effects are negligible until at least 130-140 mph. Or what the article says, I didnt read it.

I made some pretty broad claims here, let me know if im wrong.

WS6 TAs made 15 more HP and 25 more lb/ft of torque than a regular TA. In stock form they were 1-2 tenths quicker in the 1/4 mile.

Any time you reduce negative pressure in the manifold, or even turn it into positive pressure, pumping losses must be reduced. I wish the author of the article had finished testing for fuel economy before publishing the article. Right now it's just kind of a tease. I'm curious how the ECU will react to what might be unusual ratios of MAP vs TPS. If this were a MAF controlled engine the results would probably not be positive, mpg wise.

I'm aware of what the factory rated them, the truth is you put an un-modded t/a next to a ws6 and race them and there is no definate which is the faster car. this has been debated time and again on ls1tech.com and each time it comes out the same - they are equal cars.

Likely good for peak HP, but when FE driving you target the minimum power needed to drive your route. That means lower manifold pressure, obtained via whatever combination of partly closed throttle valve and upstream restriction gets you to that needed manifold pressure.

Reducing upstream restrictions just means you'll hold the throttle closed more, and increasing upstream restrictions means you'll hold the throttle open a bit more. The end result is the same.

Back in my max. HP days I played with that sort of ram air, but just like the equations say, there's pitifully little pressure available from forward speed until you exceed about 90 mph. In any case, for hypermiling, it's a waste of time.

You should At least read the article. Auto speed has a series of articles on "eliminating negative boots" and "fordward facing intakes". They did the modification on a both NA and turbo cars including a honda Insight. Its all there.
As for my previous claim, I followed the Autospeed articles to the letter. i installed large sealed forward facing intakes on 3 cars. 2 volvos that originally had thermostatic variable hot/cold intakes, and 1 BMW that simply breathed all its air from inside the engine bay near the radiator. On the bmw i was able to to measure the temperature drop from 20-40f above ambient stock down to 0-5f above ambient.
http://www.matthewsvolvosite.com/airbox.php
M42club.com - Home of the BMW E30/E36 318i/iS - View Single Post - Looking for cold air intake

No, thats not how it works. The engine will still breath the same ammount of air and have the same intake if you increase air pressure, reduce throttle angle and maintain the same load. Take the engine up to 30k feet where it can only produce 30% as much power at WOT and it will still consume the same amount of fuel at the same load.
[QUOTE=garys_1k;39268]
Read the autospeed articles. Its not about pressure, its about reducing restriction. The large forward facing intake improves fuel economy by making the engine a more efficient air pump at low RPM and high load. This will allow you to use 1 or 2 gears higher at any given load.


HAPPY READING
Eliminating Negative Boost - Part 1
http://www.autospeed.com/cms/A_0629/article.html
Eliminating Negative Boost - Part 2
http://www.autospeed.com/cms/A_0637/article.html
Eliminating Negative Boost - Part 3
http://www.autospeed.com/cms/A_0646/article.html
Eliminating Negative Boost - Part 4
http://www.autospeed.com/cms/A_0652/article.html
Eliminating Negative Boost - Part 5
http://www.autospeed.com/cms/A_0663/article.html

Negative Boost Revisited, Part 1
http://www.autospeed.com/cms/A_107824/article.html
Negative Boost Revisited, Part 2
http://www.autospeed.com/cms/A_107825/article.html
Negative Boost Revisited, Part 3
http://www.autospeed.com/cms/A_107826/article.html
Negative Boost Revisited, Part 4
http://www.autospeed.com/cms/A_107827/article.html
Negative Boost Revisited, Part 5
http://www.autospeed.com/cms/A_107828/article.html

Doing the Impossible
http://www.autospeed.com/A_109877/cms/article.html

Modifying the VL Turbo Intake
http://www.autospeed.com/cms/A_0779/article.html

Into the Intake - Part 1
http://www.autospeed.com/cms/A_1361/article.html

We Have a Record!
http://autospeed.com/cms/article.html?&A=109217

Hello, McFly? You have a throttle plate.

Thin air (hot, humid or altitude) will reduce engine maximum output and increase efficiency. It reduces pumping losses in the engine (but also reduces effective compression ratio) and it reduces wind resistance.

No. You really need some data to back up that claim. Reducing the ambiant air pressure has exactly the same effect as closing off the throttle plate. There is no efficiency to be gained. But it does reduce aerodynamic air resistance for the vehicle body.

Sorry I don't really know how to bring up them fancy quote boxes, but these are from tjts1:

"On the bmw i was able to to measure the temperature drop from 20-40f above ambient stock down to 0-5f above ambient."

Then we know your cold air works. It should decrease fuel economy for the reasons I listed above. Thanks for clearing up what you were talking about with the factory systems, btw.

"Read the autospeed articles. Its not about pressure, its about reducing restriction. The large forward facing intake improves fuel economy by making the engine a more efficient air pump at low RPM and high load. This will allow you to use 1 or 2 gears higher at any given load."

The exact opposite. At a given rpm, the load will be reduced, which is bad for engine efficiency. I understand it's not intuitive, but you have to realize that throttle plate is more than happy to compensate for any restriction you are able to reduce with a CAI/ram air/magic jelly beans whatever. Except, once again, at WOT. You are probably more efficient at WOT. In the second case, for a given load, the rpm will be reduced, which puts it farther out of the range of the next gear, not closer. Engines don't like lugging.

I hate to sound like I'm ganging up on you here, tj, but jon and garys are right. In your high-altitude example, that engine only produces 30% of its power because its only getting 30% of the mass of air it needs. Assuming the computer could compensate (which it most certainly could not) it would only use 30% of its regular load of fuel. The air/fuel ratio stays the same. Heck with no pumping losses it might even be more efficient. Imagine more on the order of 90% here and you have the concept behind a warm air intake.

Well you have your point of view, I have mine. I installed large forward facing cold air intakes on 3 cars so far and all three had improved fuel economy after the modification. The autospeed tests on 5 different cars back up my real world experience. There is not much else I can add.

cheers
justin

I feel very argumentative at this point, but I finally flipped through the articles, and the author mentions fuel economy in only one sentence: a "gut feel" of "fractional" improvement that he himself admitted was "not very scientific." But that's fine, that's what I would expect from an article about improving performance from a magazine called autospeed.

As for your results (and the magazine's for that matter), I'm not saying they're inaccurate, but unfortunately there are dozens of variables affecting fuel economy. Outside temperature, the particular road used, speed traveled, weather, traffic, the driver, accessories, cetane/blend of fuel, other modifications done on the car at the same time as the CAI, and adaptations performed by the ECU could all have major, major effects on fuel economy between tests. With all other variables accounted for, I just simply do not understand how better economy is possible from a theoretical standpoint outside of the exceptions I presented above.

I used "Spectre" pieces to modify the stock intake on both our SX4 and Caravan...

http://i237.photobucket.com/albums/f...21200811-1.jpghttp://i237.photobucket.com/albums/f...20081311-1.jpghttp://i237.photobucket.com/albums/f...21200812-1.jpg

I've noticed both an HP increase and an improvement in mileage. I think a CAI type of intake is the most efficient way to go.

Quote:

Originally Posted by garys_1k
Reducing upstream restrictions just means you'll hold the throttle closed more, and increasing upstream restrictions means you'll hold the throttle open a bit more. The end result is the same.

No, thats not how it works. The engine will still breath the same ammount of air and have the same intake if you increase air pressure, reduce throttle angle and maintain the same load. Take the engine up to 30k feet where it can only produce 30% as much power at WOT and it will still consume the same amount of fuel at the same load.

Exactly, that demonstrates my point -- reducing restriction at one place (say, the air inlet system) and replacing it somewhere else (e.g. a more closed throttle valve, or high altitude) makes ZERO difference. We agree.

Originally Posted by garys_1k
Back in my max. HP days I played with that sort of ram air, but just like the equations say, there's pitifully little pressure available from forward speed until you exceed about 90 mph. In any case, for hypermiling, it's a waste of time.

Read the autospeed articles. Its not about pressure, its about reducing restriction. The large forward facing intake improves fuel economy by making the engine a more efficient air pump at low RPM and high load. This will allow you to use 1 or 2 gears higher at any given load.

Thanks, I did read them and am aware of how reducing pressure drop across the intake system can allow higher power via higher air mass flow. But when you're only asking for a relatively small fraction of the engine's peak torque (at its present speed) then those restrictions don't matter -- the total restriction, air system + throttle valve, do.

Getting good fuel economy is NOT about very high loads, it's about moderate loads at low-ish speeds. Lugging the holy hey out of an engine may seem to give great volumetric efficiency but the enrichment and spark retard will kill the overall efficiency. Most peak efficiency islands (BSFC) are about 2/3 or so of peak torque, maybe 3/4. Above that you get enrichment and spark retard, both FE killers.

The combustion chamber could care less what caused the particular mass of air to enter via the intake valve, throttle, dirty air filter or a piece of duct tape across the inlet pipe. All it "knows" is that there's a certain mass of air in there, plus a proportional amount of fuel, and when those are compressed they're burned and pressure is the result.

Low restriction air intakes are all about maximum torque. They won't let you upshift sooner at part pedal. In fact, given that pressure drop increases with velocity squared, they're biggest impact will be at high load at high engine speeds. Down in economy-RPM-land, like 1200-200 rpm, low restriction intakes are a total waste for fuel economy. Just keep the air filter reasonably clean and you're fine.

As a side note, I find it funny that Autospeed says the Insight intake is 'tiny' then say it's the lowest restriction ever at peak power.

That whole chart makes little sense as you have cars being tested at a few hundred horsepower, and the "lowest restriction ever" being tested at only 70ish hp.

So really, the Insight intake box is HUGE for 70hp, not tiny. And if you were to run the other cars at 70hp, it probably wouldn't be the lowest restriction intake ever anymore.

One comment on cold air intakes - vehicles with MAF sensors are particularly sensitive to how air goes over them. If you force air over a MAF sensor on the highway, the MAF tends to overcompensate and move up to higher load table in ecu and inject more fuel than is actually required for that load condition. I've seen drops on a GT time every time with any time of cold air intake that forced air over MAF. On really effective intakes, there was actually an accompanied drop in power as the vehicle ran too rich.

If you are going to do cold air on MAF sensor vehicle, I would put the intake 90 degrees to the air flow so as to not change air going over sensor.

I don't think low restriction is the only thing that Honda was aiming for, but my thinking goes into wave theory, length of intake track, etc.. gives me something to try, more than time to get into.

To make generalizations one of the things common among commercially-available cold air intakes is that they replace the stock air filter box and short hose to the throttle body with a long tube placing a reusable filter near the front of the vehicle and somehow duct the stagnant air from the nose to this filter.

The "wave theory" brought up by whatthe could more than explain how such a setup would improve fuel economy. By using a longer intake duct you are actually tuning the intake to improve volumetric efficiency at a lower engine speed. Engines do not pull air at steady flow but rather in pulses as each cylinder fills only once every two revolutions and no two cylinders fill in unison. CAIs often produce a sound because they eliminate a resonant chamber (the air box) and replace it with an organ pipe (the tube) thereby allowing that unsteady flow pulse to resonate and produce sound. Since sound is an alternation of positive and negative sound pressures you can acoustically tune your engine to shift the torque curve to a lower engine speed. When it is in tune the positive air pressure pulse will continue past the throttle and hit the open intake valve improving port velocity (increasing swirl and chamber turbulence, improving fuel burn and reducing knock tendency). The acoustic pressure pulse induced by the unsteady intake flow will likely exceed any "ram" pressure seen at normal highway speeds.

If the torque curve were improved VERY low in the engine speed range, below 2000 rpm, this could very conceivably improve fuel economy by allowing more high-load operation without lugging or allowing earlier upshifts. Shifting torque to a lower speed could shift a BSFC iso-efficiency island lower as well. I envision improving ultra-low speed torque (and efficiency) improving hypermiling by allowing a shorter-duration higher-load pulse followed by an EOC, effectively decreasing the percentage of the time the engine is on and under load.

As much as hypermiling depends on DIY and testing to compare I'm confused by the overt hostility to a mod just because it is perceived as a "performance" mod for racer-types. I tend to think most people's perceptions are wrong and would rather see data. If someone could do a good a-b-a on any mod and prove a FE improvement I'm all for it but debating the merits in the absence of data using only preconceived notions or dismissing an improvement because it's negligible (it's *still* an improvement) seems like a waste.

Great post. I couldn't have summed it up that well. Cylinder filling and length of intake duct were my thoughts exactly. A longer pipe should lower the rpm that this theoretical improved filling occurs at.

The question of do you want a 2, 3, 4, or 5 foot pipe on the end for your car should find it's own answers on a forum like this. I'll try different lengths just to see what works.

I couldn't agree more with you on this as well. It seems all too often that you come across a post on a car forum where the poster says 'that sucks' without a list of reasons or data to show why.

IMO, CAI will hurt you. A tuned intake system could help you (some?), but only at a a very limited rpm/load range. More applicable to stationary engines driving load controlled generators at fixed rpm.

Low rpm is not an all good thing either - piston speeds are lower so the conversion of heat into movement is less efficient.

Acoustic effects significant to FE lie between the throttle valve and the intake valves. Nothing upstream of the throttle will change the acoustic tuning at these part loads.

Keep you air filter reasonably clean and you'll do fine, unless you want high RPM power. FE calls for limited amounts of air so efforts spent tweaking out a small pressure drop are most definitely spent elsewhere.

It goes without saying a-b-a controlled experiments, especially with different lengths of pipe to test the applicability of Mech's wave theory, would be far and away more conclusive and useful than a forum theoretical discussion. Keep us posted, whatthe. Until then we don't have any.

Secondly, I'm going to do something dumb and defend myself against these oblique attacks on my character, but I don't understand why this has to be personal. "Overt hostility?" I think not. I do not care whether CAI's are performance mods, but that is what they are designed for. So when someone comes by and says "btw, they increase fuel economy too, here's my hunch as evidence" a little red flag goes up in my head. Now Mech has finally presented a theoretical explanation, good, lets test it!

Finally there is no such thing as a negligible improvement, it either offsets the cost of installation, labor, and additional noise or it doesn't.

I guess, whatthe, my list of reasons for saying "that sucks" is no explanation towards how its possible (until Mech's post), no data to the contrary, and no adoption from the factory (except in sports cars). Manufacturers take great pains to tune their intakes (albeit mostly for noise reduction), and if CAI's were worth it they'd be everywhere. Again, sorry this is personal, but it seems all too often that you come across a post on a car forum where the poster says 'this is magic' without a list of reasons or data to show why.

Stock fuel cut on my GT is 7500rpms. Max FE for me is going to be below 4000rpms and if I'm hypermiling I should theoretically never see above 4000 again. Therefore, my factory intake is poorly tuned for the 750-4000rpm range and it is an area worth investigation. Although, I will say that I do agree that CAI is not necessarilly the way.

Why do you say that acoustic tuning will not be effected at part load? As I see it, the air is still pulsing even past the throttle valve. If you go home and stick an 8 foot section of pipe on your intake, go for a drive, and tell me that it didn't make a difference at part throttle.... I will be incredibly surprised. I have an exhaust/intake theory book that has a few graphs showing the effects of cylinder pressure/filling against valve opening for a few different lengths of intake. This length of pipe was placed before the "carburetor/intake manifold" (older book).

From an incredibly limited experience stand-point, and a premature update for Vanner, I put a 6-7 foot length on my GT yesterday, put the wideband on, and went for a drive today. The pipe is longer than the theoretical values I was thinking of, but I used some old intercooler pipes and common sense says it's easier to make it shorter than longer later. There have been some interesting changes that I can better get into after a tank of gas.

Some people will never be convinced no matter how overwhelming the evidence. Oh well.
http://www.karlsnet.com/mopar/ramair.shtml

Tuning upstream of the throttle valve will change the acoustic signature (sound levels) apparent to the driver and outside environment, yes. Car makers add Helmholtz resonators to the intake boxes to quiet certain frequencies that would sound objectionable to the driver.

But those effects are lost on the other side of the throttle valve, inside the manifold. Acoustics there, which would cause local pressure wave optimizations right at the intake valve (for improved volumetric efficiency) are almost entirely (>90%) caused by reflections between the throttle plate itself and the various parts inside the manifold and intake ports. The throttle valve is still more than 50% closed at those operating points where we run for best FE, so that plate is a HUGE chamber end reflector for acoustic waves inside and outside the manifold.

Now, open the throttle valve and yes, the entire intake system becomes important. A plate at 90 degrees to the flow will have a minor acoustic impact. Racers and those looking for wide open or no, (i.e. diesel) throttle operation should look at the impact of the whole system for tuning effects.

A bit off topic, but for part throttle FE I think we'd be better off looking at a tuned exhaust system. That's always "wide open" and adjusting its length for constructive interference acoustics at the exhaust valve (where constructive means improved breathing) will work at ALL throttle openings. With a better exhaust flow you ought to reduce the total engine friction, but overdoing it could cause some of the incoming intake charge to be pulled right out of the exhaust valve. Reducing cam overlap could help optimize that.

I agree, either tune for resonance from the throttle downstream or work on the exhaust. Possibly something could be done with rubber diaphragms instead of long pipes (think drum vs organ pipe).

75% or so throttle is best for acceleration, but we don't do much of that and so are most often at less than 20% (ie, mostly closed).

Correct. As another F body guy I can attest to this, I have seen dyno sheets. The widely varying ratings for different LS1 engined cars (Z28/Trans Am, SS/WS6, Corvette) are just marketing, not reality. All LS1 powered cars made very similar power.

Manufacturers have also used Helmholtz resonators for wave ram effect at low rpm (diesel apps).

Yes, the majority of benefits are going to come elsewhere, however the air still enters at the air filter at all rpms and throttle conditions... so, perhaps it's the wrong view to consider it a more crushed or disturbed "slinky", but air still has to come from point A and slinky it's way back to end up at point B (at least in my mind and not accounting for inertia effects, etc).

I swapped a 1.8L mazda BP into an MX3 years ago and I recall there being an H-box inline with the flapper MAF (most of the boxes seem to be placed after filter, off to side, or whatever). On that particular car, even if it 'shouldn't' have, torque output decreased removing the h-box. Mazda was big into their resonance tuning at that time, but perhaps its more likely that it changed something with the MAF or air going through MAF and that was the performance drop I felt at the time.

At any rate, for the Suzuki - the longer pipe definitely reduced some objectionable noise. Also my perception to torque, etc.. changed, but it would be nice to put it back on the dyno to have actual data. The car gained a few more mpg, but this could also have been attributed to changes with my right foot or the MAF.

The big drawback is that just like a CAI, it changed how the air goes through the MAF and thus altered the MAF signal and thus effects results. When I say these MAFs are sensitive, I really mean that they are sensitive. I can take this car from 18:1 lean at part throttle, to 11:1 rich at anything over 10-20% throttle just by changing pipe diameters, in front of and behind the MAF.

I datalogged a few of the runs with the wideband against tps and rpm for future reference. This also alerted me that this car is going too rich too early and of some other issues. Going to fix part of those issues for the next tank.

This is just more a comment that some of these tweaks really will be vehicle specific. Like I say, CAI likely will cause problems on a hot-wire MAF type vehicle just because of the design of the sensors. If the ECU doesn't compensate well enough, you could see very little or no performance increase, and less mpg.

If you have a Honda or some other commonly MAP sensor based vehicle... you may want to try cramming as much air down the throat as you can to see what results you can obtain.

I took a rather stupid approach and used a 4" dryer vent from my air filter, up the side of the engine compartment and dropped it out into the grille. It looks dumb, but it seems to help. I noticed a 2.4 mpg gain, but that could have just been me, as I am new to this....

I don't think it's dumb at all... the air isn't pressurized and it gets it from point A to point B... grassroots is good!