F I air flow upgrade

[bowlsby]

I have a stock 74 2.0 with D-jet FI intact...its works very well. But I've seen the K&N air filters that are reputed to give minor boost to airflow...not impressed enough to purchase.

Has anyone ever tried to attach an extension tube off the throttle body and attach a cone filter...hooking up the various vacuum connections to the extension tube? Does it result in any improved performance, if so how?

Would the FI need tweaking under this set-up and if so how?

[agent914]

Why yes I have. I used a K&N for a 95 chevy truck. Its huge! I ran a 2"x2" pvc pipe off the throttle body into a (2" into 3") adapter then a 4" long piece of 3" pipe into the K&N. Wow what a mouth full. I then glued a barbed fitting the matching od size of the vacuum line id into the 3" pvc pipe. It seemed to work fine, execpt the vacuum line should really be going into the filter element first not the intake pipe.
It is also really loud for an intake. My friends honestly said they could hear my intake over my exhaust. And I was running a dual monza exhaust. Minimal torque increase an a major boost on impression ratio. Over all a good way you engine breaths freely.
---Agent914---

[Jim T]

What makes you think that the airfilter is the bottleneck in the intake/exhaust system? If the stock air filter set up flows more than enough air that the tiny throttle body requires, modifying the air filteration system will get you nothing.

If HP could be improved by simply having a larger airbox, or a freer flowing airfilter, I'd say that the engineers at Porsches are not very smart.

[mike mueller]

Jim,
I don't think it's an issue of the engineers being smart or not, they had certain design and cost objectives to meet, all factory cars have some comprimises in one area or another due to cost, noise (which the intake mods fall into)etc....
I belive on the 964RS or 993RS the factory offered a bigger airbox with "holes" in it
for increased and less restrictive flow.

Jeff, if you do make up some sort of new intake, make sure the filter will be shielded from water, also, watch where you place the filter so that is would get more cool air verses hot air rising off of the engine.

------------------
Mike Mueller
Antioch, CA
1970 1.8
http://www.pelicanparts.com/MotorCity/mmueller/personal.html

[bowlsby]

Good points so far...

We've all heard that more air means more power...I was toying with the idea of boring out the throttle body and had considered that the air filter and housing (although its reputed that the stock one is very free flowing) might be made more efficient as well.

Agent 914: Any significant power boost in your mods?

[iustasail]

The best thing to do is clean out your engine compartment and remove the air filter box and drive the car with no air filter( not for long though a big chunk of something could ruin your day), If you think it makes a difference and you like the wooosshhh of the intake air then go through the effort of fabricating a "free flow" type intake.

Remember, a "free flow" intake only works if the heads have been flowed and /or ported and polished and the exhaust system is of a tuned nature. More HP can only be had if all three work together and the engine is set up to take advantage of the less restricted air ie... big webbers and a cam with a lot of overlap. it won't idle worth a dam but at high RPM the HP will be impressive

Your D-Jet is the exact opposite! It's a good system for reliability, clean idle and decent convent power(if maintained correctly).

The more you try to modify the D-jet setup for more power the less reliability you will have and the potential gains are small!

good luck):

[oredith]

i think it was steve iverson (sp?) and i that had the "home depot special" intakes.. 4" PVC to a reducer that fit over the throttle body. i did have a problem with the intake sucking in water when i rained.. so now there's an aluminum shield over the filter. i've never tested the sound of the car without the headers, but from what i've been told.. people can hear my car from about 12 car lengths away while on the freeway.. not a good thing when you suddenly spot a cop, even if he's just sitting at the side of the freeway.. i suddenly catch myself going to "coast mode".. and then i realize that the deep burbly sound from the headers doesn't help..

performance?.. i don't know.. it was kinda put in at the same time as the headers.. so i attribute most of the gain to the headers.. but the motor definitely spools faster and launches better.

[Jim T]

Mike, I agree with you, I am just asking if there is any reason to believe that the airbox is the restriction on a 914. Is it possible? Yes. Likely? I doubt it, in this case.

More air DOES NOT NECESSARILY MEAN MORE POWER! That's the K&N myth. It does not matter if the K&N flows a billion times more air than the stock filter, *if the stock filter already is capable of flowing more air than the car can use*. Which is apparently the case in 99% of cars.

The 914 was made a long time ago, when I doubt there were little if any restrictions on intake noise. If the airbox were choking the car, I doubt there would have been any legal restriction with simply fitting a bigger airbox, with a larger opening! The 914 does not suck air like a 300 hp 911, which could make some significant intake noise.

So I guess my point is this: I doubt the airbox and filter is the point of restriction in a 914, and that the stock system provides more air than the engine can use. This just makes sense. Until it is *proven* otherwise (which I am not saying is impossible), I would not waste my time fabricating a new intake, unless you are just intereted in having a noiser car (as the Honda Krew knows, noise=power!).

On the other hand, if you think it works, I guess thats just as good as it working. Just ask all the suckers that bought the Zuc Powerflow for their 911s. These people all raved about the huge power increase that they *definately* could feel. Until excellence magazine did their own dyno tests and found that the Powerflow actually DECREASED power!

[This message has been edited by Jim T (edited 04-20-2000).]

[bowlsby]

Thanks everyone..especially Jim T.

I'll stick with the stock setup...the car is noisy enough...I don't need to draw attention in that way.

[Germain]

Okay, Ill throw my take on all this

If I can't get 200 h.p. out of these Type 4's, then um... time for an engine swap

More seriously, the more air/fuel you can deliver for the spark plug to fire, the more power you get. Now like everyone is saying, it a combination of being able to get it in and get it out and how much of it there is (it being gas/air).

I've thought about this alot, and if your looking to get alot more power from these engines, I would say your out of luck. The heat that would be generated would almost be unmeasureable with a 2.0l putting out 200 horses. (Yes its a dream of mine to run a 200h.p. power plant under the old bonnet). So I would loose the engine and do a swap, but thats me, and you would need to make up your own mind.

Hmm, I wonder now if I really had a point to all this. Well if you find this a rambleing, sorry about that, and if ya think I have some useful advise in here - see a doctor

[Jim T]

Nah, 200 hp from a 2.0 is nothing!

You can get 240 hp (smooth, reliable hp) from a 2.0, just stick a Honda S2000 engine in there!

How far we've come with intake and fuel delivery in the last 30 years!

[Germain]

doh!

I meant from out Type 4 2.0L engines. Not todays engines...

And with your comment, I rest my case on the engine swap idea

[turbo6bar]

Interestingly, Ben Watson states that bigger air filters like the K&N may help engines, despite the fact there may be no restriction in the stock setup. His reasoning is as such. When you crack open the throttle, there is an increase in airflow. The increase in airflow is dependent on the pressure differential and restriction. If the stock filter provides 225 CFM @ xx inches of mercury and the K&N flows 345 CFm @ xx inches of mercury, the engine with K&N will increase flow quicker, generating greater torque and more horsepower. At steady throttle, though, this is just a moot point.

Derived from "How to Build & Modify Intake & Exhaust Systems," a decent book for the relative newbie, but not very in depth like I would want.

So... for you drag racing 914 enthusiasts, the aftermarket filter may provide that extra grunt needed to smoke that 996 Turbo.

Young and stupid

[Jim T]

Again, that only assumes that your engine can USE the extra air. In your example, for example, if the stock air filter can flow a max of 225 CFM, but the most that the engine can intake, combust and expell, under any circumstance (i.e. even with NO air filter) is 200 CFM, then having an airfilter than flows 345 CFM will not make any difference.

Unless you are saying that in the Watson example, the stock air filter, on the subject car flowed a measured 225 CFM into the engine, and the K&N flowed 345 CFM on that same engine. If that is the case, I would agree the K&N will help the engine produce more power. But if that's the case, the first part of your statement is wrong, because if that's the case, the stock air filter IS a restriction in the system. And, we are back where we started: Is the stock filter a restriction in the system? Again, I doubt it!

[This message has been edited by Jim T (edited 04-21-2000).]

[turbo6bar]

Jim, sorry if my post is confusing. What I am trying to point out is that airflow will increase quicker with a larger air filter. I am IN NO WAY stating that larger air filters always generate more HP.

Watson states: "The more open and free-flowing the intake system is both upstream and downstream of the throttle plates the faster and air mass will build, and therefore, the faster torque will build."

The key word in the above sentence is "faster." Torque builds faster.

He goes on to state that airflow of the filter should be at least 15-20 times the displacement of a single cylinder. Don't get me wrong. I think the K&N is a hyped up filter, but there is some science behind it. That science may be worth .2 HP. It may be worth .002 HP. I don't know. I certainly concur with your statements. We are basically in agreement.

I just like to pick fights.

Young and stupid

[turbo2.0]

An engine is basically an air pump. The more air it pumps the more power it makes, assuming the fuel is added in the correct proportions. The stock air cleaner system flows more than enough air, up to a point. As the rpm's rise, so does the need for less restriction. The 914 engine is designed to provide a flat torque curve, while sacrificing high end horsepower. This makes it more streetable, but slower in a drag race or on top end. If someone wanted to give up the smooth torque of this motor, They need to make it flow more air. The first and largest bottle neck is the cam. It falls on it's face around 5500 to 6000 rpm. The second would be the intake runners/plenum. Changing to carbs or a hand made intake system would take care of this. Having done all of that, the stock air cleaner would be the restriction and would need to be changed. If you have a stock cam and a stock intake manifold system, your stock air cleaner flows more that enough for the motor. Slight increases may be obtainable in throttle response, but not enough to justify the change. Notice I have made reference to air cleaners, not filters. The air cleaner is adequate, but a free flowing filter that fits into the stock cleaner is a good thing, if you can find one.
Having said all that, I run a K&N air filter with a relatively stock cam, but I've also got a turbo forcing the air in, so I need all the air I can get into the turbo.
As far as a 200hp motor generating too much heat, I disagree, with an explaination:
A stock motor is designed to run lean so it can get good gas mileage and pass smog requirements. Lean is hot. Period.
Making a big horsepower motor is do-able, as long as you are willing to run the motor rich on the top end. The rich mixture will dramatically reduce the combustion temperatures, and help to control the amount of heat generated. The drawback? Terrible gas mileage and air pollution. Also, a 200 hp motor will probably not last anywhere near 100,000 miles because it will have to spin very fast, and the stresses on it will take their toll.
Summary: a 120 hp motor running very lean (like a 75 with smog stuff installed) will run hotter that a 200 hp motor running very rich. Of course, this is all based on my opinions, which I have formed by listening and learning from old farts, by reading, and through trial and error. BTW, I have a 2.0 liter motor that I drive on the street and plan to hit the 200 hp mark on premium pump gas before the end of summer. I am getting close, I just need some better measuring devices (gauges)so I can make the correct changes. I'm too close to the fine line to be making guesses at this point. All I need to do is to control the air/fuel mixture, dial in the timing advance more precisely, and carefully increase the boost.

[Germain]

Okay, why would engines be designed to run lean? That makes no sense to me. Wouldn't they design the engine to burn the correct amount of fuel/air. I can see that dumping extra air into the engine then needed can help get past smog laws by saturating it, but better gas mileage? They could lower the amount of gas that enters the engine and the amount of air equaly and end up with the same gas mileage. For an explosion, proper perporsions of air and fuel need to exist, and only the air and fuel that is properly mixed will burn. If there is extra air there it wil not create a larger explosion, same with if there is too much fuel. As for the smog stuff, I would think they could come up with something better, but I could be wrong.

[JP Noonan]

When I wash my car it is faster. Yes, I'm serious, I'm also smarter and better looking the more beer I drink.

Sorry, just a Friday comment.

I have K&N Filters in all my cars/trucks. On my F-150 Lightning it made the biggest difference but the stock system is very restrictive for noise concerns I guess. I like them on the other cars because they are no maintainence, my family keeps our car for a long time so for us not having to change filters saves money. That and I'm the one doing the maintainence.

IMHO a cold air intake would help more than a K&N. Also there are two major problems with them: 1) Service station steal/throw them away when you have a "tune up", it is important to use the sticker that comes with the filter. 2) People put the cone type ones in a cramp, hot engine compartment. The filter takes in hot air from the fan wash so any improvement in flow is counteracted by the air temp.

[turbo6bar]

Germain asks about lean running engines. Why? Well, I was perusing my environmental engineering textbook from my younger years (actually just a few years ago). Lean running engines were the automaker's attempt to reduce hydrocarbon and carbon monoxide emissions. Lean burn also manages to reduce gas consumption, simple because less fuel is used for a certain amount of motion. However, there is a drawback to such action. As Turbodude pointed out, lean burning engines tend to run hot. They show a loss in performance. The use of lean burn operation also increases NOx emissions. Lean burning operation is simply an action to meet an end. The extra air and fuel you mention are just that, extra air and fuel, but that does not imply that such conditions do not affect running. Lean mixtures are harder to ignite. Rich mixtures improve performance, etc.

[Germain]

It looks like I'm going to need to do some reading on the subject. Sounds weird to me. Well, guess I'm off the the library.