Idea for Replacing Airbox Lid on CIS

[911nut]

I got to thinking the other day about how to get rid of the airbox lid and that little tiny snorkel and make my engine a little more free-breathing. I came up with this:

It's basically a frame that holds the air cleaner to the top of the airbox. The frame is held in place with 2 small bungee cords.

It's only good for fair-weather driving but a roof could be added to it for wet weather.

I made this one from of steel just as a prototype. Next week I'll make another one from aluminum.

[speeder]

If the idea was to reduce intake restriction for performance reasons, it won't do anything because all 911 tuners agree that the only flow restriction on your motor is on the exhaust side. One look at the size of that stock air-filter tells us that. K&N filter actually reduces HP on this motor, according to dyno tests. I do admire your hot-rodding spirit, but that is the wrong end of the pump.

[Jim T]

Originally posted by 911nut
I got to thinking the other day about how to get rid of the airbox lid and that little tiny snorkel and make my engine a little more free-breathing.

What makes you think that removing the "little tiny snorkel" will make your engine more "free-breathing"???

[911nut]

Originally posted by speeder
If the idea was to reduce intake restriction for performance reasons, it won't do anything because all 911 tuners agree that the only flow restriction on your motor is on the exhaust side.

Well, the engine is limited by flow through the stock exhaust, which I've already done away with. Where the restriction is now I'm not sure as many of the "tuners" aren't sure either.

As for the K&N, I hear all sorts of things and see data supporting both points of view. I bought it because the paper filters didn't seal worth a s**t.

Either way I figure it makes sense to try to leverage all of the easy things first before I spend cubic $$$ ripping the engine apart.

[Adam]

What will you do when it rains? Perhaps a perspex/acrylic deflector shield...

[speeder]

Basically you just have to look at the square inch area of stock air-filter/ displacement of engine, (3.0 liter or 181 cubic inches), there ain't no flow problem there. I've seen 400cu.in. V-8's with smaller air filters. (And they ran good). I don't have an engineering degree, others here do, but when it comes to air flow in and out, there is an optimum restriction and it isn't zero. Otherwise all race cars would have NO EXHAUST whatsoever, headers would not exist. Stock exhaust is a little restrictive on our cars, but if you reduce back-pressure too much, you start going backwards in the HP race. You say that you have seen "data supporting both points of view" in regards to K&N filters on 911SC's? I would like to know the source of data showing HP increase over stock, it would contradict (unbiased) dyno testing done by members of this forum.

Finally, I want to repeat that I respect your hot-rodding spirit, it is a big part of what bonds us here and my response is not intended to flame, but some of us are members of the sceptics society around here which I consider a healthy thing. I am constantly on snake-oil patrol(K&N), I DO NOT want to see anyone waste one performance dollar so that some infomercial queen can buy a new cigarette boat or something.

[Neophyte]

I am constantly on snake-oil
patrol(K&N), I DO NOT want to see anyone waste one performance dollar so that some
infomercial queen can buy a new cigarette boat or something.


I so agree!

Well said.

[BlueSkyJaunte]

Actually, once you remove the exhaust restriction, the next bottleneck is downstream of the filter. From the sensor plate south, it's pretty convoluted.

[Doug Zielke]

Bungee Cords??

[speeder]

Blue sky, Thanks, I forgot to mention that: the big restriction on CIS cars IS sensor plate, (as opposed to air cleaner cover), now if someone can just figure out a way to eliminate THAT THING.

[Adam]

In my mind's eye, I see Doug saying "Bungee Cords??" the same way "Blue" Lou Marini says "Chicken Wire??" in the Blues Brothers.

[k9handler]

As a fellow CIS pcar owner, I understand what you are doing and think the idea looks great and pure "Hot Rod". On the other hand I do feel it must be a little more functional for the pcar before it's put in use...until then Pep Boys will be the ones selling them. As for the other's who posted, lay off and give the guy credit for his effort.

[wckrause]

Seems to me that the real bottleneck is those little bitty intake valves, and the small amount of time that the cam allows each one to be open.

[Tony911Z]

He didn't mention this but, I'll bet his intake sounds great when he gets on it now. I saw something like this mod when I was in Germany a few years back-someone had cut most of the stock snorkle away leaving not much more that a frame with a slight scoop.

[Adam]

911nut,

Check out this recent thread about alternatives for the CIS box. When our winter is over (we're Southern Hemisphere), I'll give my idea a try.

Good Luck!

[911nut]

This post was enlightning. It brought to light a big issue that rages in our electronic community.

There's one thing that I already knew: CIS is a magic black box to most of us. No one knows how to modify it (myself included). I assume that is because no one has really tried. Yet, many who hang out on this bb are experts based on the fact that they continually read posts espousing one opinion or another. Only a couple of people actually said "yeah, I tried that too and it didn't work". That was the type of post that I was looking for.

When I was in grad school I was told that the academic community weren't interested in your opinion until you did some actual research and wrote a thesis. It ought to be the same way here too.

To all those guys who actually try stuff out; keep posting and educating us. You have my admiration and respect. To the rest of the "experts"; shut up, read and learn.

[thrown_hammer]

I think it looks good and probably sounds good(with a air sucking noise , like when I used to turn my air cleaner lid upside down on my old V-8 cars ) Can we have the dimensions for that thing. I may try that just for the sound. My Bursch 3M is just TOO quiet.

[k9handler]

Maybe this would work?

[wckrause]

No one knows how to modify it (myself included). I assume that is because no one has really tried.

In my Bosch fuel injection book (Probst) there is a chapter on performance modifications to CIS. Most of the chapter is devoted to lists of things that people have tried. It includes stuff like boring out the throttle body, using the cold start injector for creating a richer mixture at full throttle. I think it even describes using a larger sensor plate (I may have read that elsewhere). None of the modifications listed made more than a 2-3% improvement.

Not to criticize your efforts, but if there was any easy hp gain to be found by modifying the air intake, I think the engineers at Porsche would have found it.

[speeder]

911nut,

You are absolutely right about the scientific method and "contempt prior to investigation". There is one pretty good substitute for actually trying every concievable thing one's self, however, and that would be the experience of others. This was a key factor in many advances of civilisation, the early days of avionics springs to mind.

I based my comments on the experience of some true 911 experts who have done a lot of the heavy-lifting for us in terms of expensive dyno-time, experimentation with every concievable modification, etc. I will reserve the right to be wrong with my opinion on your idea, like I said before I admire your hot-rod mentality, but I just don't believe that stock CIS airbox is restrictive relative to size of motor/valves/etc. The exhaust is another story; what exhaust are you running?