: Air Filter box - more air???

05-05-04, 07:53 PM
'99 Deville
Replacing my air filter, I noticed that the bottom of the filter box sits on top of some other 'container', in which appears to me some sort of aluminum housing of some part or another (ABS pump???) - but the inlet for cold air to get into the filter and then on it's way to the engine doesn't seem to be all that large - and the base of the filter box has a largeish area about 2 by 5 or so that looks ripe for either a nice rectangular hole or a bunch of 1/2" drilled hole, in order to allow more atmosphere into the ol filter.

Would this be 1) a bad idea 2) a good idea , or (my thought, kinda) 3) not really worth the trouble.

I'd always thought that the more cold air you can help get into the engine, the better off it would be, but with all the sensors and adjustments and computer controlled everything, I'm wondering if this relatively minor help would do anything..

Thoughts on this are welcomed...thanks

05-05-04, 11:34 PM
Isn't that aluminum box your PCM module? If so, you want cool air flowing over it to keep it cool or you are in for some really big headaches. Dyno test results that others have posted show about a 5 hp increase at max rpm with a relieved airbox. Hardly worth the effort imho.

05-06-04, 06:29 AM
Yeah, it may be - the box it's in is kinda loose, just wobbles around if you try to lift it out - it's not heavy (it's my brother?... lol). I wasn't planning on trying to reduce the flow over/through it. It just seemed to me that the amount of air flow coming up through there and then in to the air box was not as optimized as it could be. Not that I'm a street racer or anything, and the Deville seems to have a nice bit of pep when I really stand on it, but cars are getting to be like computers - you spend 20 hours tuning the damn things to get an almost immeasurable amount of improvement. Most of my driving is expressway stuff between home and work, very little 'city' driving overall. Thanks for the input, though..

05-06-04, 12:21 PM
The silver box is the PCM and it is designed to get the cooling air flowing over it from the inlet system. It will overheat and fail if not cooled by the induction air stream.

The inlet system is of adequate capacity for most any type of use with the Northstar. Even completely removing the entire system will only deliver about 6-7 HP on an engine dyno and that is correcting for the MAF flow changes and such. Certainly not a seat of the pants improvement. And not really achievable in the car anyway due to hot underhood air.

Many flow modifications to the air inlet system can cause problems with the MAF reading as it IS flow sensitive and is compensated correctly for the production system flow characteristics.

Even if you did make mods to the system and improved air flow/reduced restriction (not all "eyeball" mods work as expected) the improvement potential is small and only at the higher engine speeds...i.e...5500-6500 RPM. Below that range the system easily flows as much air as the engine can flow at WOT. Absolutely no basis for anticipating any fuel economy improvement or claims with an induction system mod. At low engine speeds associated with fuel economy the system is WAY overcapacity for the needs of the engine.

A very important consideration of the induction system that is often overlooked is to keep any water out of the engine. The system is designed to prevent injesting any water into the engine when driving in rain or thru standing water or deep puddles. Any extra holes or vents in the system will seriously detract from the water intrusion prevention....particularily if the added holes or vents are underhood or routed to the fender wells or other underhood areas. Hitting a deep puddle on a dark night in a rain storm can cause the engine compartment to fill with water and pour into any openings in the induction system. High compression engines, especially engines with highly tuned induction systems, are especially sensitive to even the least amount of water intrusion into the engine as they can easily hydrostatically lock and cause total engine destruction.

Aside from the water intrusion issue the induction system is designed for minimum induction noise and roar (that WAAAAAA you heard when you turned the air cleaner lid upside down on your mom's Buick). Punching extra holes in the system will destroy the noise cancelling effects of the system. If you like the induction roar this might be a good thing but to most people it becomes tiresome on a regular basis.

With very little to gain and a lot to loose I would recommend leaving the induction system alone on a daily driver.....

05-06-04, 12:51 PM
BBob, thankx much for a clear and authoritative answer - no alterations were made, as per my gut feeling. With my average speed (as per DIC) hovering at 36MPH over the last 12 months, I didn't REALLY think a "ram-air" system would make much difference for me...I was curious as to what you'd recommend, which is part of the reason for the post. I'd always thought that once we went to EFI and computer controlled fuel mixing and sparking and all, the days of shoving a big ol' tube out your front bumper and duct-taping the other end to your carb were pretty well over.. http://cadillacforums.com/forums/images/smilies/biggrin.gif

I know what it feels like to have your brain picked, so thank you again...


05-06-04, 01:02 PM
Well....it is always good to get cold air to the engine and "ram air" (if it really worked...LOL) is always a good thing. As long as you are ramming water into the engine.

Fuel injection and electronics don't negate the need for cold air. That is why the air ducting to the inlet system goes forward of the engine compartment and picks up outside air. If you look at the displacement of the engine (the air pump) vs. the displacment of the air induction system it is easy to see that at high RPM the engine will be pulling cold air from the outside within milliseconds of reaching WOT/high RPM. The air exchange inside the system happens very fast when the engine is loaded. Other times, at part throttle and light load, hot air is actually good for fuel atomization and complete combustion by creating more of a homogeneous mixture. At high speeds the rapid flow and violent in cylinder motion will atomize the fuel but at low speeds and loads the extra temperature is helpful in atomizing the fuel for complete combustion.

"Ram air" is good for ducting cold (er....cooler...) air to the induction system but few, if any, ram air systems really "ram" any air or creat a positive pressure to the induction system....on production cars, that is. Ram air is virtually ineffective unless the vehicle speeds are really high...so even if the car has a working, effective ram air system it will not produce any additional HP until very high speeds...like over 80 or more..... About the best you can hope for with a good ram air system is a constant supply of cooler air and the ability of the system to self purge itself of hotter under hood air thru natural circulation as the vehicle picks up speed.

So....that big ole tube duct taped to the carb really didn't do THAT much even back then.....LOL. I had one , too, BTW.....

05-07-04, 10:44 AM
Well....it is always good to get cold air to the engine and "ram air" (if it really worked...LOL) is always a good thing. As long as you are ramming water into the engine.

I assume that last line is a typo... ??? http://cadillacforums.com/forums/images/smilies/wink.gif

"Ram air" systems on standard street cars probably do about as much good as those goofy looking spoilers the kids stick on the back of their (FWD!!!) rice-rockets these days.. oh well.. youth..