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Fogg Airbox Mod Notes (LONG) (archive)

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Posted by Mario on October 25, 2000 at 09:25:50:

Did the Fogg mod on my '97 1.9 late last night. Initially wanted to do it over the weekend but my enthusiasm got the better of me.

Took me between 1.5 - 2 hours.

Here are some tips that helped me make the project go faster:
Have all the parts available before you start.

From what I have seen with regards to duct, get it from Pep Boys. Most of my Flemington, NJ based auto supply stores did not have that 4" hose. Pep boys are sure to have it, also got the hose clmaps there.
All for less than $15

At the Home Depot I got everything except the rodent screen. Well they had some but it was in 24" x 38" rolls. Just a bit too much for this application. Will upgrade later.
The 5" to 4" adapter was like $2.50

I did not have a 4" hole saw, matching arbor nor a hot glue gun so I had to buy those items. Get the biggest hot glue gun you can find. A nice thick bead does wonders for filling gaps small or large. A small glue gun = small bead = significantly more difficult to fill gaps with.
Figure $25 for the hole saw/arbor combo and another $20 for the glue gun and glue sticks.

Unless you have all the tools, actual parts expenditure, like Shawn stated is about $20.

As a result of recent upgrades, I have spent a lot of time under the hood of my car in the last few weeks. Knowing where parts and systems are under the hood and what they look like is 75% of the battle. Taking the stuff out is the other 25%.

Pretty much followed Shawns instructions but I did deviate somewhat.

Disassembling the air intake system:

Removed all the covers as instructed, but detached the hose/elbow combo from the intake directlt at the intake. This is a clip on the stock hose connector elbow that you press in then lift the hose/elbow assembly up.

This clears the way to remove the airbox.

After the box was out I removed the elbow from the air intake duct and is small.

I initially tried to remove the hose at the elbow after I took the cover off but found it difficult due to space.

The next step is a partial point of no return! If you get cold feet, the airbox can still be reinstalled without the sound deadening material. The only consequence may be increased intake noise.

With the airbox out came the task of removing the foam and retaining grid. There is a clip right over a partial duct at the airbox entry hole that needs to be pressed in and lifted up. This will loosen and partially remove just the corner by the intake.

After getting that corner loose and fumbling with the rest for a few minutes trying to take it out gently (The plastic is very brittle so no matter how you handle the entrails of the box, the plastic will snap or crack and quite possibly pinch or cut you)
I decided just to rip it out and throw it away. Took less time anyway and saved my hands. I would use thin gloves for this part next time around.

If you get cold feet, at this point, you may have to go back to the parts you just took out and reinstall just the small intake duct. It may or may not be attached to the grid so you may have to cut it loose. Forget the grid, it will be broken. The foam will not stay in place without the grid.

Drilling the hole: Once you are committed!

I used my 12V drill to cut the hole. I used no jigs, but this is what worked for me. However I placed the box between my knees while on the floor on my knees. I held the drill with my right hand and staedied the box with my left.

For me the key was to get a "rolling start". This means that the saw should be turning at full speed before you place it on the marked area to be cut (If you place the saw on the plastic and start to go at it, it will wander) It will bounce and skip untill so you have to hold it steady, but a groove slowly forms on the airbox.

Getting a "pilot" groove may take several attempts. Once the groove is deep, large enough and somehat round you can exert more pressure on the drill. The saw will set and do its job, cutting through the box wall, once the cut is through, you will encounter resistance on the inside of the box and the saw may seize. That resistnace is caused by structural ribs on the inside of the box.

Lift the saw slightly and go at it again untill the saw goes all the way through. Beware that there will be a LOT of plastic shave dust, crumbs.

Fitting the new gateway to power:

After the hole is in, take the 4" duct and place it in the hole. it will not fit. Mark the areas that are impeding the insertion of the duct. Use a circular sanding/grinding attachment for your drill to remove the excess material or use a round file.

I used a round file to remove the excess material. Takes a bit longer but you have definately more control. File and fit, file and fit untill the duct fits in there snugly from the outside in.

You may or may not have this following problem: When the time comes to place the new duct in the box from the inside out, you may notice that it will not go through. Chances are that the "rib or shoulder" of the new duct gets hung up on some molded in structural plastic box on the bottom of the airbox that was an attachment point/support for the stock internal duct.
If this is the case will have to snip away at gradually in order to get the duct to go through the hole. Again, it will be a snip and test fit untill it really fits good procedure.

After all the cutting is done, clean the shavings out of the box. I washed mine out.

The next step is to glue the new duct in and this is where a big ass glus gun is great. Chances are you will have some gaps between the new duct and the housing. A nice thick glue bead does wonders for gaps.

While you are re-installing the lower airbox make sure that when you run the duct along the side of the radiator and between the power steering reservoir, that the majority of the duct has been pulled down. If you dont, the duct will bunch up by the power steering pump and you will have difficulty in properly fitting the lower half of the airbox into its space. If you dont catch it here, it will be readily apparent when all the covers are on again. It just wont look right and you will have clearance problems. If you do, check the hose routing.

The rest of the modification is just like Shwan described in his instructions.

Make sure you use a 4" dia hole saw. The hole will be 1/16" to 1/8"smaller than the duct and will consequesntly require filling. It is much easier to take material away from a smaller hole than it is to ad material to a larger hole.

How does it feel, sound?
(Please note that my 97 1.9 has a supersprint oval tip exhaust.)

Air intake noise is louder but not significantly noticeable. The car feels quicker in general. Motor revs faster across the whole range, but the magic really happens after 3K - 4K RPMs. After that range a stock Z3 1.9 torque range will flatten and fizzle. With the fogg mod, it keeps on pulling all the way to redline. There now is torque where there was none before and you can feel it. It is a miracle.

Thank you Shawn for developing this modification!


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