Write-Up: Building a Custom PVC Fenderwell Intake

Here's how I built my 4" FWI. I'd been running a "warm air" intake previously, having jammed my 9" by 4" ID cone filter into the riviera's stock intake tube. It fit perfectly and demanded little effort, but with a 3.4" pulley and a cam on the way, I thought it was time to try something new.

Here's the finished result!


On startup, it makes a mean suction sound. Bye bye helmholtz resonator! Stomp on the gas, and the SC's wail is quite noticeable. The filter is fairly isolated from roadgrime and I have had no issues with it sucking up water or debris, but I have not driven through very deep standing water. Throttle response is better than stock and it pulls better all the way to the redline.

Here's what you'll need to make a similar setup

1 9" x 4" inlet diameter cone filter
1 4" to 3" rubber reducer (ideally you should use a silicone reducer. They aren't that much more expensive)
1 weatherproof rubber roof flashing, 4"
2 foot section of 4" PVC pipe (sewer pipe... larger ID than black ABS)
1 90 deg 4" PVC male-female elbow (NOT the sharp bend kind)
1 45 deg 4" PVC elbow
1 45 deg 4" PVC male-female elbow
your tools

[img]http://carphotos.cardomain.com/ride_images/2/4086/4341/22714670019_large.jpg/img]


The cone filter sits in the fenderwell area, fore of the wheelwell. I used a 9" cone filter with a 4" inlet duct, but it's a very tight fit. It might be adviseable to go with a 7" S&B powerstack filter. I already had the 9"x4", so I wasn't about to go spend more of my hard earned money on another damn filter.

See that black metal bracket? that has to come off to wedge the filter in there, and note how the horn gets in the way.

By the way, a hint for anyone who needs to pull out or reinstall the balck plastic fasteners that litter the plastic wheelwell, airdam etc.: the pin is made of two partspull out the central pin, and the outer pin will be easily removed. When reinstalling, place the outer pin and insert the inner pin.

[img]http://carphotos.cardomain.com/ride_images/2/4086/4341/22714670021_large.jpg/img]
This 45 deg male-female PVC elbow has a round, flat protusion on it. It just so happens to be the exact size of the IAT sensor. Drill a hole in it and use a rotary tool to enlarge the hole to the shape of the sensor's housing (it has prongs on it) only slightly smaller. It should pop right in and be snug.

Keep in mind the IAT sensor's harness wire's are really short. You basically have to put them in the same general area as I did.



I attached the filter to a 90 deg male-female PVC elbow. The male end goes into the filter. Use a hairdryer to soften the filter's collar and use some lube on the male end of the PVC pipe. It will fit with some effort, as they both have the same outside diameter.
I used a weatherproof roof flashing (cut to the shape I wanted) to keep the engine bay's heat out of the filter. You'll have to enlarge the existing hole in the fenderwell, wedge the attached filter and elbow and persuade it to fit through the flashing.

^towards front of car^


Assemble the pipes like in the pics. it will be snug. The 45 deg male-female (with the IAT sensor) goes into the reducer.



Afterthoughts: The 9" filter is a little snug. If I had to buy a filter (I already had the 9" from a previous car) I'd probably now go with a 7" S&B powerstack cone filter, which has a 2nd recessed cone in the top section of the cone, effectively increasing the filter area.

Very nice write-up!

You know, if that horn is getting in the way, you can just remove it. There's another one in the other fender that's quite loud by itself.

Do not use to small of a filter. gnttype.org has the following calculations, provided by k&n. Use the them to figure out what size filter you need.

1. Square inches of filter required for a motor = CID x Maximum RPM / 20839

2. CFM required for a 4 stroke motor = CID x Maximum RPM / 3456

3. CFM required for a supercharged motor = Pounds of Boost / 14.7

Add 1.0 to this answer. This relates to #2

Example: (CID x maximum RPM x #3 ) / 3456


CFM Formulas for Filters

* Round: Diameter x Height x 6 x 3.14
* Flat Panel: Length x Width x 6
* Universal Round Taper: (Base + Top) / 2 = A
Take A x Length x 6 x 3.14
* Universal Round Straight: Diameter x Length x 6 x 3.14

OK THe formula makes my head hurt ...I'm looking at an S&B Inverted Power Stack 4" ID x 6" (5.25" DIA)...Is that what I want???

CFM required for the series II SC riviera: 752.70 CFM

Pounds of Boost / 14.7 = 12/14.7 = 0.82
0.82 + 1 = 1.82

(CID x maximum RPM x 1.82 ) / 3456 = ( 231 * 6200 * 1.82)/3456 = 752.70 CFM

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Concerning the S&B, I happen to have a 6" S&B with a 3.75" ID, which I have calculated to flow 740 CFM using the provided formula, which I would deem adequate.

The powerstack filter is essentially 2 cones, so just use the "universal round taper" formula twice: once for the outer portion and once for the inner portion. If you want to spare yourself the hassle of calculating it, it will be fine for your application.

This looks nice, well done.I like the PVC, you know its not going anywhere. I also like how you used 4in diameter.

I have a similar setup with a 7inch cone. I removed the horn (Riv has a second in the other fender). And used this used 4inch rubber hose.

hmm did u notice a difference in power from the FWI compareds to the so called WARM AIR INTAKE>???

The "warm air" intake is an appropriate name for the short ram. In supercharged engines, the intake air temps makes a noticeable difference in engine output and level of KR. Have you ever noticed how much faster your car is on a cool day?

Furthermore, warm air intakes can actually damage your SC and engine. Here's some info from Kenne Bell, makers of SC kits for Mustang Cobras:

"It is, of course, your decision if you choose for your engine to suck in this hot underhood air with one of these over the counter or "custom" kits. However, these things are not good for our superchargers and we not only don't recommend them, we are warning against the use of them. Look at the facts. 10° of hotter air is equivalent to 1 psi of boost.That means the difference between the fenderwell ambient 70° system and the hot underhood air temp can be an amazing 130° (200°-70°=130°) hotter. That 130° equates to about 13 psi of additional boost (13x10°=130°). So, you thought your engine was only seeing the increased temperature of 100° from 10 psi boost (10x10°=100°). Wrong. It's 100°+130° or 230° plus the ambient. That's the air temp of 23 psi boost! Surprised? Are you getting the picture yet?

The Kenne Bell supercharger - or any supercharger - doesn't like another 130° of air temp that is the fault of someone else's product. Neither does your engine. As the old saying goes, "Don't make your problem my problem." Don't make those "cool air" kit problems Kenne Bell problems. We've had our fill of these things. Lose those lame excuses for an inlet system. Our warranty is void if using one - and we can tell if you did. We apologize for our frank unwavering approach, but the many warnings throughout our literature has failed to curb their use with our supercharger kits - and caused Kenne Bell some expensive warranties.Try sending your supercharger repair bill to one of these "hot air" kit manufacturers and tell them their "hot air" system killed your supercharger. Are these underhood filter kits any less liable than: 1. Tires that split or separate, 2. Wires that catch fire, 3. Sand polluted oil, 4. Spark plug tips that fall off. I think not.There's no warning in the products.They are most certainly detrimental to engine performance. If ANYONE disagrees, get a magazine writer and let's do the tests.

WARNING: It's an accepted known fact that any engine makes more power on cold air than hot air. Use of this product negatively alters the "cool air" design of the stock OEM inlet system and instead inhales underhood "hot air." This device reduces air density (HP and torque), increases the engines tendency to knock/detonate/ping which can result in lost power and potential engine damage, especially with superchargers or turbos. Not recommended for Kenne Bell supercharger kits. Voids warranty.

Read the full scoop here: http://www.kennebell.net/techinfo/general-info/HotAirWARNING.pdf

UH OH i hope i'll be fine till may or JUne>>>??? ahhh so u really think with my SHORT RAM intake that when i go to the FWI i'll notice a pretty decent increase?

If you had a scanner, and could monitor IAT (intake air temp) with your short ram, you'd probably build a CAI or FWI before May. We don't just build these things because they look pretty.

AA wrote:

hmmmmmmmm how much ???????? realistically like 10-15 hp or what???????

I've never dyno'd, but going from a gutted OEM air box w/ K&N to a FWI with cone showed the following differences with 3.4" pulley & 1:9:1 rockers:

OEM IAT @ idle: 81-82ºF @ 55ºF
FWI IAT @ idle: 73-77ºF @ 61ºF

OEM IAT @ WOT, 70 mph: 78-80ºF @ 55ºF
FWI IAT @ WOT, 70 mph: 81-87ºF @ 61ºF

OEM Max Mass Air Flow: 32.7 lb/min @ 55ºF
FWI Max Mass Air Flow: 31.5 lb/min @ 61ºF

OEM Max Boost: 10.8 PSI @ 55ºF
FWI Max Boost: 12.2 PSI @ 61ºF

OEM 0-60 mph best: 6.85 secs @55ºF
OEM 0-60 mph best: 6.80 secs @61ºF

Note that FWI testing was done in 6º warmer ambient temps. Data is a result of 3 runs for each intake design.

I noticed the gain from the cone filter stays constant with the FWI. With the warm air intake, the power increase lessened after running the car for a while.

On page 248 of the latest jegs catalog,there is a picture of a modular 4" intake system that looks good for our applications. check it out!

Please post their part number, I don't hold onto their catalogs very long.

ok. 41" flex intake tube(not the dryer kind ,but a true smooth flex kind) #865-9751. then there are various aluminum straighs,and bends,and silicone rings. it looks like i might get the flex ducting. i allready have a kn filter that would fit perfectly. take a look. its cool looking set up

update on this jegs tube. went to the spectre web site,and yes its just a bullshit corrugated type of tube....sorry,i got my hopes up

Just bought some pvc myself and painted it black. Should have it built tomorrow. thanks for the write up!

Update for me: apparently this write up doesn't work for a 96 , as the throttle body is much closer to the coolant tank and the elbow doesnt not clear it. I think im just gonna use some pvc bends mounted to the stock intake tube and route that into the fender , but not till monday.

im kind of curious about clearance issues, i noticed you said the filter was a tight fit but what about as far as the pipe and the coolant tank specifically. also i know our motors rock pretty good shifting gears and the like, is this a concern? also have you ever had your reducer to your throttle body get wrenched on and popped loose? i expect you would have said ne thing you ran into like that but just double checking cause if its all good for your i will definatly do this asap. currently i am running a "warm air" intake for about 30,000 miles and after reading that little article i want it GONE. lemme know, thanks.

i finally got around to doing this much anticipated mod. several trips to the hardware store and she's all done!
i used a 3.5"-4" coupler on the TB, then 4" PCV pieces like Jason used. i couldnt find a roof flashing to fit the pvc so i didnt use one. i also painted all the white pvc black with black caliper paint to make it look more...uh attractive. i used a S&B cone 7" filter part# R0851 and it fits just fine with no room to spare.
i dont really feel that much of a difference compared to the gutted box+K&N+ modified box. the real difference is in the sound it makes i find myself dropping it into N and revving it up more now
anyways here are some pic of my setup.
oh, and i havent had a chance to drill a hole for the IAT yet, so it is tucked away next to the pipe under some wires. beside not having perfect A/C will that effect performance? any reason i cant just leave it out?

...ok serverimg isnt working right now, so i'll post them up later today.

Coolness MR. RIVIERA

thanks.

Nice! The paint is a great touch.

You really should reinstall the IAT sensor, or at least plug it in, even if it's not in the tube. I think it can effect the commanded timing.

The improvements made by FWI are not felt in the seat, but scanning airflow and boost numbers show a slight increase in upper RPMs, more with added mods. Take it for a sprint with the scanner, maybe you've shaved a tenth or so?

it is pluged in, just not in the flow of incoming air.
i plan on going to the track again soon, and a plog, stage 1 TB, and TUNER is in my near list of mods. goal of 13.9 come winter time and full track prep. 14.2 w/street weight/gas.