Cold Air Intake (CAI) vs Fender Well Intake (FWI)

CAI: Cold Air Intake

FWI: Fender Well Intake

One of the great things about our engines using forced induction (supercharging) is that they really benefit from breathing cool air. You will notice as air temperatures drop, your Riviera will seem a little faster. You aren't imagining this; colder air is denser than warmer, so with more air molecules entering the intake, more fuel can be added by the PCM. The result is more power. It can be estimated that for every 10ºF drop in ambient air temperature, our engines gain about 2-5 hp. When you go from 90ºF in the summer to 30ºF in the winter, the difference is more than noticeable.

A cold air intake system is simply an intake that replaces the OEM air box, and goes a step further by better isolating the intake air from the heat produced in the engine bay. There are two basic ways for doing this. 1) Construct a box inside the engine bay using a heat-reflective material to house the air filter. This is commonly called a "CAI". 2) Route the intake far from the engine so that the air filter is located completely outside the heated engine bay. This is commonly called a "FWI". Of course, the major benefit of either type of system is the air coming in to the throttle body is kept cool, thus you get lower IAT (intake air temperatures), which means denser air into the engine, even on warmer days. Another plus is both types of intake will likely flow more air than the OEM box. Unfortunately, there are no manufactured intake products or kits available for the Riviera; if one is desired, it must be custom made.

1) CAI

Generally, the CAI design uses the OEM intake tube or a piece of PVC tubing to pull air from an insulated box made from acrylic or some other type of material such as plastic or sheet metal. The walls of the box and the tube can be lined with a heat-reflective material called Reflectux to keep the air inside the intake cooler than that of the engine bay. The air filter resides inside the box, which must have an opening to the outside of the car in order to pull in fresh, cool air. The square opening that exists under the OEM air box serves this purpose very well. For better air flow, this opening may be enlarged by cutting the sheet metal.

An advantage of the CAI is that it can house a potentially larger filter than the FWI type. Also, the CAI box is located inside the engine bay, so it is close to the throttle body. Air is sucked through the bottom opening of the box, then through the air filter, and finally through a very short length of tube. This means the air flows extremely well, and a well-made CAI may out-flow some FWI designs. The filter unit in a CAI usually stays clean and dry, and it may require less maintenance and last longer than a FWI.

A disadvantage to CAI designs is they are difficult to build correctly. One must create the box to fit in the engine bay, assemble it sturdily, without leaks, and insulate it to be effective. The Reflectux insulation isn't attractive to some, as it looks like insulation, giving the CAI an unfinished quality. Another possible disadvantage of the CAI is the intake air may not be as cool as with the FWI because there's more air inside the box, which which gives it a chance to "heat sink" before it enters the engine (This fact is debatable in cases of top-quality CAI designs).

2) FWI

The FWI is so named because it uses a separate compartment, the fender well, the house the air filter. This set-up can be as simple as a PVC or steel tube extending from the throttle body to a hole in the side or bottom of the engine bay. Because the air filter is placed outside the engine bay, the car's own sheet metal serves to deflect heat from the intake/filter.

The FWI's chief advantage is the air being fed into the filter is near ambient temperature when the vehicle is moving. Another positive is the FWI uses a long, narrow tube, so intake air moves very quickly to the throttle body. Because of this the air doesn't have a chance to "heat sink" as much as with CAI designs, so the FWI may be made without the use of insulating material, giving it a more polished or OEM look. Finally, a FWI can be made of common PVC plumbing tube, or other plastic/silicone/metal tubes intended for intake fabrication. The cost and build difficulty can be kept relatively low compared to the CAI.

One of the disadvantages of the FWI design is the tube is long, narrow, and consists of bends. If too narrow, or if bends are severe, it could limit the volume of air flow severely compared to a CAI box. Another theoretical problem with the FWI is the positioning of the air filter nearer to the ground, possibly exposing it to the elements more so than a CAI. This fact raises fears with some that water may splash up into the air filter, but this has yet to happen in the case of a Riviera using a FWI design. There is little chance of the filter being exposed to water unless driven through a flooded street, or if by chance the fender well became damaged or disconnected. Even so, the filter in a FWI will receive more exposure from the elements because it is less shielded from the outside. Expect to clean/change filters more often than with a CAI design, and expect that to be a chore, as the fender panel must be removed to service (works best with the wheel removed).

Both FWI and normal CAI designs utilize cone or round-straight air filters, which tend to flow more air than the OEM panel due to their greater surface area. Also, both tend to out-flow the OEM intake when properly designed. A well-made intake sytem has fewer bends and a smoother interior surface than the stock tube, so air can flow faster and with less turbulence.

It should be noted that a cone air filter simply mounted inside the engine bay without concern for heat shielding (often termed a "short ram" intake) does not count as a CAI. While such a design may increase air flow, the IATs will be higher than that of the stock air box, which defeats the purpose of the CAI modification. The unsheilded short ram can be a benefit in naturally aspirated engines, but our engines truly need colder air to operate without knock. Sucking in hot engine bay air could actually prove to be a detriment to the engine's performance and reliability.

Both types of CAI will greatly amplify blower whine to levels that may not be appreciated by all. If you are not so turned on by the idea of making your Riviera scream like a banshee when stepping into the throttle, you might want to think about staying with a gutted air box, or at least opting out of the FWI option, as it is the louder of the two designs.

As mentioned, there are no prefab CAI or FWI units sold for the Riviera (although some are working on this), so systems must be custom built. This is partly a good thing because the needed parts are inexpensive and can be found at local hardware and home improvement stores. The total cost will depend on what types of materials you use, and can range anywhere from $100-300.

Note: higher-flowing intake designs allow more air to enter the engine. Normally, the PCM will counter this by adding more fuel, but it is advised that you switch to 2-range cooler plugs after installation to lessen the chance of knock resulting from the extra air flow.

Write-ups for constructing custom CAI & FWI designs (thanks to Jason and 98riv):

https://rivperformance.editboard.com/Series-II-3800-Supercharged-c2/Engine-Transmission-f4/Write-Up-4-FWI-t107.htm

https://rivperformance.editboard.com/Series-II-3800-Supercharged-c2/Engine-Transmission-f4/-p43.htm#43


A few links to sources for ducting, elbows, and tubes. Thanks to jax95riv and 98riv!

http://jagsthatrun.com/Pages/Parts_AirClean_Ducting.html

http://intakehoses.com/

http://www.turbohoses.com/products.htm

http://www.intakehoses.com

Info on FWI design:

Link1

Link2

Anyone hear of Spectre Performance? They have a modular intake system with all the couplers and pipes in a variety of sizes. Seems pretty straightforward to have an intake created without a problem. They even have a mockup kit for $15 bucks so you can test which parts will actually work. I am thinking it wouldn't be a bad idea and the flow on the inside of the pipes should be pretty good. Should look quite a bit better than a pvc pipe. Any input would be appreciated though.

That's a cool site, thanks. Here's a link: www.spectreperformance.com/#CATALOG

I know that CAI's are not made for our cars, but this one says it is. I wonder if it would work?? Ebay auction # 220175226059

its a short ram not a cai it would probably work but would make the temps go up rather then down therefor is a waste of money (at least what ive learned from reading the intake stuff a bunch of times)

does anyone know where to get a system from. please reply thank you

ok a 98 is series 2, for a intake kit do you want a short ram intake or a full cold air intake

Link

or if you want to make more hp, i would say go for FWI( fenderwell intake) you can make them out of 4" PVC pipe from lowes or home depot

There is no "full" cold air intake. It's either cold air or it isn't, and the short ram is not. A better name for short ram is "hot air" intake.

Currently there are no CAI or FWI products on the market for our cars. For more on making your own, see: https://rivperformance.editboard.com/series-ii-engine-transmission-f4/what-are-cai-fwi-t29.htm

AA: There is one "pre-fab" option, sort of.

The Intense FWI. RhinoFLA has successfully used their tubing, though nobody has used the complete system on the Riviera yet. I plan on doing so, and I'm going to attempt to run it through a stock airbox to keep it looking stock, with the gains of the FWI.

Link

Here it is. RhinoFLA's tubing length matched up with what is provided, so...

I guess I'll find out in a few weeks.

just gut your box , cut a big hole in it and call it a day...
it will sound nice and youll be happy beileve me
throttle response will improve nicely

darren wrote:

does anyone know where to get a system from. please reply thank you

Home Depot... Homemade PVC FTW! Took me about 3 hours and $40 including the filter.

I wonder if this could be easily modified to fit a 99Riv?
http://www.psmbuick.com/products_coldair.asp

I used to own a 87GN and installed one on that car, nice piece.
I sent Pete a message axesking if he might have a kit for the Rivs...

Bert

This looks identical to Intense performance's FWI, but it is available in 4" plus the 3.5" is $40 cheaper!!

However, it looks like they supply a cheaper brand of filter, whereas Intense provides a 9" K&N filter.

I'm sure they could figure out a setup for a Riv real easy.

Hey, this looks like something we can use! Spectre makes a series of intake tubes which clamp together into a custom CAI or FWI -

Link 1

It looks like the way this works is, first you buy a cheap ($10) fitment kit -

Link 2

You use this to figure out what parts you need for your installation, so you can order only the parts you need.

Unless anyone knows a reason why this wouldn't work for us, I'm all over it.

Do we need 3" or 4" tubes?

That is very cool. the 3" or 4" is up to you. If you are going to build one, might as well make it 4" :8

I like that you can return the fitment kit to spectre for a full refund after you are done with it!

If it's my choice, I'm going for the big one

Now I've just got to find that 4" fitment kit!

It's too bad they don't have 3.5" dia, like: http://www.turbohoses.com/45%20degree.htm

check this out for hose!

http://www.ramairbox.com/tubes.html

Jack the R wrote:

...................

Do we need 3" or 4" tubes?

The TB opening is 3.5" ID, so that would be a direct fit. I wouldn't go smaller, do the 4". I'm using a silicone 3.5" to 4" 45deg elbow to get to 4" pipe. Elbow should be here end of this week, early next week.

I can't find a 4" fitment kit anywhere. You guys reckon there's any reason the 3" kit wouldn't work? I can probably figure out to buy the 4" 45 degree elbow instead of the 3" 45 degree elbow and all.

I wonder if this could be used with a ram air scoop to get true cold air into the engine? Now I've got to go find that ram air thread!

AA wrote:

It's too bad they don't have 3.5" dia, like: http://www.turbohoses.com/45%20degree.htm

They've got a coupler/reducer that goes from 4" down to 3.5"

Link

Scroll down to the coupler/reducer section.

Yes, I see that, but running a 4" tube, then reducing to a 3.5" TB looks odd to me, and doesn't add much extra flow, imo. Just use a 3.5" tube and you're looking like stock.

But the 3.5" turbo hose tubing is 3X as much (comparing 45 degree elbows).

Fitment kit ordered! Let's see how far down this rabbit hole goes . . .