Ultimate TBI

By Pablo Morales ([email protected])

Aircleaner options, mods, and specifications

Stock Aircleaner

The stock aircleaner element can only effectively feed a 305 motor to 4500 rpm and that isnt even the greatest restriction, the single neck that is approximately 1" by 2" is, not enough flow for all but the weakest of 4 cylinders. With that said some modifications are still possible.

Remove air silencer ring that is tack welded around the mouth of the aircleaner that encircles the throttle body. This requires air to enter directly from the top. Removal requires breaking the tack welds.

Removal of Thermac Device: The thermac is a temperature/vacuum controlled valve that directs heat from the exhaust manifold to the intake when it is below a certain temperature to decrease emmisions. The flap is a direct threat to intake airflow. To remove: The vacuum hose that connects to the aircleaner from the throttle body must be plugged. Remove the preheater duct hose that comes from the top of the exhaust manifold. It may be left at that however for added gains one may "Gut" the device by removing the flap, rod and plunger from the intake path. This requires a bit of ingenuity and a bit of a hack job. You will need to cover the hole on the bottom of the neck if you are ducting cooler air to the aircleaner.

Ram Air. The neck to the aircleaner has an opening that is 3" in diameter. Most hardware/home stores sell 3" diameter aluminum ducting typically used to expell hot clothing drier gasses. If your battery is on the passenger side of the car you are in luck. You will need to relocate your evaporative canister located in the front driver side engine compartment. I have moved it over to the framerail next to the radiator though removal of cruise control is neccesary. From there you will need to make a slightly larger than 3" hole in the sheet metal where the EVAP. canister used to sit. Run the aluminum ducting from the neck through the hole and affix it to the bottom of the car facing forward. At speeds this will create a ram air effect pushing cool air into the tubing.

Lid from 350 GM pickup truck Any aircleaner lid from any carbureted or TBI chevy truck from 1968 to current allows for the use of a taller aircleaner element. This will provide gains until the rpm at which the neck becomes the greatest restriction.

H.O. Dual Snorkel aircleaner

The H.O. dual snorkle air cleaner was available on L69 305 carbureted f-body engines up until ’87. It features two air inlet necks on opposite sides which are larger than the single neck stock aircleaner. It uses the same filter element and can also use the same chevy truck lid to use a larger element.

  • Advantages: Cold air induction, more than twice the flow potential of the stock unit, and no hot underhood air getting sucked in.
  • Disadvantages: It may be of some difficulty to adapt to TBI cars with A.I.R. components in the way on the passenger side above valve cover. The necks are still a limiting factor to airflow, but this does outperform the stock air cleaner by far. Also, the snorkels do come with THERMAC valves, limiting airflow. Typical cost: From $20 (used), to $250 (new).

Aftermarket Open Element

Open element air cleaners are just that. The element is exposed on all sides to the open air. They are available from numerous companies in a variety of styles and prices.
To accomplish this mod the vacuum line to the thermac must be plugged, the IAT (Intake air temperature) sensor must be removed from the stock aircleaner. It can be relocated to the open element base but is not necessary. Power may be gained by relocating to a cool area. The breather may be left to the open air without worry. Any Drop aircleaner will work. All will give noticeable gains. Please see THE ULTIMATE below before you spend your cash.

  • Advantages: Almost unlimited flow potential. Very low price, very good horsepower to dollar ratio. Huge seat of the pants difference. Very easy mod to accomplish.
  • Disadvantages: Engine now takes in slightly hotter air allbeit more air. Non factory appearance.

The Ultimate

Take note of the gold iridite finish spacer ring on the TBI unit. This serves to lift the stock drop aircleaner so as to not interfere with the TBI components which surround it. Talk about compromises! GM used a spacer to raise the drop aircleaner! The spacer greatly limits flow since it forces air to flow only through the top of the TBI unit this causes the injectors over the TBI to be another flow restriction.

The solution for improvement:
A typical non drop aircleaner that is slightly clearanced for throttle linkage works perfectly as long as a larger 3" tall element is used. GREATLY improving flow not only with a larger element but by unshrouding the TB bores. A Double whammy! Look for the typical "Mr. Gasket" Non drop aircleaner sold at most autoparts stores. Remember you will need a larger element to keep the lid at the right height.

For even more flow
Try an Xstream aircleaner lid along with K&N filter. The Xstream lid makes the entire lid another filtering surface. The K&N filter flows more as well. For a ram effect you can go as far as a ram air hood or a cowl induction hood.

Reccomendations: Removal of the rear hood seal, this is an old-school hot-rodder tip to let some hot air out. *Warning* removal of hood seal may let some water in the engine compartment, and on the distributor, but I haven’t had any problems with it so far.

****NOTE**** If your air cleaner housing rubs against the coil wires, I suggest adding a piece of cardboard to stop the rubbing, if these wires ground out, your car is screwed, big time. You will be stranded on the side of the road.