Custom Made Drop Base for 2nd Gen Trans Am

Last fall I made a custom drop base for my Trans Am. The drop base is needed in order to fit the shaker under the factory hood when using aftermarket parts that raise the intake flange (mounting point for carburetor/throttle body) higher than factory.

Before I go any further, I want to make it clear that I do not recommend building your own drop base. I spent about $150 on materials, an initial 8 hours making the drop base, plus endless hours afterward trying to make it work. The final product was not as I hoped. See the photos to see the results. Please consider one of the solutions I list next before making your own drop base.

Permanent drop base solution

A permanent drop base solution is to do one of the following.

  • Factory Intake – You can modify a factory intake then use an adapter such as the Edelbrock 2732 (if necessary, was not in my case), assuming the carb/EFI provides mounting holes for spread-bore mounting. FiTech EFI throttle body provides spreadbore mounting holes, so no adapter was needed. Please see Modified Factory Pontiac Quadrajet Intake for Square-bore FiTech Throttle Body EFI.
  • Edelbrock Performer (not RPM) – The Edelbrock Performer intake puts the carb/throttle body at about the same position as factory and provides direct square bore mounting. Note a factory Pontiac intake will more than likely outperform an Edelbrock Performer. Other than weight savings, I would recommend modifying a factory intake before switching to a Performer intake.
  • Other aftermarket factory height intake. There are some single plane intakes but if your engine is designed for dual plane I would not switch.

Alternative drop base solutions

Get a drop base from a reputable Pontiac supplier…

All of the above solutions are a compromise. All of the above require that your shaker is cut in order to function properly.

The Airaid solution utilizes the traditional round air filter method. The good thing about this solution is that other than the drop base itself, the air filter is sealed like factory with a round air cleaner lid. The disadvantage is air turbulence created when the air first flows into the shaker, then around the air cleaner lid then through the filter. I did blow some air with a fan through the filter at angles and could not tell if it was impacting the speed of the air but I think it is a concern none the less. More importantly it puts a smaller clearance between the actual carburetor and the lid top which is restrictive. If you are running a throttle body, that clearance may not be as critical, but if you are using a quadrajet, the secondary walls may be very close to the top of the air cleaner lid.

The rectangular air filter solution requires that your shaker be modified to allow air to flow through the square filter. This solution presents the same issue as the Airaid filter in that the air flows through the filter at an angle. One advantage is the air only has to make one turn, rather than flow around a lid then up and into the carb/throttle body. The biggest drawback to this solution is sealing. Air filtration could be breached around the edges from the plate that is glued to the top of your shaker as well as from the gab between your shaker and drop base.

A solution to the problem no one produces today

One solution to this problem is a re-designed shaker. I have a few ideas but no time to make them a reality.

Another solution is to redesign a completely different air filter lid. Perhaps someone can take inspiration from the K&N filter lid I modified to build something better.

Custom drop base construction

I do not recommend building your own drop base, but for those who want to know how I built mine, here are the quick and dirty instructions.

Custom Drop Base Custom Drop Base

I used a K&N drop base #3549, a 16″ diameter 1.5″ deep pizza pan, and an Airaid #801-452 filter (14″ diameter on the bottom and 10.75″ diameter at the top), and a K&N filter lid #66-1101. I cut a hole in the pizza pan and then used bolts with rivet style heads and lock washer nuts to fasten the drop base to the pizza pan. Other than drilling holes for the rivet style bolts, I did not modify the drop base. I also modified the filter lid with a slight cut in order for it to clear the shaker.

Once I put this all together I was initially quite pleased with the results. The shaker did not rub against the filter lid with my relief cut in the filter lid which was initially my primary concern. What I did not anticipate was the shaker not fitting properly on the pizza pan because the diameter was exactly 16″ in diameter, whereas the factory air cleaner lid was actually 16-1/2″ in diameter. To compensate, I added 4 pieces of metal at four corners. This worked except it allowed the lid to slowly turn. A quick solution was then to add duct tape at each corner to provide enough friction for the top shaker not to move once the shaker ring is tightened. AS soon as I added duct tape to the assembly I realized this was not worth my time.

What I am going to do…

I am going to take the factory intake off the motor and take a grinding wheel to it! The plan is to open up the holes to allow for a square bore to be mounted directly to it with the use of a very thin adapter (Edelbrock 2732). I will post when I do this.

Update: I did what I wanted and modified a factory intake, which is the best solution to this problem. Please see Modified Factory Pontiac Quadrajet Intake for Square-bore FiTech Throttle Body EFI for details.

16 thoughts on “Custom Made Drop Base for 2nd Gen Trans Am”

    1. I have built two shakers that are fully height adjustable and functional I will make one for anyone interested and it will work with any intake and carb as long as it sits 2,5 inches from the hood
      and it will attach to the carb

      1. What would it cost to build one for a factory intake and carb on a 77 400? I have the shaker but the base is for a 301. I have nothing else. The car is a 80 bird with 77 400

        1. If you get the correct base you will not have to build anything, everything factory wise bolts right up as long as you use a factory intake.

  1. First time I came across your site.. And I see I’m in the same hood situation! I have a 79 TA that I’ve been redoing forever.. and I bought those same pans a while back… I have a torker 2 intake with dropped Global west bushings.. So my offset is effectively more higher

    Did you try to heat and unwrap the top circle seam of the pan.. I plan to try that this weekend.. If flattened out, it should give you 16.5 inches to use the ring.

    1. Hello Dennis,

      I grew so frustrated by the drop bases that I ended up modifying the intake so I could bolt the FiTech directly to the intake. Link:

      The “torker 2”, like the “performer RPM” put the carburetor at a much higher than factory height. There is not much you can really do. I would recommend switching to a throttle body (if you have a carburetor) and running a K&N filter lid #66-1101. I would not run the K&N filter lid though if you have a carburetor as I believe the lid shape being consistent is important and I think the K&N filter lid would create turbulence for a carburetor, where-as with a throttle body just needs air.

  2. Hi again Angelo

    Would you know off hand the amount of drop from carb pad and height of the sides of the factory air cleaner pan? I don’t have mine anymore and I’m thinking you probably measured this.


    1. I believe the drop is 1-3/4″. The side (outer loop) of the air cleaner was 2″ high. Essentially it put the shaker 1.25″ higher than the rim of the carburetor.

      This custom base had about the same drop, 1-3/4″ drop, but what was different was the height of the side (outer loop) was about 1-1/2″ high. Using a thinner gasket than what you would normally use with a Quadrajet and bolting the pizza pan under (not over) the drop base I netted an overall drop of 3/4″. The spacer I used was 7/8″, 1/8″ is nothing to freak out about, you could still run two fingers between the shaker and hood.

  3. Correct me if I’m not calculating right but if its 1.75 drop and air cleaner pan is 2″ high doesn’t that put the shaker at 1/4 inch higher than rim of carburetor? Does that sound right?

    1. Yes I think that is correct. The lid that goes with the filter is domed to fit under the shaker. The air cleaners for the shaker were actually 2-1/2″ high, where-as a regular air cleaner base for a Pontiac used a 3″ high filter. If you used a 3″ filter the dome would hit the shaker. It is a very tight fit when everything is “factory”, so when you introduce even more drop for the shaker, you cannot use the factory air cleaner lid, a 2″ filter would be too low and the dome of the lid would suffocate the carb. With a Quadrajet carb, the lid would hit the air horn with a 2″ filter. By bringing the drop down you essentially eliminate the ability to run a normal filter, it needs to either be cone shaped to clear up within the shaker or you need to come up with something completely different.

      Air filter reference: Wix 42102 = 2-1/2″ height, Wix 42095 = 3″ height

  4. so thought about a easier way to make this work , cut the round bowl part of the stock shaker air cleaner out , go get a after market cheap air cleaner with a dropped base cut it and fit to the shaker cleaner , should be simple to do , anybody tried this it would have to work ?

    1. This would not work, aftermarket air cleaners are not enclosed, they do not go an extra 2″ in diameter to reach where the shaker attaches to the factory base. Remember afteramrket drop bases are open, where-as the factory is enclosed. This is why I used a very large pizza pan. You could cut the factory base and find yourself a pizza pan to attach to it, but there are aftermarket bases with the same amount and some with more drop than the factory base which is what you are ultimately after. A factory shaker base is worth $150-200+, I would not cut it.

      If you are running a factory intake, please check out my post titled
      Modified Factory Pontiac Quadrajet Intake for Square-bore FiTech Throttle Body EFI.

  5. I have a 1981 trans am with a FiTech on it. I followed your instructions on modifying a factory intake and it worked great. The problem I have is that I run a return line on the system and I wanted to know if the drop bases you’ve listed above will prevent the return line from hitting. I know my factory air cleaner hits because I have the 305 5.0 Litre.

    1. With my drop base (for a Pontiac 400), if had to have a return line, the return line would have to use the same 90 degree elbow from the FiTech to clear. I suspect it would not clear though as it has to go in the back of the FiTech (not the front). You may have to dent your air cleaner base in that area to make clearance. It shouldn’t take much though.

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