Engine and Components News

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.

Comments are closed.