Instructions for improving performance on 2.5 liter Chevy engine with TBI
Step 1 - Get a K&N or similar air filter.
Step 2 - Find a cookie tin 10" or a bit more in diameter and cut the bottom off, or make a 10" circle out of your choice of metal. Thicker is better as it will provide a better seal to the filter.
Step 3 - Put the air cleaner top over the metal and mark the holes on the metal, then drill the same size holes. If you use a tin for your metal, you can cut off the bottom of a coffee can and drill the same holes for added strength.
Step 4 - Place the new top on the air cleaner assy (coffee can on top, if you use it) and tighten the nuts so there is a good seal, but not so tight as to bend the metal. There will be a 1/4 to 3/8" gap all the way around the air cleaner for more air to get in your engine.
Here's what it looks like. I used a side cutting can opener to cut off the lids.
That's it. Get in and go for a spin. You'll notice the difference when you hit the gas. This simple modification has provided me with a significant gain in horsepower and a 15% increase in gas mileage
