Join Date: Feb 2006
Location: Boise, ID
Bronco Info: 1981 300ci 6cyl w/4bbl conversion. 4spd NP-435 manual. 32" tires.
The 300 is a great engine in stock form, but there ARE performance parts for it.
However, 90% of them are for the carb'd engine. The fuel injected computer doesn't take too well to mods.
The 300's biggest issue is its inability to breath. The carb'd model especially. The carb, intake, head, and exhaust manifold was simply too restrictive for the amount of cubic inches the engine it.
For my 300, I have exhaust manifolds from a fuel injected 4.9, which is a great upgrade and flow way better than stock. There are also headers available, but they're significantly more expensive, and come with problems of their own. For a mildly built 300, the EFI manifolds are where it's at. Pair that with a 2.5" exhaust out the back. I have a turbo muffler on mine and really like it.
The 1bbl carb is also much too small. It's only about 190cfm, which doesn't let the engine rev much above 3000 RPMs. Clifford performance and offenhauser both make 4bbl intakes for the 300 that'll let you put on a nearly infinite range of carbs. A well tuned 4bbl should be able to get you way more power, plus nearly the same gas mileage as the stock 1bbl. Mine has WAAAY more power than stock, and I get 17 - 19 on the interstate and around 14 around town.
Just an intake/carb and exhaust is going to really wake that motor right up. But, if you want to take it further, port and polish the head to really let it breath. Then, you can pick a cam of your choice (a 260h is a common choice). Installing larger valves into the head will do a lot for it as well.
1981 Bronco. 300 I6. 465cfm Holley 4bbl. BFG A/T KO2 32x11.5" tires. NP-435 trans. EFI exhaust manifolds. 2.5" Exhaust. DUI performance ignition.
1984 Bronco. *sold*