This is a free modification that I did on my 1992 Ford Ranger 2.3L that surprised me with the extra hp that resulted. I don't know what the exact hp increase is but I sure noticed the improvement. I'm guessing about 5 hp which is quite noticeable.
Before the modification, there was a small hill that I drove up almost everyday coming home from work. At the bottom of the hill, I would be in 4th gear going 80 km/h (50 mph), halfway up I would have to downshift to third to continue going up at 70 km/h (about 45 mph). The little engine was laboring to keep the speed.
Another problem was that there was pretty well no torque below 2000 rpm in 3rd, 4th or 5th gears. 5th gear was almost unusable as I have horrible 3:08 gearing (3:73 or 4:11 gearing would be ideal for a 4 cylinder).
After the mod, I can go up the hill in 4th and maintain 90 km/h (55 mph) without downshifting! That astonished me - its a real life gain of 20 km/h (10 mph) in 4th gear going up that hill! I've also found that I've got usable torque below 2000 rpm. I actually used 5th gear (which I've previously been avoiding) and the rpms were down around 1500 and I still could cruise.
Here's the main culprit that is at the center of the problem:
Intake muffler between mass air flow sensor and throttle body housing
The ideal modification - almost!
The original modification was to replace the intake muffler with 3" furnace aluminum ducting and a baked beans can. It looked great and it worked great (for a while)! The baked beans can was used to mate the 3" ducting to the throttle body housing.
Original 3" aluminum furnace ducting
Unfortunately, there is a lot of flexing between the engine and the fixed air filter housing during normal driving. The aluminum ducting was not up to the task and after 1200 km, the ducting started splitting and letting in air. That's a no-no as the ducting is between the mass air flow sensor and the throttle body. The results were a severely mixed up computer and a vehicle that wouldn't idle. The symptons of an air leak between the mass air flow sensor and fuel injection housing is rough idle, won't idle or surging idle.
I went to the local building supply store to look for existing piping: copper, plastic, PVC or ABS but none had the right external diameter of 3"
The easy modification - 2nd choice
I went back to the drawing board and noticed that the air intake muffler looked like two pieces, one forced inside the other. A little prying and the baffle pulls out. Removed it and everything runs better than before! It takes less than a 1/2 hour to do once you have all the parts and tools.
NOTE: The baffle is used to mellow out the intake air when you downshift. I've had the check engine light come on when I used the engine to slow the truck down by downshifting. The first time it happened, I was quite puzzled as the truck was running absolutely fine. I stopped, turned off the engine, checked the engine and started up. The check engine light turned off. The next time, I downshifted, the same thing happened. The cure is to reset the computer by disconnecting the battery for 5 minutes. When you reconnect the battery, the computer will spend the next 15 miles relearning your engines settings.
That's the modification in a nutshell - it doesn't get anymore difficult. The muffler really restricts the air flow to the fuel injector body. My friend commented that this is what the K&N filter system does. Except my method is much cheaper. Here's the picture of the "intake muffler":
Ranger 2.3l restricted air intake muffler with baffle removed
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