Hello, I am a new member as I recently bought my first truck ever. 1991 Silverado ext cab 2WD with a LO3 and a 5 speed. This is the first TBI engine I have owned since 2001 so its been awhile and I seem to have forgotten alot of the quirks about these engines. I have been working on LT1 and LS1 engine in the last decade. I finally broke down and bought a truck because I was tired of borrowing trucks or pulling trailers with my car every time I needed to pick up a big item. Anyway, this is by far the slowest vehicle I own now and was looking to upgrade it some what. I wanted a truck with the LO5 but I had a hard time as it was finding any half ton with a V8 and a manual. This one was cheap, in great shape so I got it.
This truck has the original exhaust and the muffler is rusted out. It still has the large cat on it also. I was looking to buy a cat back for the truck and either elimate or replace the cat with a higher flow model. What I wanted to know, and I'm sure this may cause a debate, is do the computer chip need to be retuned to get the most out of your new exhaust upgrade. The reason I ask, is my first car was an 88 Caprice with the LG4 5.OL 4bbl roller cam engine rated at a crappy 150hp. After putting dual exhaust on the car, with flowmaster mufflers and no cats, the engine really came alive. I big seat of the pants improvement, of course the car was really slow to begin with. Fast forward a year and after totalling the car, I bought and 89 Caprice with a TBI 305 LO3 roller cam engine. It was factory rated at 170 hp. I transferred over the same exact exhaust system and it made no difference what so ever on the otherwise good running car.
Later I scrapped this car for a 1994 Caprice with an LT1 and bought a cat back for it, and with that car, the exhaust made a noticeable difference. I came to the conclusion that the carb responded to the exhaust because its a mechanical system that also is capable of flowing more CFM than the facotry TBI, and the 94 LT1 responded to the mods because it uses a MAF sensor that actually reads the air coming into the engine and adjusts the fuel. Makes sense that if more air can get out from exhaust upgrades than more can come in (to a point) and the engine adjusts. However, with TBI utilizing speed density, I figured that the computer has no way of knowing the engine is breathing more air. I seem to see alot of you guys with exhaust mods on TBI engines. What do you think I would love to be able to get LO5 hp and torque out of an LO3 without going into the engine but I dont know if that is possible even though there is only about 25-30 hp difference. the factory rated this engine at 175 HP and 275 lbs ft I believe. Thanks.
This truck has the original exhaust and the muffler is rusted out. It still has the large cat on it also. I was looking to buy a cat back for the truck and either elimate or replace the cat with a higher flow model. What I wanted to know, and I'm sure this may cause a debate, is do the computer chip need to be retuned to get the most out of your new exhaust upgrade. The reason I ask, is my first car was an 88 Caprice with the LG4 5.OL 4bbl roller cam engine rated at a crappy 150hp. After putting dual exhaust on the car, with flowmaster mufflers and no cats, the engine really came alive. I big seat of the pants improvement, of course the car was really slow to begin with. Fast forward a year and after totalling the car, I bought and 89 Caprice with a TBI 305 LO3 roller cam engine. It was factory rated at 170 hp. I transferred over the same exact exhaust system and it made no difference what so ever on the otherwise good running car.
Later I scrapped this car for a 1994 Caprice with an LT1 and bought a cat back for it, and with that car, the exhaust made a noticeable difference. I came to the conclusion that the carb responded to the exhaust because its a mechanical system that also is capable of flowing more CFM than the facotry TBI, and the 94 LT1 responded to the mods because it uses a MAF sensor that actually reads the air coming into the engine and adjusts the fuel. Makes sense that if more air can get out from exhaust upgrades than more can come in (to a point) and the engine adjusts. However, with TBI utilizing speed density, I figured that the computer has no way of knowing the engine is breathing more air. I seem to see alot of you guys with exhaust mods on TBI engines. What do you think I would love to be able to get LO5 hp and torque out of an LO3 without going into the engine but I dont know if that is possible even though there is only about 25-30 hp difference. the factory rated this engine at 175 HP and 275 lbs ft I believe. Thanks.
