I have a 95 Z28 with cold air, mass air flow sensor, underdrive pulleys headers, 3" exhaust to highflow cat w borla. edelbrock rpm intake, 58mm throttle body, centerforce clutch, and its also a four bolt main. i took it out of 95 vette. can i put bigger injectors and would it make a difference?

 

Flywheel horsepower determines what size injectors you need. There are detailed discussions on this board that you need to search out. Most likely with the mods mentioned yours are adequate. To find out get a dyno tune and the tuner can tell you what percentage the stock injectors are of their capacity. At the least the tuner can get you some cheap horsepower. Find an expert tuner with the LT1 programed software for your car and your question will be answered.

 

You have a lot of parts that add little, if any HP. There is little to be gained with U/D pullies, the Edelbrock intake manifold, mass air flow sensor (what kind?), 58mm TB, centerforce clutch and 4-bolt mains. Worth next to nothing in the way of extra HP. Does not increase the demand for fuel.

Essentially, you have a CAI, headers (what kind) and a 3" catback. Those might be good for 30-40HP on top of the stock 275 flywheel HP. At 315 flywheel HP, you still have at least 40-50HP to go before you reach the 80-85% duty cycle recommended limit on the stock 24 #/HR injectors (programmed as 24.9 #/HR). Many push upwards of 400 flywheel HP with the stockers.

As noted, a good tune will net you more HP, with less fuel consumption. Stock programming is way too rich at WOT. If you get lucky with something like an intentionally miscalibrated MAF sensor, like the Granatelli, you might see similar gains due to the leaning the engine out in power enrichment (PE) mode, but they aren't very reliable. A tune is a guaranteed 10-15HP.