I did a ton of research when I was going to retrofit a TBI into a mid-70s Chevy truck years ago. They can be made to run better, but they were never meant to be fire-breathers. The TBI systems were designed for fuel mileage, torque, and snappy throttle response.

You can have your MAP reflashed to account for it, but the computer system never seems happy even after that's done. The idle will go up and down, up and down, and never settle. What will happen is that the MAP will be trying to find the best vacuum number and it'll be sending that data to the computer, which will tell the IAC (idle area controller) to speed the idle. Too high a duration or too low of a lobe seperation will cause the MAP sensor to go nuts. You can step slightly out of bounds when choosing a cam for a TBI, but you have to be careful. If you look at a factory GM cam, the lobe seperation on the computer cars is usually 114 or higher, mostly due to the MAP sensor's desire for an optimum vacuum number.

The higher the lobe seperation number, the better the vacuum signal, the broader the powerband, and the better the idle quality. The second most important number to look for is the lobe seperation, which is the distance in degrees, as measured on the cam, between the point of peak lift on the intake lobe and the peak lift on the exhaust lobe.

050 number is, the longer the valve will be off the seat (hence the term duration), which will affect vacuum. 050 on a TBI will cause the MAP sensor to go nuts because the MAP wants to keep the vacuum within a certain range (which if I remember correctly is 17-19 inches). The LT1 cam is also a good choice as well.įor a TBI application, the number to be the most concerned with is the duration. 050 is good (206/212) and the lobe seperation (112) is also good. I think the 12-249-4 is better cam between the two you listed.

Chevy 350 performance cam