350 throttle body swap and rewire??????

[Legendjet]

Ok here is my situation. I have a '91 C1500 with a 350. I have found a holley tbi direct replacement throttle body that flows 670 cfm. the problem is it is made for an '87-'89(model 502-6). i found another one made for '90-'95 (model 502-9). the throttle position sensors are diferent on the two throttle bodies. I was wondering could i get a tps plug for an old truck and wire it to my new truck. both have three wires. or i have heard that a 454 throttle body would fit on my truck but with some minor rewiring. i know to really pull anything out of the engine i need a different intake, heads, headers,and cam. i will get to those but right now i just need help with this. and when i look for a cam shaft i noticed some say not computer compatible.... dose anybody know why. thanks.

[sreve]

loping idles do not play well with the computer expecting a stock cam

[Blue Bowtie]

Your TBI is a speed/density control scheme, which means it monitors throttle angle, engine RPM, intake air temperature, and manifold vacuum (absolute pressure) and calculates the amount of air entering the engine from these variables. It doesn not actually measure the air like a MAF based control system. This means that anything which moght change hte volumetric efficiency of the engine (such as a different cam, heads, exhaust, boost, etc.) will affet the actual amount of intake air without the ECM calculating it anywhere near correctly. With a "lopey" (high overlap) cam profile, manifold vacuum will be less in lower RPM ranges, and hte ECM with factory programming will interpret the decrease in vacuum as increased load. Generally, the ECM will add fuel based on the erroneous data, and it will run terribly rich. At higher RPM, when the cam profile starts to increase volumetric efficiency, the difference in MAP (vacuum) will be less distinct, even though a lot more air would likely be entering the engine. The result will be a ;ean micture which can lead to serious problems.

As a result, cam grinders recommend only using those lobes with shorter durations that can mimick the original vacuum profiles while admitting only a bit more air. If you want to get a little crazy with a cam, you'll have to reprogram the ECM, just as you would have to tune a carburetor differently for a different vacuum signal.