Can anyone tell me if having a larger cam changes the timing on an engine? Here’s my issue – I have a 1995 K1500 4.3 (VIN Z engine). A head gasket blew in the original engine at around 124,000 miles, and I pulled it for repair and to go through it. Once I got it out, it was junk. I sourced a good used engine from a 1995 S10 with comparable miles from a guy I know and I pulled it. It was a VIN W 4.3 which had the CPI versus the TBI. No problem I figured I had all my accessories; I’d just strip it to the bare bones and put it back with my TBI components. Little did I know until after I reassembled and reinstalled the engine the cams are different between the Z and W engines. It runs good, but runs rich. I have read every forum on these TBI engines running rich and there seems to be no single consensus on a culprit. Dang near every sensor is new, distributor is new, fuel pump/filter is new, fuel return line is clear, injectors are new, throttle body rebuilt, ECM replaced. It also ran rich with the old engine in it. Aside from running rich, it seems a little sluggish to me. Upon replacing the distributor I initially set the timing by ear. I then ran it into town to a buddy to put a timing gun on it. It seemed to run the best it ever ran with plenty of HP and throttle response on that trip to town. We put the gun on it and timed it to the mark (Yes, I unplugged the timing advance) and while it runs good, seems a little sluggish again. Any more experienced engines guys want to take a shot at what affect on performance the different cams has? Here are the specs between the two cams: Vin Z (Original engine)/Vin W (CPI engine) -
Exhaust Advertised Duration: 264 degrees/274 degrees, Exhaust Duration at 0.050 inch lift: 193 degrees/208 degrees, Intake Duration at 0.050 inch lift: 183 degrees/208 degrees, Exhaust Lift: .402 inch./439 inch, Intake advertised duration: 254 degrees/277 degrees, Intake Lift: .376 inch/.432 inch

Thanks for the help!

 

Are you speaking of ignition timing or valve timing?

 

 

I doubt it will. With the 4.3L Vortec motor which uses the Enhanced Distributor Ignition system (EDI), turning the distributor will have no affect on the timing. The ignition timing is controlled by the camshaft sensor and the VCM.

 

The VIN W has the EDI, VIN Z (TBI) has the vertical distributor and has initial timing set with a gun.

 

What did you set the initial ignition timing to? TDC?

 

I did, yes. Initial timing is 0 degrees TDC. I think I'm narrowing in on the problem. I noticed when I changed plugs one bank is considerably richer than the other. It just happens that one bank has the older injector. I had ordered two new rebuilt replacement injectors, but one was bad. The company sent me a replacement, and the replacement was bad. The new one and old one, at least to the naked eye, appeared to have a similar spray pattern so I just left it, and took the refund. I've since ordered a replacement from a different supplier, so we shall see. I will post once I've done that.