I've got an 81 Vette with all the computer control wiring. I'm swapping in a BBC and I'm concerned about the factory harness/computer. The majority of the harness wont be used, O2 sensor, vapor canister, emission...I'm not wanting check engine lights or starting issues tied to the computer. Can I use a earlier harness from a Vette or a Painless harness or just try to use the factory harness?

 

Hello there dean8757!

Welcome to the Corvette Forum! This is the place to be when you have questions regarding your Corvette!

Is there enough room under the hood of a 1981 C3 to hold the BB? I have a 1968 C3 with it's 427 BB and I still break parts when I get good traction and my C3 was made for the extra HP of the BB engines of the time. The 1981 was not made to handle the same power levels and you could end up breaking a lot of parts. You will have to make the suspension changes as the BB is a heavy engine with cast iron heads on it.

There are several people who have made the swap to BB's in their later C3's. Hopefully they will speak up and help you understand what you will need to do.

 

I'm still building my C3. I don't anticipate a lot of breakage or fit problems. Its a 68 model 325/396 with TH350 to handle it. got to have headers with side pipes. Yours is probably a 425/427 so I'm way below you. My concern is the wiring harness. I'm looking forward to reading this forum. Thanks for taking me!

 

396 is a nice not-so-little engine. ditch the th350. you need an OD unit. 200r, 700r or figure out stand alone controller for the much easier to find 4L60 or 80 type. you can blow an aluminum dana 44 rear with a V6 if you try hard enough. the iron 63-79 rears also. the engine compartment is the same size as the 68-74 that came with big blocks from the factory. wiring harness is not that big a deal. you need ignition, oil pressure gauge, temp and alternator. like every other carburated car. sell the 81 CCC setup on ebay. carb, distrib, ecm...

 

Is the engine management a separate harness? I guess you have 2 choices eliminate the computer, leave the wiring and bypass what ever doesnt work which will be the coil basically. You would just need a stand alone HEI system and a normal carb. That would make it simple.
If you rip out all of the old engine management harness you need to replace switched power to the coil ( power during cranking and power during run, switched power to the starter solenoid ) you can eliminate the rest if you do not live in Cali. You will have to swap out all your gauges as they all probably go through that computer. I guess the simple way is to gut all your wiring and buy an earlier harness for your interior and the engine compartment along with the gaugesto keep all the small stuff from being and issue. I would look at the latest model that didnt have the computers at all.

FYI the 396 and 427 are the same size externally. If you want to lighten it up just swap the intake, heads and fuel pump to aluminum and you will be about the same weight as a full cast iron small block. The down side is finding heads tto fit the smaller 396 cylinder size. Most aftermarket heads are sized for the big bore motors now so you have to do a little shopping or do some minor surgery to the top of the cylinder to accomodate the bigger valves most economy heads use

 

i don't think the gauges are interfaced with ecm like modern stuff. if you take the ecm out the car can be driven as-is. no advance and no fuel management, but runs and drives. if you replace the carb and distributor with 75-80 HEI type you will just have extra wires sitting there. i would get it running with the current setup and decide then if you want to start trimming excess or replacing stuff. alt, starter, temp and oil pressure will be unchanged. really only need to figure out which ignition wire does the trick.

 

The CCC system harness is totally standalone from the starter, distributor power, gauges, etc. You can remove it and not have to buy anything else.

 

well that is good news. I say rip it out, down with computers!!!!

 

not all computers. but definitely that one...

 

Thanks for the input, everyone. Replacing the engine, wiring to run and all that entails is no problem. I've never delt with a old school to new school swap (a few LS swaps) and did not know if the CCC would turn on "Check Engine" light or cause starting issues. I've got everything for the engine swap, I'm wanting to clean up all the excess wiring under hood and if needed install a Painless Performance 28 circuit harness (I've installed 3 already). So from what Fly skids up says I can split the wiring harnesses and remove excess wires to satisfy my **** cleanliness affliction.
I've had hardened valve seats installed in the head and used thicker head gaskets to lower the CR to 9.5 - 9.75. Also a TH 350 will work fine for me with a hardened input shaft/red clutches/valve body upgrades, I've built TH350's behind 10 second Pontiacs so I'm confident it will live behind a mild 396.
I bought this car in terrible shape with a locked up 350 and trashed interior and I'm rebuilding the whole car and will post updates on how I do engine, interior, brakes, paint..... Again thanks everyone.

 

I also got BB coil springs for a 1974 Vette and cut 1/2 spring off after rebuilding the entire front suspension. A $175 idler arm? Vett stuff is expensive!