Thread: Big Block Chevy Help

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I have a newley assembled 396. I got this thing in a big trade, and dont know much about it. Here is what i know. It is 10.5:1 compression, a lunati Bracket master 2 294 cam, dual quads on a tunnel ram, a complete msd ignition. I know the heads are in ok, but not great shape. the problem is i cannot seem to get this thing tunned right. It really runs terrible, and back fires through the carbs constantly when accelerating. I would like any suggestions as how to cure this. I dont want to drag race this thing, i just want it to run respectable. the carbs are brand new Holley 450 cfm right out of the box. I have tried to use a timing light on it, but the timing is too eratic. Once it is running at idle, it sounds good and stays cool. My goal with this thing is to have some drivability with it. Any suggestions would be appriciated as i am guite new with setting up dual quads, and big blocks in general.

I was trying to ponder your question (thinking is hard for me) but I kept having questions. Have you run a compression check on the engine? By constantly you do mean multiple times during acceleration? If you find a cylinder with no compression you may want to check the valve lash on the intake valve for that cylinder. Did you unhook your advance to try and set your timing?

Try taking off the tunnel ram and switch to a dual plane intake. Tunnel ram run really crappy for a street driven vehicle as they are made to make power at over 3000 rpm (not good for daily driver).And, since you said you are running dual Holley 450 cfm. On backfire can destroy you power valves, and that may be your problem. Try an Edelbrock. As for the backfiring problem, make sure the distributor is in right, maybe when the engine was assembled the distributor was off 180 degrees. Also, check the firing order. Make sure all of your head and intake bolts are properly tourqed and the are no leaks under any of your gaskets.

thanks for the replies. I found the problem was # 4 & 6 cylinders were cross firing. A new set of wires and its good to go. Runs like a rocket ship. thanks for your help.

not really. Just forgot to post what the fix was. but i dont drive the truck so i guess if it did take 8 mos there wouldnt be any harm in it.