QuestionI just got my 69 el camino out of the shop. Specs 454 4 bolt, rebuilt with solid roller cam, custom ross forged pistons, 10.2:1 compression with afr 315 cc heads. After getting it out. I am extremely dissapointed with the performance. It is backfiring through the exhaust on occassion, knocks after shutting her down and is very soft on power. I am oing to go through it saturday but is it premature to guess a cylinder with low compression? Bad valve lash?
AnswerHi Shane:
I don't usually answer street car questions. I will try to help you some though.
Backfiring is caused by raw gas in the exhaust pipe- - -how did it get there ? A leaky valve, incorrect ignition timing, cross firing through the plug wires, or cross firing within the distributor, and finally incorrect camshaft timing. The question I must ask is who did the rebuilding ? and did they know what they were doing with the different camshaft and lifter arrangement. Did they know what to do with the valve lash adjustments ?
If it was just rebuilt it shouldn't have a bad cylinder and a bad cylinder wouldn't cause the backfiring or the "running on" that you mention (knocking after shut down) . A compression check will tell you the truth about the condition of the cylinder, but a leak down test will tell you more precisely how that cylinder is performing, and if there's something wrong, where to look first. You can buy a leak down tester from Summit Racing for about $75 - - -go to www.summitracing.com and have a look around.
Finally, back to the running on. In a 10.5 to 1 motor, you should be very careful to deburr the combustion chamber areas to prevent detonation. Also it may be necessary to use premium fuel to prevent it.
Good luck with your project, hope you find all the gremlins
Dan Liddy
Sarasota, Florida
