68 firebird
am343148
04-20-2008, 12:48 AM
i have a 68 with the 400 and i have been having some issues with it. when it is at idle and reved around 5500 rpm she has a loud pop out of the exhaust. i took her out the other day and drove approx. 1/2 mile and there was a serious loss of power. Any ideas?
gorgepr
04-20-2008, 02:16 PM
how old are the valve springs?
MrPbody
04-22-2008, 03:42 PM
Could also be a bad camshaft lobe. 5,500 is stretching it a bit if that's an original and "stock" 400. Unlike Chevys, Pontiacs make most of their power at lower RPM and revving a stocker is the kiss of death.
Another possibility is that it has "grabbed" a rod bearing. I would have it checked for compression loss and camshaft issues. If nothing there, pull it out and repair the crankshaft before it blows the rod. Pontiacs in stock form were notorious for breaking rods when over-revved. Under no circumstances should you simply apply more throttle trying to "break it free", as you'll just "break it". 400s are still available but not as easily (or as cheap) as in years past. If you don't hurt the block, the sky is the limit for a modern build.
Jim
Another possibility is that it has "grabbed" a rod bearing. I would have it checked for compression loss and camshaft issues. If nothing there, pull it out and repair the crankshaft before it blows the rod. Pontiacs in stock form were notorious for breaking rods when over-revved. Under no circumstances should you simply apply more throttle trying to "break it free", as you'll just "break it". 400s are still available but not as easily (or as cheap) as in years past. If you don't hurt the block, the sky is the limit for a modern build.
Jim
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