[WThanel]

1965 Chevelle SS 327 4 spd


I recently had my my 65 327 short block rebuilt and stroked to a 350. The reason I did this is because it was burning alot of oil but otherwise running fine.

After I recieved the short block I put on new Edelbrock heads, a new Comp cams 270 mag cam, roller rockers, L-79 intake manifold and Holley carb.

After putting the engine in the car and waiting months to get my car runnning again I fired it up. Now a get a very pronounced popping/pulsating coming from the exhaust pipe. Its loud. The engine seems to run fairly smooth otherwise, except it really pops when you rev it up a little and let off.

It sounded like I have a bad camshaft to me, but everyone I have talked to thinks its a sticking valve, bad muffler(both are near new and worked fine before) or improperly adjusted valve lash.

I am now checking everything out, I started first with a leak down check of all the cyls. On the drivers side everything was looking good until cyl no 7. I never get both valves closed at TDC on the compression stroke. The exhaust valve is well on its way down. Hmmmm Could this be a bad cam? Has anyone ever experienced this before?

Thanks

Bill
[email protected]
through the drivers side exhaust pipe.

 

[67_454_Hardtop]

Before you go tearing into the engine, try a new set of plugs and wires.My 454 was popping loudly and I found a few burned plug wires which caused those cylderes to not fire good and it also fouled the plugs. I fixed the wires and put in a new set of plugs and its now running great

 

[JWagner]

Frequently, the cause of popping in the exhaust on deceleration is an air leak in the exhaust system. This can be from poorly fitting headers (or manifolds) or pipe connections. What happens is that when you let off the throttle the air is cut off but the wet fuel in the inlet manifold vaporizes, causing a very rich mixture in the exhaust. The air added from the leak makes a good mixture. This gets ignited by the exhaust from other cylinders.

 

[Steve S]

Sounds like a bad cam to me. I have never had this problem before but seems like I have seen a post or two on this site. In this day and age of computer controlled processes it seams unlikely that only one lobe would be off. More likely the cam was marked or packaged wrong.

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Steve Strasemeier (70SS 396, Fathom Blue/White Stripes)

 

[283v8]

WOAH - before tearing anything out, check your valve lash (if solid lifters) or your hydraulic lifter pre load. Sounds to me like the valves may be way too tight!if as you say "I never get both valves closed at TDC on the compression stroke.
Maybe a bad lifter or sticking valve.

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Gotta have a Chevy !